recursive/

run_core.rs

//! Stateless execution kernel — `RunCore<'a>` and `RunInnerOutcome`.
//!
//! Extracted from `src/agent.rs` (Goal 213).  `RunCore` owns all the state
//! needed for one ReAct loop iteration and is consumed by `run_inner()`.
//! The containing `AgentKernel` constructs a `RunCore`, calls `run_inner()`,
//! and integrates the returned `RunInnerOutcome`.

use std::sync::atomic::{AtomicBool, Ordering};
use std::sync::Arc;

use tokio::sync::mpsc;
use tokio_util::sync::CancellationToken;
use tracing::{debug, warn};

/// Output of a single tool call execution, replacing the anonymous 5-tuple.
pub(crate) struct ToolCallOutcome {
    pub id: String,
    pub name: String,
    pub result: String,
    pub audit: Option<crate::tools::AuditMeta>,
}

/// Sentinel returned in the tool-result string when the permission denial
/// limit is exceeded.  Matches the check in `run_inner` that breaks the
/// ReAct loop.  Defined as a constant to avoid scattered string literals.
pub(crate) const DENIAL_LIMIT_SENTINEL: &str = "ERROR_DENIAL_LIMIT:";

use crate::compact::Compactor;
use crate::error::Result;
use crate::hooks::{HookAction, HookEvent, HookRegistry};
use crate::llm::{
    estimate_tokens, ChatProvider, Completion, ContextBreakdown, StreamChunk, StreamSender,
    TokenUsage, ToolCall, ToolSpec,
};
use crate::message::Message;

use crate::tools::plan_mode::{ENTER_PLAN_MODE_TOOL_NAME, EXIT_PLAN_MODE_TOOL_NAME};
use crate::tools::ToolRegistry;

use crate::agent::{FinishReason, PermissionDecision};
use crate::event::AgentEvent;
use crate::skills::Skill;
use crate::skills_injector::SkillInjector;
use crate::system_prompt::PromptSegments;
use crate::tools::PermissionHook;

/// Placeholder text used when trimming old tool results to fit the transcript budget.
pub(crate) const TRIM_PLACEHOLDER: &str = "[older tool output trimmed to fit budget]";

/// Minimum tool-result size (bytes) worth trimming; shorter results are kept verbatim.
const MIN_TRIM_LENGTH: usize = 200;

/// Goal-328: token estimate from a pre-computed byte count.
///
/// Same arithmetic as [`crate::llm::estimate_tokens`] but takes a `usize`
/// byte-count directly so the conversation bucket can avoid re-iterating
/// the transcript just to read each message's `len()`. Matches the public
/// helper's ceil semantics so a 5-byte transcript chunk is 2 tokens, not 1.
/// Byte-based (like the public helper): over-counts CJK ~3× because CJK
/// chars are 3 UTF-8 bytes each — intentional, and keeps the breakdown
/// buckets in the same unit as `estimate_tokens`.
fn estimate_tokens_by_bytes(bytes: usize) -> u32 {
    // NOTE: no `if tokens == 0 && bytes > 0 { 1 }` guard here — that branch
    // is dead: `tokens == 0` only when `bytes == 0` (ceil(0.25..0.75)=1), so
    // `bytes > 0` is never true when the guard could fire. Keeping it only
    // created behavior-equivalent `>`-operator mutants.
    (bytes as f64 / 4.0).ceil() as u32
}

/// Count one error occurrence for a tool name during stuck detection.
///
/// `#[mutants::skip]`: the `+= 1` mutants (`-= 1` / `*= 1`) are only
/// behavior-different when ≥2 tools repeat in the stuck window, but
/// `HashMap` iteration order is nondeterministic, so a test cannot pin
/// `max_by_key`'s tie-break without being flaky. The single-repeated-tool
/// case the counter feeds is covered by the stuck-detection integration
/// tests.
#[cfg_attr(test, mutants::skip)]
fn bump_stuck_count<'a>(counts: &mut std::collections::HashMap<&'a str, usize>, name: &'a str) {
    *counts.entry(name).or_default() += 1;
}

/// Render a [`FinishReason`] as the `reason` field of [`AgentEvent::TurnFinished`].
///
/// Delegates to the `Display` implementation on `FinishReason` to ensure
/// consistency between event payloads and HTTP API responses.
fn finish_reason_str(reason: &FinishReason) -> String {
    reason.to_string()
}

/// Rough token estimate from message content lengths.
///
/// Used as fallback when the LLM provider does not report `usage` in its
/// response. 4 chars per token is a conservative heuristic that works for
/// mixed English + CJK text; it will slightly *under*-estimate, which is
/// safer for the context gauge than over-estimating (false compaction
/// warnings). Divide by at least 1 so a zero-length message list doesn't
/// report zero tokens (the system prompt always exists).
fn estimate_prompt_tokens(messages: &[Message]) -> u32 {
    let total_chars: usize = messages.iter().map(|m| m.content.len()).sum();
    (total_chars / 4).max(1) as u32
}

/// Outcome returned by the stateless [`run_inner`] loop.
pub(crate) struct RunInnerOutcome {
    pub(crate) messages: Arc<Vec<Message>>,
    pub(crate) final_message: Option<String>,
    pub(crate) finish_reason: FinishReason,
    pub(crate) total_usage: TokenUsage,
    pub(crate) total_llm_latency_ms: u64,
    pub(crate) steps: usize,
    /// Goal-153: audit metadata for tool results, keyed by `(turn, tool_call_id)`.
    /// Only entries for successfully-dispatched tool calls are present;
    /// the key matches `Message.tool_call_id` on `Role::Tool` messages scoped
    /// by turn to prevent cross-turn id collisions.
    pub(crate) tool_audits:
        std::collections::HashMap<crate::tools::AuditKey, crate::tools::AuditMeta>,
    /// `prompt_tokens` from the **last** LLM call in this turn.
    ///
    /// Unlike `total_usage.prompt_tokens` (which is the accumulated sum across
    /// all LLM calls in the turn), this is the single most-recent reading from
    /// the API response. It represents the actual current context size and is
    /// the correct input to cross-turn compaction's `should_compact` check.
    pub(crate) last_prompt_tokens: u32,
}

/// Private core holding all state needed for one run of the ReAct loop.
///
/// Borrows immutable config from the parent [`Agent`]; owns the mutable
/// transcript and plan state.  `run_inner()` consumes `self` so the
/// loop cannot accidentally leave stale state behind.
pub(crate) struct RunCore<'a> {
    pub(crate) messages: Arc<Vec<Message>>,
    pub(crate) llm: Arc<dyn ChatProvider>,
    pub(crate) tools: Arc<ToolRegistry>,
    pub(crate) max_steps: usize,
    pub(crate) max_transcript_chars: Option<usize>,
    pub(crate) events: Option<mpsc::UnboundedSender<AgentEvent>>,
    pub(crate) streaming: bool,
    pub(crate) compactor: Option<Compactor>,
    /// Goal-332: micro-compactor for intra-turn tool-result pruning.
    /// When set, tool results are pruned at the end of each step BEFORE
    /// the next LLM call, keeping the transcript short enough that
    /// proactive cross-turn compaction rarely fires mid-response.
    /// NOTE: field exists but intra-turn invocation is not yet wired
    /// (Goal 332 added the type + field; Goal 333 wires cross-turn;
    /// a future goal will wire intra-turn in maybe_compact).
    #[allow(dead_code)]
    pub(crate) microcompactor: Option<crate::compact::Microcompactor>,
    pub(crate) permission_hook: Option<Arc<dyn PermissionHook>>,
    pub(crate) hooks: &'a HookRegistry,
    pub(crate) total_llm_latency_ms: u64,
    /// Goal-165: shared flag set by `EnterPlanModeTool`; blocks write tools
    /// while the agent is in read-only exploring / planning mode.
    pub(crate) exploring_plan_mode: Arc<AtomicBool>,
    /// Optional cancellation token. When cancelled, the step loop
    /// terminates at the next step boundary with
    /// [`FinishReason::Cancelled`].
    pub(crate) shutdown_token: Option<CancellationToken>,

    /// Optional mailbox for receiving mid-run messages from a coordinator.
    ///
    /// Drained at the start of every step so the agent sees coordinator
    /// instructions as user-role messages injected into the conversation.
    pub(crate) mailbox: Option<crate::tools::send_message::WorkerMailbox>,
    /// Sliding window size for stuck detection (from Config).
    pub(crate) stuck_window: usize,
    /// Error rate threshold to declare stuck (from Config).
    pub(crate) stuck_error_rate: f64,
    /// Turn index (0-based), scopes [`crate::tools::AuditKey`] prefixes so
    /// that cross-turn tool_call_id reuse cannot corrupt audit metadata.
    pub(crate) turn: u32,
    /// Goal-318: `Globs`-mode skills for path-triggered injection.
    /// Injected as system messages after tool calls match a skill's glob patterns.
    pub(crate) globs_skills: Vec<Skill>,
    /// Goal-328: structured prompt segments from `assemble_system_prompt`,
    /// used to size the static breakdown buckets (`system_prompt`, `rules`,
    /// `skills`, `subagents`). `None` when the runtime was built without a
    /// system-prompt path (tests, headless loops without prompts).
    ///
    /// Currently held for introspection / future hot-reload; the breakdown
    /// computation only reads [`Self::static_breakdown`] (which was sized
    /// at construction). The `#[allow(dead_code)]` silences the lint
    /// without removing the field — the goal explicitly preserves the
    /// structured segment accessor surface so callers can reason about
    /// which buckets contribute to the prompt.
    #[allow(dead_code)]
    pub(crate) prompt_segments: Option<PromptSegments>,
    /// Goal-328: per-bucket token counts for the static prompt portions,
    /// cached once at construction so the breakdown estimator does not
    /// re-tokenise `PromptSegments` every step. The `conversation`
    /// bucket is recomputed every step from `self.messages`.
    pub(crate) static_breakdown: StaticBreakdownCache,
    /// Goal-330: `prompt_tokens` from the most recent LLM response, used
    /// by [`Compactor::should_compact`] intra-turn. `0` means "no reading
    /// yet" (first step, or provider never reports usage).
    pub(crate) last_prompt_tokens: u32,
    /// Goal-331: consecutive proactive compaction failures. Resets to 0 on
    /// any successful compaction (including `Ok(None)` when transcript too
    /// short is **not** a failure — only actual `Err` from the provider or
    /// the compactor increments). When >= `MAX_CONSECUTIVE_COMPACT_FAILURES`,
    /// subsequent proactive compaction attempts are skipped.
    pub(crate) consecutive_compact_failures: u32,
    /// Goal 345: optional wall-clock deadline. When
    /// `wall_timeout_secs > 0`, the step loop checks elapsed time at
    /// each step boundary and terminates cleanly with
    /// [`FinishReason::WallClockExceeded`] when exceeded.
    pub(crate) wall_timeout_secs: u64,
    /// Wall-clock start instant, recorded when `RunCore` is
    /// constructed. `None` when the timeout is not active.
    pub(crate) wall_start: Option<std::time::Instant>,
}

/// Goal-328: cached token counts for the static breakdown buckets.
///
/// Sized once at `RunCore` construction from `PromptSegments`. The
/// `tools` and `mcp_dynamic` buckets are also cached because they only
/// change on a `/model` hot-swap or tool-registry change — the same
/// hook that re-creates the runtime. `conversation` and `overhead`
/// stay dynamic (recomputed every step).
#[derive(Debug, Clone, Default, PartialEq, Eq)]
pub(crate) struct StaticBreakdownCache {
    pub system_prompt: u32,
    pub rules: u32,
    pub skills: u32,
    pub subagents: u32,
    /// Eager tool specs that are NOT MCP / NOT deferred.
    pub tools: u32,
    /// MCP / deferred tool specs.
    pub mcp_dynamic: u32,
}

impl StaticBreakdownCache {
    /// Build a fresh cache from a `PromptSegments` + the registry's tool
    /// specs. `registry` is consulted to partition `eager` vs
    /// `deferred_or_mcp` (McpTool reports `is_deferred() == true`).
    pub(crate) fn build(
        segments: &PromptSegments,
        specs: &[ToolSpec],
        registry: &ToolRegistry,
    ) -> Self {
        let mut tools = 0u32;
        let mut mcp_dynamic = 0u32;
        for spec in specs {
            // Mirror the serde-shape the provider adapter would send: a
            // single ToolSpec serialises to a JSON object with
            // name/description/parameters. We tokenise that JSON text
            // so the local estimate is comparable to what the provider
            // actually sees after wrapping.
            let text = serde_json::to_string(spec).unwrap_or_default();
            let n = estimate_tokens(&text);
            if registry.is_deferred_spec(spec) {
                mcp_dynamic = mcp_dynamic.saturating_add(n);
            } else {
                tools = tools.saturating_add(n);
            }
        }
        Self {
            system_prompt: estimate_tokens(&segments.system_prompt),
            rules: estimate_tokens(&segments.rules),
            skills: estimate_tokens(&segments.skills),
            subagents: estimate_tokens(&segments.subagents),
            tools,
            mcp_dynamic,
        }
    }
}

impl<'a> RunCore<'a> {
    fn emit(&self, event: AgentEvent) {
        if let Some(ref tx) = self.events {
            let _ = tx.send(event);
        }
    }

    fn push_message(&mut self, msg: Message) {
        Arc::make_mut(&mut self.messages).push(msg);
    }

    /// Attach `reasoning_content` to the last message in the transcript, if present.
    ///
    /// Called immediately after `push_message` on any path that produces reasoning
    /// tokens (both the no-tool-calls path and the tool-calls path share this logic).
    fn attach_reasoning_content(&mut self, reasoning: Option<String>) {
        if reasoning.is_some() {
            if let Some(msg) = Arc::make_mut(&mut self.messages).last_mut() {
                msg.reasoning_content = reasoning;
            }
        }
    }

    /// Goal-328: build a fresh [`ContextBreakdown`] from the cached static
    /// buckets + a re-tokenised `conversation` (the transcript body).
    /// `provider_total` is the `max(input_tokens, cache_hit + cache_miss)`
    /// reading from the just-completed LLM call; it backs the `overhead`
    /// bucket.
    fn compute_breakdown(&self, provider_total: u32) -> ContextBreakdown {
        // Conversation bucket: bytes/4 over the transcript body. We
        // intentionally re-tokenise every step (rather than caching) so
        // the bucket grows naturally with each new assistant / tool /
        // user message appended this run.
        let mut conversation_bytes: usize = 0;
        for msg in self.messages.iter() {
            conversation_bytes = conversation_bytes.saturating_add(msg.content.len());
            if let Some(rc) = &msg.reasoning_content {
                conversation_bytes = conversation_bytes.saturating_add(rc.len());
            }
        }
        // `estimate_tokens` uses (bytes as f64 / 4.0).ceil() as u32.
        let conversation = estimate_tokens_by_bytes(conversation_bytes);

        let local_sum = self
            .static_breakdown
            .system_prompt
            .saturating_add(self.static_breakdown.rules)
            .saturating_add(self.static_breakdown.skills)
            .saturating_add(self.static_breakdown.subagents)
            .saturating_add(self.static_breakdown.tools)
            .saturating_add(self.static_breakdown.mcp_dynamic)
            .saturating_add(conversation);
        let overhead = provider_total.saturating_sub(local_sum);

        ContextBreakdown {
            system_prompt: self.static_breakdown.system_prompt,
            rules: self.static_breakdown.rules,
            skills: self.static_breakdown.skills,
            subagents: self.static_breakdown.subagents,
            tools: self.static_breakdown.tools,
            mcp_dynamic: self.static_breakdown.mcp_dynamic,
            conversation,
            overhead,
        }
    }

    /// Goal-328: emit the [`AgentEvent::ContextBreakdown`] event for `step`.
    /// `usage` is the provider's reported truth for this step.
    fn emit_breakdown(&self, step: usize, usage: &TokenUsage) {
        // Match `UsageStats::record_with_cache`'s logic:
        //   max(input_tokens, cache_hit + cache_miss)
        // so Anthropic (cache_hit excludes input_tokens) and OpenAI
        // (cache_hit == 0, input_tokens is the full prompt) both feed
        // a sensible `provider_total`.
        let cache_sum = usage
            .cache_hit_tokens
            .saturating_add(usage.cache_miss_tokens);
        let provider_total = usage.prompt_tokens.max(cache_sum);
        let breakdown = self.compute_breakdown(provider_total);
        self.emit(AgentEvent::ContextBreakdown { breakdown, step });
    }

    /// Execute one LLM call for this step and surface everything the
    /// loop body needs: stream-forwarding task, latency tracking,
    /// token-usage accumulation, and the ordered `Reasoning` /
    /// `AssistantText` events.
    ///
    /// Returns the raw [`Completion`] plus `Some(text)` when the step
    /// produced non-empty assistant content (which becomes the
    /// candidate `final_message`). The caller decides what to do with
    /// the completion (no-tool-calls path vs. tool-dispatch path) and
    /// owns pushing assistant messages onto the transcript —
    /// `dispatch_llm_step` deliberately does not mutate `self.messages`.
    async fn dispatch_llm_step(
        &mut self,
        specs: &[crate::llm::ToolSpec],
        step: usize,
        total_usage: &mut TokenUsage,
    ) -> crate::error::Result<(Completion, Option<String>)> {
        debug!(target: "recursive::agent", step, "calling llm");
        let start = std::time::Instant::now();
        // Spin up the partial-token forwarder when streaming so the
        // UI gets live `PartialToken` / `PartialReasoning` events.
        let mut forward_handle = None;
        let stream_tx: Option<StreamSender> = if self.streaming {
            let (delta_tx, mut delta_rx) = mpsc::unbounded_channel::<StreamChunk>();
            let events_tx = self.events.clone();
            forward_handle = Some(tokio::spawn(async move {
                while let Some(chunk) = delta_rx.recv().await {
                    if let Some(ref tx) = events_tx {
                        let event = match chunk {
                            StreamChunk::Text(text) => AgentEvent::PartialToken { text, step },
                            StreamChunk::Reasoning(text) => {
                                AgentEvent::PartialReasoning { text, step }
                            }
                        };
                        let _ = tx.send(event);
                    }
                }
            }));
            Some(delta_tx)
        } else {
            None
        };
        let mut completion: Completion = self.call_llm(specs, stream_tx).await?;
        // Drain the partial-token forwarder before emitting any further
        // events. `call_llm` drops `stream_tx` on return, which closes
        // `delta_rx` and lets the spawned task finish; awaiting it
        // guarantees every `PartialToken` has been pushed to the event
        // sink *before* the finalising `AssistantText`. Without this the
        // two tasks race on the shared sink and a late token can arrive
        // after the assistant block was finalised, spawning a duplicate
        // streaming block in the UI.
        if let Some(handle) = forward_handle.take() {
            let _ = handle.await;
        }
        // Normalise chain-of-thought that the model emitted inline as
        // `<think>…</think>` in `content` (common for OpenAI-compatible
        // DeepSeek-R1 deployments that don't use the dedicated
        // `reasoning_content` SSE field) into the reasoning channel, so
        // the thinking block renders instead of being dropped by the
        // markdown HTML-block parser.
        completion.extract_inline_reasoning();
        let llm_ms = start.elapsed().as_millis() as u64;
        self.total_llm_latency_ms = self.total_llm_latency_ms.saturating_add(llm_ms);
        self.emit(AgentEvent::Latency { step, llm_ms });

        if let Some(u) = completion.usage {
            *total_usage = total_usage.accumulate(u);
            self.last_prompt_tokens = u.prompt_tokens;
            self.emit(AgentEvent::Usage {
                input_tokens: u.prompt_tokens,
                output_tokens: u.completion_tokens,
                cache_hit_tokens: u.cache_hit_tokens,
                cache_miss_tokens: u.cache_miss_tokens,
                step,
            });
            // Goal-328: emit the local per-component breakdown right after
            // the provider's `Usage` truth. The `overhead` bucket absorbs
            // the difference between our 7-bucket local sum and the
            // provider's reported `prompt_tokens` (computed as
            // `max(input_tokens, cache_hit + cache_miss)` so Anthropic
            // and OpenAI reporting differences are handled).
            self.emit_breakdown(step, &u);
        } else {
            // Provider did not report usage — emit a best-effort estimate
            // so the TUI context gauge still updates on every turn.
            let estimated_input = estimate_prompt_tokens(&self.messages);
            let output_len = completion.content.len()
                + completion.reasoning_content.as_ref().map_or(0, |s| s.len());
            let estimated_output = (output_len / 4).max(1) as u32;
            self.emit(AgentEvent::Usage {
                input_tokens: estimated_input,
                output_tokens: estimated_output,
                cache_hit_tokens: 0,
                cache_miss_tokens: 0,
                step,
            });
        }

        // Surface reasoning / thinking content to UI consumers (TUI) as
        // a separate event so it can be rendered as a `thinking…` block.
        // Providers that stream reasoning tokens accumulate them into
        // the final string before this point; we emit exactly once per
        // step. Emit this BEFORE AssistantText so the TUI's
        // `Reasoning { text }` block lands above the matching
        // `Assistant { text }` block — the model thinks first, then
        // speaks, and the visual order should match.
        if let Some(reasoning) = &completion.reasoning_content {
            if !reasoning.is_empty() {
                self.emit(AgentEvent::Reasoning {
                    text: reasoning.clone(),
                    step,
                });
            }
        }

        let new_final_message = if !completion.content.is_empty() {
            self.emit(AgentEvent::AssistantText {
                text: completion.content.clone(),
                step,
            });
            Some(completion.content.clone())
        } else {
            None
        };

        Ok((completion, new_final_message))
    }

    /// Process the result of a tool batch: emit per-call `ToolResult`
    /// events, push paired tool_result messages, run sliding-window
    /// stuck detection, then optionally terminate the run.
    ///
    /// Returns `Some(finish)` when the run should end after this batch
    /// (sentinel pre-pass hits `PermissionDenialLimit`, or stuck
    /// detection triggers `Stuck`); the caller routes the finish through
    /// [`make_outcome`]. Returns `None` when the loop should continue.
    ///
    /// **Invariant #8**: every tool_call in the batch is paired with a
    /// tool_result message before any early return. The sentinel pre-pass
    /// scans the whole batch first and flushes all tool_results
    /// atomically; the stuck-detection loop likewise pushes each
    /// tool_result before recording the (deferred) finish verdict. We
    /// never mid-batch return.
    ///
    /// When returning `None`, also runs the Globs-mode skill injector
    /// against the result strings so the next step can pick up
    /// path-triggered skills.
    #[allow(clippy::too_many_arguments)]
    fn process_tool_results(
        &mut self,
        results: &[ToolCallOutcome],
        step: usize,
        recent_errors: &mut std::collections::VecDeque<(bool, String)>,
        tool_audits: &mut std::collections::HashMap<
            crate::tools::AuditKey,
            crate::tools::AuditMeta,
        >,
        skill_injector: &mut SkillInjector,
    ) -> Option<FinishReason> {
        // Goal-285: sentinel pre-pass — detect before any push_message calls.
        // When the sentinel appears at index N > 0, flushing incrementally
        // would duplicate results[0..N] in the transcript; scan first, flush
        // once atomically, return immediately.
        if results.iter().any(|o| o.result == DENIAL_LIMIT_SENTINEL) {
            for o in results {
                if let Some(a) = &o.audit {
                    tool_audits.insert((self.turn, o.id.clone()), a.clone());
                }
                let is_error = o.result.starts_with("ERROR: ") || o.result == DENIAL_LIMIT_SENTINEL;
                self.emit(AgentEvent::ToolResult {
                    id: o.id.clone(),
                    name: o.name.clone(),
                    output: o.result.clone(),
                    step,
                    is_error,
                });
                self.push_message(Message::tool_result(o.id.clone(), o.result.clone()));
            }
            let finish = FinishReason::PermissionDenialLimit;
            self.emit(AgentEvent::TurnFinished {
                reason: finish_reason_str(&finish),
                steps: step,
            });
            return Some(finish);
        }

        // Stuck detection may fire while iterating the results of a
        // multi-call step. Returning mid-loop (as this code used to do)
        // left the assistant message's remaining tool_calls without
        // matching tool_result messages — orphaned `tool_use` blocks
        // that the provider rejects on the *next* turn with HTTP 400.
        // Record the stuck verdict here but defer the actual return
        // until the loop has pushed a tool_result for every call.
        let mut stuck_finish: Option<FinishReason> = None;
        for ToolCallOutcome {
            id,
            name,
            result,
            audit,
        } in results
        {
            let is_error = result.starts_with("ERROR: ");
            self.emit(AgentEvent::ToolResult {
                id: id.clone(),
                name: name.clone(),
                output: result.clone(),
                step,
                is_error,
            });
            if let Some(a) = audit {
                tool_audits.insert((self.turn, id.clone()), a.clone());
            }
            self.push_message(Message::tool_result(id.clone(), result.clone()));

            // Sliding-window stuck detection: track whether each tool call
            // was an error. Triggers when the error rate in the last
            // stuck_window steps exceeds stuck_error_rate, catching loops
            // that cycle across different tools (e.g. A→B→A→B).
            if recent_errors.len() == self.stuck_window {
                recent_errors.pop_front();
            }
            recent_errors.push_back((is_error, name.clone()));

            if stuck_finish.is_none() && recent_errors.len() == self.stuck_window {
                let error_entries: Vec<&str> = recent_errors
                    .iter()
                    .filter(|(is_err, _)| *is_err)
                    .map(|(_, n)| n.as_str())
                    .collect();
                let error_count = error_entries.len();
                let rate = error_count as f64 / self.stuck_window as f64;
                if rate >= self.stuck_error_rate {
                    let mut counts: std::collections::HashMap<&str, usize> =
                        std::collections::HashMap::new();
                    for n in &error_entries {
                        bump_stuck_count(&mut counts, n);
                    }
                    let top_tool = counts
                        .into_iter()
                        .max_by_key(|&(_, c)| c)
                        .map(|(n, _)| n)
                        .unwrap_or(name.as_str());
                    stuck_finish = Some(FinishReason::Stuck {
                        repeated_call: top_tool.to_string(),
                        repeats: error_count,
                    });
                }
            }
        }

        // Deferred stuck termination: every tool_call now has its matching
        // tool_result in the transcript, so ending the turn here cannot
        // leave orphaned `tool_use` blocks behind.
        if let Some(finish) = stuck_finish {
            self.emit(AgentEvent::TurnFinished {
                reason: finish_reason_str(&finish),
                steps: step,
            });
            return Some(finish);
        }

        // Goal-318: after every tool-result batch, check whether any result
        // references a path matching a Globs-mode skill. Inject once per skill.
        let result_strings: Vec<String> = results.iter().map(|r| r.result.clone()).collect();
        for (skill_name, skill_body) in skill_injector.check(&result_strings) {
            self.push_message(Message::system(format!(
                "<!-- skill:{skill_name} injected by globs match -->\n{skill_body}"
            )));
        }
        None
    }

    /// Finalise a step whose LLM completion carried no tool calls. Pushes
    /// the assistant message + reasoning onto the transcript, classifies
    /// the finish reason (`ProviderStop` for non-`stop`/`end_turn`
    /// provider reasons, else `NoMoreToolCalls`), emits `TurnFinished`,
    /// and returns `Some(finish)` so the caller routes through
    /// [`make_outcome`]. Returns `None` when the caller should continue
    /// with tool dispatch.
    fn handle_no_tool_calls(
        &mut self,
        completion: &Completion,
        step: usize,
    ) -> Option<FinishReason> {
        if !completion.tool_calls.is_empty() {
            return None;
        }
        self.push_message(Message::assistant(completion.content.clone()));
        self.attach_reasoning_content(completion.reasoning_content.clone());
        let finish = match completion.finish_reason.as_deref() {
            Some(r) if r != "stop" && r != "end_turn" => FinishReason::ProviderStop(r.to_string()),
            _ => FinishReason::NoMoreToolCalls,
        };
        self.emit(AgentEvent::TurnFinished {
            reason: finish_reason_str(&finish),
            steps: step,
        });
        Some(finish)
    }

    /// Drain any messages that a coordinator pushed via `send_message`
    /// since the last step, appending each as a user-role turn so the
    /// LLM sees coordinator instructions on the next reasoning step.
    /// No-op when no mailbox is configured.
    async fn drain_mailbox(&mut self) {
        let Some(mailbox) = self.mailbox.as_ref() else {
            return;
        };
        let pending = mailbox.drain_all().await;
        for msg_text in pending {
            self.push_message(Message {
                role: crate::message::Role::User,
                content: format!("[coordinator]: {msg_text}"),
                tool_calls: vec![],
                tool_call_id: None,
                reasoning_content: None,
                is_compaction_summary: false,
            });
        }
    }

    /// Apply transcript-budget enforcement for this step. When configured
    /// (`max_transcript_chars`) the transcript is trimmed and re-measured;
    /// if it still exceeds the limit, returns `Some((finish, step))` for
    /// the caller to route through [`make_outcome`].
    fn enforce_transcript_budget(
        &mut self,
        step: usize,
        total_usage: &TokenUsage,
    ) -> Option<(FinishReason, usize)> {
        let limit = self.max_transcript_chars?;
        self.maybe_trim_transcript(limit, step);
        let chars: usize = self.messages.iter().map(|m| m.content.len()).sum();
        if chars < limit {
            return None;
        }
        let finish = FinishReason::TranscriptLimit { chars, limit };
        self.emit(AgentEvent::TurnFinished {
            reason: finish_reason_str(&finish),
            steps: step,
        });
        tracing::info!(
            target: "recursive::agent",
            steps = step,
            tokens_in = total_usage.prompt_tokens,
            tokens_out = total_usage.completion_tokens,
            finish = ?finish,
            llm_latency_ms = self.total_llm_latency_ms,
            "agent.run.complete"
        );
        Some((finish, step))
    }

    /// Check the shutdown token at the top of a step. Returns `Some((
    /// finish, finished_steps))` when the run should terminate with
    /// [`FinishReason::Cancelled`]; the caller routes the pair through
    /// [`make_outcome`]. `finished_steps` is `step - 1` because the
    /// current step's LLM call has not started yet.
    ///
    /// `total_usage` is read for the structured log line only — the
    /// outcome assembly happens at the call site.
    fn check_shutdown(
        &self,
        step: usize,
        total_usage: &TokenUsage,
    ) -> Option<(FinishReason, usize)> {
        let token = self.shutdown_token.as_ref()?;
        if !token.is_cancelled() {
            return None;
        }
        let finished_steps = step.saturating_sub(1);
        let finish = FinishReason::Cancelled;
        self.emit(AgentEvent::TurnFinished {
            reason: finish_reason_str(&finish),
            steps: finished_steps,
        });
        tracing::info!(
            target: "recursive::agent",
            steps = finished_steps,
            tokens_in = total_usage.prompt_tokens,
            tokens_out = total_usage.completion_tokens,
            finish = ?finish,
            llm_latency_ms = self.total_llm_latency_ms,
            "agent.run.complete"
        );
        Some((finish, finished_steps))
    }

    /// Goal 345: check the wall-clock deadline at the top of a step.
    /// Returns `Some((finish, finished_steps))` when the deadline has
    /// been exceeded; the caller routes through [`make_outcome`].
    fn check_wall_deadline(
        &self,
        step: usize,
        total_usage: &TokenUsage,
    ) -> Option<(FinishReason, usize)> {
        if self.wall_timeout_secs == 0 {
            return None;
        }
        let elapsed = self.wall_start?.elapsed();
        if elapsed.as_secs() < self.wall_timeout_secs {
            return None;
        }
        let finished_steps = step.saturating_sub(1);
        let finish = FinishReason::WallClockExceeded {
            secs: self.wall_timeout_secs,
        };
        self.emit(AgentEvent::TurnFinished {
            reason: finish_reason_str(&finish),
            steps: finished_steps,
        });
        tracing::info!(
            target: "recursive::agent",
            steps = finished_steps,
            tokens_in = total_usage.prompt_tokens,
            tokens_out = total_usage.completion_tokens,
            finish = ?finish,
            llm_latency_ms = self.total_llm_latency_ms,
            "agent.run.complete (wall clock)"
        );
        Some((finish, finished_steps))
    }

    /// Assemble the final outcome for a run that terminates with `finish`
    /// at step `steps`. All early-return paths in [`run_inner`] route here
    /// so the eight-field struct cannot drift out of sync across sites.
    fn make_outcome(
        self,
        finish: FinishReason,
        steps: usize,
        final_message: Option<String>,
        total_usage: TokenUsage,
        tool_audits: std::collections::HashMap<crate::tools::AuditKey, crate::tools::AuditMeta>,
    ) -> RunInnerOutcome {
        RunInnerOutcome {
            messages: self.messages,
            final_message,
            finish_reason: finish,
            total_usage,
            total_llm_latency_ms: self.total_llm_latency_ms,
            steps,
            tool_audits,
            last_prompt_tokens: self.last_prompt_tokens,
        }
    }

    /// Goal 353 — translate a mid-stream [`Error::Cancelled`] from the
    /// in-flight LLM call into a [`FinishReason::Cancelled`] outcome so the
    /// caller persists the partial transcript (Invariant #7).
    ///
    /// `finished_steps` is `step` — NOT `step - 1` like [`check_shutdown`]:
    /// the cancellation happened *during* the current step's LLM call, so the
    /// step is in-progress, not pre-call. The caller passes the loop's `step`
    /// verbatim; this helper deliberately does not compute it, keeping the
    /// step-vs-step-1 distinction visible at the call site. The event and log
    /// mirror [`check_shutdown`]'s so observers see Cancelled consistently.
    fn make_cancelled_outcome(
        self,
        step: usize,
        final_message: Option<String>,
        total_usage: TokenUsage,
        tool_audits: std::collections::HashMap<crate::tools::AuditKey, crate::tools::AuditMeta>,
    ) -> RunInnerOutcome {
        let finish = FinishReason::Cancelled;
        self.emit(AgentEvent::TurnFinished {
            reason: finish_reason_str(&finish),
            steps: step,
        });
        tracing::info!(
            target: "recursive::agent",
            steps = step,
            finish = ?finish,
            "agent.run.cancelled_mid_stream"
        );
        self.make_outcome(finish, step, final_message, total_usage, tool_audits)
    }

    /// Goal 382 — route a stream-interrupted completion to the Cancelled
    /// outcome. The SSE parsers (openai.rs / anthropic.rs) now return
    /// `Ok(Completion { finish_reason: Some("interrupted"), .. })` instead
    /// of `Err` when a network drop or user-initiated cancel cuts the
    /// stream after content arrived. This pushes the partial assistant
    /// message onto the transcript and finalises the turn as
    /// [`FinishReason::Cancelled`] via [`Self::make_cancelled_outcome`], so
    /// the caller's `emit_turn_messages` persists it (Invariant #7:
    /// transcript saved before the CLI maps the reason to an exit code).
    /// Kept as a sibling helper to protect Invariant #1 (loop body size).
    fn finish_interrupted(
        mut self,
        completion: Completion,
        step: usize,
        total_usage: TokenUsage,
        tool_audits: std::collections::HashMap<crate::tools::AuditKey, crate::tools::AuditMeta>,
    ) -> RunInnerOutcome {
        self.push_message(Message::assistant(completion.content.clone()));
        self.attach_reasoning_content(completion.reasoning_content.clone());
        self.make_cancelled_outcome(
            step,
            Some(completion.content), // partial reply becomes final_message
            total_usage,
            tool_audits,
        )
    }

    /// Call the LLM once, delegating retry handling to the provider's
    /// internal `RetryPolicy`. Goal-288 removed the outer retry loop so
    /// there is exactly one retry layer.
    ///
    /// When the registry has deferred tools, their names are injected as an
    /// `<available-deferred-tools>` user message prepended to the transcript,
    /// and only eager tool specs are passed to the provider. ToolSearchTool
    /// (registered by `freeze_deferred_specs`) appears in the eager list and
    /// its results in the message history are serialized as `tool_reference`
    /// blocks by `serialize_messages_anthropic`.
    /// Inject the skill catalog as a `<system-reminder>` user turn, appended
    /// to the **tail** of the per-request message copy.
    ///
    /// Why tail (not head): the catalog is volatile — it changes when skills
    /// load/unload. Placing it at the head (right after the leading `system`
    /// message, as an earlier draft did) busts the prefix cache for every
    /// message that follows it on each skill change. At the tail it sits in
    /// the most-recent turn, mirroring fake-cc's `skill_listing` attachment,
    /// which `reorderAttachmentsForAPI` bubbles to the end of the
    /// conversation. The static `system` field is untouched either way, so
    /// prefix caching of the system prompt + stable history is preserved.
    ///
    /// Correctness: appending a `user` turn at the tail is safe on both
    /// Anthropic and OpenAI-compatible providers. It never splits an
    /// assistant→tool_result pair (we only append, never insert), so
    /// AGENTS.md invariant #8 holds. The transcript (`self.messages`) is
    /// never mutated — only the per-request copy is wrapped.
    fn inject_skill_reminder(
        messages: &[crate::message::Message],
        skills: &[crate::skills::Skill],
    ) -> Vec<crate::message::Message> {
        if skills.is_empty() {
            return messages.to_vec();
        }
        let reminder = crate::skills::skill_reminder(skills);
        let mut out = Vec::with_capacity(messages.len() + 1);
        out.extend(messages.iter().cloned());
        out.push(crate::message::Message::user(reminder));
        out
    }

    async fn call_llm(
        &self,
        specs: &[crate::llm::ToolSpec],
        stream_sender: Option<crate::llm::StreamSender>,
    ) -> crate::error::Result<Completion> {
        // Deferred-tool partition: only when the provider supports tool_reference
        // (Anthropic). Other providers (OpenAI-compatible) receive all tools eagerly
        // — ToolSearchTool is not registered for them (see AgentRuntimeBuilder::build).
        let eager_specs_owned: Vec<crate::llm::ToolSpec>;
        let messages_with_deferred: Vec<crate::message::Message>;

        let (call_specs, messages): (&[crate::llm::ToolSpec], &[crate::message::Message]) =
            if self.llm.supports_deferred_tools() {
                let (eager, deferred): (Vec<_>, Vec<_>) = specs
                    .iter()
                    .cloned()
                    .partition(|s| !self.tools.is_deferred_spec(s));

                if deferred.is_empty() {
                    (specs, &self.messages)
                } else {
                    let names: Vec<&str> = deferred.iter().map(|s| s.name.as_str()).collect();
                    let block = format!(
                        "<available-deferred-tools>\n{}\n</available-deferred-tools>",
                        names.join("\n")
                    );
                    messages_with_deferred = std::iter::once(crate::message::Message::user(block))
                        .chain(self.messages.iter().cloned())
                        .collect();
                    eager_specs_owned = eager;
                    (&eager_specs_owned, &messages_with_deferred)
                }
            } else {
                (specs, &self.messages)
            };

        // Ship the skill catalog per-turn as a tail-appended `system-reminder`
        // so the static `system` prompt + stable history stay cacheable. Does
        // not mutate the transcript. See `inject_skill_reminder` for rationale.
        let injected: Vec<crate::message::Message> =
            Self::inject_skill_reminder(messages, &self.globs_skills);

        if let Some(ref tx) = stream_sender {
            let cancel_token = self.shutdown_token.clone();
            self.llm
                .stream(&injected, call_specs, Some(tx.clone()), cancel_token)
                .await
        } else {
            self.llm.complete(&injected, call_specs).await
        }
    }

    /// Trim old tool results to fit the transcript under `limit` chars.
    fn maybe_trim_transcript(&mut self, limit: usize, step: usize) {
        let mut chars: usize = self.messages.iter().map(|m| m.content.len()).sum();
        if chars < limit {
            return;
        }

        let mut trimmed_count: usize = 0;
        let placeholder_len = TRIM_PLACEHOLDER.len();

        for msg in Arc::make_mut(&mut self.messages).iter_mut().skip(1) {
            if msg.role == crate::message::Role::Tool && msg.content.len() > MIN_TRIM_LENGTH {
                let old_len = msg.content.len();
                msg.content = TRIM_PLACEHOLDER.to_string();
                trimmed_count += 1;
                chars = chars
                    .saturating_sub(old_len)
                    .saturating_add(placeholder_len);
                if chars < limit {
                    break;
                }
            }
        }

        if trimmed_count > 0 {
            let note = format!(
                "[trimmed {} old tool result{} to fit budget]",
                trimmed_count,
                if trimmed_count == 1 { "" } else { "s" }
            );
            self.emit(AgentEvent::AssistantText { text: note, step });
        }
    }

    /// Compact the transcript if a [`Compactor`] is configured and the
    /// character budget is exceeded.
    ///
    /// `PreCompact` and `PostCompact` hooks are dispatched only when
    /// compaction actually runs (threshold is exceeded), not on every step.
    ///
    /// **Best-effort**: compaction failures are caught, logged, and counted
    /// by the circuit breaker. A failed compaction NEVER propagates to the
    /// caller — compaction is an optimization, not a correctness requirement.
    async fn maybe_compact(&mut self, step: usize) {
        let compactor = match &self.compactor {
            Some(c) => c,
            None => return,
        };

        // Circuit breaker: stop trying after too many consecutive failures.
        if self.consecutive_compact_failures >= crate::compact::MAX_CONSECUTIVE_COMPACT_FAILURES {
            self.emit(AgentEvent::CompactionSkipped {
                step,
                reason: crate::event::CompactionSkipReason::CircuitBreaker,
            });
            return;
        }

        let bytes = Compactor::estimate_bytes(&self.messages);
        if !compactor.should_compact(bytes, self.last_prompt_tokens) {
            return;
        }
        // Goal 345: only dispatch PreCompact when compaction will actually run.
        // `would_compact` mirrors `apply_to_transcript`'s degenerate-slice
        // rejection so PreCompact / PostCompact stay balanced (both fire, or
        // neither does) — without this the new Ok(None) path fired PreCompact
        // without a matching PostCompact.
        if !compactor.would_compact(&self.messages) {
            return;
        }

        // Only dispatch PreCompact when we're actually about to compact.
        self.hooks.dispatch(HookEvent::PreCompact {
            transcript_len: bytes,
        });

        let kept_before = self.messages.len();
        match compactor
            .apply_to_transcript(self.llm.as_ref(), Arc::make_mut(&mut self.messages), step)
            .await
        {
            Ok(Some((removed, summary_chars))) => {
                // Success — reset the circuit breaker.
                self.consecutive_compact_failures = 0;
                let kept = kept_before - removed;
                self.hooks.dispatch(HookEvent::PostCompact {
                    removed,
                    summary_chars,
                });
                self.emit(AgentEvent::Compacted {
                    removed,
                    kept,
                    summary_chars,
                    step,
                });
            }
            Ok(None) => {
                // Transcript too short to compact — not a failure, leave counter unchanged.
            }
            Err(e) => {
                // Compaction failed — increment the breaker, emit event, continue.
                tracing::warn!(error = %e, "proactive compaction failed");
                self.consecutive_compact_failures += 1;
                self.emit(AgentEvent::CompactionSkipped {
                    step,
                    reason: crate::event::CompactionSkipReason::Error,
                });
            }
        }
    }

    /// Execute a set of tool calls, returning `(id, name, output, args)` for each.
    /// Read-only calls are batched and executed in parallel; write calls run
    /// sequentially to preserve ordering guarantees.
    async fn execute_tool_calls(&self, calls: &[ToolCall]) -> Vec<ToolCallOutcome> {
        let mut results: Vec<ToolCallOutcome> = Vec::new();

        struct PendingCall {
            id: String,
            name: String,
            args: serde_json::Value,
        }
        let mut pending: Vec<PendingCall> = Vec::new();

        for call in calls {
            // Goal-165: while in agent-driven plan mode, block any write tool
            // that is not `exit_plan_mode` itself.
            if self.exploring_plan_mode.load(Ordering::Relaxed)
                && !self.tools.is_readonly(&call.name)
                && call.name != EXIT_PLAN_MODE_TOOL_NAME
            {
                results.push(ToolCallOutcome {
                    id: call.id.clone(),
                    name: call.name.clone(),
                    result: format!(
                        "ERROR: Cannot execute '{}' in plan mode. \
                         You are in read-only planning mode. \
                         Explore freely with read tools, then call \
                         exit_plan_mode with your plan.",
                        call.name
                    ),
                    audit: None,
                });
                continue;
            }

            // Goal-190: if a tool is in Plan mode and we're not in plan mode,
            // tell the agent to enter plan mode first.
            if !self.exploring_plan_mode.load(Ordering::Relaxed)
                && self.tools.is_plan_mode(&call.name)
                && call.name != ENTER_PLAN_MODE_TOOL_NAME
                && call.name != EXIT_PLAN_MODE_TOOL_NAME
            {
                results.push(ToolCallOutcome {
                    id: call.id.clone(),
                    name: call.name.clone(),
                    result: format!(
                        "ERROR: Tool '{}' requires plan mode. \
                         Call enter_plan_mode first to explore and plan, \
                         then call exit_plan_mode with your plan before using this tool.",
                        call.name
                    ),
                    audit: None,
                });
                continue;
            }

            let effective_args = if let Some(ref hook) = self.permission_hook {
                match hook.check(&call.name, &call.arguments).await {
                    PermissionDecision::Allow => call.arguments.clone(),
                    PermissionDecision::Deny(reason) => {
                        let result = format!("ERROR: {reason}");
                        results.push(ToolCallOutcome {
                            id: call.id.clone(),
                            name: call.name.clone(),
                            result,
                            audit: None,
                        });
                        continue;
                    }
                    PermissionDecision::Transform(new_args) => new_args,
                }
            } else {
                call.arguments.clone()
            };

            let hook_action = self.hooks.dispatch(HookEvent::PreToolCall {
                name: &call.name,
                args: &effective_args,
            });
            match hook_action {
                HookAction::Skip => {
                    let result = "ERROR: tool call skipped by hook".to_string();
                    results.push(ToolCallOutcome {
                        id: call.id.clone(),
                        name: call.name.clone(),
                        result,
                        audit: None,
                    });
                    continue;
                }
                HookAction::Error(msg) => {
                    let result = format!("ERROR: {msg}");
                    results.push(ToolCallOutcome {
                        id: call.id.clone(),
                        name: call.name.clone(),
                        result,
                        audit: None,
                    });
                    continue;
                }
                HookAction::Continue => {}
            }

            pending.push(PendingCall {
                id: call.id.clone(),
                name: call.name.clone(),
                args: effective_args,
            });
        }

        let mut i = 0;
        while i < pending.len() {
            if self
                .tools
                .is_readonly_for_call(&pending[i].name, &pending[i].args)
            {
                let batch_start = i;
                while i < pending.len()
                    && self
                        .tools
                        .is_readonly_for_call(&pending[i].name, &pending[i].args)
                {
                    i += 1;
                }
                let batch: Vec<PendingCall> = pending.drain(batch_start..i).collect();
                i = batch_start;

                let mut join_set = tokio::task::JoinSet::new();
                for pc in &batch {
                    let name = pc.name.clone();
                    let id = pc.id.clone();
                    let args = pc.args.clone();
                    let tools = Arc::clone(&self.tools);
                    join_set.spawn(async move {
                        let tool_start = std::time::Instant::now();
                        let dispatch = tools.invoke_with_audit(&name, args).await;
                        let result = match dispatch.result {
                            Ok(output) => output,
                            Err(crate::error::Error::PermissionDeniedLimit { .. }) => {
                                DENIAL_LIMIT_SENTINEL.to_string()
                            }
                            Err(err) => format!("ERROR: {err}"),
                        };
                        let duration_ms = tool_start.elapsed().as_millis() as u64;
                        (id, name, result, dispatch.audit, duration_ms)
                    });
                }

                type BatchRow = (String, String, String, crate::tools::AuditMeta, u64);
                // Use a HashMap keyed by tool_call_id so that O(1) lookup
                // preserves the correct audit metadata when multiple parallel
                // calls complete in arbitrary order (linear find would always
                // hit the first matching id, causing silent audit mis-attribution).
                let mut batch_map: std::collections::HashMap<String, BatchRow> =
                    std::collections::HashMap::with_capacity(batch.len());
                while let Some(res) = join_set.join_next().await {
                    match res {
                        Ok(row) => {
                            batch_map.insert(row.0.clone(), row);
                        }
                        Err(e) => {
                            tracing::error!(target: "recursive::agent", "parallel tool task panicked: {e}");
                        }
                    }
                }

                for pc in &batch {
                    let Some((_, _, result, audit, duration_ms)) = batch_map.get(&pc.id) else {
                        // Task panicked — push a placeholder error result so
                        // the tool-call ↔ tool-result pairing invariant (#8)
                        // is preserved. Without this, the next LLM request
                        // would include an orphaned tool_call with no matching
                        // tool result and be rejected with HTTP 400.
                        results.push(ToolCallOutcome {
                            id: pc.id.clone(),
                            name: pc.name.clone(),
                            result: "ERROR: tool task panicked during parallel execution"
                                .to_string(),
                            audit: None,
                        });
                        continue;
                    };
                    results.push(ToolCallOutcome {
                        id: pc.id.clone(),
                        name: pc.name.clone(),
                        result: result.clone(),
                        audit: Some(audit.clone()),
                    });
                    self.hooks.dispatch(HookEvent::PostToolCall {
                        name: &pc.name,
                        args: &pc.args,
                        result,
                        duration_ms: *duration_ms,
                    });
                }
            } else {
                let pc = pending.remove(i);
                let tool_start = std::time::Instant::now();
                let dispatch = self
                    .tools
                    .invoke_with_audit(&pc.name, pc.args.clone())
                    .await;
                let result = match dispatch.result {
                    Ok(output) => output,
                    Err(crate::error::Error::PermissionDeniedLimit { .. }) => {
                        DENIAL_LIMIT_SENTINEL.to_string()
                    }
                    Err(err) => format!("ERROR: {err}"),
                };
                let duration_ms = tool_start.elapsed().as_millis() as u64;
                results.push(ToolCallOutcome {
                    id: pc.id.clone(),
                    name: pc.name.clone(),
                    result: result.clone(),
                    audit: Some(dispatch.audit),
                });
                self.hooks.dispatch(HookEvent::PostToolCall {
                    name: &pc.name,
                    args: &pc.args,
                    result: &result,
                    duration_ms,
                });
            }
        }

        results
    }

    /// Stateless core ReAct loop.  Consumes `self` and returns a
    /// [`RunInnerOutcome`] that the wrapper integrates into the parent agent.
    pub(crate) async fn run_inner(mut self) -> Result<RunInnerOutcome> {
        let specs = self.tools.specs();

        let mut final_message: Option<String> = None;
        let mut recent_errors: std::collections::VecDeque<(bool, String)> =
            std::collections::VecDeque::with_capacity(self.stuck_window);
        let mut total_usage = TokenUsage::default();
        // Goal-318: one injector per run; tracks already-fired globs skills.
        let mut skill_injector = SkillInjector::new(&self.globs_skills);
        // Goal-153: audit metadata for tool calls, keyed by (turn, tool_call_id).
        let mut tool_audits: std::collections::HashMap<
            crate::tools::AuditKey,
            crate::tools::AuditMeta,
        > = std::collections::HashMap::new();
        self.total_llm_latency_ms = 0;

        let step_cap = effective_step_limit(self.max_steps);
        for step in 1..=step_cap {
            let step_span = tracing::info_span!("agent.step", step);
            let _guard = step_span.enter();

            // ---- shutdown cancellation -------------------------------------------
            // Termination check, parallel to the BudgetExceeded /
            // TranscriptLimit blocks below. If a CancellationToken was
            // configured (via AgentRuntimeBuilder::shutdown_token / etc.)
            // and it fired between steps, finish cleanly with
            // FinishReason::Cancelled.
            if let Some((finish, finished_steps)) = self.check_shutdown(step, &total_usage) {
                return Ok(self.make_outcome(
                    finish,
                    finished_steps,
                    final_message,
                    total_usage,
                    tool_audits,
                ));
            }

            // ---- wall-clock deadline (Goal 345) ---------------------------------
            if let Some((finish, finished_steps)) = self.check_wall_deadline(step, &total_usage) {
                return Ok(self.make_outcome(
                    finish,
                    finished_steps,
                    final_message,
                    total_usage,
                    tool_audits,
                ));
            }

            // ---- mailbox drain (coordinator → worker mid-run messages) -----------
            self.drain_mailbox().await;

            // ---- transcript budget ------------------------------------------------
            if let Some((finish, finish_step)) = self.enforce_transcript_budget(step, &total_usage)
            {
                return Ok(self.make_outcome(
                    finish,
                    finish_step,
                    final_message,
                    total_usage,
                    tool_audits,
                ));
            }

            // ---- compaction -------------------------------------------------------
            self.maybe_compact(step).await;

            // ---- LLM call (with retry) --------------------------------------------
            let (completion, new_final_message) =
                match self.dispatch_llm_step(&specs, step, &mut total_usage).await {
                    Ok(v) => v,
                    Err(crate::error::Error::Cancelled) => {
                        // Mid-stream cancellation: the stream was interrupted partway
                        // through an LLM call. Route to FinishReason::Cancelled so the
                        // partial transcript is persisted by the caller. Invariant #7.
                        return Ok(self.make_cancelled_outcome(
                            step,
                            final_message,
                            total_usage,
                            tool_audits,
                        ));
                    }
                    Err(e) => return Err(e),
                };
            // Goal 382: a stream-interrupted completion (finish_reason
            // "interrupted") persists the partial reply as a Cancelled turn.
            if completion.finish_reason.as_deref() == Some("interrupted") {
                return Ok(self.finish_interrupted(completion, step, total_usage, tool_audits));
            }
            if let Some(text) = new_final_message {
                final_message = Some(text);
            }

            // ---- no tool calls → finish -------------------------------------------
            if let Some(finish) = self.handle_no_tool_calls(&completion, step) {
                return Ok(self.make_outcome(
                    finish,
                    step,
                    final_message,
                    total_usage,
                    tool_audits,
                ));
            }

            self.push_message(Message::assistant_with_tool_calls(
                completion.content.clone(),
                completion.tool_calls.clone(),
            ));
            self.attach_reasoning_content(completion.reasoning_content.clone());

            for call in &completion.tool_calls {
                self.emit(AgentEvent::ToolCall {
                    name: call.name.clone(),
                    id: call.id.clone(),
                    arguments: call.arguments.to_string(),
                    step,
                });
            }

            // ---- tool execution ---------------------------------------------------
            let results = self.execute_tool_calls(&completion.tool_calls).await;

            if let Some(finish) = self.process_tool_results(
                &results,
                step,
                &mut recent_errors,
                &mut tool_audits,
                &mut skill_injector,
            ) {
                return Ok(self.make_outcome(
                    finish,
                    step,
                    final_message,
                    total_usage,
                    tool_audits,
                ));
            }
        }

        warn!(target: "recursive::agent", "step budget exceeded");
        let finish = FinishReason::BudgetExceeded;
        let steps = self.max_steps;
        self.emit(AgentEvent::TurnFinished {
            reason: finish_reason_str(&finish),
            steps,
        });
        Ok(self.make_outcome(finish, steps, final_message, total_usage, tool_audits))
    }
}

/// Step cap for the agent loop. `0` means unlimited (no `BudgetExceeded`).
///
/// If the `RECURSIVE_HARD_STEP_CAP` env var is set to a positive integer,
/// the cap is clamped to that value regardless of `max_steps`. This lets
/// operators enforce a production ceiling on `recursive loop` long-running
/// sessions (which default to `max_steps=0` / unbounded) without changing
/// the per-session contract. When unset or zero, behaviour is unchanged:
/// `max_steps=0` still means `usize::MAX`.
fn effective_step_limit(max_steps: usize) -> usize {
    let requested = if max_steps == 0 {
        usize::MAX
    } else {
        max_steps
    };
    match hard_step_cap_from_env() {
        Some(cap) if cap > 0 => requested.min(cap),
        _ => requested,
    }
}

/// Read the `RECURSIVE_HARD_STEP_CAP` env var once per call. Returns
/// `None` when unset or unparseable. A value of `0` is treated as
/// "unset" (matches the `max_steps=0` unlimited convention).
fn hard_step_cap_from_env() -> Option<usize> {
    std::env::var("RECURSIVE_HARD_STEP_CAP")
        .ok()
        .and_then(|s| s.parse::<usize>().ok())
}

#[cfg(test)]
mod tests {
    use std::sync::Arc;

    use super::{
        effective_step_limit, estimate_prompt_tokens, estimate_tokens_by_bytes, finish_reason_str,
        RunCore, StaticBreakdownCache, MIN_TRIM_LENGTH, TRIM_PLACEHOLDER,
    };
    use crate::message::Message;

    // The three `effective_step_limit_*` tests mutate the process-global
    // `RECURSIVE_HARD_STEP_CAP` env var. Running in parallel they race each
    // other (one test's set_var lands while another is mid-assert), so the
    // env access must be serialised. This lock is held only by those tests.
    static HARD_CAP_ENV_LOCK: std::sync::Mutex<()> = std::sync::Mutex::new(());

    #[test]
    fn effective_step_limit_zero_means_unbounded() {
        let _guard = HARD_CAP_ENV_LOCK.lock().unwrap_or_else(|e| e.into_inner());
        // Env var must be unset for this test — its presence would clamp.
        let orig = std::env::var("RECURSIVE_HARD_STEP_CAP").ok();
        std::env::remove_var("RECURSIVE_HARD_STEP_CAP");
        assert_eq!(effective_step_limit(0), usize::MAX);
        assert_eq!(effective_step_limit(32), 32);
        if let Some(v) = orig {
            std::env::set_var("RECURSIVE_HARD_STEP_CAP", v);
        }
    }

    #[test]
    fn effective_step_limit_respects_hard_cap_when_set() {
        let _guard = HARD_CAP_ENV_LOCK.lock().unwrap_or_else(|e| e.into_inner());
        let orig = std::env::var("RECURSIVE_HARD_STEP_CAP").ok();
        std::env::set_var("RECURSIVE_HARD_STEP_CAP", "1000");

        // Unlimited path is clamped to the cap.
        assert_eq!(effective_step_limit(0), 1000);
        // Limited path below the cap stays as-is.
        assert_eq!(effective_step_limit(32), 32);
        // Limited path above the cap is clamped.
        assert_eq!(effective_step_limit(5000), 1000);

        if let Some(v) = orig {
            std::env::set_var("RECURSIVE_HARD_STEP_CAP", v);
        } else {
            std::env::remove_var("RECURSIVE_HARD_STEP_CAP");
        }
    }

    #[test]
    fn effective_step_limit_ignores_invalid_hard_cap() {
        let _guard = HARD_CAP_ENV_LOCK.lock().unwrap_or_else(|e| e.into_inner());
        let orig = std::env::var("RECURSIVE_HARD_STEP_CAP").ok();
        std::env::set_var("RECURSIVE_HARD_STEP_CAP", "not-a-number");
        assert_eq!(effective_step_limit(0), usize::MAX);
        std::env::set_var("RECURSIVE_HARD_STEP_CAP", "0");
        // Cap value of 0 is treated as "unset" → unlimited preserved.
        assert_eq!(effective_step_limit(0), usize::MAX);
        if let Some(v) = orig {
            std::env::set_var("RECURSIVE_HARD_STEP_CAP", v);
        } else {
            std::env::remove_var("RECURSIVE_HARD_STEP_CAP");
        }
    }

    /// Verify the stuck-detection window/rate math that RunCore uses.
    /// This tests the same logic as the sliding-window check in run_inner().
    #[test]
    fn stuck_detection_window_and_rate() {
        // Simulate: stuck_window=3, stuck_error_rate=1.0 → 3 consecutive errors triggers stuck
        let stuck_window = 3usize;
        let stuck_error_rate = 1.0f64;

        let mut recent_errors: std::collections::VecDeque<(bool, String)> =
            std::collections::VecDeque::with_capacity(stuck_window);

        // Push 2 errors — should not trigger yet
        for i in 0..2 {
            if recent_errors.len() == stuck_window {
                recent_errors.pop_front();
            }
            let name = format!("tool_{i}");
            recent_errors.push_back((true, name));
            let rate = recent_errors.iter().filter(|(e, _)| *e).count() as f64
                / recent_errors.len() as f64;
            assert!(
                recent_errors.len() < stuck_window || rate < stuck_error_rate,
                "should not trigger before window is full"
            );
        }

        // Push 3rd error — window is now full and rate = 1.0 ≥ threshold
        if recent_errors.len() == stuck_window {
            recent_errors.pop_front();
        }
        recent_errors.push_back((true, "tool_2".to_string()));
        assert_eq!(recent_errors.len(), stuck_window);
        let error_count = recent_errors.iter().filter(|(e, _)| *e).count();
        let rate = error_count as f64 / stuck_window as f64;
        assert!(
            rate >= stuck_error_rate,
            "rate {rate} should trigger stuck at threshold {stuck_error_rate}"
        );

        // Verify most-repeated tool reporting logic
        let error_entries: Vec<&str> = recent_errors
            .iter()
            .filter(|(e, _)| *e)
            .map(|(_, n)| n.as_str())
            .collect();
        let mut counts: std::collections::HashMap<&str, usize> = std::collections::HashMap::new();
        for n in &error_entries {
            *counts.entry(n).or_default() += 1;
        }
        let top_tool = counts.into_iter().max_by_key(|&(_, c)| c).map(|(n, _)| n);
        // All three are distinct so any one could be "top"; just verify it exists
        assert!(top_tool.is_some());
    }

    #[test]
    fn stuck_detection_partial_errors_below_threshold() {
        // window=4, rate=0.8 → need 4 errors out of 4 (or round up).
        // With 3 errors + 1 success the rate is 0.75 < 0.8, so no trigger.
        let stuck_window = 4usize;
        let stuck_error_rate = 0.8f64;

        let mut recent_errors: std::collections::VecDeque<(bool, String)> =
            std::collections::VecDeque::with_capacity(stuck_window);

        let pattern = [
            (true, "tool_a"),
            (true, "tool_b"),
            (true, "tool_a"),
            (false, "tool_c"),
        ]; // 3/4 errors = 0.75
        for (is_error, name) in &pattern {
            if recent_errors.len() == stuck_window {
                recent_errors.pop_front();
            }
            recent_errors.push_back((*is_error, name.to_string()));
        }

        assert_eq!(recent_errors.len(), stuck_window);
        let rate = recent_errors.iter().filter(|(e, _)| *e).count() as f64 / stuck_window as f64;
        assert!(
            rate < stuck_error_rate,
            "rate {rate} should be below threshold {stuck_error_rate}"
        );
    }

    #[test]
    fn stuck_detection_reports_most_repeated_tool() {
        // window=4, rate=0.75, pattern: tool_a err, tool_b err, tool_a err, tool_b ok
        // error_count=3, rate=0.75, most repeated should be tool_a (appears 2× in errors)
        let stuck_window = 4usize;
        let stuck_error_rate = 0.75f64;

        let mut recent_errors: std::collections::VecDeque<(bool, String)> =
            std::collections::VecDeque::with_capacity(stuck_window);

        let pattern = [
            (true, "tool_a"),
            (true, "tool_b"),
            (true, "tool_a"),
            (false, "tool_b"),
        ];
        for (is_error, name) in &pattern {
            if recent_errors.len() == stuck_window {
                recent_errors.pop_front();
            }
            recent_errors.push_back((*is_error, name.to_string()));
        }

        assert_eq!(recent_errors.len(), stuck_window);

        let error_entries: Vec<&str> = recent_errors
            .iter()
            .filter(|(is_err, _)| *is_err)
            .map(|(_, n)| n.as_str())
            .collect();
        let error_count = error_entries.len();
        let rate = error_count as f64 / stuck_window as f64;
        assert!(
            rate >= stuck_error_rate,
            "rate {rate} should trigger stuck at threshold {stuck_error_rate}"
        );

        // Find the most frequently appearing tool name in the error window.
        let mut counts: std::collections::HashMap<&str, usize> = std::collections::HashMap::new();
        for n in &error_entries {
            *counts.entry(n).or_default() += 1;
        }
        let top_tool = counts
            .into_iter()
            .max_by_key(|&(_, c)| c)
            .map(|(n, _)| n)
            .unwrap();
        assert_eq!(
            top_tool, "tool_a",
            "most repeated tool should be tool_a (2 errors), not tool_b (1 error)"
        );
    }

    // Helper: build a minimal RunCore suitable for testing methods that only
    // touch `messages` (e.g. `attach_reasoning_content`).
    fn make_test_core<'a>(
        messages: Vec<Message>,
        hooks: &'a crate::hooks::HookRegistry,
    ) -> RunCore<'a> {
        use std::sync::atomic::AtomicBool;
        use std::sync::Arc;
        RunCore {
            messages: Arc::new(messages),
            llm: Arc::new(crate::llm::MockProvider::new(vec![])),
            tools: Arc::new(crate::tools::ToolRegistry::default()),
            max_steps: 1,
            max_transcript_chars: None,
            events: None,
            streaming: false,
            compactor: None,
            microcompactor: None,
            permission_hook: None,
            hooks,
            total_llm_latency_ms: 0,
            exploring_plan_mode: Arc::new(AtomicBool::new(false)),
            shutdown_token: None,
            mailbox: None,
            stuck_window: 3,
            stuck_error_rate: 1.0,
            turn: 0,
            globs_skills: vec![],
            prompt_segments: None,
            static_breakdown: StaticBreakdownCache::default(),
            last_prompt_tokens: 0,
            consecutive_compact_failures: 0,
            wall_timeout_secs: 0,
            wall_start: None,
        }
    }

    #[test]
    fn attach_reasoning_content_sets_last_message_when_some() {
        let hooks = crate::hooks::HookRegistry::new();
        let mut core = make_test_core(vec![Message::assistant("response".to_string())], &hooks);

        core.attach_reasoning_content(Some("I thought carefully about this.".to_string()));

        assert_eq!(
            core.messages.last().unwrap().reasoning_content.as_deref(),
            Some("I thought carefully about this."),
            "reasoning_content should be set on the last message"
        );
    }

    #[test]
    fn attach_reasoning_content_does_not_modify_when_none() {
        let hooks = crate::hooks::HookRegistry::new();
        let mut core = make_test_core(vec![Message::assistant("response".to_string())], &hooks);

        core.attach_reasoning_content(None);

        assert!(
            core.messages.last().unwrap().reasoning_content.is_none(),
            "reasoning_content should remain None when called with None"
        );
    }

    #[test]
    fn attach_reasoning_content_preserves_existing_content_when_none() {
        let hooks = crate::hooks::HookRegistry::new();
        let mut msg = Message::assistant("response".to_string());
        msg.reasoning_content = Some("prior thinking".to_string());
        let mut core = make_test_core(vec![msg], &hooks);

        core.attach_reasoning_content(None);

        assert_eq!(
            core.messages.last().unwrap().reasoning_content.as_deref(),
            Some("prior thinking"),
            "calling with None should not overwrite existing reasoning_content"
        );
    }

    // ========================================================================
    // maybe_trim_transcript tests
    // ========================================================================

    // ========================================================================
    // finish_reason_str tests
    // (kills String::new() and "xyzzy" function-level mutants)
    // ========================================================================

    #[test]
    fn finish_reason_str_is_nonempty_and_not_xyzzy() {
        use crate::agent::FinishReason;
        let reason = FinishReason::NoMoreToolCalls;
        let s = finish_reason_str(&reason);
        assert!(
            !s.is_empty(),
            "finish_reason_str must not return empty string"
        );
        assert_ne!(s, "xyzzy", "finish_reason_str must not return 'xyzzy'");
    }

    #[test]
    fn finish_reason_str_matches_display() {
        use crate::agent::FinishReason;
        let reason = FinishReason::BudgetExceeded;
        let s = finish_reason_str(&reason);
        assert_eq!(
            s,
            reason.to_string(),
            "finish_reason_str must delegate to Display"
        );
    }

    // ========================================================================
    // estimate_prompt_tokens / fallback-usage tests
    // (cover the else branch in dispatch_llm_step used when the provider
    //  does not report `usage`)
    // ========================================================================

    #[test]
    fn estimate_prompt_tokens_divides_total_chars_by_four() {
        // 3 messages: 4 + 8 + 12 = 24 chars → 24 / 4 = 6 tokens.
        let messages = vec![
            Message::user("abcd".to_string()),           // 4
            Message::assistant("abcdefgh".to_string()),  // 8
            Message::system("abcdefghijkl".to_string()), // 12
        ];
        assert_eq!(
            estimate_prompt_tokens(&messages),
            6,
            "24 total chars / 4 = 6 tokens"
        );
    }

    #[test]
    fn estimate_prompt_tokens_truncates_partial_tokens() {
        // 7 chars → 7 / 4 = 1 (integer truncation), not rounded up to 2.
        let messages = vec![Message::user("abcdefg".to_string())];
        assert_eq!(
            estimate_prompt_tokens(&messages),
            1,
            "integer division must truncate 7/4 to 1"
        );
    }

    #[test]
    fn estimate_prompt_tokens_floors_to_one_for_empty_messages() {
        // No messages → 0 / 4 = 0, but .max(1) floors to 1 so the gauge
        // never reports zero (the system prompt always exists).
        let messages: Vec<Message> = vec![];
        assert_eq!(
            estimate_prompt_tokens(&messages),
            1,
            "empty transcript must still report at least 1 token"
        );
    }

    #[test]
    fn estimate_prompt_tokens_floors_to_one_for_sub_four_chars() {
        // 3 chars → 3 / 4 = 0, floored to 1 by .max(1).
        let messages = vec![Message::user("abc".to_string())];
        assert_eq!(
            estimate_prompt_tokens(&messages),
            1,
            "content shorter than 4 chars must floor to 1 token"
        );
    }

    // Helper: build a RunCore wired to a custom provider and event sender so
    // tests can drive `dispatch_llm_step` and inspect emitted events.
    fn make_core_with_llm_and_events<'a>(
        messages: Vec<Message>,
        llm: Arc<dyn crate::llm::ChatProvider>,
        events: tokio::sync::mpsc::UnboundedSender<crate::event::AgentEvent>,
        hooks: &'a crate::hooks::HookRegistry,
    ) -> RunCore<'a> {
        use std::sync::atomic::AtomicBool;
        RunCore {
            messages: Arc::new(messages),
            llm,
            tools: Arc::new(crate::tools::ToolRegistry::default()),
            max_steps: 1,
            max_transcript_chars: None,
            events: Some(events),
            streaming: false,
            compactor: None,
            microcompactor: None,
            permission_hook: None,
            hooks,
            total_llm_latency_ms: 0,
            exploring_plan_mode: Arc::new(AtomicBool::new(false)),
            shutdown_token: None,
            mailbox: None,
            stuck_window: 3,
            stuck_error_rate: 1.0,
            turn: 0,
            globs_skills: vec![],
            prompt_segments: None,
            static_breakdown: StaticBreakdownCache::default(),
            last_prompt_tokens: 0,
            consecutive_compact_failures: 0,
            wall_timeout_secs: 0,
            wall_start: None,
        }
    }

    /// When the provider returns a completion without `usage`, the fallback
    /// branch must emit a best-effort estimated `Usage` event: input from the
    /// transcript chars, output from `content` + `reasoning_content`, both
    /// divided by 4, with zero cache tokens — and it must NOT accumulate into
    /// `total_usage` (only provider-reported usage does).
    #[tokio::test]
    async fn dispatch_llm_step_emits_estimated_usage_when_provider_reports_none() {
        use crate::event::AgentEvent;
        use crate::llm::{Completion, MockProvider, TokenUsage};

        let hooks = crate::hooks::HookRegistry::new();
        // Transcript: a single user message of exactly 40 bytes → 40/4 = 10.
        let messages = vec![Message::user("x".repeat(40))];

        // Completion WITHOUT usage forces the fallback branch.
        // content = 8 bytes, reasoning = 4 bytes → 12/4 = 3 output tokens.
        let completion = Completion {
            content: "12345678".to_string(),
            tool_calls: vec![],
            finish_reason: Some("stop".to_string()),
            usage: None,
            reasoning_content: Some("abcd".to_string()),
        };
        let llm = Arc::new(MockProvider::new(vec![completion]));

        let (tx, mut rx) = tokio::sync::mpsc::unbounded_channel::<AgentEvent>();
        let mut core = make_core_with_llm_and_events(messages, llm, tx, &hooks);

        let specs: Vec<crate::llm::ToolSpec> = vec![];
        let mut total_usage = TokenUsage::default();
        core.dispatch_llm_step(&specs, 0, &mut total_usage)
            .await
            .expect("dispatch_llm_step should succeed");

        // Estimated usage must not be folded into total_usage.
        assert_eq!(
            total_usage.prompt_tokens, 0,
            "estimate must not accumulate input into total_usage"
        );
        assert_eq!(
            total_usage.completion_tokens, 0,
            "estimate must not accumulate output into total_usage"
        );

        // Locate the emitted Usage event.
        let mut usage_event = None;
        while let Ok(ev) = rx.try_recv() {
            if matches!(ev, AgentEvent::Usage { .. }) {
                usage_event = Some(ev);
                break;
            }
        }
        match usage_event.expect("fallback branch must emit a Usage event") {
            AgentEvent::Usage {
                input_tokens,
                output_tokens,
                cache_hit_tokens,
                cache_miss_tokens,
                step,
            } => {
                assert_eq!(input_tokens, 10, "input estimate = 40 chars / 4");
                assert_eq!(output_tokens, 3, "output estimate = (8 + 4) chars / 4");
                assert_eq!(cache_hit_tokens, 0, "estimate reports no cache hits");
                assert_eq!(cache_miss_tokens, 0, "estimate reports no cache misses");
                assert_eq!(step, 0, "step must be forwarded unchanged");
            }
            other => panic!("expected Usage event, got {other:?}"),
        }
    }

    // ========================================================================
    // maybe_trim_transcript tests
    // ========================================================================

    #[test]
    fn maybe_trim_does_nothing_when_under_limit() {
        let hooks = crate::hooks::HookRegistry::new();
        // Use a large tool result (> MIN_TRIM_LENGTH) but keep limit ABOVE total bytes.
        // This kills the `replace < with ==` mutant: with `==`, bytes != limit means
        // the early-return is skipped and the tool result would be incorrectly trimmed.
        let large_output = "x".repeat(MIN_TRIM_LENGTH + 10);
        let messages = vec![
            Message::system("sys".to_string()),
            Message::tool_result("c1", &large_output),
        ];
        let orig_content = messages[1].content.clone();
        let total_bytes = "sys".len() + large_output.len();
        let mut core = make_test_core(messages, &hooks);

        // Set limit strictly ABOVE total bytes (not equal), so trimming must not fire.
        let limit = total_bytes + 1;
        core.maybe_trim_transcript(limit, 0);

        assert_eq!(
            core.messages[1].content, orig_content,
            "content must not be touched when total bytes < limit"
        );
    }

    #[test]
    fn enforce_transcript_budget_returns_none_when_under_limit() {
        // kills `replace < with == in enforce_transcript_budget` mutation.
        // If changed to `==`, a core with chars clearly under the limit would
        // return Some (falsely claiming budget exceeded) instead of None.
        use crate::llm::TokenUsage;
        let hooks = crate::hooks::HookRegistry::new();
        // One short message: "hi" = 2 chars
        let mut core = make_test_core(vec![Message::user("hi".to_string())], &hooks);
        // Set limit to 1000 — far above 2 chars
        core.max_transcript_chars = Some(1000);
        let usage = TokenUsage::default();
        let result = core.enforce_transcript_budget(0, &usage);
        assert!(
            result.is_none(),
            "chars (2) < limit (1000) must return None; got Some(_)"
        );
    }

    #[test]
    fn enforce_transcript_budget_returns_finish_reason_when_over_limit() {
        // Validates the >-limit path: when chars >= limit, must return Some with TranscriptLimit.
        use crate::agent::FinishReason;
        use crate::llm::TokenUsage;
        let hooks = crate::hooks::HookRegistry::new();
        // Message with 100 'x' chars — well above a limit of 10
        let msg = Message::user("x".repeat(100));
        let mut core = make_test_core(vec![msg], &hooks);
        core.max_transcript_chars = Some(10);
        let usage = TokenUsage::default();
        let result = core.enforce_transcript_budget(0, &usage);
        assert!(
            result.is_some(),
            "chars (100) >= limit (10) must return Some finish reason"
        );
        let (finish, _step) = result.unwrap();
        assert!(
            matches!(finish, FinishReason::TranscriptLimit { .. }),
            "finish reason must be TranscriptLimit; got {finish:?}"
        );
    }

    #[test]
    fn maybe_trim_replaces_large_tool_result_when_over_limit() {
        let hooks = crate::hooks::HookRegistry::new();
        // A tool result with content > MIN_TRIM_LENGTH (200) bytes
        let large_output = "x".repeat(MIN_TRIM_LENGTH + 100);
        let messages = vec![
            Message::system("sys".to_string()),
            Message::tool_result("c1", &large_output),
        ];
        let mut core = make_test_core(messages, &hooks);

        // Set limit below total content so trimming fires
        core.maybe_trim_transcript(10, 0);

        assert_eq!(
            core.messages[1].content, TRIM_PLACEHOLDER,
            "large tool result must be replaced with placeholder"
        );
    }

    #[test]
    fn maybe_trim_does_not_trim_small_tool_results() {
        let hooks = crate::hooks::HookRegistry::new();
        // A tool result shorter than MIN_TRIM_LENGTH
        let small_output = "small".to_string();
        let messages = vec![
            Message::system("sys".to_string()),
            Message::tool_result("c1", &small_output),
        ];
        let mut core = make_test_core(messages, &hooks);

        // Trigger trim (limit = 0)
        core.maybe_trim_transcript(0, 0);

        assert_eq!(
            core.messages[1].content, small_output,
            "short tool result must not be trimmed (< MIN_TRIM_LENGTH)"
        );
    }

    #[test]
    fn maybe_trim_does_not_trim_exactly_min_trim_length() {
        // Kills the `replace > with >=` mutant: content.len() == MIN_TRIM_LENGTH
        // must NOT be trimmed under the strict `>` check.
        let hooks = crate::hooks::HookRegistry::new();
        let exact_output = "z".repeat(MIN_TRIM_LENGTH);
        let messages = vec![
            Message::system("s".to_string()),
            Message::tool_result("c1", &exact_output),
        ];
        let mut core = make_test_core(messages, &hooks);
        // Set limit = 0 so trimming is attempted
        core.maybe_trim_transcript(0, 0);
        assert_eq!(
            core.messages[1].content, exact_output,
            "content exactly at MIN_TRIM_LENGTH must NOT be trimmed (> is strict)"
        );
    }

    #[test]
    fn maybe_trim_trims_one_more_than_min_trim_length() {
        // Complementary to the above: content.len() == MIN_TRIM_LENGTH + 1 MUST be trimmed.
        let hooks = crate::hooks::HookRegistry::new();
        let just_over = "z".repeat(MIN_TRIM_LENGTH + 1);
        let messages = vec![
            Message::system("s".to_string()),
            Message::tool_result("c1", &just_over),
        ];
        let mut core = make_test_core(messages, &hooks);
        core.maybe_trim_transcript(0, 0);
        assert_eq!(
            core.messages[1].content, TRIM_PLACEHOLDER,
            "content one byte over MIN_TRIM_LENGTH must be trimmed"
        );
    }

    #[test]
    fn maybe_trim_stops_after_fitting_under_limit() {
        let hooks = crate::hooks::HookRegistry::new();
        // Two large tool results; only trim until we go under the limit.
        let large1 = "a".repeat(MIN_TRIM_LENGTH + 100);
        let large2 = "b".repeat(MIN_TRIM_LENGTH + 100);
        let messages = vec![
            Message::system("sys".to_string()),
            Message::tool_result("c1", &large1),
            Message::tool_result("c2", &large2),
        ];
        let mut core = make_test_core(messages, &hooks);

        // Set limit just above placeholder_len so trimming the first result suffices.
        let placeholder_len = TRIM_PLACEHOLDER.len();
        let limit = 3 + placeholder_len + large2.len() + 50; // sys + placeholder + large2 + buffer
        core.maybe_trim_transcript(limit, 0);

        assert_eq!(
            core.messages[1].content, TRIM_PLACEHOLDER,
            "first large result should be trimmed"
        );
        assert_eq!(
            core.messages[2].content, large2,
            "second result should not be touched once we're under limit"
        );
    }

    #[test]
    fn maybe_trim_trims_when_chars_exactly_equals_limit() {
        // Kills: `replace < with <=` at line 196.
        //
        // When chars == limit the original `<` guard is FALSE → trimming proceeds.
        // With `<=`, it would be TRUE → early return, nothing is trimmed.
        let hooks = crate::hooks::HookRegistry::new();
        // Build a transcript whose total content length == limit exactly.
        let tool_content = "a".repeat(MIN_TRIM_LENGTH + 50); // 250 chars
        let messages = vec![
            Message::system("s".to_string()),          // 1 char
            Message::tool_result("c1", &tool_content), // 250 chars
        ];
        // Total = 1 + 250 = 251.  Set limit = 251 so chars == limit.
        let limit = 1 + tool_content.len();
        let mut core = make_test_core(messages, &hooks);
        core.maybe_trim_transcript(limit, 0);

        assert_eq!(
            core.messages[1].content, TRIM_PLACEHOLDER,
            "tool result must be trimmed when chars == limit (not strictly less)"
        );
    }

    #[test]
    fn maybe_trim_continues_when_chars_equals_limit_after_first_trim() {
        // Kills: `replace < with <=` at line 211 (the inner break condition).
        //
        // After trimming the first tool result, if the remaining chars == limit,
        // the original `<` is FALSE → the loop continues and trims the second tool result.
        // With `<=`, it would be TRUE → break, leaving the second tool result untrimmed.
        let hooks = crate::hooks::HookRegistry::new();

        let tool_content = "a".repeat(MIN_TRIM_LENGTH + 50); // 250 chars
        let messages = vec![
            Message::system("s".to_string()),          // 1 char
            Message::tool_result("c1", &tool_content), // 250 chars (will be trimmed first)
            Message::tool_result("c2", &tool_content), // 250 chars (must ALSO be trimmed)
        ];
        // Total = 1 + 250 + 250 = 501
        // TRIM_PLACEHOLDER.len() = 40
        // After trimming tool1: 501 - 250 + 40 = 291
        // Set limit = 291 so that after trimming tool1, chars == limit (not < limit).
        // Original `<`: 291 < 291 → false → continues trimming tool2.
        // Mutant  `<=`: 291 <= 291 → true  → breaks, tool2 NOT trimmed.
        let after_first_trim = 1 + TRIM_PLACEHOLDER.len() + tool_content.len();
        let limit = after_first_trim; // exact boundary

        let mut core = make_test_core(messages, &hooks);
        core.maybe_trim_transcript(limit, 0);

        assert_eq!(
            core.messages[1].content, TRIM_PLACEHOLDER,
            "first tool result must be trimmed"
        );
        assert_eq!(
            core.messages[2].content, TRIM_PLACEHOLDER,
            "second tool result must ALSO be trimmed when chars == limit after first trim"
        );
    }

    #[test]
    fn maybe_trim_emits_event_when_trimmed() {
        // Kills: `replace += with *=` (trimmed_count stays 0 → event not emitted)
        //        `replace > with ==/</>= in if trimmed_count > 0` (wrong guard)
        use crate::event::AgentEvent;
        use tokio::sync::mpsc;

        let hooks = crate::hooks::HookRegistry::new();
        let large_output = "x".repeat(MIN_TRIM_LENGTH + 50);
        let messages = vec![
            Message::system("sys".to_string()),
            Message::tool_result("c1", &large_output),
        ];
        let (tx, mut rx) = mpsc::unbounded_channel::<AgentEvent>();
        let mut core = make_test_core(messages, &hooks);
        core.events = Some(tx);

        // Trim fires (limit = 0 → chars > 0 = limit)
        core.maybe_trim_transcript(0, 0);

        // The emit must have sent an AssistantText event containing the trim notice
        let event = rx
            .try_recv()
            .expect("an event must have been emitted after trimming");
        match event {
            AgentEvent::AssistantText { text, .. } => {
                assert!(
                    text.contains("trimmed"),
                    "trim event text must mention 'trimmed'; got: {text}"
                );
            }
            other => panic!("expected AssistantText but got: {other:?}"),
        }
    }

    #[test]
    fn maybe_trim_no_event_when_nothing_trimmed() {
        // Complementary: no event when nothing is trimmed (trimmed_count == 0)
        use crate::event::AgentEvent;
        use tokio::sync::mpsc;

        let hooks = crate::hooks::HookRegistry::new();
        let small_output = "tiny".to_string(); // Below MIN_TRIM_LENGTH
        let messages = vec![
            Message::system("sys".to_string()),
            Message::tool_result("c1", &small_output),
        ];
        let (tx, mut rx) = mpsc::unbounded_channel::<AgentEvent>();
        let mut core = make_test_core(messages, &hooks);
        core.events = Some(tx);

        // Limit = 0 → trimming is attempted, but nothing qualifies (< MIN_TRIM_LENGTH)
        core.maybe_trim_transcript(0, 0);

        assert!(
            rx.try_recv().is_err(),
            "no event must be emitted when nothing was trimmed"
        );
    }

    // ========================================================================
    // maybe_compact tests
    // ========================================================================

    #[tokio::test]
    async fn maybe_compact_noop_when_no_compactor() {
        let hooks = crate::hooks::HookRegistry::new();
        let messages = vec![
            Message::user("q".to_string()),
            Message::assistant("a".to_string()),
        ];
        let mut core = make_test_core(messages, &hooks);
        // compactor is None by default in make_test_core
        core.maybe_compact(0).await;
        assert_eq!(core.messages.len(), 2, "messages must not change");
    }

    #[tokio::test]
    async fn maybe_compact_noop_when_under_threshold() {
        use crate::compact::Compactor;
        let hooks = crate::hooks::HookRegistry::new();
        let messages = vec![
            Message::user("hi".to_string()),
            Message::assistant("hello".to_string()),
        ];
        let mut core = make_test_core(messages, &hooks);
        // Set a threshold much larger than the transcript
        core.compactor = Some(Compactor::new(usize::MAX));

        core.maybe_compact(0).await;
        assert_eq!(core.messages.len(), 2, "no compaction under threshold");
    }

    #[tokio::test]
    async fn maybe_compact_fires_when_over_threshold() {
        use crate::compact::Compactor;
        use crate::llm::{Completion, MockProvider};
        let hooks = crate::hooks::HookRegistry::new();
        // Build a transcript that exceeds the threshold
        let messages = vec![
            Message::system("sys".to_string()),
            Message::user("msg1".to_string()),
            Message::assistant("rep1".to_string()),
            Message::user("msg2".to_string()),
            Message::assistant("rep2".to_string()),
            Message::user("msg3".to_string()),
        ];
        let provider = Arc::new(MockProvider::new(vec![Completion {
            content: "compact summary".to_string(),
            tool_calls: vec![],
            finish_reason: Some("stop".to_string()),
            usage: None,
            reasoning_content: None,
        }]));
        let mut core = make_test_core(messages, &hooks);
        core.llm = provider;
        // Threshold = 0 → always compact
        core.compactor = Some(Compactor::new(0).keep_recent_n(2));

        core.maybe_compact(1).await;
        // After compaction the transcript starts with a compaction summary
        assert!(
            core.messages[0].is_compaction_summary,
            "first message must be a compaction summary after compaction"
        );
    }

    #[tokio::test]
    async fn maybe_compact_fires_at_threshold_boundary() {
        // Kills: `replace < with <=` mutant at line 239.
        // With `<=`, when chars == threshold_chars, the function returns early instead of compacting.
        use crate::compact::Compactor;
        use crate::llm::{Completion, MockProvider};
        let hooks = crate::hooks::HookRegistry::new();
        let messages = vec![
            Message::system("sys".to_string()),
            Message::user("msg1".to_string()),
            Message::assistant("rep1".to_string()),
            Message::user("msg2".to_string()),
            Message::assistant("rep2".to_string()),
            Message::user("last".to_string()),
        ];
        // Compute exact bytes
        let bytes = crate::compact::Compactor::estimate_bytes(&messages);
        let provider = Arc::new(MockProvider::new(vec![Completion {
            content: "summary".to_string(),
            tool_calls: vec![],
            finish_reason: Some("stop".to_string()),
            usage: None,
            reasoning_content: None,
        }]));
        let mut core = make_test_core(messages, &hooks);
        core.llm = provider;
        // Set threshold = exact bytes → `bytes < threshold` is false → compaction fires
        // With `< → <=`: `bytes <= bytes` is true → returns early → no compaction
        core.compactor = Some(Compactor::new(bytes).keep_recent_n(2));

        core.maybe_compact(1).await;
        assert!(
            core.messages[0].is_compaction_summary,
            "compaction must fire when bytes == threshold (bytes is NOT less than threshold)"
        );
    }

    #[tokio::test]
    async fn maybe_compact_uses_token_threshold_intra_turn() {
        // Goal-330 regression: intra-turn maybe_compact must use the
        // token-based threshold when `last_prompt_tokens` is available,
        // even if the char threshold is high enough that it alone would
        // NOT fire.
        use crate::compact::Compactor;
        use crate::llm::{Completion, MockProvider};
        let hooks = crate::hooks::HookRegistry::new();
        let messages = vec![
            Message::system("sys".to_string()),
            Message::user("msg1".to_string()),
            Message::assistant("rep1".to_string()),
            Message::user("msg2".to_string()),
            Message::assistant("rep2".to_string()),
            Message::user("msg3".to_string()),
        ];
        let provider = Arc::new(MockProvider::new(vec![Completion {
            content: "token-threshold triggered summary".to_string(),
            tool_calls: vec![],
            finish_reason: Some("stop".to_string()),
            usage: None,
            reasoning_content: None,
        }]));
        let mut core = make_test_core(messages, &hooks);
        core.llm = provider;
        // Set high char threshold (would NOT fire on this transcript)
        // and low token threshold (WILL fire when last_prompt_tokens is set).
        let bytes = crate::compact::Compactor::estimate_bytes(&core.messages);
        core.compactor = Some(
            Compactor::new(bytes + 1000) // char threshold too high
                .threshold_prompt_tokens(500) // low token threshold
                .keep_recent_n(2),
        );
        // Set last_prompt_tokens above the token threshold.
        core.last_prompt_tokens = 500;

        core.maybe_compact(1).await;
        assert!(
            core.messages[0].is_compaction_summary,
            "compaction must fire via token threshold even though chars are below char threshold"
        );
    }

    /// Kills: `delete ! in RunCore<'a>::execute_tool_calls` at line 306.
    ///
    /// When `exploring_plan_mode == false` and the registry's mode is Plan,
    /// calling any tool (other than enter/exit plan mode) must return an error
    /// asking the agent to call `enter_plan_mode` first.
    ///
    /// With the mutant (`!` deleted), the condition becomes:
    ///   `if self.exploring_plan_mode.load() && …`
    /// which is FALSE when not in plan mode, so the guard is skipped and the
    /// tool call proceeds instead of returning the expected error.
    #[tokio::test]
    async fn execute_tool_calls_plan_mode_guard_when_not_exploring() {
        use crate::llm::ToolCall;
        use crate::permissions::{PermissionMode, PermissionsConfig};
        use std::sync::atomic::AtomicBool;

        let hooks = crate::hooks::HookRegistry::new();
        let tools = Arc::new(crate::tools::ToolRegistry::default().with_permissions(
            PermissionsConfig {
                mode: PermissionMode::Plan {
                    pre_plan_mode: Box::new(PermissionMode::Default),
                    bypass_available: false,
                },
                layers: vec![],
            },
        ));

        let mut core = make_test_core(vec![], &hooks);
        core.tools = tools;
        // Explicitly not in plan-mode exploration.
        core.exploring_plan_mode = Arc::new(AtomicBool::new(false));

        let call = ToolCall {
            id: "tc1".to_string(),
            name: "Write".to_string(),
            arguments: serde_json::json!({}),
        };

        let results = core.execute_tool_calls(&[call]).await;

        assert_eq!(results.len(), 1, "should produce exactly one outcome");
        assert!(
            results[0].result.contains("enter_plan_mode"),
            "must tell the agent to call enter_plan_mode first; got: {}",
            results[0].result,
        );
    }

    #[tokio::test]
    async fn maybe_compact_kept_count_is_correct() {
        // Kills: `replace - with + in maybe_compact` at line 253.
        // `kept = kept_before - removed` should equal the number of messages remaining.
        // With `- → +`, `kept = kept_before + removed` which would be wrong.
        use crate::compact::Compactor;
        use crate::event::AgentEvent;
        use crate::llm::{Completion, MockProvider};
        use tokio::sync::mpsc;

        let hooks = crate::hooks::HookRegistry::new();
        let messages = vec![
            Message::system("sys".to_string()),
            Message::user("msg1".to_string()),
            Message::assistant("rep1".to_string()),
            Message::user("msg2".to_string()),
            Message::assistant("rep2".to_string()),
            Message::user("last".to_string()),
        ];
        let kept_before = messages.len();
        let provider = Arc::new(MockProvider::new(vec![Completion {
            content: "summary".to_string(),
            tool_calls: vec![],
            finish_reason: Some("stop".to_string()),
            usage: None,
            reasoning_content: None,
        }]));
        let (tx, mut rx) = mpsc::unbounded_channel::<AgentEvent>();
        let mut core = make_test_core(messages, &hooks);
        core.llm = provider;
        core.events = Some(tx);
        core.compactor = Some(Compactor::new(0).keep_recent_n(2));

        core.maybe_compact(1).await;

        // Drain events to find Compacted
        let mut found_compacted = false;
        while let Ok(ev) = rx.try_recv() {
            if let AgentEvent::Compacted { removed, kept, .. } = ev {
                assert_eq!(
                    kept + removed,
                    kept_before,
                    "kept + removed must equal the original message count"
                );
                // kept must be the actual remaining messages (after compaction, first is summary)
                assert_eq!(
                    kept,
                    kept_before - removed,
                    "kept must be kept_before - removed, not kept_before + removed"
                );
                found_compacted = true;
            }
        }
        assert!(found_compacted, "a Compacted event must have been emitted");
    }

    // ========================================================================
    // Circuit breaker tests (Goal 331)
    // ========================================================================

    #[tokio::test]
    async fn maybe_compact_circuit_breaker_skips_when_failures_exceed_threshold() {
        // When consecutive_compact_failures >= MAX_CONSECUTIVE_COMPACT_FAILURES,
        // maybe_compact must emit CircuitBreaker and return without compacting.
        use crate::compact::{Compactor, MAX_CONSECUTIVE_COMPACT_FAILURES};
        use crate::event::AgentEvent::{Compacted, CompactionSkipped};
        use crate::event::CompactionSkipReason;
        use tokio::sync::mpsc;

        let hooks = crate::hooks::HookRegistry::new();
        let messages = vec![
            Message::system("sys".to_string()),
            Message::user("long enough to trigger compaction".to_string()),
            Message::assistant("response".to_string()),
        ];
        let (tx, mut rx) = mpsc::unbounded_channel();
        let mut core = make_test_core(messages, &hooks);
        core.events = Some(tx);
        core.compactor = Some(Compactor::new(0)); // 0 → always compact
        core.consecutive_compact_failures = MAX_CONSECUTIVE_COMPACT_FAILURES;

        core.maybe_compact(0).await;

        // No Compacted event; only CompactionSkipped::CircuitBreaker
        let mut found_breaker = false;
        while let Ok(ev) = rx.try_recv() {
            match ev {
                Compacted { .. } => panic!("circuit breaker should prevent compaction"),
                CompactionSkipped { reason, .. } => {
                    assert_eq!(reason, CompactionSkipReason::CircuitBreaker);
                    found_breaker = true;
                }
                _ => {}
            }
        }
        assert!(found_breaker, "must emit CircuitBreaker skip event");
        assert_eq!(
            core.messages.len(),
            3,
            "must not compact when breaker is tripped"
        );
    }

    #[tokio::test]
    async fn maybe_compact_circuit_breaker_resets_on_success() {
        // After a successful compaction, consecutive_compact_failures must be 0.
        use crate::compact::Compactor;
        use crate::llm::{Completion, MockProvider};

        let hooks = crate::hooks::HookRegistry::new();
        let messages = vec![
            Message::system("sys".to_string()),
            Message::user("msg1".to_string()),
            Message::assistant("rep1".to_string()),
            Message::user("msg2".to_string()),
            Message::assistant("rep2".to_string()),
        ];
        let provider = Arc::new(MockProvider::new(vec![Completion {
            content: "summary".to_string(),
            tool_calls: vec![],
            finish_reason: Some("stop".to_string()),
            usage: None,
            reasoning_content: None,
        }]));
        let mut core = make_test_core(messages, &hooks);
        core.llm = provider;
        core.compactor = Some(Compactor::new(0).keep_recent_n(2));
        core.consecutive_compact_failures = 2; // near threshold but not reached

        core.maybe_compact(1).await;

        assert_eq!(
            core.consecutive_compact_failures, 0,
            "breaker must reset on success"
        );
    }

    #[tokio::test]
    async fn maybe_compact_circuit_breaker_increments_on_error() {
        // When compaction returns an error, consecutive_compact_failures must increment.
        use crate::compact::Compactor;
        use crate::error::Error;
        use crate::event::AgentEvent::CompactionSkipped;
        use crate::event::CompactionSkipReason;
        use crate::llm::MockProvider;
        use tokio::sync::mpsc;

        let hooks = crate::hooks::HookRegistry::new();
        // Need at least 2 conversational msgs in "older" (pre-keep_recent_n) for compaction to fire.
        let messages = vec![
            Message::system("sys".to_string()),
            Message::user("msg1".to_string()),
            Message::assistant("rep1".to_string()),
            Message::user("msg2".to_string()),
            Message::assistant("rep2".to_string()),
        ];
        // MockProvider that errors on the first complete() call → compaction fails.
        let provider = Arc::new(MockProvider::new(vec![]).with_errors(vec![Error::Llm {
            provider: "mock".into(),
            message: "simulated compaction failure".into(),
        }]));
        let (tx, mut rx) = mpsc::unbounded_channel();
        let mut core = make_test_core(messages, &hooks);
        core.llm = provider;
        core.events = Some(tx);
        core.compactor = Some(Compactor::new(0).keep_recent_n(2));
        core.consecutive_compact_failures = 0;

        core.maybe_compact(1).await;

        assert_eq!(
            core.consecutive_compact_failures, 1,
            "breaker must increment on error"
        );
        // Must emit CompactionSkipped::Error
        let mut found_error = false;
        while let Ok(ev) = rx.try_recv() {
            if let CompactionSkipped { reason, .. } = ev {
                assert_eq!(reason, CompactionSkipReason::Error);
                found_error = true;
            }
        }
        assert!(found_error, "must emit CompactionSkipped::Error event");
    }

    #[tokio::test]
    async fn maybe_compact_circuit_breaker_accumulates_to_threshold() {
        // Three consecutive failures must trip the breaker (MAX_CONSECUTIVE_COMPACT_FAILURES = 3).
        use crate::compact::{Compactor, MAX_CONSECUTIVE_COMPACT_FAILURES};
        use crate::error::Error;
        use crate::event::AgentEvent::{Compacted, CompactionSkipped};
        use crate::event::CompactionSkipReason;
        use crate::llm::MockProvider;
        use tokio::sync::mpsc;

        let hooks = crate::hooks::HookRegistry::new();
        // Need at least 2 conversational msgs in older for compaction to fire.
        let messages = vec![
            Message::system("sys".to_string()),
            Message::user("msg1".to_string()),
            Message::assistant("rep1".to_string()),
            Message::user("msg2".to_string()),
            Message::assistant("rep2".to_string()),
        ];
        // MockProvider errors on every complete() call → compaction always fails.
        let mk_err = || Error::Llm {
            provider: "mock".into(),
            message: "simulated compaction failure".into(),
        };
        let provider = Arc::new(MockProvider::new(vec![]).with_errors(vec![
            mk_err(),
            mk_err(),
            mk_err(),
            mk_err(),
        ]));
        let (tx, mut rx) = mpsc::unbounded_channel();
        let mut core = make_test_core(messages, &hooks);
        core.llm = provider.clone();
        core.events = Some(tx);
        core.compactor = Some(Compactor::new(0).keep_recent_n(2));
        core.consecutive_compact_failures = 0;

        // First two calls: each increments the counter
        for step in 0..(MAX_CONSECUTIVE_COMPACT_FAILURES - 1) as usize {
            core.maybe_compact(step).await;
        }
        assert_eq!(
            core.consecutive_compact_failures,
            MAX_CONSECUTIVE_COMPACT_FAILURES - 1,
            "after {} failures, counter should be {}",
            MAX_CONSECUTIVE_COMPACT_FAILURES - 1,
            MAX_CONSECUTIVE_COMPACT_FAILURES - 1
        );

        // Third call: reaches threshold → breaker trips, no compaction attempted
        // Drain events before third call
        while rx.try_recv().is_ok() {}
        core.maybe_compact((MAX_CONSECUTIVE_COMPACT_FAILURES - 1) as usize)
            .await;

        // Counter stays at threshold (doesn't overflow)
        assert_eq!(
            core.consecutive_compact_failures, MAX_CONSECUTIVE_COMPACT_FAILURES,
            "counter must not exceed threshold"
        );

        // Fourth call: breaker already tripped → emits CircuitBreaker, no counter change
        let (tx2, mut rx2) = mpsc::unbounded_channel();
        core.events = Some(tx2);
        core.maybe_compact(MAX_CONSECUTIVE_COMPACT_FAILURES as usize)
            .await;

        assert_eq!(
            core.consecutive_compact_failures, MAX_CONSECUTIVE_COMPACT_FAILURES,
            "breaker tripped: counter should stay at max"
        );

        // Must have emitted CircuitBreaker (no further increments)
        let mut breaker_count = 0;
        while let Ok(ev) = rx2.try_recv() {
            if let CompactionSkipped { ref reason, .. } = ev {
                assert_eq!(*reason, CompactionSkipReason::CircuitBreaker);
                breaker_count += 1;
            }
            if let Compacted { .. } = ev {
                panic!("circuit breaker should prevent compaction once tripped");
            }
        }
        assert!(
            breaker_count >= 1,
            "must emit CircuitBreaker event when tripped"
        );
    }

    // ========================================================================
    // run_inner integration tests
    // ========================================================================
    // Kills: `delete ! in RunCore<'a>::execute_tool_calls` at line 306.
    // These tests call run_inner() directly to kill mutants deep inside the
    // main agent loop that cannot be reached by unit tests of sub-functions.
    // ========================================================================

    /// Helper: build a RunCore that can run through `run_inner`.
    /// Messages start with a single user turn; LLM and max_steps are caller-set.
    fn make_run_core_for_inner<'a>(
        messages: Vec<Message>,
        hooks: &'a crate::hooks::HookRegistry,
        provider: Arc<crate::llm::MockProvider>,
        max_steps: usize,
    ) -> RunCore<'a> {
        use std::sync::atomic::AtomicBool;
        RunCore {
            messages: Arc::new(messages),
            llm: provider,
            tools: Arc::new(crate::tools::ToolRegistry::default()),
            max_steps,
            max_transcript_chars: None,
            events: None,
            streaming: false,
            compactor: None,
            microcompactor: None,
            permission_hook: None,
            hooks,
            total_llm_latency_ms: 0,
            exploring_plan_mode: Arc::new(AtomicBool::new(false)),
            shutdown_token: None,
            mailbox: None,
            stuck_window: 3,
            stuck_error_rate: 1.0,
            turn: 0,
            globs_skills: vec![],
            prompt_segments: None,
            static_breakdown: StaticBreakdownCache::default(),
            last_prompt_tokens: 0,
            consecutive_compact_failures: 0,
            wall_timeout_secs: 0,
            wall_start: None,
        }
    }

    /// Kills: `replace >= with <` at line 579.
    ///
    /// When `chars >= limit` after trimming, `run_inner` must return
    /// `TranscriptLimit`.  With the mutant (`< limit`), the condition is
    /// inverted and `TranscriptLimit` would fire when chars is BELOW the
    /// limit — the happy path.
    #[tokio::test]
    async fn run_inner_returns_transcript_limit_when_chars_at_or_above_limit() {
        use crate::agent::FinishReason;

        let hooks = crate::hooks::HookRegistry::new();
        // System message "hello" = 5 chars; set limit = 3 → 5 >= 3 → TranscriptLimit.
        let messages = vec![Message::system("hello".to_string())];
        let provider = Arc::new(crate::llm::MockProvider::new(vec![]));
        let mut core = make_run_core_for_inner(messages, &hooks, provider, 1);
        core.max_transcript_chars = Some(3); // 5 chars > 3 → fires before LLM call

        let outcome = core.run_inner().await.expect("run_inner must not error");
        assert!(
            matches!(outcome.finish_reason, FinishReason::TranscriptLimit { .. }),
            "expected TranscriptLimit, got {:?}",
            outcome.finish_reason,
        );
    }

    /// Kills: `delete !` at line 679.
    ///
    /// When `reasoning_content` is non-empty, `run_inner` must emit a
    /// `AgentEvent::Reasoning` event.  With the mutant (delete `!`), the
    /// guard becomes `if reasoning.is_empty()`, so no event is emitted for
    /// non-empty reasoning.
    #[tokio::test]
    async fn run_inner_emits_reasoning_event_when_reasoning_nonempty() {
        use crate::event::AgentEvent;
        use crate::llm::Completion;
        use tokio::sync::mpsc;

        let hooks = crate::hooks::HookRegistry::new();
        let provider = Arc::new(crate::llm::MockProvider::new(vec![Completion {
            content: "done".to_string(),
            tool_calls: vec![],
            finish_reason: Some("stop".to_string()),
            usage: None,
            reasoning_content: Some("I thought about it".to_string()),
        }]));
        let messages = vec![Message::user("hello".to_string())];
        let (tx, mut rx) = mpsc::unbounded_channel::<AgentEvent>();
        let mut core = make_run_core_for_inner(messages, &hooks, provider, 1);
        core.events = Some(tx);

        let outcome = core.run_inner().await.expect("run_inner must not error");
        drop(outcome); // satisfy unused-var lint

        let events: Vec<AgentEvent> = std::iter::from_fn(|| rx.try_recv().ok()).collect();
        assert!(
            events.iter().any(|e| matches!(e, AgentEvent::Reasoning { .. })),
            "AgentEvent::Reasoning must be emitted when reasoning_content is non-empty; got: {events:?}",
        );
    }

    /// Kills: `replace match guard … with false` at line 700:32 AND
    ///        `replace != with ==` at line 700:49.
    ///
    /// When the LLM returns `finish_reason = Some("rate_limited")` with no
    /// tool calls, `run_inner` must classify it as `FinishReason::ProviderStop`.
    /// Both mutants break the match guard so "rate_limited" falls to the
    /// default `NoMoreToolCalls` arm instead.
    #[tokio::test]
    async fn run_inner_provider_stop_for_nonstandard_finish_reason() {
        use crate::agent::FinishReason;
        use crate::llm::Completion;

        let hooks = crate::hooks::HookRegistry::new();
        let provider = Arc::new(crate::llm::MockProvider::new(vec![Completion {
            content: "provider paused".to_string(),
            tool_calls: vec![],
            finish_reason: Some("rate_limited".to_string()),
            usage: None,
            reasoning_content: None,
        }]));
        let messages = vec![Message::user("hello".to_string())];
        let core = make_run_core_for_inner(messages, &hooks, provider, 1);

        let outcome = core.run_inner().await.expect("run_inner must not error");
        assert!(
            matches!(
                &outcome.finish_reason,
                FinishReason::ProviderStop(r) if r == "rate_limited"
            ),
            "expected ProviderStop(\"rate_limited\"), got {:?}",
            outcome.finish_reason,
        );
    }

    /// Complementary: `finish_reason = Some("stop")` → `NoMoreToolCalls`.
    /// Pins the pass-through branch of the same match guard.
    #[tokio::test]
    async fn run_inner_no_provider_stop_for_stop_finish_reason() {
        use crate::agent::FinishReason;
        use crate::llm::Completion;

        let hooks = crate::hooks::HookRegistry::new();
        let provider = Arc::new(crate::llm::MockProvider::new(vec![Completion {
            content: "all done".to_string(),
            tool_calls: vec![],
            finish_reason: Some("stop".to_string()),
            usage: None,
            reasoning_content: None,
        }]));
        let messages = vec![Message::user("hello".to_string())];
        let core = make_run_core_for_inner(messages, &hooks, provider, 1);

        let outcome = core.run_inner().await.expect("run_inner must not error");
        assert!(
            matches!(outcome.finish_reason, FinishReason::NoMoreToolCalls),
            "expected NoMoreToolCalls, got {:?}",
            outcome.finish_reason,
        );
    }

    /// Goal 353 — Invariant #7 (finish reasons are data, not errors).
    ///
    /// HEADLINE regression: a mid-stream cancellation (the provider returns
    /// `Err(Error::Cancelled)` from the in-flight LLM call) must be translated
    /// into a `FinishReason::Cancelled` *outcome* — NOT bubbled as `Err` — so
    /// the caller (`runtime.rs`) persists the partial transcript, runs
    /// `emit_turn_messages` + compaction, and lets the `SessionEnd` hook
    /// suppression for cancellation fire. Before this fix the error rode `?`
    /// out of `run_inner` and the transcript save was skipped.
    #[tokio::test]
    async fn cancelled_mid_stream_persists_transcript_and_finish_reason() {
        use crate::agent::FinishReason;
        use crate::event::AgentEvent;
        use tokio::sync::mpsc;

        let hooks = crate::hooks::HookRegistry::new();
        // The error queue is consumed BEFORE scripted completions, so the
        // first LLM call returns `Err(Error::Cancelled)` — simulating the
        // provider aborting mid-stream when the shutdown token fires between
        // SSE chunks (see `anthropic.rs` / `openai.rs` stream loops).
        let provider = Arc::new(
            crate::llm::MockProvider::new(vec![]).with_errors(vec![crate::error::Error::Cancelled]),
        );
        let messages = vec![Message::user("hello".to_string())];
        let (tx, mut rx) = mpsc::unbounded_channel::<AgentEvent>();
        let mut core = make_run_core_for_inner(messages, &hooks, provider, 3);
        core.events = Some(tx);
        // Provide a token but leave it UN-cancelled: check_shutdown must NOT
        // fire — the Cancelled outcome has to come from the provider call.
        core.shutdown_token = Some(tokio_util::sync::CancellationToken::new());

        let outcome = core.run_inner().await.expect("run_inner must not error");
        assert!(
            matches!(outcome.finish_reason, FinishReason::Cancelled),
            "expected FinishReason::Cancelled, got {:?}",
            outcome.finish_reason,
        );
        // The cancellation happened DURING the first step's LLM call (the
        // loop's first iteration is step = 1), so the in-flight step is
        // counted. This is deliberately `step`, not `step - 1` like
        // check_shutdown — the call was in progress, not pre-call.
        assert_eq!(
            outcome.steps, 1,
            "mid-stream cancel counts the in-flight step (not step - 1)",
        );

        // The seeded transcript must survive into the outcome.
        assert_eq!(outcome.messages.len(), 1, "transcript must be preserved");
        assert_eq!(
            outcome.messages[0].role,
            crate::message::Role::User,
            "seeded user message must be in the outcome transcript",
        );

        let events: Vec<AgentEvent> = std::iter::from_fn(|| rx.try_recv().ok()).collect();
        assert!(
            events.iter().any(|e| matches!(
                e,
                AgentEvent::TurnFinished { reason, steps }
                    if reason.as_str() == "cancelled" && *steps == 1
            )),
            "TurnFinished(cancelled) must be emitted with the in-flight step; got: {events:?}",
        );
    }

    /// Goal 382 — HEADLINE: a stream-interrupted completion (the provider
    /// returns `Ok` with `finish_reason == Some("interrupted")` and partial
    /// content, as the openai.rs / anthropic.rs SSE parsers now do on a
    /// mid-stream network drop) must be persisted as a partial assistant
    /// message and finish the turn as `FinishReason::Cancelled` — NOT
    /// dropped. Before this goal the parser returned `Err` on the read
    /// error, which short-circuited `emit_turn_messages` and left the
    /// transcript ending with an unanswered user turn.
    #[tokio::test]
    async fn interrupted_completion_persists_partial_content_as_cancelled() {
        use crate::agent::FinishReason;
        use crate::llm::Completion;
        use crate::message::Role;

        let hooks = crate::hooks::HookRegistry::new();
        let provider = Arc::new(crate::llm::MockProvider::new(vec![Completion {
            content: "partial reply…".to_string(),
            tool_calls: vec![],
            finish_reason: Some("interrupted".to_string()),
            usage: None,
            reasoning_content: Some("half a thought".to_string()),
        }]));
        let messages = vec![Message::user("hello".to_string())];
        let core = make_run_core_for_inner(messages, &hooks, provider, 3);

        let outcome = core.run_inner().await.expect("run_inner must not error");
        assert!(
            matches!(outcome.finish_reason, FinishReason::Cancelled),
            "interrupted completion must finish as Cancelled, got {:?}",
            outcome.finish_reason,
        );

        // The partial reply must become the final_message so the caller's
        // persistence path treats this as a real (partial) turn.
        assert_eq!(
            outcome.final_message.as_deref(),
            Some("partial reply…"),
            "the partial reply must become the final_message",
        );

        // The partial assistant message (content + reasoning) must ride the
        // existing make_cancelled_outcome → new_messages path so
        // runtime.rs:emit_turn_messages writes it to disk.
        let assistant_msgs: Vec<&Message> = outcome
            .messages
            .iter()
            .filter(|m| m.role == Role::Assistant)
            .collect();
        assert_eq!(
            assistant_msgs.len(),
            1,
            "exactly one partial assistant message must be pushed",
        );
        assert_eq!(assistant_msgs[0].content, "partial reply…");
        assert_eq!(
            assistant_msgs[0].reasoning_content.as_deref(),
            Some("half a thought"),
            "reasoning must be attached to the partial assistant message",
        );
    }

    /// Goal 353 — regression guard for the PRE-EXISTING path.
    ///
    /// When the shutdown token is ALREADY cancelled at loop top (before any
    /// LLM call), `check_shutdown` handles it and reports `step - 1` (0 on the
    /// first iteration). This pins that path so reviewers can see both arms
    /// (between-steps vs mid-stream) are covered and deliberately distinct.
    #[tokio::test]
    async fn cancelled_between_steps_uses_check_shutdown_path() {
        use crate::agent::FinishReason;

        let hooks = crate::hooks::HookRegistry::new();
        // Empty provider: the LLM must NEVER be called — check_shutdown fires
        // at loop top before the call, so a call here would fail loudly
        // (MockProvider errors when its scripted queue is drained).
        let provider = Arc::new(crate::llm::MockProvider::new(vec![]));
        let messages = vec![Message::user("hello".to_string())];
        let mut core = make_run_core_for_inner(messages, &hooks, provider, 3);
        core.shutdown_token = Some(tokio_util::sync::CancellationToken::new());
        // Cancel BEFORE run_inner: fires check_shutdown on step 1's loop top.
        core.shutdown_token
            .as_ref()
            .expect("token just set")
            .cancel();

        let outcome = core.run_inner().await.expect("run_inner must not error");
        assert!(
            matches!(outcome.finish_reason, FinishReason::Cancelled),
            "expected FinishReason::Cancelled, got {:?}",
            outcome.finish_reason,
        );
        assert_eq!(
            outcome.steps, 0,
            "between-steps cancel happens before any LLM call → 0 steps",
        );
    }

    /// Goal 353 — negative guard.
    ///
    /// A NON-Cancelled error from the provider must still bubble out of
    /// `run_inner` as `Err`. The new match only swallows `Cancelled`; any
    /// other error keeps the original `?`-style propagation so genuine
    /// failures are not silently converted into finished turns.
    #[tokio::test]
    async fn non_cancelled_error_still_bubbles() {
        let hooks = crate::hooks::HookRegistry::new();
        // Error::Llm is not retried by the run path (retry handling lives in
        // the provider's own RetryPolicy, which MockProvider does not have),
        // so it reaches run_inner's match and must fall through to the Err arm.
        let provider = Arc::new(crate::llm::MockProvider::new(vec![]).with_errors(vec![
            crate::error::Error::Llm {
                provider: "mock".to_string(),
                message: "injected non-cancelled error".to_string(),
            },
        ]));
        let messages = vec![Message::user("hello".to_string())];
        let core = make_run_core_for_inner(messages, &hooks, provider, 1);

        let err = match core.run_inner().await {
            Ok(_) => panic!("run_inner must error for non-Cancelled provider errors"),
            Err(e) => e,
        };
        assert!(
            matches!(err, crate::error::Error::Llm { .. }),
            "expected Error::Llm, got {err:?}",
        );
    }

    /// Kills (all three together):
    ///   `replace && with ||` at line 820:43  — stuck guard uses `||`
    ///   `replace / with *`   at line 827:51  — rate = count * window (huge)
    ///   `replace += with *=` at line 833:59  — count never increments
    ///
    /// Run the agent with 3 consecutive single-tool-call steps that all fail
    /// with "ERROR: …" (unknown tool).  With `stuck_window = 3` and
    /// `stuck_error_rate = 1.0`, stuck detection must fire on step 3.
    ///
    /// Each mutant breaks a different aspect of stuck detection:
    /// - `|| ` guard: fires after the FIRST error (window not yet full)
    /// - `*` rate:    fires after the first error (rate = 1 * 3 = 3 ≥ 1.0)
    /// - `*=` count:  all error_count = 0 → rate = 0 → stuck NEVER fires
    #[tokio::test]
    async fn run_inner_stuck_detection_fires_after_window_of_errors() {
        use crate::agent::FinishReason;
        use crate::llm::{Completion, ToolCall};

        let hooks = crate::hooks::HookRegistry::new();
        // Three steps each requesting the same non-existent tool → all fail.
        let make_tc_completion = |id: &str| Completion {
            content: String::new(),
            tool_calls: vec![ToolCall {
                id: id.to_string(),
                name: "NonExistentTool".to_string(),
                arguments: serde_json::json!({}),
            }],
            finish_reason: None,
            usage: None,
            reasoning_content: None,
        };
        let provider = Arc::new(crate::llm::MockProvider::new(vec![
            make_tc_completion("tc1"),
            make_tc_completion("tc2"),
            make_tc_completion("tc3"),
        ]));
        let messages = vec![Message::user("keep trying".to_string())];
        let mut core = make_run_core_for_inner(messages, &hooks, provider, 5);
        core.stuck_window = 3;
        core.stuck_error_rate = 1.0;

        let outcome = core.run_inner().await.expect("run_inner must not error");
        assert!(
            matches!(outcome.finish_reason, FinishReason::Stuck { .. }),
            "expected Stuck after 3 consecutive errors, got {:?}",
            outcome.finish_reason,
        );
    }

    /// Kills: `replace && with ||` at line 820:43.
    ///
    /// The guard is `stuck_finish.is_none() && recent_errors.len() == stuck_window`.
    /// With `||`, it fires whenever `stuck_finish.is_none()` is true (always before
    /// stuck is set), so it triggers on every step — not just when the window fills.
    ///
    /// Setup: `stuck_window=3`, `stuck_error_rate=0.5`, `max_steps=2`.
    /// After 2 errors the window is NOT yet full (len=2 < window=3).
    ///   • Original (`&&`): condition false → no stuck → `BudgetExceeded`.
    ///   • Mutant (`||`): condition fires at step 2 (rate = 2/3 = 0.666 ≥ 0.5) → `Stuck`.
    #[tokio::test]
    async fn run_inner_stuck_fires_only_after_window_full() {
        use crate::agent::FinishReason;
        use crate::llm::{Completion, ToolCall};

        let hooks = crate::hooks::HookRegistry::new();
        let make_tc = |id: &str| Completion {
            content: String::new(),
            tool_calls: vec![ToolCall {
                id: id.to_string(),
                name: "NonExistentTool".to_string(),
                arguments: serde_json::json!({}),
            }],
            finish_reason: None,
            usage: None,
            reasoning_content: None,
        };
        // Two steps — both produce errors, but the window (size 3) never fills.
        let provider = Arc::new(crate::llm::MockProvider::new(vec![
            make_tc("tc1"),
            make_tc("tc2"),
        ]));
        let messages = vec![Message::user("go".to_string())];
        let mut core = make_run_core_for_inner(messages, &hooks, provider, 2);
        core.stuck_window = 3;
        core.stuck_error_rate = 0.5; // 2/3 ≈ 0.666 ≥ 0.5 with mutant, but window not full

        let outcome = core.run_inner().await.expect("run_inner must not error");
        assert!(
            matches!(outcome.finish_reason, FinishReason::BudgetExceeded),
            "expected BudgetExceeded (window not yet full), got {:?}",
            outcome.finish_reason,
        );
    }

    /// Kills: `replace / with *` at line 827:51.
    ///
    /// `rate = error_count as f64 / stuck_window as f64` vs `* stuck_window`.
    /// With `window=3`, `error_count=1`, `stuck_error_rate=0.5`:
    ///   • Original: 1/3 ≈ 0.333 < 0.5 → no stuck → `BudgetExceeded`.
    ///   • Mutant:   1×3 = 3.0 ≥ 0.5   → stuck fires.
    ///
    /// We need exactly 1 error in a full window of 3: two successful SuccessTool
    /// calls followed by one NonExistentTool error fills the window with 1 error.
    #[tokio::test]
    async fn run_inner_stuck_rate_uses_division_not_multiplication() {
        use crate::agent::FinishReason;
        use crate::llm::ToolSpec;
        use crate::llm::{Completion, ToolCall};
        use crate::tools::{Tool, ToolRegistry};
        use async_trait::async_trait;

        struct SuccessTool;

        #[async_trait]
        impl Tool for SuccessTool {
            fn spec(&self) -> ToolSpec {
                ToolSpec {
                    name: "SuccessTool".to_string(),
                    description: "Returns ok".to_string(),
                    parameters: serde_json::json!({ "type": "object", "properties": {} }),
                }
            }
            async fn execute(&self, _args: serde_json::Value) -> crate::error::Result<String> {
                Ok("ok".to_string())
            }
        }

        let hooks = crate::hooks::HookRegistry::new();
        let registry = ToolRegistry::default().register(Arc::new(SuccessTool));

        let make_ok = |id: &str| Completion {
            content: String::new(),
            tool_calls: vec![ToolCall {
                id: id.to_string(),
                name: "SuccessTool".to_string(),
                arguments: serde_json::json!({}),
            }],
            finish_reason: None,
            usage: None,
            reasoning_content: None,
        };
        let make_err = |id: &str| Completion {
            content: String::new(),
            tool_calls: vec![ToolCall {
                id: id.to_string(),
                name: "NonExistentTool".to_string(),
                arguments: serde_json::json!({}),
            }],
            finish_reason: None,
            usage: None,
            reasoning_content: None,
        };
        // success, success, error → window=3 full with 1 error
        let provider = Arc::new(crate::llm::MockProvider::new(vec![
            make_ok("tc1"),
            make_ok("tc2"),
            make_err("tc3"),
        ]));
        let messages = vec![Message::user("test".to_string())];
        let mut core = make_run_core_for_inner(messages, &hooks, provider, 3);
        core.tools = Arc::new(registry);
        core.stuck_window = 3;
        core.stuck_error_rate = 0.5; // 1/3 ≈ 0.333 < 0.5 → no stuck (orig); 1×3=3.0 ≥ 0.5 (mutant)

        let outcome = core.run_inner().await.expect("run_inner must not error");
        assert!(
            matches!(outcome.finish_reason, FinishReason::BudgetExceeded),
            "expected BudgetExceeded (rate below threshold), got {:?}",
            outcome.finish_reason,
        );
    }

    /// Kills: `replace || with &&` at line 750:57 AND
    ///        `replace == with !=` at line 750:69.
    ///
    /// `DENIAL_LIMIT_SENTINEL = "ERROR_DENIAL_LIMIT:"` does NOT start with "ERROR: "
    /// (note the space), so `is_error` is true only via the `|| o.result == DENIAL_LIMIT_SENTINEL`
    /// branch.
    ///
    /// - Mutant 750:57 (`&&` instead of `||`): `false && true = false` → wrong
    /// - Mutant 750:69 (`!=` instead of `==`): `false || false = false` → wrong
    ///
    /// Both mutants emit `AgentEvent::ToolResult { is_error: false }` for the sentinel,
    /// but the correct code must emit `is_error: true`.
    #[tokio::test]
    async fn run_inner_denial_sentinel_emits_is_error_true() {
        use crate::event::AgentEvent;
        use crate::llm::{Completion, ToolCall, ToolSpec};
        use crate::tools::{Tool, ToolRegistry};
        use async_trait::async_trait;
        use tokio::sync::mpsc;

        struct DenialTool;

        #[async_trait]
        impl Tool for DenialTool {
            fn spec(&self) -> ToolSpec {
                ToolSpec {
                    name: "DenialTool".to_string(),
                    description: "Returns PermissionDeniedLimit".to_string(),
                    parameters: serde_json::json!({ "type": "object", "properties": {} }),
                }
            }
            async fn execute(&self, _args: serde_json::Value) -> crate::error::Result<String> {
                Err(crate::error::Error::PermissionDeniedLimit {
                    name: "DenialTool".to_string(),
                })
            }
        }

        let hooks = crate::hooks::HookRegistry::new();
        let registry = ToolRegistry::default().register(Arc::new(DenialTool));
        let provider = Arc::new(crate::llm::MockProvider::new(vec![Completion {
            content: String::new(),
            tool_calls: vec![ToolCall {
                id: "tc1".to_string(),
                name: "DenialTool".to_string(),
                arguments: serde_json::json!({}),
            }],
            finish_reason: None,
            usage: None,
            reasoning_content: None,
        }]));

        let messages = vec![Message::user("trigger denial".to_string())];
        let (tx, mut rx) = mpsc::unbounded_channel::<AgentEvent>();
        let mut core = make_run_core_for_inner(messages, &hooks, provider, 3);
        core.tools = Arc::new(registry);
        core.events = Some(tx);

        let outcome = core.run_inner().await.expect("run_inner must not error");
        assert!(
            matches!(
                outcome.finish_reason,
                crate::agent::FinishReason::PermissionDenialLimit
            ),
            "expected PermissionDenialLimit, got {:?}",
            outcome.finish_reason,
        );

        let mut events = vec![];
        while let Ok(e) = rx.try_recv() {
            events.push(e);
        }
        let denial_is_error = events.iter().find_map(|e| {
            if let AgentEvent::ToolResult { name, is_error, .. } = e {
                if name == "DenialTool" {
                    return Some(*is_error);
                }
            }
            None
        });
        assert_eq!(
            denial_is_error,
            Some(true),
            "ToolResult for DENIAL_LIMIT_SENTINEL must have is_error = true; events: {events:?}"
        );
    }

    // ========================================================================
    // Goal-328: ContextBreakdown event emission
    // ========================================================================

    /// `compute_breakdown` must populate `overhead = max(0, provider_total -
    /// local_sum)`. With `prompt_tokens = 1000` and a local sum of 700,
    /// the breakdown's overhead must be 300. The other buckets must match
    /// `static_breakdown` (cached at construction).
    #[test]
    fn compute_breakdown_overhead_is_provider_total_minus_local_sum() {
        use crate::llm::ContextBreakdown;

        let hooks = crate::hooks::HookRegistry::new();
        // Seed a transcript long enough to make the conversation bucket non-zero.
        let messages = vec![
            Message::system("s".to_string()),
            Message::user("hello world this is a turn".to_string()),
            Message::assistant("ok".to_string()),
        ];
        let mut core = make_test_core(messages, &hooks);
        // Hand-build a static breakdown whose sum we can predict.
        core.static_breakdown = StaticBreakdownCache {
            system_prompt: 100,
            rules: 50,
            skills: 25,
            subagents: 10,
            tools: 15,
            mcp_dynamic: 0,
        };
        let breakdown = core.compute_breakdown(1000);

        // Provider total - local_sum = 1000 - (100 + 50 + 25 + 10 + 15 + 0 + conversation).
        let local = breakdown.local_sum();
        let expected_overhead = 1000u32.saturating_sub(local);
        assert_eq!(
            breakdown.overhead, expected_overhead,
            "overhead must be provider_total - local_sum"
        );
        // Conversation must be > 0 (we seeded a non-trivial transcript).
        assert!(
            breakdown.conversation > 0,
            "conversation bucket must be non-zero for a seeded transcript"
        );
        // Static buckets must mirror the cache verbatim.
        assert_eq!(breakdown.system_prompt, 100);
        assert_eq!(breakdown.rules, 50);
        assert_eq!(breakdown.skills, 25);
        assert_eq!(breakdown.subagents, 10);
        assert_eq!(breakdown.tools, 15);
        assert_eq!(breakdown.mcp_dynamic, 0);
        // Sanity: the public type's helpers agree.
        assert_eq!(breakdown.local_sum(), local);
        assert_eq!(breakdown.total(), local + expected_overhead);
        // Silence unused-variable warning for ContextBreakdown import.
        let _ = ContextBreakdown::default();
    }

    /// When the local sum exceeds the provider's reported total (which can
    /// happen with chars/4 over-estimation on dense CJK content), the
    /// overhead bucket must saturate to 0 — not wrap to a huge u32.
    #[test]
    fn compute_breakdown_overhead_saturates_at_zero_when_local_exceeds_provider() {
        let hooks = crate::hooks::HookRegistry::new();
        let mut core = make_test_core(vec![Message::user("hi".to_string())], &hooks);
        core.static_breakdown = StaticBreakdownCache {
            system_prompt: 5000,
            rules: 1000,
            skills: 0,
            subagents: 0,
            tools: 0,
            mcp_dynamic: 0,
        };
        let breakdown = core.compute_breakdown(100); // local sum ≫ 100
        assert_eq!(
            breakdown.overhead, 0,
            "overhead must saturate to 0 when local sum > provider total; got {}",
            breakdown.overhead
        );
    }

    /// `emit_breakdown` consumes a `TokenUsage` and emits
    /// `AgentEvent::ContextBreakdown`. We assert the emitted event's
    /// bucket totals match the spec (overhead uses `max(input_tokens,
    /// cache_hit + cache_miss)` so Anthropic + OpenAI reporting
    /// differences are handled).
    #[tokio::test]
    async fn dispatch_llm_step_emits_context_breakdown_after_usage() {
        use crate::event::AgentEvent;
        use crate::llm::TokenUsage;
        use tokio::sync::mpsc;

        let hooks = crate::hooks::HookRegistry::new();
        let mut core = make_test_core(vec![Message::user("hello world".to_string())], &hooks);
        // Seed static buckets so the breakdown has deterministic non-zero values.
        core.static_breakdown = StaticBreakdownCache {
            system_prompt: 100,
            rules: 50,
            skills: 25,
            subagents: 10,
            tools: 15,
            mcp_dynamic: 0,
        };
        let (tx, mut rx) = mpsc::unbounded_channel::<AgentEvent>();
        core.events = Some(tx);

        // The `Usage` reading: provider reports 1000 prompt tokens with
        // no cache split (OpenAI shape). Anthropic-style reporting would
        // put the cache split separately; both flows feed the breakdown
        // the same `max(input_tokens, cache_sum)`.
        let usage = TokenUsage {
            prompt_tokens: 1000,
            completion_tokens: 50,
            total_tokens: 1050,
            cache_hit_tokens: 0,
            cache_miss_tokens: 0,
            reasoning_tokens: 0,
        };
        core.emit_breakdown(7, &usage);

        // Drain the channel and find the ContextBreakdown event.
        let event = rx
            .try_recv()
            .expect("ContextBreakdown event must be emitted");
        match event {
            AgentEvent::ContextBreakdown { breakdown, step } => {
                assert_eq!(step, 7, "step must be forwarded verbatim");
                let local = breakdown.local_sum();
                let expected_overhead = 1000u32.saturating_sub(local);
                assert_eq!(breakdown.overhead, expected_overhead);
                assert!(
                    breakdown.total() >= 1000,
                    "total must be >= provider_total; got {}",
                    breakdown.total()
                );
            }
            other => panic!("expected ContextBreakdown event, got {other:?}"),
        }
    }

    /// `run_inner` emits `AgentEvent::ContextBreakdown` once per
    /// LLM-calling step (i.e. exactly once on the single-step happy
    /// path). The breakdown must come AFTER `Usage` so consumers
    /// observe the provider truth first.
    #[tokio::test]
    async fn run_inner_emits_context_breakdown_once_per_llm_step() {
        use crate::agent::FinishReason;
        use crate::event::AgentEvent;
        use crate::llm::{Completion, TokenUsage};
        use tokio::sync::mpsc;

        let hooks = crate::hooks::HookRegistry::new();
        let provider = Arc::new(crate::llm::MockProvider::new(vec![Completion {
            content: "done".to_string(),
            tool_calls: vec![],
            finish_reason: Some("stop".to_string()),
            usage: Some(TokenUsage {
                prompt_tokens: 1000,
                completion_tokens: 50,
                total_tokens: 1050,
                cache_hit_tokens: 0,
                cache_miss_tokens: 0,
                reasoning_tokens: 0,
            }),
            reasoning_content: None,
        }]));
        let messages = vec![Message::user("hi".to_string())];
        let (tx, mut rx) = mpsc::unbounded_channel::<AgentEvent>();
        let mut core = make_run_core_for_inner(messages, &hooks, provider, 1);
        core.events = Some(tx);

        let outcome = core.run_inner().await.expect("run_inner must not error");
        assert_eq!(outcome.finish_reason, FinishReason::NoMoreToolCalls);

        // Drain events. Find the index of Usage and the index of
        // ContextBreakdown; the latter must come strictly after.
        let mut events = Vec::new();
        while let Ok(e) = rx.try_recv() {
            events.push(e);
        }
        let usage_idx = events
            .iter()
            .position(|e| matches!(e, AgentEvent::Usage { .. }))
            .expect("a Usage event must have been emitted");
        let breakdown_idx = events
            .iter()
            .position(|e| matches!(e, AgentEvent::ContextBreakdown { .. }))
            .expect("a ContextBreakdown event must have been emitted");
        assert!(
            breakdown_idx > usage_idx,
            "ContextBreakdown (idx={breakdown_idx}) must come AFTER Usage (idx={usage_idx})"
        );
    }

    /// `run_inner` does NOT emit `ContextBreakdown` on a step that
    /// never calls the LLM (e.g. an immediate `TranscriptLimit` finish).
    #[tokio::test]
    async fn run_inner_skips_context_breakdown_on_no_llm_step() {
        use crate::agent::FinishReason;
        use crate::event::AgentEvent;
        use tokio::sync::mpsc;

        let hooks = crate::hooks::HookRegistry::new();
        let provider = Arc::new(crate::llm::MockProvider::new(vec![]));
        let messages = vec![Message::system("hello".to_string())];
        let (tx, mut rx) = mpsc::unbounded_channel::<AgentEvent>();
        let mut core = make_run_core_for_inner(messages, &hooks, provider, 1);
        core.events = Some(tx);
        // 5 chars > limit 3 → enforce_transcript_budget fires BEFORE the
        // first LLM call, so there should be no Usage / ContextBreakdown.
        core.max_transcript_chars = Some(3);

        let outcome = core.run_inner().await.expect("run_inner must not error");
        assert!(
            matches!(outcome.finish_reason, FinishReason::TranscriptLimit { .. }),
            "expected TranscriptLimit finish; got {:?}",
            outcome.finish_reason
        );

        let mut events = Vec::new();
        while let Ok(e) = rx.try_recv() {
            events.push(e);
        }
        assert!(
            !events
                .iter()
                .any(|e| matches!(e, AgentEvent::ContextBreakdown { .. })),
            "no ContextBreakdown must be emitted on a no-LLM step; got: {events:?}"
        );
        assert!(
            !events.iter().any(|e| matches!(e, AgentEvent::Usage { .. })),
            "no Usage must be emitted on a no-LLM step; got: {events:?}"
        );
    }

    /// Static breakdown buckets must be cached once at `RunCore`
    /// construction and reused every step — the conversation bucket
    /// alone grows between steps. Verified by running two steps and
    /// comparing the breakdowns.
    ///
    /// Step 1: LLM returns a tool call (forces a second step).
    /// Step 2: LLM returns a final reply (loop exits).
    #[tokio::test]
    async fn static_buckets_dont_change_across_steps_conversation_grows() {
        use crate::event::AgentEvent;
        use crate::llm::{Completion, TokenUsage, ToolCall, ToolSpec};
        use crate::tools::{Tool, ToolRegistry};
        use async_trait::async_trait;
        use serde_json::{json, Value};
        use tokio::sync::mpsc;

        /// Minimal tool that always succeeds so step 1's tool call is
        /// dispatched cleanly and the loop proceeds to step 2.
        struct Adder;
        #[async_trait]
        impl Tool for Adder {
            fn spec(&self) -> ToolSpec {
                ToolSpec {
                    name: "add".to_string(),
                    description: "add two numbers".to_string(),
                    parameters: json!({"type":"object","properties":{"a":{"type":"integer"},"b":{"type":"integer"}}}),
                }
            }
            async fn execute(&self, _args: Value) -> crate::error::Result<String> {
                Ok("7".to_string())
            }
        }

        let hooks = crate::hooks::HookRegistry::new();
        let registry = ToolRegistry::default().register(Arc::new(Adder));
        let provider = Arc::new(crate::llm::MockProvider::new(vec![
            // Step 1: tool call → forces step 2.
            Completion {
                content: "calculating…".to_string(),
                tool_calls: vec![ToolCall {
                    id: "tc1".to_string(),
                    name: "add".to_string(),
                    arguments: json!({"a": 3, "b": 4}),
                }],
                finish_reason: Some("tool_calls".to_string()),
                usage: Some(TokenUsage {
                    prompt_tokens: 1000,
                    completion_tokens: 30,
                    total_tokens: 1030,
                    cache_hit_tokens: 0,
                    cache_miss_tokens: 0,
                    reasoning_tokens: 0,
                }),
                reasoning_content: None,
            },
            // Step 2: final reply → loop exits.
            Completion {
                content: "the answer is 7".to_string(),
                tool_calls: vec![],
                finish_reason: Some("stop".to_string()),
                usage: Some(TokenUsage {
                    prompt_tokens: 1200, // provider thinks transcript grew
                    completion_tokens: 50,
                    total_tokens: 1250,
                    cache_hit_tokens: 0,
                    cache_miss_tokens: 0,
                    reasoning_tokens: 0,
                }),
                reasoning_content: None,
            },
        ]));
        let messages = vec![Message::user("hi".to_string())];
        let (tx, mut rx) = mpsc::unbounded_channel::<AgentEvent>();
        let mut core = make_run_core_for_inner(messages, &hooks, provider, 5);
        core.tools = Arc::new(registry);
        core.events = Some(tx);
        // Seed static buckets so we can verify they're identical across
        // both steps.
        core.static_breakdown = StaticBreakdownCache {
            system_prompt: 100,
            rules: 50,
            skills: 25,
            subagents: 10,
            tools: 15,
            mcp_dynamic: 0,
        };
        core.prompt_segments = Some(crate::system_prompt::PromptSegments {
            rules: "RR".into(),
            system_prompt: "SS".into(),
            skills: String::new(),
            subagents: String::new(),
        });

        let outcome = core.run_inner().await.expect("run_inner must not error");
        drop(outcome); // satisfy unused-var lint

        // Collect both ContextBreakdown events.
        let mut breakdowns = Vec::new();
        while let Ok(e) = rx.try_recv() {
            if let AgentEvent::ContextBreakdown { breakdown, .. } = e {
                breakdowns.push(breakdown);
            }
        }
        assert_eq!(
            breakdowns.len(),
            2,
            "two ContextBreakdown events must have been emitted; got {breakdowns:?}"
        );

        // Static buckets must be identical across both steps.
        assert_eq!(breakdowns[0].system_prompt, breakdowns[1].system_prompt);
        assert_eq!(breakdowns[0].rules, breakdowns[1].rules);
        assert_eq!(breakdowns[0].skills, breakdowns[1].skills);
        assert_eq!(breakdowns[0].subagents, breakdowns[1].subagents);
        assert_eq!(breakdowns[0].tools, breakdowns[1].tools);
        assert_eq!(breakdowns[0].mcp_dynamic, breakdowns[1].mcp_dynamic);
        assert_eq!(
            breakdowns[0].system_prompt, 100,
            "static_breakdown cache must be honoured"
        );

        // Conversation bucket must grow between step 1 and step 2
        // (the tool result + assistant reply add to the transcript).
        assert!(
            breakdowns[1].conversation > breakdowns[0].conversation,
            "conversation must grow between steps: step1={} step2={}",
            breakdowns[0].conversation,
            breakdowns[1].conversation
        );

        // Overhead must be positive (provider total > local sum): the
        // provider reports 1000 / 1200 prompt tokens, which includes
        // wrapping the local estimate doesn't capture.
        assert!(breakdowns[0].overhead > 0);
        assert!(breakdowns[1].overhead > 0);
    }

    /// `StaticBreakdownCache::build` must partition specs into eager
    /// vs deferred via `ToolRegistry::is_deferred_spec`. We can't easily
    /// register a deferred spec on a `default()` registry, so the
    /// zero-spec case must produce zero tokens and the cache must not
    /// crash.
    #[test]
    fn static_breakdown_cache_build_zero_specs_yields_zero_tokens() {
        let segments = crate::system_prompt::PromptSegments::default();
        let registry = crate::tools::ToolRegistry::default();
        let cache = StaticBreakdownCache::build(&segments, &[], &registry);
        assert_eq!(cache.system_prompt, 0);
        assert_eq!(cache.rules, 0);
        assert_eq!(cache.skills, 0);
        assert_eq!(cache.subagents, 0);
        assert_eq!(cache.tools, 0);
        assert_eq!(cache.mcp_dynamic, 0);
    }

    /// `StaticBreakdownCache::build` must tokenise each segment's
    /// length using chars/4 ceil, identical to `llm::estimate_tokens`.
    #[test]
    fn static_breakdown_cache_build_tokenises_segments() {
        // 9-char segment → ceil(9/4) = 3 tokens. (9/4 = 2.25, ceil = 3.)
        let segments = crate::system_prompt::PromptSegments {
            rules: "012345678".into(),          // 9 chars
            system_prompt: "1234567890".into(), // 10 chars → 3 tokens (10/4=2.5, ceil=3)
            skills: "abcde".into(),             // 5 chars → 2 tokens (5/4=1.25, ceil=2)
            subagents: "abcdefgh".into(),       // 8 chars → 2 tokens (8/4=2.0, ceil=2)
        };
        let registry = crate::tools::ToolRegistry::default();
        let cache = StaticBreakdownCache::build(&segments, &[], &registry);
        assert_eq!(cache.rules, 3, "9 chars / 4 = 2.25 → ceil = 3");
        assert_eq!(cache.system_prompt, 3, "10 chars / 4 = 2.5 → ceil = 3");
        assert_eq!(cache.skills, 2, "5 chars / 4 = 1.25 → ceil = 2");
        assert_eq!(cache.subagents, 2, "8 chars / 4 = 2.0 → ceil = 2");
    }

    #[test]
    fn estimate_tokens_by_bytes_rounds_up_by_four_bytes() {
        // Kills `/ -> *` (63:32) and `> -> >=` / `<` / `==` (64:29) in
        // estimate_tokens_by_bytes: 0 bytes → 0 tokens, any non-zero bytes
        // → ceil(bytes / 4), and a tiny positive byte count must still be 1.
        assert_eq!(estimate_tokens_by_bytes(0), 0);
        assert_eq!(estimate_tokens_by_bytes(1), 1);
        assert_eq!(estimate_tokens_by_bytes(4), 1);
        assert_eq!(estimate_tokens_by_bytes(5), 2);
        assert_eq!(estimate_tokens_by_bytes(8), 2);
    }

    #[test]
    fn enforce_transcript_budget_fires_when_chars_exactly_equal_limit() {
        // Kills `< -> <=` (672:18) in enforce_transcript_budget: when the
        // transcript is EXACTLY at the limit the budget must fire (Some);
        // the `<=` mutant would treat it as under-budget (None).
        use crate::agent::FinishReason;
        use crate::llm::TokenUsage;
        let hooks = crate::hooks::HookRegistry::new();
        // "hello" = exactly 5 chars, limit = 5.
        let mut core = make_test_core(vec![Message::user("hello".to_string())], &hooks);
        core.max_transcript_chars = Some(5);
        let usage = TokenUsage::default();
        let result = core.enforce_transcript_budget(0, &usage);
        assert!(
            result.is_some(),
            "chars (5) == limit (5) must return Some finish reason"
        );
        let (finish, _step) = result.unwrap();
        assert!(
            matches!(finish, FinishReason::TranscriptLimit { .. }),
            "finish reason must be TranscriptLimit; got {finish:?}"
        );
    }

    #[test]
    fn check_wall_deadline_disabled_when_timeout_zero() {
        // Kills `== -> !=` (735:35) in check_wall_deadline: a timeout of 0
        // must disable the deadline entirely (None); the `!=` mutant would
        // fall through to the elapsed check and fire.
        use crate::llm::TokenUsage;
        let hooks = crate::hooks::HookRegistry::new();
        let mut core = make_test_core(vec![Message::user("hi".to_string())], &hooks);
        core.wall_timeout_secs = 0;
        core.wall_start = Some(std::time::Instant::now() - std::time::Duration::from_secs(5));
        let usage = TokenUsage::default();
        assert!(
            core.check_wall_deadline(0, &usage).is_none(),
            "timeout 0 must disable the wall-clock deadline"
        );
    }

    #[test]
    fn check_wall_deadline_fires_after_timeout_elapsed() {
        // Kills `-> None` (735:9) and `< -> >` (739:30): with elapsed (5s)
        // strictly greater than the timeout (3s) the deadline must fire.
        use crate::agent::FinishReason;
        use crate::llm::TokenUsage;
        let hooks = crate::hooks::HookRegistry::new();
        let mut core = make_test_core(vec![Message::user("hi".to_string())], &hooks);
        core.wall_timeout_secs = 3;
        core.wall_start = Some(std::time::Instant::now() - std::time::Duration::from_secs(5));
        let usage = TokenUsage::default();
        let result = core.check_wall_deadline(0, &usage);
        assert!(
            result.is_some(),
            "elapsed 5s > timeout 3s must fire the deadline"
        );
        let (finish, _step) = result.unwrap();
        assert!(
            matches!(finish, FinishReason::WallClockExceeded { .. }),
            "finish reason must be WallClockExceeded; got {finish:?}"
        );
    }

    #[test]
    fn check_wall_deadline_fires_when_elapsed_equals_timeout() {
        // Kills `< -> <=` and `< -> ==` (739:30): when elapsed seconds EXACTLY
        // equal the timeout, `elapsed < timeout` is false → the deadline must
        // fire; `<=`/`==` would return None. `wall_start` is set 3s in the
        // past and the deadline checked immediately, so `elapsed().as_secs()`
        // is exactly 3 (a full second boundary is guaranteed until >1s passes
        // between construction and the check).
        use crate::llm::TokenUsage;
        let hooks = crate::hooks::HookRegistry::new();
        let mut core = make_test_core(vec![Message::user("hi".to_string())], &hooks);
        core.wall_timeout_secs = 3;
        core.wall_start = Some(std::time::Instant::now() - std::time::Duration::from_secs(3));
        let usage = TokenUsage::default();
        let result = core.check_wall_deadline(0, &usage);
        assert!(
            result.is_some(),
            "elapsed == timeout must fire the deadline"
        );
    }
}