synaps-engine 0.8.0

//! Hook events — typed payloads for each extension point.
//!
//! Each [`HookKind`] maps to a discrete phase of SynapsCLI's execution loop.
//! [`HookEvent`] is the concrete payload dispatched to subscribers at that
//! phase; [`HookResult`] is what a handler returns to control execution flow.
//!
//! Permission enforcement lives in [`crate::extensions::permissions`]:
//! every `HookKind` declares a [`required_permission`][HookKind::required_permission]
//! so the runtime can gate subscriptions before any payload is delivered.

use serde::{Deserialize, Serialize};
use serde_json::Value;

use crate::extensions::permissions::Permission;

/// Maximum hook output size (bytes) before truncation on the JSON-RPC path.
/// Matches `max_tool_buffer` (256 KB) — keeps the payload bounded while still
/// giving transform extensions the full buffered output to work with.
/// Exported so tests can build payloads that derive from the real cap and
/// won't rot when the constant changes.
pub const MAX_HOOK_OUTPUT: usize = 256 * 1024; // 256 KB

// ── HookKind ──────────────────────────────────────────────────────────────────

/// All hook event kinds in the phase-1 catalog.
///
/// Each variant identifies a well-defined extension point in the agent loop.
/// The set is intentionally closed; new kinds are added via a breaking version
/// bump so existing permission grants stay coherent.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum HookKind {
    /// Fires immediately before a tool is invoked. Handlers may block the call.
    BeforeToolCall,
    /// Fires immediately after a tool returns. Handlers receive the output.
    AfterToolCall,
    /// Fires before an LLM message is sent. Handlers may inspect or block.
    BeforeMessage,
    /// Fires after an assistant response is completed and added to history.
    OnMessageComplete,
    /// Fires after conversation compaction creates a replacement session.
    OnCompaction,
    /// Fires when a new session is created.
    OnSessionStart,
    /// Fires when a session is torn down.
    OnSessionEnd,
}

impl HookKind {
    /// Every hook kind, in declaration order.
    ///
    /// Exhaustiveness is enforced by `all_covers_every_variant` in this
    /// module's tests. This list is what `docs/extensions/contract.json` is
    /// drift-checked against (see
    /// `crates/agent-tui/tests/extensions_contract.rs`).
    pub const ALL: &'static [HookKind] = &[
        Self::BeforeToolCall,
        Self::AfterToolCall,
        Self::BeforeMessage,
        Self::OnMessageComplete,
        Self::OnCompaction,
        Self::OnSessionStart,
        Self::OnSessionEnd,
    ];

    /// Canonical string identifier for this kind, suitable for serialization
    /// keys, log output, and manifest declarations.
    pub fn as_str(&self) -> &'static str {
        match self {
            Self::BeforeToolCall => "before_tool_call",
            Self::AfterToolCall => "after_tool_call",
            Self::BeforeMessage => "before_message",
            Self::OnMessageComplete => "on_message_complete",
            Self::OnCompaction => "on_compaction",
            Self::OnSessionStart => "on_session_start",
            Self::OnSessionEnd => "on_session_end",
        }
    }

    /// Parse from the canonical string representation.
    ///
    /// Returns `None` for unrecognised strings so callers can surface
    /// a manifest validation error rather than silently dropping hooks.
    #[allow(clippy::should_implement_trait)]
    pub fn from_str(s: &str) -> Option<Self> {
        match s {
            "before_tool_call" => Some(Self::BeforeToolCall),
            "after_tool_call" => Some(Self::AfterToolCall),
            "before_message" => Some(Self::BeforeMessage),
            "on_message_complete" => Some(Self::OnMessageComplete),
            "on_compaction" => Some(Self::OnCompaction),
            "on_session_start" => Some(Self::OnSessionStart),
            "on_session_end" => Some(Self::OnSessionEnd),
            _ => None,
        }
    }

    /// Supported action names for this hook in the extension contract.
    pub fn allowed_action_names(&self) -> &'static [&'static str] {
        match self {
            Self::BeforeToolCall => &["continue", "block", "confirm", "modify"],
            Self::AfterToolCall => &["continue", "replace"],
            Self::BeforeMessage => &["continue", "inject"],
            // Session-scoped context. Injected ONCE when the session starts
            // and carried on the system prompt for the rest of it, rather
            // than re-appended on every message the way `before_message`
            // injection is.
            Self::OnSessionStart => &["continue", "inject"],
            Self::OnMessageComplete | Self::OnCompaction | Self::OnSessionEnd => &["continue"],
        }
    }

    /// Whether this hook can be filtered by tool name in a manifest.
    pub fn allows_tool_filter(&self) -> bool {
        matches!(self, Self::BeforeToolCall | Self::AfterToolCall)
    }

    /// Whether this hook accepts a handler result action.
    pub fn allows_result(&self, result: &HookResult) -> bool {
        matches!(
            (self, result),
            (_, HookResult::Continue)
                | (Self::BeforeToolCall, HookResult::Block { .. })
                | (Self::BeforeToolCall, HookResult::Confirm { .. })
                | (Self::BeforeToolCall, HookResult::Modify { .. })
                | (Self::AfterToolCall, HookResult::Replace { .. })
                | (Self::BeforeMessage, HookResult::Inject { .. })
                | (Self::OnSessionStart, HookResult::Inject { .. })
        )
    }

    /// The [`Permission`] an extension must hold to subscribe to this hook.
    ///
    /// Called by the permission gate before delivering any event; if the
    /// extension's [`PermissionSet`][crate::extensions::permissions::PermissionSet]
    /// does not include this permission, `HookBus::subscribe()` returns an error.
    pub fn required_permission(&self) -> Permission {
        match self {
            Self::BeforeToolCall | Self::AfterToolCall => Permission::ToolsIntercept,
            Self::BeforeMessage | Self::OnMessageComplete | Self::OnCompaction => {
                Permission::LlmContent
            }
            Self::OnSessionStart | Self::OnSessionEnd => Permission::SessionLifecycle,
        }
    }
}

// ── HookEvent ─────────────────────────────────────────────────────────────────

/// A hook event payload dispatched to extension handlers.
///
/// Fields are optional and populated only when relevant to the hook kind:
///
/// | Kind                  | tool_name | tool_input | tool_output | message | session_id |
/// |-----------------------|-----------|------------|-------------|---------|------------|
/// | `before_tool_call`    | ✓         | ✓          |             |         |            |
/// | `after_tool_call`     | ✓         | ✓          | ✓           |         |            |
/// | `before_message`      |           |            |             | ✓       |            |
/// | `on_message_complete` |           |            |             | ✓       |            |
/// | `on_compaction`       |           |            |             | ✓       | ✓          |
/// | `on_session_start`    |           |            |             |         | ✓          |
/// | `on_session_end`      |           |            |             |         | ✓          |
///
/// The `data` field is available on all events for extensions that need to
/// attach arbitrary structured context when constructing synthetic events.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct HookEvent {
    /// Which hook fired.
    pub kind: HookKind,
    /// Tool name for tool-specific hooks; `None` for general hooks.
    /// This is the API-safe name (sanitized for the LLM).
    pub tool_name: Option<String>,
    /// Original runtime name of the tool (before API sanitization).
    /// Extension authors typically write runtime names in their manifests.
    #[serde(default)]
    pub tool_runtime_name: Option<String>,
    /// Tool input arguments for `before_tool_call` and `after_tool_call`.
    pub tool_input: Option<Value>,
    /// Tool output for `after_tool_call`.
    pub tool_output: Option<String>,
    /// LLM message content for `before_message`.
    pub message: Option<String>,
    /// Session identifier for session lifecycle hooks.
    pub session_id: Option<String>,
    /// Session message history for `on_session_end`.
    /// Contains the conversation transcript so extensions (like Stelline)
    /// can extract memories without reaching into runtime internals.
    #[serde(default)]
    pub transcript: Option<Vec<crate::SharedMessage>>,
    /// Arbitrary extension-defined data, passed through without inspection.
    pub data: Value,
}

impl HookEvent {
    /// Construct a `before_tool_call` event.
    pub fn before_tool_call(tool_name: &str, input: Value) -> Self {
        Self {
            kind: HookKind::BeforeToolCall,
            tool_name: Some(tool_name.to_string()),
            tool_input: Some(input),
            tool_output: None,
            message: None,
            session_id: None,
            tool_runtime_name: None,
            transcript: None,
            data: Value::Null,
        }
    }

    /// Construct an `after_tool_call` event carrying both input and output.
    /// Output is truncated to MAX_HOOK_OUTPUT to bound the JSON-RPC payload
    /// to extensions. This cap matches the runtime's `max_tool_buffer`
    /// (the OOM safety net) so transform extensions see the FULL buffered
    /// tool output and can decide what to keep — the final context-budget
    /// truncation to `max_tool_output` happens AFTER the hook in
    /// `emit_after_tool_call` (compress-then-truncate).
    pub fn after_tool_call(tool_name: &str, input: Value, output: String) -> Self {
        let bounded = agent_core::BoundedText::new(&output, MAX_HOOK_OUTPUT);
        let truncated_output = if bounded.truncated {
            format!(
                "{}…[truncated, {} total bytes]",
                bounded.text, bounded.original_bytes
            )
        } else {
            output
        };
        Self {
            kind: HookKind::AfterToolCall,
            tool_name: Some(tool_name.to_string()),
            tool_input: Some(input),
            tool_output: Some(truncated_output),
            message: None,
            session_id: None,
            tool_runtime_name: None,
            transcript: None,
            data: Value::Null,
        }
    }

    /// Construct a `before_message` event.
    pub fn before_message(message: &str) -> Self {
        Self {
            kind: HookKind::BeforeMessage,
            tool_name: None,
            tool_input: None,
            tool_output: None,
            message: Some(message.to_string()),
            session_id: None,
            tool_runtime_name: None,
            transcript: None,
            data: Value::Null,
        }
    }

    /// Construct an `on_message_complete` event.
    pub fn on_message_complete(message: &str, data: Value) -> Self {
        Self {
            kind: HookKind::OnMessageComplete,
            tool_name: None,
            tool_input: None,
            tool_output: None,
            message: Some(message.to_string()),
            session_id: None,
            tool_runtime_name: None,
            transcript: None,
            data,
        }
    }

    /// Construct an `on_compaction` event.
    pub fn on_compaction(
        old_session_id: &str,
        new_session_id: &str,
        summary: &str,
        message_count: usize,
        mut data: Value,
    ) -> Self {
        if !data.is_object() {
            data = Value::Object(Default::default());
        }
        if let Some(object) = data.as_object_mut() {
            object.insert(
                "old_session_id".to_string(),
                Value::String(old_session_id.to_string()),
            );
            object.insert(
                "new_session_id".to_string(),
                Value::String(new_session_id.to_string()),
            );
            object.insert(
                "message_count".to_string(),
                Value::Number(message_count.into()),
            );
        }
        Self {
            kind: HookKind::OnCompaction,
            tool_name: None,
            tool_input: None,
            tool_output: None,
            message: Some(summary.to_string()),
            session_id: Some(new_session_id.to_string()),
            tool_runtime_name: None,
            transcript: None,
            data,
        }
    }

    /// Construct an `on_session_start` event.
    pub fn on_session_start(session_id: &str) -> Self {
        Self {
            kind: HookKind::OnSessionStart,
            tool_name: None,
            tool_input: None,
            tool_output: None,
            message: None,
            session_id: Some(session_id.to_string()),
            tool_runtime_name: None,
            transcript: None,
            data: Value::Null,
        }
    }

    /// Construct an `on_session_end` event.
    pub fn on_session_end(session_id: &str, transcript: Option<Vec<crate::SharedMessage>>) -> Self {
        Self {
            kind: HookKind::OnSessionEnd,
            tool_name: None,
            tool_input: None,
            tool_output: None,
            message: None,
            session_id: Some(session_id.to_string()),
            tool_runtime_name: None,
            transcript,
            data: Value::Null,
        }
    }
}

// ── HookResult ────────────────────────────────────────────────────────────────

/// What an extension handler returns after processing a hook event.
///
/// The runtime resolves multiple handlers by precedence:
/// - `Block`, `Confirm`, and `Modify` stop the handler chain for `before_tool_call`.
/// - `Inject` results are accumulated for `before_message`.
/// - `Continue` is the no-op default — processing continues normally.
#[derive(Debug, Clone, Default, PartialEq, Serialize, Deserialize)]
#[serde(tag = "action", rename_all = "snake_case")]
pub enum HookResult {
    /// Allow execution to proceed unchanged.
    #[default]
    Continue,
    /// Prevent the hooked operation. The `reason` is surfaced to the user.
    Block { reason: String },
    /// Inject context — the extension provides text for the current request.
    /// Placement depends on the hook (#297): `on_session_start` content is
    /// appended to the system prompt (session-stable, cache-safe);
    /// `before_message` content is attached to the newest user message on the
    /// outgoing request as an ephemeral trailing block positioned AFTER the
    /// conversational cache marker (per-turn, uncached tail, cache-neutral).
    Inject { content: String },
    /// Ask the runtime to get explicit user confirmation before proceeding.
    /// Only valid on before_tool_call hooks.
    Confirm { message: String },
    /// Replace the tool **input** before execution (structured JSON args).
    /// Only valid on before_tool_call hooks. The output-side counterpart is
    /// [`HookResult::Replace`]. The first modifier stops the handler chain.
    Modify { input: Value },
    /// Replace the tool **output** after execution (flat string), before it
    /// enters history. Only valid on after_tool_call hooks. The input-side
    /// counterpart is [`HookResult::Modify`] — distinct name because the payload
    /// is an unstructured `String`, not structured `Value`. Enables native
    /// output transforms (compression, redaction, summarization) by extensions.
    /// The first transform stops the handler chain.
    Replace { output: String },
}

// ── Tests ─────────────────────────────────────────────────────────────────────

impl HookEvent {
    /// Set the runtime name for tool-related events.
    pub fn with_runtime_name(mut self, name: &str) -> Self {
        self.tool_runtime_name = Some(name.to_string());
        self
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use serde_json::json;

    /// The extension wire format `{"action":"replace","output":"..."}`
    /// deserializes to HookResult::Replace via the serde action tag — and
    /// round-trips back. This locks the contract a transform extension speaks.
    #[test]
    fn replace_action_roundtrips_extension_wire_format() {
        // Inbound: what a process extension sends on hook.handle.
        let wire = json!({"action": "replace", "output": "compressed"});
        let parsed: HookResult = serde_json::from_value(wire).expect("must deserialize");
        match parsed {
            HookResult::Replace { output } => assert_eq!(output, "compressed"),
            other => panic!("expected Replace, got {other:?}"),
        }

        // Outbound: the action tag is exactly "replace".
        let out = serde_json::to_value(HookResult::Replace { output: "x".into() }).unwrap();
        assert_eq!(out["action"], "replace");
        assert_eq!(out["output"], "x");
    }

    // ── HookKind ──────────────────────────────────────────────────────────────

    /// after_tool_call may return Replace; other hooks may not, and
    /// after_tool_call advertises "replace" in its action contract.
    #[test]
    fn after_tool_call_allows_replace_output() {
        let replace = HookResult::Replace {
            output: "compressed".into(),
        };

        // The transform seam: after_tool_call accepts Replace.
        assert!(
            HookKind::AfterToolCall.allows_result(&replace),
            "after_tool_call must permit Replace to enable output transforms"
        );

        // Replace is scoped strictly to after_tool_call.
        assert!(
            !HookKind::BeforeToolCall.allows_result(&replace),
            "before_tool_call must not permit Replace (input-only)"
        );
        assert!(
            !HookKind::BeforeMessage.allows_result(&replace),
            "before_message must not permit Replace"
        );

        // The extension-facing action contract advertises "replace".
        assert!(
            HookKind::AfterToolCall
                .allowed_action_names()
                .contains(&"replace"),
            "after_tool_call must advertise the 'replace' action"
        );
    }

    /// Every variant's as_str round-trips through from_str.
    #[test]
    fn hook_kind_as_str_roundtrip() {
        let all = [
            HookKind::BeforeToolCall,
            HookKind::AfterToolCall,
            HookKind::BeforeMessage,
            HookKind::OnMessageComplete,
            HookKind::OnCompaction,
            HookKind::OnSessionStart,
            HookKind::OnSessionEnd,
        ];
        for kind in all {
            let s = kind.as_str();
            assert_eq!(
                HookKind::from_str(s),
                Some(kind),
                "round-trip failed for {s}"
            );
        }
    }

    /// Unknown strings return None, not a panic or a default.
    #[test]
    fn hook_kind_from_str_unknown_returns_none() {
        assert_eq!(HookKind::from_str(""), None);
        assert_eq!(HookKind::from_str("BeforeToolCall"), None); // wrong case
        assert_eq!(HookKind::from_str("on_crash"), None);
    }

    /// Serde uses snake_case via the attribute — spot-check two variants.
    #[test]
    fn hook_kind_serde_snake_case() {
        let serialized = serde_json::to_string(&HookKind::BeforeToolCall).unwrap();
        assert_eq!(serialized, r#""before_tool_call""#);

        let back: HookKind = serde_json::from_str(r#""on_session_end""#).unwrap();
        assert_eq!(back, HookKind::OnSessionEnd);
    }

    /// Each kind maps to the expected permission.
    #[test]
    fn hook_kind_required_permission() {
        assert_eq!(
            HookKind::BeforeToolCall.required_permission(),
            Permission::ToolsIntercept
        );
        assert_eq!(
            HookKind::AfterToolCall.required_permission(),
            Permission::ToolsIntercept
        );
        assert_eq!(
            HookKind::BeforeMessage.required_permission(),
            Permission::LlmContent
        );
        assert_eq!(
            HookKind::OnMessageComplete.required_permission(),
            Permission::LlmContent
        );
        assert_eq!(
            HookKind::OnCompaction.required_permission(),
            Permission::LlmContent
        );
        assert_eq!(
            HookKind::OnSessionStart.required_permission(),
            Permission::SessionLifecycle
        );
        assert_eq!(
            HookKind::OnSessionEnd.required_permission(),
            Permission::SessionLifecycle
        );
    }

    // ── HookEvent constructors ────────────────────────────────────────────────

    #[test]
    fn hook_event_before_tool_call() {
        let input = json!({"path": "/tmp/foo"});
        let ev = HookEvent::before_tool_call("read_file", input.clone());

        assert_eq!(ev.kind, HookKind::BeforeToolCall);
        assert_eq!(ev.tool_name.as_deref(), Some("read_file"));
        assert_eq!(ev.tool_input.as_ref(), Some(&input));
        assert!(ev.tool_output.is_none());
        assert!(ev.message.is_none());
        assert!(ev.session_id.is_none());
        assert_eq!(ev.data, Value::Null);
    }

    #[test]
    fn hook_event_after_tool_call() {
        let input = json!({"query": "select 1"});
        let ev = HookEvent::after_tool_call("sql_query", input.clone(), "1 row".to_string());

        assert_eq!(ev.kind, HookKind::AfterToolCall);
        assert_eq!(ev.tool_name.as_deref(), Some("sql_query"));
        assert_eq!(ev.tool_input.as_ref(), Some(&input));
        assert_eq!(ev.tool_output.as_deref(), Some("1 row"));
        assert!(ev.message.is_none());
        assert!(ev.session_id.is_none());
    }

    #[test]
    fn hook_event_before_message() {
        let ev = HookEvent::before_message("Hello, LLM");

        assert_eq!(ev.kind, HookKind::BeforeMessage);
        assert!(ev.tool_name.is_none());
        assert!(ev.tool_input.is_none());
        assert!(ev.tool_output.is_none());
        assert_eq!(ev.message.as_deref(), Some("Hello, LLM"));
        assert!(ev.session_id.is_none());
    }

    #[test]
    fn hook_event_on_message_complete() {
        let ev = HookEvent::on_message_complete("Done", json!({"content_block_count": 1}));

        assert_eq!(ev.kind, HookKind::OnMessageComplete);
        assert!(ev.tool_name.is_none());
        assert!(ev.tool_input.is_none());
        assert!(ev.tool_output.is_none());
        assert_eq!(ev.message.as_deref(), Some("Done"));
        assert_eq!(ev.data["content_block_count"], 1);
        assert!(ev.session_id.is_none());
    }

    #[test]
    fn hook_event_on_compaction() {
        let ev = HookEvent::on_compaction(
            "old-session",
            "new-session",
            "Summary",
            7,
            json!({"source": "manual"}),
        );

        assert_eq!(ev.kind, HookKind::OnCompaction);
        assert_eq!(ev.message.as_deref(), Some("Summary"));
        assert_eq!(ev.session_id.as_deref(), Some("new-session"));
        assert_eq!(ev.data["old_session_id"], "old-session");
        assert_eq!(ev.data["new_session_id"], "new-session");
        assert_eq!(ev.data["message_count"], 7);
        assert_eq!(ev.data["source"], "manual");
        assert!(ev.transcript.is_none());
    }

    #[test]
    fn hook_event_on_session_start() {
        let ev = HookEvent::on_session_start("sess-abc-123");

        assert_eq!(ev.kind, HookKind::OnSessionStart);
        assert_eq!(ev.session_id.as_deref(), Some("sess-abc-123"));
        assert!(ev.tool_name.is_none());
        assert!(ev.message.is_none());
    }

    #[test]
    fn hook_event_on_session_end() {
        let ev = HookEvent::on_session_end("sess-abc-123", None);

        assert_eq!(ev.kind, HookKind::OnSessionEnd);
        assert_eq!(ev.session_id.as_deref(), Some("sess-abc-123"));
        assert!(ev.tool_name.is_none());
        assert!(ev.message.is_none());
    }

    /// HookEvent is round-trippable through JSON without loss.
    #[test]
    fn hook_event_serde_roundtrip() {
        let ev = HookEvent::before_tool_call("bash", json!({"cmd": "ls"}));
        let json = serde_json::to_string(&ev).unwrap();
        let back: HookEvent = serde_json::from_str(&json).unwrap();

        assert_eq!(back.kind, ev.kind);
        assert_eq!(back.tool_name, ev.tool_name);
        assert_eq!(back.tool_input, ev.tool_input);
    }

    // ── HookResult ────────────────────────────────────────────────────────────

    /// Default is Continue.
    #[test]
    fn hook_result_default_is_continue() {
        assert!(matches!(HookResult::default(), HookResult::Continue));
    }

    /// Block carries its reason through serialization.
    #[test]
    fn hook_result_block_serde() {
        let r = HookResult::Block {
            reason: "denied by policy".to_string(),
        };
        let json = serde_json::to_string(&r).unwrap();
        // `tag = "action"` means the JSON object has {"action":"block","reason":"..."}
        assert!(json.contains(r#""action":"block""#));
        assert!(json.contains("denied by policy"));

        let back: HookResult = serde_json::from_str(&json).unwrap();
        assert!(matches!(back, HookResult::Block { reason } if reason == "denied by policy"));
    }

    /// Confirm carries its message through serialization.
    #[test]
    fn hook_result_confirm_serde() {
        let r = HookResult::Confirm {
            message: "Run this command?".to_string(),
        };
        let json = serde_json::to_string(&r).unwrap();
        assert_eq!(
            json,
            r#"{"action":"confirm","message":"Run this command?"}"#
        );

        let back: HookResult = serde_json::from_str(&json).unwrap();
        assert!(matches!(back, HookResult::Confirm { message } if message == "Run this command?"));
    }

    /// Modify carries replacement input through serialization.
    #[test]
    fn hook_result_modify_serde() {
        let r = HookResult::Modify {
            input: json!({"command": "echo safe"}),
        };
        let json = serde_json::to_string(&r).unwrap();
        assert_eq!(
            json,
            r#"{"action":"modify","input":{"command":"echo safe"}}"#
        );

        let back: HookResult = serde_json::from_str(&json).unwrap();
        assert!(
            matches!(back, HookResult::Modify { input } if input == json!({"command": "echo safe"}))
        );
    }

    /// Continue serialises as {"action":"continue"}.
    #[test]
    fn hook_result_continue_serde() {
        let json = serde_json::to_string(&HookResult::Continue).unwrap();
        assert_eq!(json, r#"{"action":"continue"}"#);
    }

    /// `HookKind::ALL` must list every variant exactly once. Adding a variant
    /// makes the match below non-exhaustive => compile error => the author is
    /// forced to update `ALL` and, via the contract test, contract.json.
    #[test]
    fn all_covers_every_variant() {
        for kind in HookKind::ALL {
            match kind {
                HookKind::BeforeToolCall
                | HookKind::AfterToolCall
                | HookKind::BeforeMessage
                | HookKind::OnMessageComplete
                | HookKind::OnCompaction
                | HookKind::OnSessionStart
                | HookKind::OnSessionEnd => {}
            }
        }
        assert_eq!(
            HookKind::ALL.len(),
            7,
            "a HookKind variant was added or removed -- update HookKind::ALL \
             and docs/extensions/contract.json to match"
        );
        let unique: std::collections::HashSet<HookKind> = HookKind::ALL.iter().copied().collect();
        assert_eq!(
            unique.len(),
            HookKind::ALL.len(),
            "HookKind::ALL has a duplicate"
        );
    }

    /// Every hook kind must round-trip through its canonical wire string.
    #[test]
    fn all_hook_kinds_round_trip_through_wire_format() {
        for kind in HookKind::ALL {
            assert_eq!(
                HookKind::from_str(kind.as_str()),
                Some(*kind),
                "{} does not round-trip",
                kind.as_str()
            );
        }
    }

    /// `allowed_action_names` is the contract's action list, and
    /// `allows_result` is what the hook bus actually enforces. They must
    /// agree, or the documented action set is a lie in one direction or the
    /// other. (#291: on_session_start advertised only "continue" while Axel
    /// returned "inject" -- caught here now.)
    #[test]
    fn advertised_actions_match_enforced_actions() {
        let samples: [(&str, HookResult); 6] = [
            ("continue", HookResult::Continue),
            ("block", HookResult::Block { reason: "r".into() }),
            (
                "confirm",
                HookResult::Confirm {
                    message: "m".into(),
                },
            ),
            (
                "modify",
                HookResult::Modify {
                    input: serde_json::json!({}),
                },
            ),
            ("replace", HookResult::Replace { output: "o".into() }),
            (
                "inject",
                HookResult::Inject {
                    content: "c".into(),
                },
            ),
        ];
        for kind in HookKind::ALL {
            for (name, result) in &samples {
                let advertised = kind.allowed_action_names().contains(name);
                let enforced = kind.allows_result(result);
                assert_eq!(
                    advertised,
                    enforced,
                    "hook {} disagrees about action {:?}: advertised={} enforced={}",
                    kind.as_str(),
                    name,
                    advertised,
                    enforced
                );
            }
        }
    }
}