supercode_harness/

subagents.rs

//! P5-3 (COMPOSABLE-HARNESS-DESIGN.md §2 module 9 `subagents`: "D1 spawn
//! tool; D3 sub-agents/named-defs/background+resume/teams; D5 subagent
//! transcripts"; §2.1 D-1 "subagents → core.session(lineage), core.tools;
//! background-mode → permissions.approvals"; §2.2 C6): the data shapes and
//! pure-function resource-bound checks the spawn/join/background machinery
//! in `crate::agent::Agent` builds on. Kept separate from `agent.rs` so the
//! depth/concurrency-cap arithmetic and the lineage record shape are
//! unit-testable without a full `Agent`/mock-`Provider` harness — the same
//! "pure config → set, testable without the loop" precedent P3's
//! `crate::modules` module documents for itself.
//!
//! **Activation.** Everything here is inert until `Agent` actually consults
//! it, which only happens when `Config::subagents_enabled` is `true`
//! (`capabilities.subagents.enabled`, default `false`) — so importing this
//! module changes nothing for an agent that never turns the module on.

use std::collections::BTreeMap;
use std::sync::atomic::{AtomicUsize, Ordering};
use std::sync::Arc;

use serde::{Deserialize, Serialize};

use crate::error::{Error, Result};

/// A named subagent type (`[capabilities.subagents.agents.<name>]`, §3.1) —
/// the CC "subagent definition" shape: its own system prompt, an optionally
/// NARROWED tool set (a spawned child's tool surface is always the
/// intersection of the parent's already-enabled tools and this list — see
/// `Agent::run_spawn_subagent`'s doc comment for why it can only narrow,
/// never widen), and an optional model override.
#[derive(Debug, Clone, Default, PartialEq, Eq)]
pub struct NamedAgentDefinition {
    /// The name the model passes as `spawn_subagent`'s `agent_type` arg.
    pub name: String,
    /// The child's system prompt (replaces the parent's).
    pub system_prompt: String,
    /// If `Some`, the child's enabled-tool set is narrowed to the
    /// intersection of this list and the parent's own enabled tools.
    /// `None` inherits the parent's tool set unchanged.
    pub tools: Option<Vec<String>>,
    /// If `Some`, the child runs this model instead of the parent's.
    pub model: Option<String>,
}

/// `capabilities.subagents.background_prompts` (§2.2 C6's schema value,
/// §3.1): how a BACKGROUND child's tool-approval `Ask` decisions are
/// resolved, since a detached background task cannot block on an
/// interactive prompt it has no way to answer.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum BackgroundPromptsPolicy {
    /// Deny/allow-list only, no interactive handler ever installed on the
    /// child — see `Agent::run_spawn_subagent`'s C6 wiring: with no
    /// [`crate::permissions::PermissionsApprovalHandler`] installed, every
    /// `Ask`-tier decision fail-closed-denies
    /// ([`crate::permissions::approval::resolve_ask`]'s pre-existing "no
    /// handler ⇒ deny" contract) — exactly "deny/allow-list, no
    /// interactive asks": whatever the rule engine already resolves to
    /// `Allow` proceeds; anything routed to `Ask` is refused, never asked.
    AutoPolicy,
    /// Approval requests are pushed onto the PARENT's queue
    /// (`Agent::pending_child_approvals`) instead of blocking — the
    /// request is recorded for later parent inspection, but still resolves
    /// to `Deny` immediately (never hangs waiting for an answer that can't
    /// arrive synchronously).
    Parent,
}

impl BackgroundPromptsPolicy {
    /// Parse the §3.1 schema string (`"auto_policy"` | `"parent"`).
    pub fn parse(s: &str) -> Option<Self> {
        match s {
            "auto_policy" => Some(BackgroundPromptsPolicy::AutoPolicy),
            "parent" => Some(BackgroundPromptsPolicy::Parent),
            _ => None,
        }
    }

    /// The exact schema string this variant parses from — round-trip
    /// inverse of [`Self::parse`].
    pub fn as_str(self) -> &'static str {
        match self {
            BackgroundPromptsPolicy::AutoPolicy => "auto_policy",
            BackgroundPromptsPolicy::Parent => "parent",
        }
    }
}

/// Typed, lossless NATIVE-WRITE lineage record for a spawned child (§1.13;
/// §5.2 P5 row 3: "native write side — store already parses CC sidechains +
/// CX lineage on import"). Field names deliberately mirror the keys the
/// IMPORT-side loaders already populate on
/// [`crate::session::SessionMeta::parent_tool_use_id`]/
/// [`crate::session::SessionMeta::lineage`] (see [`Self::to_lineage_map`]),
/// so a natively-spawned session and an imported CC/CX one land in the same
/// shape rather than two parallel formats a translator would need to know
/// about separately.
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct SubagentLineage {
    /// This child's own agent id (the native analog of CC's `agentId`).
    pub child_agent_id: String,
    /// The parent session's store name/id, if the parent is itself a
    /// stored session.
    pub parent_session_id: Option<String>,
    /// The `tool_use_id` of the parent's `spawn_subagent` call that created
    /// this child — the native analog of CC's recovered
    /// `parent_tool_use_id`.
    pub parent_tool_use_id: String,
    /// How deep in the spawn tree this child is (parent's own depth + 1;
    /// a top-level agent is depth 0).
    pub depth: usize,
    /// The named `capabilities.subagents.agents.<name>` type spawned, if
    /// any (`None` for an ad-hoc inline `system_prompt` spawn).
    pub agent_type: Option<String>,
    /// The task/prompt text the child was spawned with.
    pub task: String,
    /// Whether this child was spawned in background mode.
    pub background: bool,
    /// Unix-ms wall-clock time the spawn happened.
    pub spawned_at_ms: i64,
    /// The model the child ran.
    pub model: String,
}

impl SubagentLineage {
    /// The [`crate::session::SessionMeta::lineage`] map a native-spawned
    /// child's [`crate::session::Session`] carries. `parent_thread_id` is
    /// the SAME key [`crate::session::Session::reconstruct_tree`]'s
    /// Codex-lineage nesting step already reads (see that function's doc
    /// comment) — reusing it rather than minting a new key means a
    /// native-spawned child nests under its parent via the identical
    /// mechanism an imported Codex thread-tree does.
    pub fn to_lineage_map(&self) -> BTreeMap<String, String> {
        let mut m = BTreeMap::new();
        if let Some(p) = &self.parent_session_id {
            m.insert("parent_thread_id".to_string(), p.clone());
            m.insert("parent_session_id".to_string(), p.clone());
        }
        m.insert("depth".to_string(), self.depth.to_string());
        if let Some(t) = &self.agent_type {
            m.insert("agent_role".to_string(), t.clone());
        }
        m.insert(
            "thread_source".to_string(),
            "supercode_native_spawn".to_string(),
        );
        m
    }
}

/// A queued approval request from a `background_prompts = "parent"` child,
/// surfaced via `Agent::pending_child_approvals` (§2.2 C6 "parent-surfaced
/// queue"). This struct is ALWAYS a record for the parent to inspect/audit
/// (never a pending decision the parent's answer changes retroactively) —
/// but what actually answers the underlying call depends on which
/// `PermissionsApprovalHandler` `Agent::run_spawn_subagent` installed for
/// the child:
/// - the DEFAULT [`ParentQueueApprovalHandler`] (no TUI factory installed)
///   resolves every request to `Deny` immediately, THEN records it here —
///   "queued" in name only, never actually blocking (P5-3's shipped,
///   never-blocking posture, unchanged).
/// - P5-4's `crate::tui::TuiChildApprovalHandler` (installed via
///   [`crate::agent::Agent::set_child_approval_handler_factory`]) records
///   the SAME entry here for audit purposes, but the underlying call
///   genuinely BLOCKS until a TUI operator answers it — which may resolve
///   `Allow`/`AllowForSession`, not only `Deny`. So: don't assume every
///   entry here was already denied — check the actual outcome the caller
///   observed (or the handler installed for this session) before treating
///   this queue as "purely historical, all denied."
#[derive(Debug, Clone)]
pub struct QueuedApproval {
    /// Which child raised this request.
    pub child_agent_id: String,
    /// The tool it tried to call.
    pub tool: String,
    /// The canonicalized command/path subject, if any.
    pub subject: Option<String>,
    /// Unix-ms wall-clock time it was queued.
    pub queued_at_ms: i64,
}

/// §2.2 C6 `background_prompts = "parent"`'s
/// [`crate::permissions::PermissionsApprovalHandler`]: pushes every
/// `Ask`-tier request onto the parent's queue
/// ([`crate::agent::Agent::pending_child_approvals`]) and returns
/// [`crate::permissions::ApprovalOutcome::Deny`] immediately — NEVER
/// blocks, since a detached background child has no way to wait for an
/// answer that can't arrive synchronously (the hard C6 requirement this
/// whole policy exists to satisfy). "Surfaced to the parent" means exactly
/// that: recorded for the parent to inspect/audit, not a live prompt the
/// parent's later answer retroactively changes.
pub struct ParentQueueApprovalHandler {
    /// This child's own agent id, stamped on every queued record so the
    /// parent can tell multiple background children's requests apart.
    pub child_agent_id: String,
    /// The shared queue — the SAME `Arc` as the parent's own
    /// `pending_child_approvals` field, so a push here is immediately
    /// visible to the parent.
    pub queue: Arc<std::sync::Mutex<Vec<QueuedApproval>>>,
}

impl crate::permissions::PermissionsApprovalHandler for ParentQueueApprovalHandler {
    fn ask(
        &self,
        req: &crate::permissions::ApprovalRequest,
    ) -> crate::permissions::ApprovalOutcome {
        let record = QueuedApproval {
            child_agent_id: self.child_agent_id.clone(),
            tool: req.tool.to_string(),
            subject: req.subject.map(String::from),
            queued_at_ms: now_ms(),
        };
        if let Ok(mut q) = self.queue.lock() {
            q.push(record);
        }
        crate::permissions::ApprovalOutcome::Deny
    }
}

/// Local `now_ms` (mirrors `crate::agent`'s private helper of the same
/// name/shape) — kept module-local rather than making `crate::agent`'s
/// version `pub(crate)` for one caller.
fn now_ms() -> i64 {
    std::time::SystemTime::now()
        .duration_since(std::time::UNIX_EPOCH)
        .map(|d| d.as_millis() as i64)
        .unwrap_or(0)
}

/// Fail-closed depth check (resource bound, build-brief "a parent spawning
/// children spawning children… must not fork-bomb"): `Err` NAMES the
/// exceeded cap rather than silently clamping the depth or panicking.
/// `current_depth` is the SPAWNING agent's own depth (0 for a top-level
/// agent); the new child would be spawned at `current_depth + 1`.
pub fn check_depth(current_depth: usize, max_depth: usize) -> Result<()> {
    if current_depth >= max_depth {
        return Err(Error::SubagentDepthExceeded {
            max_depth,
            attempted_depth: current_depth + 1,
        });
    }
    Ok(())
}

/// A held slot against a [`try_acquire`] concurrency gauge. Decrements the
/// gauge on drop (including an early return, a panic-unwind, or the normal
/// end of a background task's future) so a completed spawn always releases
/// its slot — no separate "remember to release" call site to forget.
pub struct ConcurrencyGuard(Arc<AtomicUsize>);

impl Drop for ConcurrencyGuard {
    fn drop(&mut self) {
        self.0.fetch_sub(1, Ordering::SeqCst);
    }
}

/// Fail-closed concurrency check-and-acquire (resource bound: "a max
/// concurrent subagents… cap, fail-closed"). Atomic compare-exchange loop
/// (not a check-then-increment race, which would let two racing spawns both
/// pass a check against the same stale count) — `None` when
/// `max_concurrent` subagents are already in flight anywhere in this spawn
/// tree (the gauge is a single `Arc` shared root-to-leaf, per
/// `crate::agent::Agent`'s doc comment on its own concurrency-gauge field),
/// `Some(guard)` otherwise, with the slot already counted.
pub fn try_acquire(gauge: &Arc<AtomicUsize>, max_concurrent: usize) -> Option<ConcurrencyGuard> {
    let mut current = gauge.load(Ordering::SeqCst);
    loop {
        if current >= max_concurrent {
            return None;
        }
        match gauge.compare_exchange(current, current + 1, Ordering::SeqCst, Ordering::SeqCst) {
            Ok(_) => return Some(ConcurrencyGuard(gauge.clone())),
            Err(actual) => current = actual,
        }
    }
}

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

    #[test]
    fn background_prompts_policy_round_trips_through_its_schema_string() {
        for p in [
            BackgroundPromptsPolicy::AutoPolicy,
            BackgroundPromptsPolicy::Parent,
        ] {
            assert_eq!(BackgroundPromptsPolicy::parse(p.as_str()), Some(p));
        }
        assert_eq!(BackgroundPromptsPolicy::parse("bogus"), None);
        assert_eq!(BackgroundPromptsPolicy::parse(""), None);
    }

    #[test]
    fn check_depth_allows_up_to_the_cap_and_refuses_past_it() {
        // max_depth = 2: a depth-0 or depth-1 spawner may spawn (landing the
        // child at depth 1 or 2); a depth-2 spawner may not (would land the
        // child at depth 3).
        assert!(check_depth(0, 2).is_ok());
        assert!(check_depth(1, 2).is_ok());
        let err = check_depth(2, 2).unwrap_err();
        match err {
            Error::SubagentDepthExceeded {
                max_depth,
                attempted_depth,
            } => {
                assert_eq!(max_depth, 2);
                assert_eq!(attempted_depth, 3);
            }
            other => panic!("expected SubagentDepthExceeded, got {other:?}"),
        }
    }

    #[test]
    fn check_depth_zero_cap_refuses_every_spawn() {
        assert!(check_depth(0, 0).is_err());
    }

    #[test]
    fn try_acquire_enforces_the_cap_and_release_frees_a_slot() {
        let gauge = Arc::new(AtomicUsize::new(0));
        let g1 = try_acquire(&gauge, 2).expect("first slot free");
        let g2 = try_acquire(&gauge, 2).expect("second slot free");
        assert!(
            try_acquire(&gauge, 2).is_none(),
            "cap of 2 must refuse a third concurrent holder"
        );
        drop(g1);
        let g3 = try_acquire(&gauge, 2).expect("a released slot must be reusable");
        drop(g2);
        drop(g3);
        assert_eq!(gauge.load(Ordering::SeqCst), 0);
    }

    #[test]
    fn try_acquire_zero_cap_never_grants_a_slot() {
        let gauge = Arc::new(AtomicUsize::new(0));
        assert!(try_acquire(&gauge, 0).is_none());
    }

    #[test]
    fn lineage_to_map_carries_parent_thread_id_alias_and_depth() {
        let rec = SubagentLineage {
            child_agent_id: "agent-1".to_string(),
            parent_session_id: Some("sess-a".to_string()),
            parent_tool_use_id: "call_1".to_string(),
            depth: 1,
            agent_type: Some("researcher".to_string()),
            task: "look into X".to_string(),
            background: false,
            spawned_at_ms: 1_700_000_000_000,
            model: "vendor/model-a".to_string(),
        };
        let m = rec.to_lineage_map();
        assert_eq!(m.get("parent_thread_id"), Some(&"sess-a".to_string()));
        assert_eq!(m.get("parent_session_id"), Some(&"sess-a".to_string()));
        assert_eq!(m.get("depth"), Some(&"1".to_string()));
        assert_eq!(m.get("agent_role"), Some(&"researcher".to_string()));
        assert_eq!(
            m.get("thread_source"),
            Some(&"supercode_native_spawn".to_string())
        );
    }

    #[test]
    fn parent_queue_handler_never_hangs_and_records_the_request() {
        use crate::permissions::{ApprovalOutcome, ApprovalRequest, PermissionsApprovalHandler};

        let queue = Arc::new(std::sync::Mutex::new(Vec::new()));
        let handler = ParentQueueApprovalHandler {
            child_agent_id: "agent-bg-1".to_string(),
            queue: queue.clone(),
        };
        let args = serde_json::json!({});
        let outcome = handler.ask(&ApprovalRequest {
            tool: "bash",
            subject: Some("rm -rf /tmp/x"),
            raw_args: &args,
        });
        // Never asks interactively — always resolves synchronously.
        assert_eq!(outcome, ApprovalOutcome::Deny);
        let recorded = queue.lock().unwrap();
        assert_eq!(recorded.len(), 1);
        assert_eq!(recorded[0].child_agent_id, "agent-bg-1");
        assert_eq!(recorded[0].tool, "bash");
        assert_eq!(recorded[0].subject.as_deref(), Some("rm -rf /tmp/x"));
    }

    #[test]
    fn lineage_round_trips_through_json() {
        let rec = SubagentLineage {
            child_agent_id: "agent-2".to_string(),
            parent_session_id: None,
            parent_tool_use_id: "call_9".to_string(),
            depth: 0,
            agent_type: None,
            task: "t".to_string(),
            background: true,
            spawned_at_ms: 42,
            model: "vendor/model-b".to_string(),
        };
        let json = serde_json::to_string(&rec).unwrap();
        let back: SubagentLineage = serde_json::from_str(&json).unwrap();
        assert_eq!(rec, back);
    }
}