lernie 0.0.9

//! Tool executor (ARCH §3.2 second bullet, §3.3).
//!
//! The harness emits a `tool_use` block from the model and the executor
//! turns it into a `tool_result` block — by spawning the tool's binary
//! per the §3.3 stdio contract, capturing stdout / stderr / exit, and
//! landing the per-tool-call disk record (`input.json`, `output.json` under
//! `<step_dir>/tools/<tool-id>/`). The executor is one direction of the
//! disk-as-bus contract (§3.1): the harness writes the request via the
//! `tool_use` block in `response.json`; the per-tool-call record makes the
//! result inspectable; the loop reads it back to assemble the next
//! step's request (§3.3 "Wire `tool_result` framing is application-layer").
//!
//! [`ToolExecutor`] is the trait the loop holds as `&dyn`. [`SpawnTool`]
//! is the production implementation; tests construct it directly against
//! a tempdir-rooted `harness_root` and shell-script fixture tools. Its
//! third resolution hop re-enters the command surface at the
//! binding-injected driver target (`cmd::Fx::driver_target`, §2.11) —
//! the library resolves no binary path by name.
//!
//! Ahead of that resolution sits the optional **host injection**
//! ([`inject`], §3.3 *Host-injected tools*): a linked binding may hand
//! the executor tool definitions of its own plus a router that answers
//! the invocations it owns, so a tool can be answered by the host instead
//! of by a binary. Everything after the answer — the result envelope, the
//! bounded projection, the disk record ([`record`]) — is identical either
//! way.

use serde_json::Value;
use std::io;
use std::path::{Path, PathBuf};
use std::sync::atomic::AtomicBool;
use std::time::Duration;
use thiserror::Error;

mod bound;
pub mod builtin;
pub mod control;
mod envelope;
pub mod inject;
mod record;
pub mod spawn;
mod subprocess;

#[cfg(test)]
mod tests;

use inject::InjectedTool;
pub use record::{INPUT_FILE, OUTPUT_FILE, ToolInputRecord, ToolOutputRecord};
pub(crate) use record::{atomic_write_json, tool_call_dir};
pub use spawn::SpawnTool;

/// SIGTERM-to-SIGKILL grace pinned by ARCH §3.3 (mirrors §4.4). The
/// tool has 5 seconds after SIGTERM to flush state and exit cleanly
/// before SIGKILL follows.
pub const DEFAULT_TOOL_DEADLINE: Duration = Duration::from_secs(5);

/// Subdirectory under the harness root where externalized tool binaries
/// live (ARCH §3.3 — "discovery mirrors §4.4: looks up `lernie-tool-<name>`
/// at `<harness-root>/tools/`").
pub const TOOLS_DIR: &str = "tools";

/// Per-step subdirectory holding tool-call records (ARCH §3.3 "Disk
/// record" → `steps/<conv-id>/<NNN>/tools/<tool-id>/`).
pub const STEP_TOOLS_SUBDIR: &str = "tools";

/// Name prefix for externalized tool binaries (ARCH §3.3, mirroring
/// §4.4's `lernie-provider-<name>` convention).
pub const EXTERNAL_PREFIX: &str = "lernie-tool-";

/// Argv used when invoking an in-process tool via the lernie binary
/// (ARCH §3.3 — "addressed as `lernie tool <name>`").
pub const IN_PROCESS_SUBCOMMAND: &str = "tool";

/// Env var conveying the conversation-repo root path to the tool
/// subprocess (ARCH §3.3 env-var bullet). Pinned here so the executor
/// (the writer) and the `dispatch` built-in (the reader) cannot drift.
pub const ENV_CONV_REPO: &str = "LERNIE_CONV_REPO";
/// Env var conveying the calling conversation's branch name (== full
/// hyphenated descent / conv-id, ARCH §2.2) to the tool subprocess.
/// Same provenance as [`ENV_CONV_REPO`].
pub const ENV_CONV_BRANCH: &str = "LERNIE_CONV_BRANCH";

/// One tool invocation as the model emitted it — the `id`, `name`, and
/// `input` fields of a `tool_use` content block (ARCH §3.3 stdin
/// contract). Borrowed because the loop owns the response the call
/// lives inside; the executor only reads it.
#[derive(Clone, Copy)]
pub struct ToolCall<'a> {
    /// `tool_use.id` from the wire (e.g. `toolu_01abc…`); also the
    /// per-tool-call directory name on disk per §3.3.
    pub id: &'a str,
    /// Tool name as the model spelled it; resolved against the harness
    /// root and PATH per §3.3.
    pub name: &'a str,
    /// `tool_use.input` JSON object; passed verbatim on the tool's
    /// stdin (§3.3 "Stdin").
    pub input: &'a Value,
}

/// Outcome of one tool invocation. The loop turns this into a wire
/// `tool_result` block on the next step's request, per ARCH §3.3
/// "Wire `tool_result` framing is application-layer".
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct ToolOutcome {
    /// Bytes destined for the `tool_result.content` field. For a tool
    /// the executor ran, this is the §3.3 *result envelope*
    /// ([`envelope::render`]): the exit code stated, the child's stdout,
    /// and its stderr under a marker whenever the child wrote any —
    /// success included — each stream first bounded per the governing
    /// `tool_output:` policy ([`bound::apply`], §3.3 *Bounded transcript
    /// projection*); the full capture stays in `output.json`. A call declined before the executor was entered
    /// (§3.3 *declaring is not permitting*) carries the harness's own
    /// decline text instead: no child ran, so there is no exit code to
    /// state and none is invented.
    pub content: Vec<u8>,
    /// Maps to `tool_result.is_error` per §3.3: `false` for exit 0,
    /// `true` otherwise.
    pub is_error: bool,
}

/// Every way [`ToolExecutor::execute`] can fail. The taxonomy
/// distinguishes harness-level faults (lost subprocess, I/O failure
/// landing the record) from in-band tool errors. Resolution itself
/// cannot fail — the §3.3 third hop is the injected driver target, so
/// an unanswerable name is declined behind the front door as an
/// ordinary non-zero tool exit, not as a variant here. In-band
/// tool errors are not failures here — they surface as
/// [`ToolOutcome::is_error`] and travel back to the agent via the
/// `tool_result` block (§3.3 "Exit code").
#[derive(Debug, Error)]
pub enum ExecError {
    /// Spawn failed (bad executable, permission, fork limits, etc.).
    #[error("spawn tool {name:?}: {source}")]
    Spawn {
        name: String,
        #[source]
        source: io::Error,
    },
    /// Tool died from a signal (SIGSEGV, SIGABRT, …). Per ARCH §3.3 /
    /// §2.10 this is a harness-level fault, not a semantic tool failure
    /// delivered to the model — *except* when it is the executor's own
    /// group SIGTERM mid-stop: `run_tool_calls` (§2.9 step 3) reads that
    /// case as the stop, not a fault, by the stop flag, so a `KilledBySignal`
    /// only ever *propagates* out of the stop path.
    #[error(
        "tool {name:?} terminated by signal {signal} (not harness SIGTERM): \
        harness-level fault per ARCH §2.10"
    )]
    KilledBySignal { name: String, signal: i32 },
    /// The calling agent's worktree — the working directory every tool
    /// subprocess runs in (§3.3 *Working directory*) — could not be
    /// resolved from `step_dir`: either the path is not the §2.2
    /// `<workspace>/steps/<agent-id>/<NNN>` shape, or the worktree it
    /// names is not a live directory. Declined rather than falling back
    /// to the harness's inherited cwd: a tool left in whatever directory
    /// its launcher happened to be sitting in writes its side effects
    /// outside the agent's branch entirely.
    #[error(
        "no worktree for tool {name:?}: cannot resolve the calling agent's worktree \
        from step dir {step_dir:?} (ARCH §3.3 Working directory)"
    )]
    NoWorktree { name: String, step_dir: PathBuf },
    /// Landing `input.json` or `output.json` failed (disk full,
    /// permission, etc.). The executor uses temp-path + atomic rename
    /// so a failure here never leaves a half-written file in `git
    /// status`.
    #[error("i/o landing tool record under {dir:?}: {source}")]
    Io {
        dir: PathBuf,
        #[source]
        source: io::Error,
    },
}

/// Trait the v0.3 loop will hold as `&dyn ToolExecutor` (per the
/// `prompt::Deps` pattern in [`crate::prompt`]). The contract is
/// minimal so the loop can integrate-test against an in-process stub
/// without spawning subprocesses.
pub trait ToolExecutor {
    /// Resolve `call.name` to a binary, invoke it per the §3.3 stdio
    /// contract, land the per-tool-call record under `<step_dir>/tools/
    /// <call.id>/`, and return the outcome the loop needs to assemble
    /// the next step's `tool_result` block.
    ///
    /// `step_dir` is the absolute conv-repo-rooted path of the
    /// `steps/<conv-id>/<NNN>/` directory the call belongs to — at the
    /// conversation-repo root, outside every worktree (ARCH §2.2 /
    /// §2.3), the directory `request.json` / `response.json` /
    /// `meta.json` are written into per [`crate::prompt::step`]. The
    /// executor owns the `tools/<tool-id>/` subtree below it.
    ///
    /// `stop` is the harness-wide cancel flag (PRINCIPLES "Stops are
    /// aggressive and cascading"): when set mid-execution, the
    /// executor sends SIGTERM and waits up to its deadline before
    /// SIGKILL. The flag is `&AtomicBool` rather than `&dyn`-of-
    /// trait because the only producer is the harness signal handler
    /// and the only consumer is the executor's polling loop —
    /// pretending it could be anything else would be premature
    /// abstraction.
    ///
    /// `output_bound` is the governing `workflow.yaml`'s `tool_output:`
    /// policy (ARCH §3.3 *Bounded transcript projection*, §6): each
    /// captured stream is bounded to its head+tail before the result
    /// envelope is rendered around them ([`bound::apply`]), while the
    /// full bytes still land in `output.json`. `None` — the block
    /// absent — projects the streams unbounded. Passed per call rather
    /// than held by the executor because it is the *calling agent's*
    /// policy, read from its governing config commit (§2.2), and the
    /// executor is constructed before any agent is resolved.
    fn execute(
        &self,
        call: ToolCall<'_>,
        step_dir: &Path,
        stop: &AtomicBool,
        output_bound: Option<crate::config::ToolOutputBound>,
    ) -> Result<ToolOutcome, ExecError>;

    /// Run `calls` **concurrently**, returning one result per tool call in
    /// the order given — never completion order, so a caller's
    /// rendering is deterministic whatever the scheduler did.
    ///
    /// This is what a `multi_tool` envelope declaring
    /// `execution: "parallel"` reaches (ARCH §3.3 *The multi-tool*).
    /// The concurrency lives here, in the one component that owns
    /// subprocesses, rather than in the step loop: the loop would have
    /// to share the whole executor across threads, which would put a
    /// `Sync` bound on the clock, the git runner, and the PATH lookup —
    /// three traits with nothing to do with threading (PRINCIPLES,
    /// severability).
    ///
    /// The default implementation runs them **serially**, which is
    /// always a correct answer to "run these": concurrency is an
    /// optimization an implementation may decline. Only the spawning
    /// executor overrides it; in-process stubs inherit this.
    fn execute_all(
        &self,
        calls: &[ToolCall<'_>],
        step_dir: &Path,
        stop: &AtomicBool,
        output_bound: Option<crate::config::ToolOutputBound>,
    ) -> Vec<Result<ToolOutcome, ExecError>> {
        calls
            .iter()
            .map(|call| self.execute(*call, step_dir, stop, output_bound))
            .collect()
    }

    /// The tool definitions this executor answers for **beyond the pool**
    /// — the binding's host injection ([`inject`], ARCH §3.3
    /// *Host-injected tools*), empty by default and for every executor
    /// that carries none.
    ///
    /// It lives on the executor, and not on `Deps` beside it, because the
    /// executor is the one component that knows what it can answer: the
    /// composer splices these into the request's `tools: [...]` and the
    /// grant gate unions their names into the effective toolset, so both
    /// halves read the same object the router belongs to and cannot drift
    /// from what will actually run (PRINCIPLES, single source of truth).
    fn injected(&self) -> Vec<InjectedTool> {
        Vec::new()
    }
}