harn_vm/agent_events/

terminal.rs

//! Typed terminal outcome for an agent-loop session (harn#4568).
//!
//! The loop seals a free-string `stop_reason` / `final_status`, which forces
//! every host to substring-match to tell a natural completion from a user
//! cancel, a provider or runtime error, a policy stop (budget / no-progress /
//! guardrail), or a suspend. That guessing is exactly how a catch-all terminal
//! message can hide a provider/VM/permission failure behind an agent-authored
//! "I stopped" (Burin #4642).
//!
//! This module produces the classification ONCE, at the loop boundary, into a
//! typed [`AgentTerminalKind`] plus a coarse [`AgentTerminalKind::owner`], and
//! carries it alongside the lossless raw `reason`. Harn owns the agent stop
//! vocabulary, so the classification is produced here rather than reconstructed
//! in Burin or any other host. The typed outcome is *additive*: the raw
//! `final_status` / `stop_reason` / `terminal_class` fields are unchanged.

use serde::{Deserialize, Serialize};

use super::agent::AgentEvent;

/// Coarse, typed classification of why an agent-loop session terminated.
/// Serialized `snake_case`. The vocabulary is deliberately extensible —
/// [`Self::Unknown`] is the honest fallback when no rule matched and the raw
/// `reason` is authoritative.
#[derive(Clone, Copy, Debug, Eq, PartialEq, Hash, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum AgentTerminalKind {
    /// The model/agent finished naturally — a clean completion or a verified
    /// `done` judgement, with no policy stop and no error.
    Natural,
    /// A user or host explicitly cancelled the in-flight turn.
    UserCancelled,
    /// A budget/cap policy stopped the loop: max iterations, a token/cost
    /// budget, a circuit breaker, or an exhausted verification cap.
    PolicyBudget,
    /// A no-progress policy stopped the loop: a thrash/stall hard stop or the
    /// text-only nudge budget.
    PolicyNoProgress,
    /// A guardrail policy stopped the loop: an input tripwire or an
    /// out-of-scope alert.
    PolicyGuardrail,
    /// A custom post-turn / terminal callback requested a stop that is not one
    /// of the specific policy kinds above. The raw `reason` names it; a future
    /// typed callback contract can attribute a finer owner.
    PolicyStop,
    /// The provider/transport failed terminally: rate limit, timeout, context
    /// overflow, or provider misconfiguration.
    ProviderError,
    /// The harness/runtime failed terminally: a host-bridge gap, an internal
    /// protocol failure, an uncaught throw, or a turn that made no LLM call.
    RuntimeError,
    /// The session suspended at a waitpoint and may resume later — its work is
    /// not finished and was not abandoned.
    Suspended,
    /// No rule matched; the raw `reason` is authoritative.
    Unknown,
}

impl AgentTerminalKind {
    pub const ALL: [Self; 10] = [
        Self::Natural,
        Self::UserCancelled,
        Self::PolicyBudget,
        Self::PolicyNoProgress,
        Self::PolicyGuardrail,
        Self::PolicyStop,
        Self::ProviderError,
        Self::RuntimeError,
        Self::Suspended,
        Self::Unknown,
    ];

    pub fn as_str(self) -> &'static str {
        match self {
            Self::Natural => "natural",
            Self::UserCancelled => "user_cancelled",
            Self::PolicyBudget => "policy_budget",
            Self::PolicyNoProgress => "policy_no_progress",
            Self::PolicyGuardrail => "policy_guardrail",
            Self::PolicyStop => "policy_stop",
            Self::ProviderError => "provider_error",
            Self::RuntimeError => "runtime_error",
            Self::Suspended => "suspended",
            Self::Unknown => "unknown",
        }
    }

    /// The party responsible for the stop — a stable, coarse attribution that
    /// pairs with the kind so hosts can bucket outcomes (agent-driven vs
    /// user vs provider vs harness vs policy) without re-deriving it.
    pub fn owner(self) -> &'static str {
        match self {
            Self::Natural | Self::Suspended => "agent",
            Self::UserCancelled => "user",
            Self::PolicyBudget
            | Self::PolicyNoProgress
            | Self::PolicyGuardrail
            | Self::PolicyStop => "policy",
            Self::ProviderError => "provider",
            Self::RuntimeError => "harness",
            Self::Unknown => "unknown",
        }
    }
}

/// Raw `stop_reason` values that seal a genuinely natural completion (a clean
/// finish or a verified `done`). When `final_status` is `done`/empty, any
/// `stop_reason` OUTSIDE this set is a policy/custom stop (e.g. a post-turn
/// callback `stop`) that must NOT be reported as a natural completion — that
/// conflation is the Burin #4642 failure mode. Sourced from the loop's own
/// terminal-`done` assignments and `__agent_loop_sealed_stop_reason`.
const NATURAL_STOP_REASONS: [&str; 9] = [
    "",
    "completed",
    "natural",
    "post_edit_reverify",
    "repeated_verified_pass",
    "required_tools_satisfied",
    "sentinel",
    "stalled_done_judge",
    "done",
];

/// Typed terminal outcome carried alongside the lossless raw reason. `owner` is
/// derived from `kind` so a single field pins the responsible party.
#[derive(Clone, Debug, Eq, PartialEq, Serialize, Deserialize)]
pub struct AgentTerminalOutcome {
    pub kind: AgentTerminalKind,
    pub reason: String,
    pub owner: String,
}

impl AgentTerminalOutcome {
    /// Build an outcome from a kind and the lossless raw `reason`, deriving the
    /// `owner` from the kind.
    pub fn new(kind: AgentTerminalKind, reason: impl Into<String>) -> Self {
        Self {
            kind,
            reason: reason.into(),
            owner: kind.owner().to_string(),
        }
    }

    pub fn to_json(&self) -> serde_json::Value {
        serde_json::json!({
            "kind": self.kind.as_str(),
            "reason": self.reason,
            "owner": self.owner,
        })
    }

    /// Project the outcome onto the existing typed-checkpoint event stream.
    pub fn checkpoint(
        &self,
        session_id: &str,
        final_status: &str,
        stop_reason: &str,
    ) -> AgentEvent {
        AgentEvent::TypedCheckpoint {
            session_id: session_id.to_owned(),
            checkpoint: serde_json::json!({
                "schema": "harn.agent_terminal.v1",
                "terminal": self.to_json(),
                "final_status": final_status,
                "stop_reason": stop_reason,
            }),
        }
    }
}

/// Classify an agent-loop terminal condition into a typed [`AgentTerminalKind`].
///
/// Inputs are the values the finalize boundary already has in hand:
/// - `canonical_status`: `final_status` with empty normalized to `done`;
/// - `stop_reason`: the sealed raw stop reason;
/// - `has_error`: whether a terminal error was recorded;
/// - `terminal_class`: the finalize host's error-only string class (e.g.
///   `rate_limited`, `timeout`, `context_overflow`, `provider_misconfigured`,
///   `host_bridge_unimplemented`, `no_llm_call`), used only to split an error
///   into provider vs harness ownership.
///
/// This is the single place stringly stop vocabulary is interpreted; every
/// consumer reads the typed result instead.
pub fn classify_agent_terminal(
    canonical_status: &str,
    stop_reason: &str,
    has_error: bool,
    terminal_class: Option<&str>,
) -> AgentTerminalKind {
    match canonical_status {
        "suspended" => AgentTerminalKind::Suspended,
        // A user/host cancel. The finalize loop does not itself seal a
        // `cancelled` status — the ACP adapter observes the cancel notification
        // one layer up and constructs the outcome directly — but classify still
        // maps it so the vocabulary is total and any host that does route a
        // cancel through finalize is attributed correctly rather than `Unknown`.
        "cancelled" | "canceled" | "aborted" => AgentTerminalKind::UserCancelled,
        "provider_error" => AgentTerminalKind::ProviderError,
        "error" | "failed" => classify_error(terminal_class),
        // A verification cap/budget was exhausted before `done` could be
        // confirmed — a budget policy stop, not a hard error.
        "budget_exhausted" | "verify_capped" | "verify_exhausted" => {
            AgentTerminalKind::PolicyBudget
        }
        "stuck" => AgentTerminalKind::PolicyNoProgress,
        // `input_guardrail`/`scope_alert` come from the loop's guardrail arms;
        // `blocked` is the UserPromptSubmit-hook block result. All three are a
        // guardrail policy denying the turn.
        "input_guardrail" | "scope_alert" | "blocked" => AgentTerminalKind::PolicyGuardrail,
        "done" => {
            if has_error {
                classify_error(terminal_class)
            } else if NATURAL_STOP_REASONS.contains(&stop_reason) {
                AgentTerminalKind::Natural
            } else {
                // `done`/empty final status with a non-natural reason — a
                // post-turn/custom policy stop wearing a completion status.
                AgentTerminalKind::PolicyStop
            }
        }
        _ => AgentTerminalKind::Unknown,
    }
}

/// Split a terminal error into provider vs harness ownership using the
/// finalize host's error class. Transport/provider classes attribute to the
/// provider; everything else (host-bridge gaps, protocol failures, uncaught
/// throws, no-LLM-call) is a harness/runtime fault.
fn classify_error(terminal_class: Option<&str>) -> AgentTerminalKind {
    match terminal_class {
        Some("rate_limited" | "timeout" | "context_overflow" | "provider_misconfigured") => {
            AgentTerminalKind::ProviderError
        }
        _ => AgentTerminalKind::RuntimeError,
    }
}

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

    #[test]
    fn kind_wire_strings_are_stable_snake_case() {
        let pairs = [
            (AgentTerminalKind::Natural, "natural"),
            (AgentTerminalKind::UserCancelled, "user_cancelled"),
            (AgentTerminalKind::PolicyBudget, "policy_budget"),
            (AgentTerminalKind::PolicyNoProgress, "policy_no_progress"),
            (AgentTerminalKind::PolicyGuardrail, "policy_guardrail"),
            (AgentTerminalKind::PolicyStop, "policy_stop"),
            (AgentTerminalKind::ProviderError, "provider_error"),
            (AgentTerminalKind::RuntimeError, "runtime_error"),
            (AgentTerminalKind::Suspended, "suspended"),
            (AgentTerminalKind::Unknown, "unknown"),
        ];
        for (variant, wire) in pairs {
            assert_eq!(variant.as_str(), wire);
            let encoded = serde_json::to_string(&variant).unwrap();
            assert_eq!(encoded, format!("\"{wire}\""));
            let decoded: AgentTerminalKind = serde_json::from_str(&encoded).unwrap();
            assert_eq!(decoded, variant);
        }
        // The wire table above must cover every variant.
        assert_eq!(pairs.len(), AgentTerminalKind::ALL.len());
    }

    #[test]
    fn owner_attribution_is_coarse_and_total() {
        for kind in AgentTerminalKind::ALL {
            let owner = kind.owner();
            assert!(
                matches!(
                    owner,
                    "agent" | "user" | "policy" | "provider" | "harness" | "unknown"
                ),
                "{kind:?} has an unexpected owner {owner}"
            );
        }
        assert_eq!(AgentTerminalKind::UserCancelled.owner(), "user");
        assert_eq!(AgentTerminalKind::ProviderError.owner(), "provider");
        assert_eq!(AgentTerminalKind::RuntimeError.owner(), "harness");
        assert_eq!(AgentTerminalKind::PolicyStop.owner(), "policy");
    }

    #[test]
    fn natural_completion_classifies_as_natural() {
        for reason in [
            "",
            "completed",
            "natural",
            "post_edit_reverify",
            "repeated_verified_pass",
            "required_tools_satisfied",
            "sentinel",
        ] {
            assert_eq!(
                classify_agent_terminal("done", reason, false, None),
                AgentTerminalKind::Natural,
                "reason {reason:?} should be natural"
            );
        }
    }

    #[test]
    fn post_turn_policy_stop_is_not_reported_as_natural() {
        // The Burin #4642 case: a post-turn callback stops with `final_status`
        // empty (canonicalized to `done`) and a custom reason. It MUST classify
        // as a policy stop, never a natural completion.
        assert_eq!(
            classify_agent_terminal("done", "post_turn_stop", false, None),
            AgentTerminalKind::PolicyStop,
        );
        assert_eq!(
            classify_agent_terminal("done", "custom_operator_halt", false, None),
            AgentTerminalKind::PolicyStop,
        );
    }

    #[test]
    fn policy_stops_map_to_specific_kinds() {
        assert_eq!(
            classify_agent_terminal("budget_exhausted", "max_iterations", false, None),
            AgentTerminalKind::PolicyBudget,
        );
        assert_eq!(
            classify_agent_terminal("verify_exhausted", "done_judge_cap_reached", false, None),
            AgentTerminalKind::PolicyBudget,
        );
        assert_eq!(
            classify_agent_terminal("stuck", "thrash_hard_stop", false, None),
            AgentTerminalKind::PolicyNoProgress,
        );
        assert_eq!(
            classify_agent_terminal("input_guardrail", "input_guardrail_tripwire", false, None),
            AgentTerminalKind::PolicyGuardrail,
        );
        assert_eq!(
            classify_agent_terminal("scope_alert", "out_of_scope", false, None),
            AgentTerminalKind::PolicyGuardrail,
        );
    }

    #[test]
    fn errors_split_provider_vs_harness_by_class() {
        assert_eq!(
            classify_agent_terminal("provider_error", "escalation_aborted", true, None),
            AgentTerminalKind::ProviderError,
        );
        for class in [
            "rate_limited",
            "timeout",
            "context_overflow",
            "provider_misconfigured",
        ] {
            assert_eq!(
                classify_agent_terminal("error", "boom", true, Some(class)),
                AgentTerminalKind::ProviderError,
                "class {class} should attribute to the provider"
            );
        }
        for class in ["host_bridge_unimplemented", "no_llm_call", "generic_throw"] {
            assert_eq!(
                classify_agent_terminal("error", "boom", true, Some(class)),
                AgentTerminalKind::RuntimeError,
                "class {class} should attribute to the harness"
            );
        }
        // A `done` status that nonetheless carries a terminal error is an error,
        // classified by its class rather than reported as a completion.
        assert_eq!(
            classify_agent_terminal("done", "completed", true, Some("no_llm_call")),
            AgentTerminalKind::RuntimeError,
        );
    }

    #[test]
    fn cancel_and_block_statuses_classify_by_owner() {
        for reason in ["cancelled", "canceled", "aborted"] {
            assert_eq!(
                classify_agent_terminal(reason, "user_cancel", false, None),
                AgentTerminalKind::UserCancelled,
                "status {reason} should attribute to the user"
            );
        }
        assert_eq!(
            classify_agent_terminal("blocked", "user_prompt_submit_blocked", false, None),
            AgentTerminalKind::PolicyGuardrail,
        );
    }

    #[test]
    fn suspended_and_unknown() {
        assert_eq!(
            classify_agent_terminal("suspended", "suspended", false, None),
            AgentTerminalKind::Suspended,
        );
        assert_eq!(
            classify_agent_terminal("some_future_status", "whatever", false, None),
            AgentTerminalKind::Unknown,
        );
    }

    #[test]
    fn outcome_carries_reason_and_derives_owner() {
        let outcome = AgentTerminalOutcome::new(AgentTerminalKind::PolicyBudget, "max_iterations");
        assert_eq!(outcome.kind, AgentTerminalKind::PolicyBudget);
        assert_eq!(outcome.reason, "max_iterations");
        assert_eq!(outcome.owner, "policy");
        let json = outcome.to_json();
        assert_eq!(json["kind"], "policy_budget");
        assert_eq!(json["reason"], "max_iterations");
        assert_eq!(json["owner"], "policy");
    }
}