BE-AGT-002: implement Agent status transition service

- New service: app/services/agent_status.py
  - transition_to_busy(): Idle → Busy/OnCall based on slot type
  - transition_to_idle(): Busy/OnCall/Exhausted/Offline → Idle
  - transition_to_offline(): Any → Offline (heartbeat timeout)
  - transition_to_exhausted(): Any → Exhausted (rate-limit/billing)
  - check_heartbeat_timeout(): auto-detect >2min heartbeat gap
  - check_exhausted_recovery(): auto-recover when recovery_at reached
  - record_heartbeat(): update timestamp, recover Offline agents
- Tests: tests/test_agent_status.py (22 test cases)

app/services/agent_status.py

@@ -0,0 +1,252 @@
+"""Agent status transitions — BE-AGT-002.
+
+Implements the state machine for Agent runtime status:
+
+    Idle  ──→  Busy       (woken by a Work slot)
+    Idle  ──→  OnCall     (woken by an OnCall slot)
+    Busy  ──→  Idle       (task finished / no more pending slots)
+    OnCall──→  Idle       (task finished / no more pending slots)
+    *     ──→  Offline    (heartbeat timeout — no heartbeat for > 2 min)
+    *     ──→  Exhausted  (API quota / rate-limit error)
+    Exhausted → Idle      (recovery_at reached)
+
+Design reference: NEXT_WAVE_DEV_DIRECTION.md §6.4 (Status transitions)
+"""
+
+from __future__ import annotations
+
+from datetime import datetime, timedelta, timezone
+from typing import Optional
+
+from sqlalchemy.orm import Session
+
+from app.models.agent import Agent, AgentStatus, ExhaustReason
+from app.models.calendar import SlotType
+
+# Heartbeat timeout threshold in seconds (2 minutes per spec §6.4)
+HEARTBEAT_TIMEOUT_SECONDS = 120
+
+# Default recovery duration when we can't parse a retry-after header
+DEFAULT_RECOVERY_HOURS = 5
+
+
+# ---------------------------------------------------------------------------
+# Transition helpers
+# ---------------------------------------------------------------------------
+
+class AgentStatusError(Exception):
+    """Raised when a requested status transition is invalid."""
+
+
+def _assert_current(agent: Agent, *expected: AgentStatus) -> None:
+    """Raise if the agent is not in one of the expected statuses."""
+    if agent.status not in expected:
+        allowed = ", ".join(s.value for s in expected)
+        raise AgentStatusError(
+            f"Agent '{agent.agent_id}' is {agent.status.value}; "
+            f"expected one of [{allowed}]"
+        )
+
+
+# ---------------------------------------------------------------------------
+# Public API
+# ---------------------------------------------------------------------------
+
+def transition_to_busy(
+    db: Session,
+    agent: Agent,
+    *,
+    slot_type: SlotType,
+    now: datetime | None = None,
+) -> Agent:
+    """Idle → Busy or OnCall depending on *slot_type*.
+
+    Parameters
+    ----------
+    slot_type : SlotType
+        The type of the slot that triggered the wakeup.
+        ``SlotType.ON_CALL`` → ``AgentStatus.ON_CALL``, everything else
+        → ``AgentStatus.BUSY``.
+    """
+    _assert_current(agent, AgentStatus.IDLE)
+
+    if slot_type == SlotType.ON_CALL:
+        agent.status = AgentStatus.ON_CALL
+    else:
+        agent.status = AgentStatus.BUSY
+
+    if now is None:
+        now = datetime.now(timezone.utc)
+    agent.last_heartbeat = now
+
+    db.flush()
+    return agent
+
+
+def transition_to_idle(
+    db: Session,
+    agent: Agent,
+    *,
+    now: datetime | None = None,
+) -> Agent:
+    """Busy / OnCall / Exhausted (recovered) → Idle.
+
+    For Exhausted agents this should only be called when ``recovery_at``
+    has been reached; the caller is responsible for checking that.
+    """
+    _assert_current(
+        agent,
+        AgentStatus.BUSY,
+        AgentStatus.ON_CALL,
+        AgentStatus.EXHAUSTED,
+        AgentStatus.OFFLINE,
+    )
+
+    agent.status = AgentStatus.IDLE
+
+    # Clear exhausted metadata if transitioning out of Exhausted
+    agent.exhausted_at = None
+    agent.recovery_at = None
+    agent.exhaust_reason = None
+
+    if now is None:
+        now = datetime.now(timezone.utc)
+    agent.last_heartbeat = now
+
+    db.flush()
+    return agent
+
+
+def transition_to_offline(
+    db: Session,
+    agent: Agent,
+) -> Agent:
+    """Any status → Offline (heartbeat timeout).
+
+    Typically called by a background check that detects
+    ``last_heartbeat`` is older than ``HEARTBEAT_TIMEOUT_SECONDS``.
+    """
+    # Already offline — no-op
+    if agent.status == AgentStatus.OFFLINE:
+        return agent
+
+    agent.status = AgentStatus.OFFLINE
+    db.flush()
+    return agent
+
+
+def transition_to_exhausted(
+    db: Session,
+    agent: Agent,
+    *,
+    reason: ExhaustReason,
+    recovery_at: datetime | None = None,
+    now: datetime | None = None,
+) -> Agent:
+    """Any active status → Exhausted (API quota error).
+
+    Parameters
+    ----------
+    reason : ExhaustReason
+        ``RATE_LIMIT`` or ``BILLING``.
+    recovery_at : datetime, optional
+        Parsed from retry-after / reset headers.  If *None*, defaults to
+        ``now + DEFAULT_RECOVERY_HOURS``.
+    """
+    if now is None:
+        now = datetime.now(timezone.utc)
+
+    agent.status = AgentStatus.EXHAUSTED
+    agent.exhausted_at = now
+    agent.exhaust_reason = reason
+
+    if recovery_at is not None:
+        agent.recovery_at = recovery_at
+    else:
+        agent.recovery_at = now + timedelta(hours=DEFAULT_RECOVERY_HOURS)
+
+    db.flush()
+    return agent
+
+
+# ---------------------------------------------------------------------------
+# Heartbeat-driven checks
+# ---------------------------------------------------------------------------
+
+def check_heartbeat_timeout(
+    db: Session,
+    agent: Agent,
+    *,
+    now: datetime | None = None,
+) -> bool:
+    """Mark agent Offline if heartbeat has timed out.
+
+    Returns ``True`` if the agent was transitioned to Offline.
+    """
+    if agent.status == AgentStatus.OFFLINE:
+        return False
+
+    if now is None:
+        now = datetime.now(timezone.utc)
+
+    if agent.last_heartbeat is None:
+        # Never sent a heartbeat — treat as offline
+        transition_to_offline(db, agent)
+        return True
+
+    elapsed = (now - agent.last_heartbeat).total_seconds()
+    if elapsed > HEARTBEAT_TIMEOUT_SECONDS:
+        transition_to_offline(db, agent)
+        return True
+
+    return False
+
+
+def check_exhausted_recovery(
+    db: Session,
+    agent: Agent,
+    *,
+    now: datetime | None = None,
+) -> bool:
+    """Recover an Exhausted agent if ``recovery_at`` has been reached.
+
+    Returns ``True`` if the agent was transitioned back to Idle.
+    """
+    if agent.status != AgentStatus.EXHAUSTED:
+        return False
+
+    if now is None:
+        now = datetime.now(timezone.utc)
+
+    if agent.recovery_at is not None and now >= agent.recovery_at:
+        transition_to_idle(db, agent, now=now)
+        return True
+
+    return False
+
+
+def record_heartbeat(
+    db: Session,
+    agent: Agent,
+    *,
+    now: datetime | None = None,
+) -> Agent:
+    """Update ``last_heartbeat`` timestamp.
+
+    If the agent was Offline and a heartbeat arrives, transition back to
+    Idle (the agent has come back online).
+    """
+    if now is None:
+        now = datetime.now(timezone.utc)
+
+    agent.last_heartbeat = now
+
+    if agent.status == AgentStatus.OFFLINE:
+        agent.status = AgentStatus.IDLE
+        # Clear any stale exhausted metadata
+        agent.exhausted_at = None
+        agent.recovery_at = None
+        agent.exhaust_reason = None
+
+    db.flush()
+    return agent

tests/test_agent_status.py

@@ -0,0 +1,301 @@
+"""Tests for Agent status transition service — BE-AGT-002.
+
+Covers:
+  - Idle → Busy / OnCall
+  - Busy / OnCall → Idle
+  - Heartbeat timeout → Offline
+  - API quota error → Exhausted
+  - Exhausted recovery → Idle
+  - Invalid transition errors
+"""
+
+import pytest
+from datetime import datetime, timedelta, timezone
+
+from app.models.agent import Agent, AgentStatus, ExhaustReason
+from app.models.calendar import SlotType
+from app.services.agent_status import (
+    AgentStatusError,
+    HEARTBEAT_TIMEOUT_SECONDS,
+    DEFAULT_RECOVERY_HOURS,
+    transition_to_busy,
+    transition_to_idle,
+    transition_to_offline,
+    transition_to_exhausted,
+    check_heartbeat_timeout,
+    check_exhausted_recovery,
+    record_heartbeat,
+)
+
+
+# ---------------------------------------------------------------------------
+# Helpers
+# ---------------------------------------------------------------------------
+
+NOW = datetime(2026, 4, 1, 12, 0, 0, tzinfo=timezone.utc)
+
+
+def _make_agent(db, *, status=AgentStatus.IDLE, last_hb=None, **kwargs):
+    """Insert and return an Agent row with a linked user."""
+    from app.models import models
+    from app.api.deps import get_password_hash
+
+    # Ensure we have a user
+    user = db.query(models.User).filter_by(id=99).first()
+    if user is None:
+        # Need a role first
+        from app.models.role_permission import Role
+        role = db.query(Role).filter_by(id=99).first()
+        if role is None:
+            role = Role(id=99, name="agent_test_role", is_global=False)
+            db.add(role)
+            db.flush()
+        user = models.User(
+            id=99, username="agent_user", email="agent@test.com",
+            hashed_password=get_password_hash("test123"),
+            is_admin=False, role_id=role.id,
+        )
+        db.add(user)
+        db.flush()
+
+    agent = Agent(
+        user_id=user.id,
+        agent_id=kwargs.get("agent_id", "test-agent-001"),
+        claw_identifier="test-claw",
+        status=status,
+        last_heartbeat=last_hb,
+        **{k: v for k, v in kwargs.items() if k not in ("agent_id",)},
+    )
+    db.add(agent)
+    db.flush()
+    return agent
+
+
+# ---------------------------------------------------------------------------
+# Idle → Busy / OnCall
+# ---------------------------------------------------------------------------
+
+class TestTransitionToBusy:
+    def test_idle_to_busy_for_work_slot(self, db):
+        agent = _make_agent(db, status=AgentStatus.IDLE)
+        result = transition_to_busy(db, agent, slot_type=SlotType.WORK, now=NOW)
+        assert result.status == AgentStatus.BUSY
+        assert result.last_heartbeat == NOW
+
+    def test_idle_to_on_call_for_on_call_slot(self, db):
+        agent = _make_agent(db, status=AgentStatus.IDLE)
+        result = transition_to_busy(db, agent, slot_type=SlotType.ON_CALL, now=NOW)
+        assert result.status == AgentStatus.ON_CALL
+
+    def test_idle_to_busy_for_system_slot(self, db):
+        agent = _make_agent(db, status=AgentStatus.IDLE)
+        result = transition_to_busy(db, agent, slot_type=SlotType.SYSTEM, now=NOW)
+        assert result.status == AgentStatus.BUSY
+
+    def test_idle_to_busy_for_entertainment_slot(self, db):
+        agent = _make_agent(db, status=AgentStatus.IDLE)
+        result = transition_to_busy(db, agent, slot_type=SlotType.ENTERTAINMENT, now=NOW)
+        assert result.status == AgentStatus.BUSY
+
+    def test_busy_to_busy_raises(self, db):
+        agent = _make_agent(db, status=AgentStatus.BUSY)
+        with pytest.raises(AgentStatusError, match="busy"):
+            transition_to_busy(db, agent, slot_type=SlotType.WORK)
+
+    def test_exhausted_to_busy_raises(self, db):
+        agent = _make_agent(db, status=AgentStatus.EXHAUSTED)
+        with pytest.raises(AgentStatusError):
+            transition_to_busy(db, agent, slot_type=SlotType.WORK)
+
+
+# ---------------------------------------------------------------------------
+# Busy / OnCall → Idle
+# ---------------------------------------------------------------------------
+
+class TestTransitionToIdle:
+    def test_busy_to_idle(self, db):
+        agent = _make_agent(db, status=AgentStatus.BUSY)
+        result = transition_to_idle(db, agent, now=NOW)
+        assert result.status == AgentStatus.IDLE
+        assert result.last_heartbeat == NOW
+
+    def test_on_call_to_idle(self, db):
+        agent = _make_agent(db, status=AgentStatus.ON_CALL)
+        result = transition_to_idle(db, agent, now=NOW)
+        assert result.status == AgentStatus.IDLE
+
+    def test_exhausted_to_idle_clears_metadata(self, db):
+        agent = _make_agent(
+            db,
+            status=AgentStatus.EXHAUSTED,
+            exhausted_at=NOW - timedelta(hours=1),
+            recovery_at=NOW,
+            exhaust_reason=ExhaustReason.RATE_LIMIT,
+        )
+        result = transition_to_idle(db, agent, now=NOW)
+        assert result.status == AgentStatus.IDLE
+        assert result.exhausted_at is None
+        assert result.recovery_at is None
+        assert result.exhaust_reason is None
+
+    def test_offline_to_idle(self, db):
+        agent = _make_agent(db, status=AgentStatus.OFFLINE)
+        result = transition_to_idle(db, agent, now=NOW)
+        assert result.status == AgentStatus.IDLE
+
+    def test_idle_to_idle_raises(self, db):
+        agent = _make_agent(db, status=AgentStatus.IDLE)
+        with pytest.raises(AgentStatusError, match="idle"):
+            transition_to_idle(db, agent)
+
+
+# ---------------------------------------------------------------------------
+# * → Offline (heartbeat timeout)
+# ---------------------------------------------------------------------------
+
+class TestTransitionToOffline:
+    def test_idle_to_offline(self, db):
+        agent = _make_agent(db, status=AgentStatus.IDLE)
+        result = transition_to_offline(db, agent)
+        assert result.status == AgentStatus.OFFLINE
+
+    def test_busy_to_offline(self, db):
+        agent = _make_agent(db, status=AgentStatus.BUSY)
+        result = transition_to_offline(db, agent)
+        assert result.status == AgentStatus.OFFLINE
+
+    def test_already_offline_noop(self, db):
+        agent = _make_agent(db, status=AgentStatus.OFFLINE)
+        result = transition_to_offline(db, agent)
+        assert result.status == AgentStatus.OFFLINE
+
+
+# ---------------------------------------------------------------------------
+# * → Exhausted (API quota)
+# ---------------------------------------------------------------------------
+
+class TestTransitionToExhausted:
+    def test_busy_to_exhausted_with_recovery(self, db):
+        recovery = NOW + timedelta(hours=1)
+        agent = _make_agent(db, status=AgentStatus.BUSY)
+        result = transition_to_exhausted(
+            db, agent,
+            reason=ExhaustReason.RATE_LIMIT,
+            recovery_at=recovery,
+            now=NOW,
+        )
+        assert result.status == AgentStatus.EXHAUSTED
+        assert result.exhausted_at == NOW
+        assert result.recovery_at == recovery
+        assert result.exhaust_reason == ExhaustReason.RATE_LIMIT
+
+    def test_exhausted_default_recovery(self, db):
+        agent = _make_agent(db, status=AgentStatus.BUSY)
+        result = transition_to_exhausted(
+            db, agent,
+            reason=ExhaustReason.BILLING,
+            now=NOW,
+        )
+        expected_recovery = NOW + timedelta(hours=DEFAULT_RECOVERY_HOURS)
+        assert result.recovery_at == expected_recovery
+        assert result.exhaust_reason == ExhaustReason.BILLING
+
+    def test_idle_to_exhausted(self, db):
+        """Edge case: agent gets a rate-limit before even starting work."""
+        agent = _make_agent(db, status=AgentStatus.IDLE)
+        result = transition_to_exhausted(
+            db, agent,
+            reason=ExhaustReason.RATE_LIMIT,
+            now=NOW,
+        )
+        assert result.status == AgentStatus.EXHAUSTED
+
+
+# ---------------------------------------------------------------------------
+# Heartbeat timeout check
+# ---------------------------------------------------------------------------
+
+class TestCheckHeartbeatTimeout:
+    def test_timeout_triggers_offline(self, db):
+        old_hb = NOW - timedelta(seconds=HEARTBEAT_TIMEOUT_SECONDS + 10)
+        agent = _make_agent(db, status=AgentStatus.IDLE, last_hb=old_hb)
+        changed = check_heartbeat_timeout(db, agent, now=NOW)
+        assert changed is True
+        assert agent.status == AgentStatus.OFFLINE
+
+    def test_recent_heartbeat_no_change(self, db):
+        recent_hb = NOW - timedelta(seconds=30)
+        agent = _make_agent(db, status=AgentStatus.BUSY, last_hb=recent_hb)
+        changed = check_heartbeat_timeout(db, agent, now=NOW)
+        assert changed is False
+        assert agent.status == AgentStatus.BUSY
+
+    def test_no_heartbeat_ever_goes_offline(self, db):
+        agent = _make_agent(db, status=AgentStatus.IDLE, last_hb=None)
+        changed = check_heartbeat_timeout(db, agent, now=NOW)
+        assert changed is True
+        assert agent.status == AgentStatus.OFFLINE
+
+    def test_already_offline_returns_false(self, db):
+        agent = _make_agent(db, status=AgentStatus.OFFLINE, last_hb=None)
+        changed = check_heartbeat_timeout(db, agent, now=NOW)
+        assert changed is False
+
+
+# ---------------------------------------------------------------------------
+# Exhausted recovery check
+# ---------------------------------------------------------------------------
+
+class TestCheckExhaustedRecovery:
+    def test_recovery_at_reached(self, db):
+        agent = _make_agent(
+            db,
+            status=AgentStatus.EXHAUSTED,
+            exhausted_at=NOW - timedelta(hours=5),
+            recovery_at=NOW - timedelta(minutes=1),
+            exhaust_reason=ExhaustReason.RATE_LIMIT,
+        )
+        recovered = check_exhausted_recovery(db, agent, now=NOW)
+        assert recovered is True
+        assert agent.status == AgentStatus.IDLE
+        assert agent.exhausted_at is None
+
+    def test_recovery_at_not_yet_reached(self, db):
+        agent = _make_agent(
+            db,
+            status=AgentStatus.EXHAUSTED,
+            exhausted_at=NOW,
+            recovery_at=NOW + timedelta(hours=1),
+            exhaust_reason=ExhaustReason.BILLING,
+        )
+        recovered = check_exhausted_recovery(db, agent, now=NOW)
+        assert recovered is False
+        assert agent.status == AgentStatus.EXHAUSTED
+
+    def test_non_exhausted_agent_returns_false(self, db):
+        agent = _make_agent(db, status=AgentStatus.IDLE)
+        recovered = check_exhausted_recovery(db, agent, now=NOW)
+        assert recovered is False
+
+
+# ---------------------------------------------------------------------------
+# Record heartbeat
+# ---------------------------------------------------------------------------
+
+class TestRecordHeartbeat:
+    def test_updates_timestamp(self, db):
+        agent = _make_agent(db, status=AgentStatus.IDLE, last_hb=NOW - timedelta(minutes=1))
+        result = record_heartbeat(db, agent, now=NOW)
+        assert result.last_heartbeat == NOW
+
+    def test_offline_agent_recovers_to_idle(self, db):
+        agent = _make_agent(db, status=AgentStatus.OFFLINE)
+        result = record_heartbeat(db, agent, now=NOW)
+        assert result.status == AgentStatus.IDLE
+        assert result.last_heartbeat == NOW
+
+    def test_busy_agent_stays_busy(self, db):
+        agent = _make_agent(db, status=AgentStatus.BUSY, last_hb=NOW - timedelta(seconds=30))
+        result = record_heartbeat(db, agent, now=NOW)
+        assert result.status == AgentStatus.BUSY
+        assert result.last_heartbeat == NOW