fix(agent): enforce idempotent resume transition

backend/src/v1/agent/service.py

@@ -2,10 +2,11 @@ from __future__ import annotations
 
 from datetime import datetime, timezone
 from decimal import Decimal
-from typing import TYPE_CHECKING
+from typing import TYPE_CHECKING, Any
 from uuid import UUID
 
 from fastapi import HTTPException
+from pydantic import BaseModel
 from sqlalchemy import func, select
 from sqlalchemy.exc import SQLAlchemyError
 
@@ -29,6 +30,10 @@ if TYPE_CHECKING:
 logger = get_logger("v1.agent.service")
 
 
+class ResumeDecisionResult(BaseModel):
+    applied: bool
+
+
 def build_session_title(first_message: str, *, now: datetime) -> str:
     title = first_message.strip().replace("\n", " ")[:24]
     if not title:
@@ -335,3 +340,38 @@ class AgentChatService(BaseService):
             raise ValueError("Interrupt ID mismatch")
         snapshot["pending_tool_call"]["status"] = status
         session.state_snapshot = snapshot
+
+    async def apply_resume_decision(
+        self,
+        *,
+        session_id: UUID,
+        interrupt_id: str,
+        decision: dict[str, Any],
+    ) -> ResumeDecisionResult:
+        stmt = select(AgentChatSession).where(AgentChatSession.id == session_id)
+        session = await self._session.scalar(stmt)
+        if session is None:
+            raise ValueError(f"Session {session_id} not found")
+
+        snapshot = session.state_snapshot
+        if snapshot is None or "pending_tool_call" not in snapshot:
+            return ResumeDecisionResult(applied=False)
+
+        pending = snapshot["pending_tool_call"]
+        if pending["interrupt_id"] != interrupt_id:
+            return ResumeDecisionResult(applied=False)
+
+        if pending["status"] != "PENDING_APPROVAL":
+            return ResumeDecisionResult(applied=False)
+
+        decision_value = decision.get("decision", "approved")
+        if decision_value == "approved":
+            new_status = "APPROVED_EXECUTING"
+        else:
+            new_status = "REJECTED"
+
+        snapshot["pending_tool_call"]["status"] = new_status
+        snapshot["pending_tool_call"]["decision"] = decision
+        session.state_snapshot = snapshot
+
+        return ResumeDecisionResult(applied=True)

backend/tests/unit/v1/agent/test_resume_idempotency.py

@@ -0,0 +1,142 @@
+from __future__ import annotations
+
+from datetime import datetime, timedelta, timezone
+from uuid import UUID, uuid4
+
+import pytest
+
+from models.agent_chat_session import (
+    AgentChatSession,
+    AgentChatSessionStatus,
+    SessionType,
+)
+from v1.agent.service import AgentChatService
+
+
+class FakeAsyncSession:
+    def __init__(self) -> None:
+        self.added: list[object] = []
+        self._sessions: dict[UUID, AgentChatSession] = {}
+
+    def add(self, obj: object) -> None:
+        self.added.append(obj)
+        if isinstance(obj, AgentChatSession):
+            self._sessions[obj.id] = obj
+
+    async def flush(self) -> None:
+        return None
+
+    async def commit(self) -> None:
+        pass
+
+    async def rollback(self) -> None:
+        pass
+
+    async def refresh(self, obj: object) -> None:
+        pass
+
+    async def execute(self, stmt: object) -> None:
+        pass
+
+    async def scalar(self, stmt: object) -> AgentChatSession | None:
+        for session in self._sessions.values():
+            return session
+        return None
+
+
+@pytest.fixture
+def fake_db() -> FakeAsyncSession:
+    return FakeAsyncSession()
+
+
+@pytest.fixture
+def session(fake_db: FakeAsyncSession) -> AgentChatSession:
+    sess = AgentChatSession(
+        id=uuid4(),
+        user_id=uuid4(),
+        session_type=SessionType.CHAT,
+        status=AgentChatSessionStatus.RUNNING,
+    )
+    fake_db.add(sess)
+    return sess
+
+
+@pytest.fixture
+def service(fake_db: FakeAsyncSession) -> AgentChatService:
+    return AgentChatService(fake_db, current_user=None)  # type: ignore[arg-type]
+
+
+class TestResumeIdempotency:
+    @pytest.mark.asyncio
+    async def test_resume_is_idempotent(
+        self, service: AgentChatService, session: AgentChatSession
+    ):
+        expires_at = datetime.now(timezone.utc) + timedelta(hours=1)
+        await service.set_pending_tool_call(
+            session_id=session.id,
+            interrupt_id="int-1",
+            tool_name="srv.transfer_funds",
+            tool_args={"to": "u2", "amount": 100},
+            expires_at=expires_at,
+        )
+
+        first = await service.apply_resume_decision(
+            session_id=session.id,
+            interrupt_id="int-1",
+            decision={"decision": "approved"},
+        )
+        second = await service.apply_resume_decision(
+            session_id=session.id,
+            interrupt_id="int-1",
+            decision={"decision": "approved"},
+        )
+
+        assert first.applied is True
+        assert second.applied is False
+
+    @pytest.mark.asyncio
+    async def test_resume_updates_status_to_approved(
+        self, service: AgentChatService, session: AgentChatSession
+    ):
+        expires_at = datetime.now(timezone.utc) + timedelta(hours=1)
+        await service.set_pending_tool_call(
+            session_id=session.id,
+            interrupt_id="int-2",
+            tool_name="srv.delete_file",
+            tool_args={"file_id": "f1"},
+            expires_at=expires_at,
+        )
+
+        result = await service.apply_resume_decision(
+            session_id=session.id,
+            interrupt_id="int-2",
+            decision={"decision": "approved"},
+        )
+
+        assert result.applied is True
+        snapshot = await service.get_state_snapshot(session.id)
+        assert snapshot["pending_tool_call"]["status"] == "APPROVED_EXECUTING"
+        assert snapshot["pending_tool_call"]["decision"] == {"decision": "approved"}
+
+    @pytest.mark.asyncio
+    async def test_resume_updates_status_to_rejected(
+        self, service: AgentChatService, session: AgentChatSession
+    ):
+        expires_at = datetime.now(timezone.utc) + timedelta(hours=1)
+        await service.set_pending_tool_call(
+            session_id=session.id,
+            interrupt_id="int-3",
+            tool_name="srv.transfer_funds",
+            tool_args={"to": "u2", "amount": 100},
+            expires_at=expires_at,
+        )
+
+        result = await service.apply_resume_decision(
+            session_id=session.id,
+            interrupt_id="int-3",
+            decision={"decision": "rejected"},
+        )
+
+        assert result.applied is True
+        snapshot = await service.get_state_snapshot(session.id)
+        assert snapshot["pending_tool_call"]["status"] == "REJECTED"