feat(plan): notify Slack on plan approval

Re-land upstream #1632 onto the modular structure. When a plan is
approved via the dashboard approve endpoint, post a thread reply to the
originating Slack thread noting the comment count and approver, after
the follow-up run is dispatched. Slack post failures never break
approval. Adapted to the fork's approve_plan (no plan_markdown read).

Refs #80, upstream #1632

agent/dashboard/plan_api.py

@@ -22,6 +22,7 @@ from langgraph_sdk import get_client
 from pydantic import BaseModel
 
 from ..dispatch import dispatch_agent_run
+from ..utils.slack import post_slack_thread_reply
 from .oauth import require_same_origin_for_mutations, require_session
 from .plan_store import (
     PLAN_STATUS_APPROVED,
@@ -139,7 +140,8 @@ async def approve_plan(thread_id: str, session: dict[str, Any] = _SESSION_DEP) -
         raise HTTPException(403, "only the plan owner can approve")
     # Read comments BEFORE mutating state: a store failure here aborts the
     # decision (500) rather than dispatching the run without the feedback.
-    feedback = _format_comments(await list_plan_comments(thread_id, raise_on_error=True))
+    comments = await list_plan_comments(thread_id, raise_on_error=True)
+    feedback = _format_comments(comments)
     await set_plan_status(thread_id, PLAN_STATUS_APPROVED, plan_mode=False)
     if feedback:
         text = (
@@ -149,6 +151,9 @@ async def approve_plan(thread_id: str, session: dict[str, Any] = _SESSION_DEP) -
     else:
         text = "The plan has been approved. Implement it now as described in the plan."
     await _dispatch_followup(thread_id, metadata, text, plan_mode=False)
+    await _maybe_post_plan_approved_to_slack(
+        metadata, comment_count=len(comments), actor=_approval_actor_name(session)
+    )
     return {"status": PLAN_STATUS_APPROVED}
 
 
@@ -181,6 +186,45 @@ def _format_comments(comments: list[dict[str, Any]]) -> str:
     return "\n".join(lines)
 
 
+def _approval_actor_name(session: dict[str, Any]) -> str:
+    return str(session.get("name") or session.get("sub") or "User").strip() or "User"
+
+
+def _slack_thread_from_metadata(metadata: dict[str, Any]) -> tuple[str, str] | None:
+    source_context = metadata.get("source_context")
+    if not isinstance(source_context, dict):
+        return None
+    slack_thread = source_context.get("slack_thread")
+    if not isinstance(slack_thread, dict):
+        return None
+    channel_id = slack_thread.get("channel_id")
+    thread_ts = slack_thread.get("thread_ts")
+    if isinstance(channel_id, str) and channel_id and isinstance(thread_ts, str) and thread_ts:
+        return channel_id, thread_ts
+    return None
+
+
+def _plan_approved_slack_text(comment_count: int, actor: str) -> str:
+    return f"Plan approved with {comment_count} comments by {actor}\nbeginning implementation"
+
+
+async def _maybe_post_plan_approved_to_slack(
+    metadata: dict[str, Any], *, comment_count: int, actor: str
+) -> None:
+    slack_thread = _slack_thread_from_metadata(metadata)
+    if slack_thread is None:
+        return
+    channel_id, thread_ts = slack_thread
+    text = _plan_approved_slack_text(comment_count, actor)
+    try:
+        posted = await post_slack_thread_reply(channel_id, thread_ts, text)
+    except Exception:  # noqa: BLE001
+        logger.warning("Failed to post plan-approval notice to Slack", exc_info=True)
+        return
+    if not posted:
+        logger.warning("Plan-approval Slack notice was not posted (channel=%s)", channel_id)
+
+
 async def _dispatch_followup(
     thread_id: str, metadata: dict[str, Any], text: str, *, plan_mode: bool
 ) -> None:

tests/test_plan_review.py

@@ -182,3 +182,60 @@ def test_plan_mode_middleware_self_activation_via_state() -> None:
     # After enter_plan_mode sets state: the next request is filtered.
     on = _FakeReq([{"name": "read_file"}, {"name": "write_file"}], {"plan_mode": True})
     assert _names(mw._filter(on)) == {"read_file"}
+
+
+def test_plan_approved_slack_text_mentions_comments_actor_and_start() -> None:
+    from agent.dashboard.plan_api import _plan_approved_slack_text
+
+    text = _plan_approved_slack_text(3, "Alice")
+    assert text == "Plan approved with 3 comments by Alice\nbeginning implementation"
+
+
+async def test_approve_plan_posts_slack_approval_notice(monkeypatch: pytest.MonkeyPatch) -> None:
+    from agent.dashboard import plan_api
+
+    metadata = {
+        "github_login": "alice",
+        "source_context": {"slack_thread": {"channel_id": "C1", "thread_ts": "1700000000.0001"}},
+    }
+    posted: dict[str, Any] = {}
+
+    async def fake_thread_metadata(thread_id: str) -> dict[str, Any]:
+        return metadata
+
+    def fake_user_owns_thread(md: dict, sub: str, email: str | None) -> bool:
+        return True
+
+    async def fake_list_plan_comments(
+        thread_id: str, *, raise_on_error: bool = False
+    ) -> list[dict]:
+        return [{"author": "bob", "body": "tweak this"}]
+
+    async def fake_set_plan_status(thread_id: str, status: str, *, plan_mode: bool) -> None:
+        posted["status"] = {"status": status, "plan_mode": plan_mode}
+
+    async def fake_dispatch_followup(
+        thread_id: str, md: dict, text: str, *, plan_mode: bool
+    ) -> None:
+        posted["dispatch"] = {"text": text, "plan_mode": plan_mode}
+
+    async def fake_post_slack_thread_reply(channel_id: str, thread_ts: str, text: str) -> bool:
+        posted["slack"] = {"channel_id": channel_id, "thread_ts": thread_ts, "text": text}
+        return True
+
+    monkeypatch.setattr(plan_api, "_thread_metadata", fake_thread_metadata)
+    monkeypatch.setattr(plan_api, "_user_owns_thread", fake_user_owns_thread)
+    monkeypatch.setattr(plan_api, "list_plan_comments", fake_list_plan_comments)
+    monkeypatch.setattr(plan_api, "set_plan_status", fake_set_plan_status)
+    monkeypatch.setattr(plan_api, "_dispatch_followup", fake_dispatch_followup)
+    monkeypatch.setattr(plan_api, "post_slack_thread_reply", fake_post_slack_thread_reply)
+
+    result = await plan_api.approve_plan("tid", session={"sub": "u1", "name": "Alice"})
+
+    assert result == {"status": plan_api.PLAN_STATUS_APPROVED}
+    assert posted["dispatch"]["plan_mode"] is False
+    assert posted["slack"] == {
+        "channel_id": "C1",
+        "thread_ts": "1700000000.0001",
+        "text": "Plan approved with 1 comments by Alice\nbeginning implementation",
+    }