Add PR comment intake and the review loop (B2) — step 6b

- poller.py: CommentPoller polls PR comments rather than taking
  webhooks, keeping the VM outbound-only (B3). On an outage it backs
  off exponentially, caps, and retries indefinitely while logging:
  polling is pure intake, so an outage delays a reaction but never
  fails a task or forces a transition
- prime() marks the existing thread as seen without delivering it, so
  starting a watch does not re-address feedback already handled
- Review loop: a comment in PR_OPEN enters the canonical transcript,
  the executor responds, and the fix is pushed to the same branch with
  a reply on the PR. No intent is recorded for a follow-up push — the
  PR already exists, so a repeated push is harmless, unlike opening a
  second PR
- Comment authors are checked against a separate Gitea operator
  allowlist: a PR comment is an instruction channel into an agent that
  writes code, so it is operator-scoped, and a Gitea login is not a
  Matrix MXID (A4 per-channel allowlists)
- Orchestrator now holds a lock: transport and the poller deliver on
  separate threads, and state transitions must not interleave
- Backoff timings are injectable, so the outage path is tested in
  milliseconds instead of being untestable

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

nisse-dev/src/nisse_dev/control.py

@@ -8,6 +8,7 @@ arrives over transport. Every position change is checkpointed through the state
 store before the loop continues, so a restart lands mid-gate, not mid-air.
 """
 
+import threading
 import uuid
 from collections.abc import Iterable, Mapping
 from dataclasses import dataclass
@@ -86,6 +87,12 @@ class MilestonePublisher(Protocol):
         self, *, task_id: str, milestone: int, project: str, plan: str
     ) -> Any: ...
 
+    def push_followup(
+        self, *, task_id: str, milestone: int, message: str
+    ) -> str | None: ...
+
+    def comment(self, index: int, body: str) -> None: ...
+
 
 class PlanningAgent(Protocol):
     def plan(
@@ -139,6 +146,7 @@ class Orchestrator:
         roles: RoleMap | None = None,
         executor: "MilestoneExecutor | None" = None,
         publisher: "MilestonePublisher | None" = None,
+        gitea_operators: Iterable[str] = (),
     ) -> None:
         self._store = store
         self._transport = transport
@@ -147,6 +155,13 @@ class Orchestrator:
         self._executor = executor
         self._publisher = publisher
         self._operators = set(operators)
+        # Per-channel allowlists (A4): a Matrix MXID and a Gitea login
+        # are different names for the same person, and neither implies
+        # the other.
+        self._gitea_operators = set(gitea_operators)
+        # Transport and the comment poller deliver on separate threads;
+        # state transitions must not interleave.
+        self._lock = threading.RLock()
         self._data = _fresh_data()
         self._project: str | None = None
         transport.on_message(self._handle)
@@ -197,6 +212,10 @@ class Orchestrator:
             )
 
     def _handle(self, msg: InboundMessage) -> None:
+        with self._lock:
+            self._handle_locked(msg)
+
+    def _handle_locked(self, msg: InboundMessage) -> None:
         if msg.sender not in self._operators:
             return
         # Every operator message enters the canonical transcript, so planning
@@ -376,6 +395,72 @@ class Orchestrator:
             pending={"kind": "milestone_stopped", "milestone": milestone},
         )
 
+    def handle_review_comment(self, comment: Any) -> None:
+        """React to a PR review comment (B2). Called from the poller thread.
+
+        Comment authors are checked against the Gitea operator allowlist:
+        a PR comment is an instruction channel into an agent that writes
+        code, so it is operator-scoped like any other (A4, and the same
+        reasoning C4 applies to tickets).
+        """
+        with self._lock:
+            self._handle_review_comment_locked(comment)
+
+    def _handle_review_comment_locked(self, comment: Any) -> None:
+        if comment.author not in self._gitea_operators:
+            self._store.oplog.emit(
+                "gitea.comment_ignored",
+                cause=f"author {comment.author!r} not an operator",
+                comment_id=comment.id,
+            )
+            return
+        state = self._store.get_state()
+        if state is None or state.state != PR_OPEN:
+            self._store.oplog.emit(
+                "gitea.comment_ignored",
+                cause=f"not in PR_OPEN (state={state.state if state else None})",
+                comment_id=comment.id,
+            )
+            return
+        if self._executor is None or self._publisher is None:
+            return
+
+        pr = self._data.get("pr") or {}
+        milestone = int(pr.get("milestone", self._data.get("milestone", 1)))
+        # The comment enters the transcript, so the executor sees review
+        # feedback as conversation rather than as an out-of-band instruction.
+        self._store.append_event(
+            UserMessage(text=comment.body, source=f"gitea:comment:{comment.id}")
+        )
+        outcome = self._executor.run(milestone)
+        if outcome.status != "completed":
+            self._await_input(
+                cause=f"review response {outcome.status}",
+                prompt=(
+                    f"could not address the review comment ({outcome.status}): "
+                    f"{outcome.note}"
+                ),
+                pending={"kind": "milestone_stopped", "milestone": milestone},
+            )
+            return
+        try:
+            sha = self._publisher.push_followup(
+                task_id=str(self._data.get("task_id")),
+                milestone=milestone,
+                message=f"Address review comment {comment.id}",
+            )
+        except (GiteaError, GitError) as exc:
+            self._transport.send_message(f"could not push the fix: {exc}")
+            return
+        note = (
+            f"pushed {sha[:8]} addressing the review comment"
+            if sha
+            else "no code change was needed for that comment"
+        )
+        self._transport.send_message(note)
+        if pr.get("number"):
+            self._publisher.comment(int(pr["number"]), note)
+
     def _publish_milestone(self, milestone: int) -> None:
         if self._publisher is None:
             return