fix(pr-review): fleet PRs are ours by branch ownership, not author identity (#668)

With a GitHub App bound, fleet PRs are authored by <app-slug>[bot] whose
author_association is NONE — the inbound classifier's author heuristics
read that as an outsider and ingested the org's own dev-stream PR as
external_pr for adversarial review (2026-07-23 live: PR #667). The
repo-owner author check only ever covered the PAT era.

_ingest_pr_if_reviewable now skips any same-repo PR whose head branch an
active task owns BEFORE the author-based classification, and
active_task_owns_branch widens from the single polled project to every
project sharing its git_url (the poll collapses a monorepo's
cell-projects to one canonical project, so a sibling cell's ownership
must count — the same sibling scope external_review_task_exists already
uses, now shared via _repo_sibling_project_ids). A deleted-fork head
(GitHub sends head.repo=null) now classifies as fork, failing closed to
review instead of risking a silent ownership skip on a branch-name
collision. Residual, documented: an org PR whose task went terminal with
the PR left open falls through to the author heuristics.

Co-authored-by: Renn F <rennf93@users.noreply.github.com>

tests/unit/runtime/test_external_pr_classify.py

@@ -198,6 +198,78 @@ async def test_skip_internal_when_disabled(monkeypatch: pytest.MonkeyPatch) -> N
     svc.ingest_external_pr.assert_not_awaited()
 
 
+@pytest.mark.asyncio
+async def test_skip_app_bot_authored_fleet_pr(monkeypatch: pytest.MonkeyPatch) -> None:
+    """The 2026-07-23 live incident: with a GitHub App bound, fleet PRs are
+    authored by <app-slug>[bot] whose author_association is NONE — the external
+    heuristic reads that as an outsider. Branch ownership must win: a same-repo
+    PR whose head an active task owns is the org's own, whoever authored it."""
+    monkeypatch.setattr(orch_mod.settings, "external_pr_enabled", True)
+    monkeypatch.setattr(orch_mod.settings, "internal_pr_enabled", True)
+    svc = _svc(owns_branch=True)
+    pr = {
+        "number": 667,
+        "is_fork": False,
+        "author_is_owner": False,
+        "user_login": "roboco-app[bot]",
+        "author_association": "NONE",
+        "head_ref": "feature/frontend/170c9578--f1957610",
+    }
+    ok = await _orch()._ingest_pr_if_reviewable(
+        svc, SimpleNamespace(id=uuid4()), pr, uuid4(), set()
+    )
+    assert ok is False
+    svc.ingest_external_pr.assert_not_awaited()
+
+
+@pytest.mark.asyncio
+async def test_app_bot_pr_without_owning_task_still_reviews(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """The documented residual: a same-repo bot-authored PR with NO active
+    owning task falls through to the author heuristics and reviews as
+    external — orphaned/unknown bot branches (dependabot included) keep
+    getting the read-only adversarial review."""
+    monkeypatch.setattr(orch_mod.settings, "external_pr_enabled", True)
+    monkeypatch.setattr(orch_mod.settings, "internal_pr_enabled", True)
+    svc = _svc(owns_branch=False)
+    pr = {
+        "number": 42,
+        "is_fork": False,
+        "author_is_owner": False,
+        "user_login": "dependabot[bot]",
+        "author_association": "NONE",
+        "head_ref": "dependabot/npm_and_yarn/foo-1.2.3",
+    }
+    ok = await _orch()._ingest_pr_if_reviewable(
+        svc, SimpleNamespace(id=uuid4()), pr, uuid4(), set()
+    )
+    assert ok is True
+    assert svc.ingest_external_pr.await_args.kwargs["source"] == "external_pr"
+
+
+@pytest.mark.asyncio
+async def test_fork_pr_never_consults_branch_ownership(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """A fork PR is external by definition — the ownership pre-check must not
+    run for it (a fork head ref can coincide with an org branch name)."""
+    monkeypatch.setattr(orch_mod.settings, "external_pr_enabled", True)
+    svc = _svc(owns_branch=True)
+    pr = {
+        "number": 7,
+        "is_fork": True,
+        "user_login": "outsider",
+        "head_ref": "feature/frontend/copycat",
+    }
+    ok = await _orch()._ingest_pr_if_reviewable(
+        svc, SimpleNamespace(id=uuid4()), pr, uuid4(), set()
+    )
+    assert ok is True
+    svc.active_task_owns_branch.assert_not_awaited()
+    assert svc.ingest_external_pr.await_args.kwargs["source"] == "external_pr"
+
+
 @pytest.mark.asyncio
 async def test_skip_owner_authored_pr(monkeypatch: pytest.MonkeyPatch) -> None:
     # The org's own account opened the PR → self-review, never ingest (even with