[F047] conventions: reviewer-aware block-finding remediation on pr_pass gate

The pr_pass (reviewer) conventions guard reused the dev-path block-finding
remediation: 'add a waiver to .roboco/conventions.yml in your branch'. A
pr_reviewer does not own the assembled cell->root / root->master branch and
has no commit verb on it, so the waiver remediation is unreachable — a false
positive stranded the gate with no self-recovery (the reviewer could neither
commit a waiver nor pr_pass). The fail-open content path is documented
precision-over-recall and stays as-is; the actionable gap is the remediation.

Fix: _conventions_rejection now branches the block-finding remediation on
reviewer=True (mirroring the could_not_run branch from F044). The reviewer
path points at pr_fail carrying the findings as issues so the PR returns to
needs_revision and the DEV fixes the violation or commits the waiver (the dev
CAN commit to the branch); waiver authorship is framed as the dev's action,
not the reviewer's. Dev i_am_done path wording unchanged. TDD
test_conventions_gate_pr_pass.py (+1).

tests/unit/gateway/test_conventions_gate_pr_pass.py

@@ -94,6 +94,32 @@ async def test_pr_pass_guard_could_not_run_remediation_uses_pr_fail(
     assert "pr_fail" in body["remediate"]
 
 
+@pytest.mark.asyncio
+async def test_pr_pass_guard_block_remediation_uses_pr_fail_not_reviewer_waiver(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    # F047: on the pr_pass (reviewer) path a block-level finding's remediation
+    # must point at pr_fail (the reviewer's only lever) and frame the waiver as
+    # the DEV's action — NOT tell the reviewer to "add a waiver to
+    # .roboco/conventions.yml in your branch". A pr_reviewer does not own the
+    # assembled cell→root / root→master branch and has no commit verb on it, so
+    # the shared dev-path waiver remediation is unreachable and would strand the
+    # gate on every false positive (no self-recovery).
+    monkeypatch.setattr(settings, "conventions_enabled", True)
+    c = _make_choreographer(check_result=_BLOCK_RESULT)
+    env = await c._conventions_guard(uuid4(), MagicMock(), {})
+    assert env is not None
+    body = env.as_dict()
+    remediate = body["remediate"]
+    # The reviewer's lever is pr_fail, not committing a waiver themselves.
+    assert "pr_fail" in remediate
+    # The offending finding is carried so the reviewer can paste it as an issue.
+    assert "app/routers/u.py:2" in remediate
+    # The reviewer must NOT be told to add a waiver "in your branch" — they
+    # can't commit to the assembled PR branch. The waiver is the dev's job.
+    assert "in your branch" not in remediate
+
+
 @pytest.mark.asyncio
 async def test_pr_pass_guard_inert_when_flag_off(
     monkeypatch: pytest.MonkeyPatch,