fix(run-hardening): break PM decision-gate, stale-agent, and empty-diff loops (#255)

Forensic triage of a 24h run reconstructed the dominant gateway.rejected
loops from the audit_log. After earlier deploys fixed the i_will_plan crash
and the open_pr push-gap, three real, recurring-capable burn loops remained.
This fixes them at the architecture level, not by prompt-nagging.

journal:decision write-then-gate (the dominant completion-path blocker):
PM decision-point verbs required a separate note(scope='decision') call
before the verb, which loaded/weak models forget to chain — so complete and
unblock hit a tracing_gap (journal:decision missing) and respawn-looped,
stranding finished tasks forever. Each verb now auto-records its OWN
rationale as the journal:decision before the gate runs (the proven
i_am_blocked -> write_struggle pattern), so the gate passes off real,
persisted reasoning. unblock gains a required `reason` (threaded MCP tool ->
request schema -> routes -> choreographer); delegate derives the decision
from its title + description; complete/submit_up/submit_root/escalate_up/
escalate_to_ceo reuse their existing notes/reason. The gate still runs as
defense-in-depth; the auto-record is idempotent within the decision window
and best-effort. Adds JournalService.write_decision and
Choreographer._ensure_pm_decision.

open_pr empty-diff 422: an overlapping-decomposition leaf with zero commits
vs its base makes GitHub 422 "No commits between ...". The generic
invalid_state "retry" looped the dev 15x on one task. open_pr now steers to a
terminal i_am_blocked hand-off so the PM completes or cancels the redundant
leaf.

owns_task stale-agent loop (41x): a superseded agent (task reassigned away)
calling i_am_done/open_pr got a PRECONDITION_OWNERSHIP tracing_gap it read as
a fixable precondition and retried forever. Both verbs now short-circuit with
the clear not_authorized "no longer yours -> give_me_work" steer that
resume/unclaim already use.

RAG docs updated for the new unblock(reason) signature; CHANGELOG entries
added under 0.11.0 (unreleased). open_pr refactored into
_open_pr_preflight_rejection + _open_pr_failure_env to stay within the
return-count and complexity budgets.

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

tests/unit/api/routes/v1/test_flow_cell_pm.py

@@ -97,7 +97,7 @@ async def test_unblock_dispatches_task_id_with_restore_true() -> None:
 
     resp = client.post(
         "/api/v1/flow/cell_pm/unblock",
-        json={"task_id": _TASK_ID},
+        json={"task_id": _TASK_ID, "reason": "block resolved upstream; restoring"},
         headers=_HEADERS,
     )
 
@@ -107,6 +107,7 @@ async def test_unblock_dispatches_task_id_with_restore_true() -> None:
     mock_chore.unblock.assert_awaited_once()
     call_kwargs = mock_chore.unblock.call_args.kwargs
     assert call_kwargs["restore"] is True
+    assert mock_chore.unblock.call_args.args[2] == "block resolved upstream; restoring"
 
 
 @pytest.mark.asyncio
@@ -120,7 +121,11 @@ async def test_unblock_with_restore_false() -> None:
 
     resp = client.post(
         "/api/v1/flow/cell_pm/unblock",
-        json={"task_id": _TASK_ID, "restore": False},
+        json={
+            "task_id": _TASK_ID,
+            "reason": "block resolved upstream; restoring",
+            "restore": False,
+        },
         headers=_HEADERS,
     )
 

tests/unit/api/routes/v1/test_flow_main_pm.py

@@ -119,7 +119,7 @@ async def test_unblock_dispatches_task_id_with_restore_true() -> None:
 
     resp = client.post(
         "/api/v1/flow/main_pm/unblock",
-        json={"task_id": _TASK_ID},
+        json={"task_id": _TASK_ID, "reason": "block resolved upstream; restoring"},
         headers=_HEADERS,
     )
 
@@ -127,6 +127,7 @@ async def test_unblock_dispatches_task_id_with_restore_true() -> None:
     mock_chore.unblock.assert_awaited_once()
     call_kwargs = mock_chore.unblock.call_args.kwargs
     assert call_kwargs["restore"] is True
+    assert mock_chore.unblock.call_args.args[2] == "block resolved upstream; restoring"
 
 
 @pytest.mark.asyncio