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owns_task stale-agent loop (41x): a superseded agent (task reassigned away)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/gateway/test_choreographer_submit_qa_gates.py

@@ -359,13 +359,13 @@ async def test_i_am_done_proceeds_when_all_gates_pass() -> None:
 
 @pytest.mark.asyncio
 async def test_i_am_done_blocks_unauthorized() -> None:
-    """Spec's PRECONDITION_OWNERSHIP rejects with tracing_gap when the
-    caller does not own the task.
+    """A caller that does not own the task gets a clear not_authorized that
+    steers to give_me_work — not the owns_task tracing_gap it would retry.
 
-    Pre-spec migration the verb returned a separate not_authorized
-    envelope from an inline ownership check; the spec now drives this
-    decision via PRECONDITION_OWNERSHIP, which surfaces as tracing_gap
-    with the `owns_task` missing token.
+    A reassignment short-circuit runs before the spec gate, so a stale /
+    superseded agent is told plainly the task is no longer its own (instead
+    of reading PRECONDITION_OWNERSHIP's tracing_gap as a fixable precondition
+    and looping i_am_done — the observed owns_task burn-loop).
     """
     agent_id = uuid4()
     other_id = uuid4()
@@ -381,5 +381,6 @@ async def test_i_am_done_blocks_unauthorized() -> None:
 
     env = await c.i_am_done(agent_id, task_id, "done")
     body = env.as_dict()
-    assert body["error"] == "tracing_gap"
-    assert "owns_task" in body["missing"]
+    assert body["error"] == "not_authorized"
+    assert "no longer assigned" in (body.get("message") or "").lower()
+    assert "give_me_work" in (body.get("remediate") or "")