feat(P03 W2): outcome backfill (REQ-317) + escalation_reason (REQ-318)

REQ-317: core/metrics/outcome_backfill.py backfills fact_decision.outcome
pending -> succeeded/failed after run.completed/run.failed; idempotent +
terminal (does not overwrite a non-pending outcome); wired into the
collector. The Post-Pilot AI Decision Accuracy denominator is now grounded
(fact_decision.outcome is not stuck pending).

REQ-318: ai.decision.made on a block band carries escalation_reason:
'confidence' (the only value in v1.26 — a block is always confidence-
driven; future milestones may add 'policy'). Persisted into fact_run by
the collector. The Post-Pilot Human Escalation Frequency denominator is
now grounded.

---ci---
project: acdl
phase: 3
milestone: v1.26
status: execute
wave: W2
---

core/metrics/run_manifest.py

@@ -27,6 +27,27 @@ def _iso8601_now():
     return datetime.datetime.now(datetime.timezone.utc).strftime("%Y-%m-%dT%H:%M:%SZ")
 
 
+def _backfill_outcome(decision_id, outcome):
+    """Transition fact_decision.outcome pending -> outcome (REQ-317).
+
+    Best-effort: logs a warning and skips if decision_id is missing or the
+    backfill raises. Never raises — the run is already completing/failing
+    and the manifest write is the source of truth for the run outcome.
+    """
+    if not decision_id:
+        # A run that failed before ai.decision.made was emitted has no
+        # decision to backfill (e.g. a schema-validation failure). Skip
+        # silently rather than pollute stderr on every clean run.
+        return None
+    try:
+        from core.metrics import outcome_backfill
+        return outcome_backfill.backfill(decision_id, outcome)
+    except Exception as exc:  # pragma: no cover - defensive
+        print(f"[run_manifest] outcome backfill skipped for {decision_id}: {exc}",
+              file=sys.stderr)
+        return None
+
+
 def _run_id():
     return f"run-{int(time.time())}-{uuid.uuid4().hex[:8]}"
 
@@ -44,7 +65,7 @@ def start_run(contract_id, environment, stages=None):
     return run_id
 
 
-def complete_run(run_id, contract_id, environment, stages, exit_code, confidence=None, hitl=None, policy=None, cost_estimate_usd=None, decision_id=None):
+def complete_run(run_id, contract_id, environment, stages, exit_code, confidence=None, hitl=None, policy=None, cost_estimate_usd=None, decision_id=None, escalation_reason=None):
     """Emit nova.run.completed + write the per-run manifest JSON.
 
     Args:
@@ -58,6 +79,10 @@ def complete_run(run_id, contract_id, environment, stages, exit_code, confidence
         policy: optional {passed, failed, skipped}
         cost_estimate_usd: optional float
         decision_id: optional string (links to the Decision Ledger)
+        escalation_reason: optional string (REQ-318) — "confidence" when
+            the ai.decision.made band was block; absent/None otherwise.
+            Persisted into the manifest so the collector can write it
+            into fact_run (Post-Pilot Human Escalation Frequency denom).
     """
     started_at = stages[0].get("started_at", _iso8601_now()) if stages else _iso8601_now()
     completed_at = _iso8601_now()
@@ -83,6 +108,8 @@ def complete_run(run_id, contract_id, environment, stages, exit_code, confidence
         manifest["cost_estimate_usd"] = cost_estimate_usd
     if decision_id:
         manifest["decision_id"] = decision_id
+    if escalation_reason:
+        manifest["escalation_reason"] = escalation_reason
 
     os.makedirs(_RUNS_DIR, exist_ok=True)
     manifest_path = os.path.join(_RUNS_DIR, f"{run_id}.json")
@@ -92,6 +119,14 @@ def complete_run(run_id, contract_id, environment, stages, exit_code, confidence
     event_type = "nova.run.completed" if exit_code == 0 else "nova.run.failed"
     emit(event_type, run_id, environment, manifest, contract_id=contract_id)
 
+    # REQ-317: backfill fact_decision.outcome pending -> succeeded/failed
+    # after the run completes. The decision_id links the run to the
+    # Decision Ledger entry written by ai.decision.made. Best-effort: a
+    # run that failed before ai.decision.made was emitted has no
+    # decision_id and the backfill is a no-op (the run outcome is still
+    # captured in the manifest above).
+    backfill_result = _backfill_outcome(decision_id, outcome)
+
     return manifest