fix(skillopt-sleep): surface codex auth/model/version failures instead of silently scoring 0

A nightly sleep cycle could run for weeks emitting held-out 0.0 -> 0.0 (gate reject, zero
edits), indistinguishable from "nothing to learn", when the real cause was the codex backend
returning an error (expired auth / model unsupported on the account / outdated CLI) that got
scored as a failed rollout.

backend (CodexCliBackend):
- split _call into _call_once + a retry wrapper: transient empties/timeouts are retried
  instead of silently returning "" (mirrors AzureOpenAIBackend's guard);
- on a non-zero exit, surface the reason via last_call_error and return "" rather than
  leaking the CLI error text as if it were a model response;
- fail fast (no retries) on fatal auth/model/version errors (401, refresh_token_reused,
  token_expired, "not supported when using Codex with a ChatGPT account",
  "requires a newer version of Codex").
backend (CliBackend.reflect): retain last_reflect_raw so a no-edits night is diagnosable.
consolidate: ConsolidationResult now carries per-task held-out detail (response, hard/soft,
  fail_reason) + reflect_raw + call_error.
cycle: write diagnostics.json per cycle so a 0.0 night self-explains instead of being a black box.
tests: 4 new (retry-not-silent-zero, auth-error-surfaced-not-scored, holdout-detail, reflect-raw).

Also gitignore the .skillopt-sleep/ runtime dir.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

skillopt_sleep/cycle.py

@@ -276,6 +276,28 @@ def run_sleep_cycle(
             live_memory_path=live_memory_path,
             report_md=report_md,
         )
+        # Observability: persist per-task held-out evidence + optimizer/codex errors so a
+        # 0.0->0.0 night self-explains (empty responses vs failing checks vs no edits) — the
+        # cycle previously captured none of this, making the gate a black box (#learning-stall).
+        try:
+            import json as _json
+            with open(os.path.join(staging_dir, "diagnostics.json"), "w", encoding="utf-8") as _fh:
+                _json.dump({
+                    "night": night,
+                    "backend": cfg.get("backend"),
+                    "gate_mode": cfg.get("gate_mode"),
+                    "n_tasks": len(tasks),
+                    "baseline_score": result.baseline_score,
+                    "candidate_score": result.candidate_score,
+                    "accepted": result.accepted,
+                    "n_applied_edits": len(result.applied_edits),
+                    "n_rejected_edits": len(result.rejected_edits),
+                    "call_error": getattr(result, "call_error", ""),
+                    "reflect_raw_head": (getattr(result, "reflect_raw", "") or "")[:1200],
+                    "holdout_detail": getattr(result, "holdout_detail", []),
+                }, _fh, indent=2)
+        except Exception:
+            pass
         state.set_last_harvest(project, started)
         state.record_night({
             "night": night, "accepted": result.accepted,