feat(sleep): nightly offline self-evolution engine + Claude Code plugin

Add skillopt/sleep — a deployment-time companion to SkillOpt that gives a
local Claude agent a nightly "sleep cycle":

  harvest ~/.claude transcripts -> mine recurring tasks -> replay offline
    -> consolidate (reflect -> bounded edit -> held-out GATE) -> stage -> adopt

Synthesizes SkillOpt (validation-gated bounded text optimization, reusing
skillopt.evaluation.gate verbatim), Claude Dreams (offline consolidation;
input never mutated; review-then-adopt), and the agent-sleep paper
(short-term experience -> long-term competence).

Engine (skillopt/sleep/, import-light, py>=3.10):
  - harvest.py   read-only parse of session JSONL + history.jsonl
  - mine.py      sessions -> TaskRecords (heuristic miner + LLM hook)
  - backend.py   MockBackend (deterministic, no API) + AnthropicBackend
  - replay.py    offline re-run -> (hard, soft) scores
  - consolidate.py  one SkillOpt epoch behind a held-out gate
  - memory.py    protected-region edits to SKILL.md / CLAUDE.md
  - staging.py   stage proposals; adopt with backup (Dreams safety contract)
  - cycle.py + __main__.py  orchestrator + CLI (run/dry-run/status/adopt/harvest)

Plugin (skillopt-sleep-plugin/): plugin.json, /sleep command, skillopt-sleep
skill, SessionEnd hook, bundled runner + cron generator.

Validation (deterministic, no API): persona experiment proves held-out lift
(researcher 0.33->1.0, programmer 0.32->1.0) AND that the gate rejects an
injected harmful edit. 13 stdlib-unittest tests pass, incl. full cycle +
adopt-with-backup and parsing of real on-disk transcripts.

Co-Authored-By: Claude Opus 4 <noreply@anthropic.com>

skillopt/sleep/state.py

@@ -0,0 +1,83 @@
+"""SkillOpt-Sleep — persistent cross-night state.
+
+state.json lives in ~/.skillopt-sleep and is the "long-term" store that
+turns nightly episodes into durable competence (the Agent-Sleep paper's
+short-term -> long-term transfer). It records:
+
+  - night counter
+  - last harvest timestamp per project (so each night only sees new data)
+  - cross-night "slow/meta" memory (lessons that persisted across nights)
+  - per-night history (scores, accept/reject) for trend reporting
+"""
+from __future__ import annotations
+
+import json
+import os
+from typing import Any, Dict, List, Optional
+
+
+def _now_iso(clock: Optional[float] = None) -> str:
+    # caller passes a timestamp; we avoid importing time at module import
+    import time as _t
+    return _t.strftime("%Y-%m-%dT%H:%M:%S", _t.localtime(clock if clock is not None else _t.time()))
+
+
+DEFAULT_STATE: Dict[str, Any] = {
+    "version": 1,
+    "night": 0,
+    "last_harvest": {},     # project -> iso timestamp of last harvested record
+    "slow_memory": "",      # cross-night consolidated lessons (meta-skill analogue)
+    "history": [],          # list of per-night summaries
+}
+
+
+class SleepState:
+    def __init__(self, path: str, data: Optional[Dict[str, Any]] = None) -> None:
+        self.path = path
+        self.data = data if data is not None else dict(DEFAULT_STATE)
+
+    # io ---------------------------------------------------------------------
+    @classmethod
+    def load(cls, path: str) -> "SleepState":
+        if os.path.exists(path):
+            try:
+                with open(path) as f:
+                    data = json.load(f)
+                merged = dict(DEFAULT_STATE)
+                merged.update(data if isinstance(data, dict) else {})
+                return cls(path, merged)
+            except Exception:
+                pass
+        return cls(path, dict(DEFAULT_STATE))
+
+    def save(self) -> None:
+        os.makedirs(os.path.dirname(self.path), exist_ok=True)
+        tmp = self.path + ".tmp"
+        with open(tmp, "w") as f:
+            json.dump(self.data, f, ensure_ascii=False, indent=2)
+        os.replace(tmp, self.path)
+
+    # accessors --------------------------------------------------------------
+    @property
+    def night(self) -> int:
+        return int(self.data.get("night", 0))
+
+    def last_harvest_for(self, project: str) -> Optional[str]:
+        return self.data.get("last_harvest", {}).get(project)
+
+    def set_last_harvest(self, project: str, iso_ts: str) -> None:
+        self.data.setdefault("last_harvest", {})[project] = iso_ts
+
+    @property
+    def slow_memory(self) -> str:
+        return str(self.data.get("slow_memory", ""))
+
+    def set_slow_memory(self, content: str) -> None:
+        self.data["slow_memory"] = content
+
+    def begin_night(self, clock: Optional[float] = None) -> int:
+        self.data["night"] = self.night + 1
+        return self.night
+
+    def record_night(self, summary: Dict[str, Any]) -> None:
+        self.data.setdefault("history", []).append(summary)