Scheduling core, state store, CLI and unit tests

One tick polls in-flight runs, posts results, classifies the first line and
moves state/assignee; failures get a structured note with transient retry and
backoff, timeouts are killed and handed over, resume failures and long threads
rebuild with a handoff summary. Then the lowest Todo items are dispatched within
terminal concurrency and serialize groups, and a heartbeat is written.
CLI: tick, new, show, comment, state, assign, smoke, check-config.

agentd/store.py

@@ -0,0 +1,61 @@
+"""JSON state store under state/: one file for all projects, an exclusive tick lock, heartbeat and log.
+
+state/agentd-state.json:
+  {"projects": {PROJECT: {"issues": {issue_uuid: rec}}}, "paused_groups": {group: {...}}}
+rec: seq, runs, thread_id, thread_on [terminal, executor], thread_rounds, tags [...], last_message,
+     seen_comments [...], last_comment_at, retries, retry {at, reason}, rebuild, inflight {...}"""
+import contextlib
+import fcntl
+import json
+import os
+import time
+from pathlib import Path
+
+
+class Busy(Exception):
+    pass
+
+
+class Store:
+    def __init__(self, state_dir, echo=True):
+        self.dir = Path(state_dir)
+        self.echo = echo
+        self.path = self.dir / "agentd-state.json"
+
+    def load(self):
+        if self.path.exists():
+            data = json.loads(self.path.read_text(encoding="utf-8"))
+        else:
+            data = {}
+        data.setdefault("projects", {})
+        data.setdefault("paused_groups", {})
+        return data
+
+    def save(self, data):
+        self.dir.mkdir(parents=True, exist_ok=True)
+        tmp = self.path.with_suffix(".tmp")
+        tmp.write_text(json.dumps(data, ensure_ascii=False, indent=1), encoding="utf-8")
+        os.replace(tmp, self.path)
+
+    @contextlib.contextmanager
+    def lock(self):
+        self.dir.mkdir(parents=True, exist_ok=True)
+        with open(self.dir / "agentd.lock", "w") as fh:
+            try:
+                fcntl.flock(fh, fcntl.LOCK_EX | fcntl.LOCK_NB)
+            except BlockingIOError:
+                raise Busy("another tick holds %s" % (self.dir / "agentd.lock")) from None
+            yield
+
+    def heartbeat(self, info):
+        self.dir.mkdir(parents=True, exist_ok=True)
+        info = dict(info, ts=time.time(), at=time.strftime("%Y-%m-%dT%H:%M:%S"))
+        (self.dir / "heartbeat.json").write_text(json.dumps(info, ensure_ascii=False, indent=1), encoding="utf-8")
+
+    def log(self, msg):
+        self.dir.mkdir(parents=True, exist_ok=True)
+        line = time.strftime("%Y-%m-%dT%H:%M:%S") + " " + msg
+        if self.echo:
+            print(line, flush=True)
+        with open(self.dir / "agentd.log", "a", encoding="utf-8") as fh:
+            fh.write(line + "\n")