feat(RMGR-WP-0001): complete T05 end-to-end vertical slice

Implement observe/reconcile/update-task-status CLI path: workplan parse,
JSON projection index, git-backed task status writeback with correlation
events, and E2E pytest plus evidence artifacts. Finish foundation workplan.

src/repo_manager/index_store.py

@@ -0,0 +1,83 @@
+"""Local JSON projection store for the vertical-slice proof (pre-Postgres)."""
+
+from __future__ import annotations
+
+import json
+from dataclasses import asdict, dataclass, field
+from datetime import datetime, timezone
+from pathlib import Path
+from typing import Any
+
+
+def _now() -> str:
+    return datetime.now(timezone.utc).isoformat()
+
+
+@dataclass
+class WorkRecordEntry:
+    kind: str
+    id: str | None
+    status: str | None
+    title: str | None
+    source_path: str
+    uuid: str | None = None
+    parent_id: str | None = None
+    extra: dict[str, Any] = field(default_factory=dict)
+
+
+@dataclass
+class RepoIndex:
+    slug: str
+    repo_root: str
+    head_sha: str | None
+    observed_at: str
+    work_records: list[WorkRecordEntry] = field(default_factory=list)
+    events: list[dict[str, Any]] = field(default_factory=list)
+    schema: str = "repo_manager.index.v0"
+
+    def to_dict(self) -> dict[str, Any]:
+        return {
+            "schema": self.schema,
+            "slug": self.slug,
+            "repo_root": self.repo_root,
+            "head_sha": self.head_sha,
+            "observed_at": self.observed_at,
+            "work_records": [asdict(r) for r in self.work_records],
+            "events": self.events,
+        }
+
+    @classmethod
+    def from_dict(cls, data: dict[str, Any]) -> RepoIndex:
+        records = [
+            WorkRecordEntry(**{k: v for k, v in r.items() if k in WorkRecordEntry.__dataclass_fields__})
+            for r in data.get("work_records", [])
+        ]
+        return cls(
+            slug=data["slug"],
+            repo_root=data["repo_root"],
+            head_sha=data.get("head_sha"),
+            observed_at=data.get("observed_at") or _now(),
+            work_records=records,
+            events=list(data.get("events") or []),
+            schema=data.get("schema") or "repo_manager.index.v0",
+        )
+
+
+def default_index_path(repo_root: Path) -> Path:
+    return repo_root / ".repo-manager" / "index.json"
+
+
+def save_index(index: RepoIndex, path: Path | None = None) -> Path:
+    path = path or default_index_path(Path(index.repo_root))
+    path.parent.mkdir(parents=True, exist_ok=True)
+    path.write_text(json.dumps(index.to_dict(), indent=2) + "\n", encoding="utf-8")
+    return path
+
+
+def load_index(path: Path) -> RepoIndex:
+    return RepoIndex.from_dict(json.loads(path.read_text(encoding="utf-8")))
+
+
+def append_event(index: RepoIndex, event: dict[str, Any]) -> None:
+    event = {**event, "emitted_at": event.get("emitted_at") or _now()}
+    index.events.append(event)