2.3.0 — the index train: local-first recall index, incremental sweep, stemming + alias expansion

One schema-bump release (recall-index schema 3, entity-index schema 2; old
recall indexes rebuild automatically, no vault migration):

- Local-first recall index: the live BM25 index lives in the machine state dir
  (keyed by endpoint hash); capture's upkeep is a zero-network atomic file
  write, no advisory lock — replacing the O(vault) GET/PUT-whole-index round
  trip per write. The vault copy is a snapshot (sweep + session-end) used to
  seed fresh machines / catch up after another client swept
  (ECHO_RECALL_SYNC_HOURS, default 24). The read path never PUTs the vault.
- Incremental sweep: entity + recall meta carry 16-char content hashes;
  `sweep --fast` fetches only new/gone/hash-missing notes plus a rotating
  weekday shard (--all-shards forces everything); deletions drop from both
  indexes; index-only so no --apply gate. `load` auto-runs it past
  ECHO_FAST_SWEEP_DAYS (7); doctor reports index freshness. Obsidian-side
  edits now reach the indexes without manual maintenance.
- Stemming + alias expansion: echo_stem.py (conservative Porter-lite, unit-
  tested families + over-stemming guards) applied at index AND query time;
  a query fuzzy-matching an entity folds its title/alias vocabulary into the
  BM25 query at half weight — expansion can only boost docs containing the
  terms. capture hashes the note's FINAL content (auto-link reordered first).

Eval gold set 8 -> 14 queries (6 paraphrases): recall@5/MRR 1.00/1.00 vs
keyword baseline 0.75/0.79. +3 unit tests, +10 e2e; test harnesses now isolate
ECHO_STATE_DIR. All seven suites green.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

echo-memory.plugin.src/skills/echo-memory/scripts/echo_session.py

@@ -135,6 +135,18 @@ def session_end_op(bundle: dict, apply: bool = False) -> dict:
         echo.cmd_put("_agent/heartbeat/last-session.md",
                      echo.temp_file(f"{path} @ {echo.now_iso()}\n".encode("utf-8")))
         steps["heartbeat"] = "ok"
+        # Index maintenance (2.3), NOT part of the bundle contract: push this
+        # machine's local recall index to the vault snapshot so other machines
+        # can seed/catch up. Best-effort — a failure never taints the bundle.
+        try:
+            import echo_recall
+            rix = echo_recall._load_local()
+            if rix and rix.n_docs:
+                rix.built = rix.built or echo.now_iso()
+                echo_recall.save_snapshot(rix)
+                steps["recall_snapshot"] = "ok"
+        except Exception:  # noqa: BLE001
+            steps["recall_snapshot"] = "skipped"
 
     data["steps"] = steps
     return echo_output.envelope("session-end", data)