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/SKILL.md

@@ -358,6 +358,8 @@ Run it after `migrate.py` (which handles structural/schema changes) — or any t
 
 The pass is cheap and pays for itself by catching drift before it requires a reorg. Write the findings as a digest; act on them only with the operator's go-ahead.
 
+**Incremental maintenance (2.3).** `sweep.py --fast` is the cheap, index-only mode: it fetches just what's new, gone, or changed (content hashes) plus a rotating daily verification shard, so edits made directly in Obsidian or by other clients reach the entity + recall indexes without a full pass. It runs **automatically at load** when this machine's last sweep is older than `ECHO_FAST_SWEEP_DAYS` (default 7) — you rarely need to invoke it. The recall index itself is **local-first**: capture maintains a machine-local copy with zero vault round-trips; the vault's `recall-index.json` is a snapshot (sweep/session-end) used to seed fresh machines.
+
 **Performance.** Full-vault scripts (`sweep.py`, `vault_lint.py`, recall rebuild) are connection-pooled (keep-alive) and read the whole vault concurrently via `echo.read_many`, so they finish in about a second on a few-hundred-note vault instead of timing out on hundreds of serial TLS handshakes. Tune with `ECHO_WORKERS` (default 8, bulk-read concurrency) and `ECHO_TIMEOUT` (default 30s, per-request). For a vault large enough that even the concurrent pass nears the tool timeout, run the script with the harness's background-execution option rather than blocking the turn.
 
 ## Daily Note — Agent Log