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>

eval/results/latest.json

@@ -3,17 +3,17 @@
   "date": "2026-07-03",
   "retrieval": {
     "current (hybrid+priors, full corpus)": {
-      "precision_at_5": 0.25,
+      "precision_at_5": 0.243,
       "recall_at_5": 1.0,
       "mrr": 1.0,
-      "session_journal_queries_answered": "2/2",
+      "session_journal_queries_answered": "3/3",
       "freshness_top1_correct": true
     },
     "baseline (keyword, entities only)": {
-      "precision_at_5": 0.2,
+      "precision_at_5": 0.186,
       "recall_at_5": 0.75,
-      "mrr": 0.75,
-      "session_journal_queries_answered": "0/2",
+      "mrr": 0.786,
+      "session_journal_queries_answered": "0/3",
       "freshness_top1_correct": false
     }
   },