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/run_eval.py

@@ -135,6 +135,16 @@ QUERIES = [
     ("contract renewal Q3", {"resources/companies/vantage-systems.md"}, False),
     ("renegotiation kickoff", {"journal/daily/2026-06-20.md"}, True),
     ("graph neighbourhood expansion", {"resources/concepts/graph-expansion.md"}, False),
+    # ---- paraphrase set (2.3): morphological variants + rephrasings the pre-2.3
+    # purely-lexical index missed — the stemming gain is measured, not assumed.
+    ("renewing enterprise contracts", {"resources/companies/vantage-systems.md"}, False),
+    ("navigational cleanup", {"projects/active/website-redesign.md",
+                              "projects/archived/old-website.md"}, False),
+    ("preferring uv for tooling", {"_agent/memory/semantic/tooling-preferences.md"}, False),
+    ("penalties in the SLA",
+     {"_agent/sessions/2026-06-20-1000-vantage-contract-review.md"}, True),
+    ("saturated term frequencies", {"resources/concepts/bm25-ranking.md"}, False),
+    ("expanded linked neighbourhoods", {"resources/concepts/graph-expansion.md"}, False),
 ]
 FRESHNESS_QUERY = "marketing site navigation"
 FRESHNESS_TOP1 = "projects/active/website-redesign.md"