Record the recall numbers after the embedder swap

recall@1 60% to 72%, answered 48% to 72%, latency 3x better. But false
recall went 1/5 to 5/5: e5 packs every score into a narrow high band, so
the 0.55 gate now admits everything. Left the gate alone as instructed.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CGeSZxh1DCtRxmFVSYVGvJ

RECALL-EVAL-31-07-2026.md

@@ -83,6 +83,66 @@ sqlite-backed `store.MemoryStore` and `memory.InMemoryStore` identically — bot
 (`internal/store/memory.go:64`) at ~150µs over 42 rows against a ~59ms query embed. An ANN index is
 not the problem to solve.
 
+## Re-measured after the embedder swap — 31-07-2026, later the same day
+
+Changed: `models/embedder/` is now **multilingual-e5-small** (quantized, 118MB), with `query: ` in
+front of a question and `passage: ` in front of a stored note (Vikunja #371). `deploy/mavend.json`
+and `make download-embedder` now name the same file, and it is the quantized one — that is what the
+column below measures (Vikunja #372). Everything else is unchanged: same fixture, same store, same
+0.55 gate. The old column is the baseline and is left as it was.
+
+| | recall+onnx, MiniLM (baseline) | recall+onnx, e5-small (new) |
+|---|---|---|
+| **recall@1** | 60.0% (15/25) | **72.0% (18/25)** |
+| recall@3 | 80.0% (20/25) | 84.0% (21/25) |
+| **answered after the 0.55 gate** | 48.0% (12/25) | **72.0% (18/25)** |
+| wrong note on top / tie on top | 10 / 0 | 7 / 0 |
+| ranked first, then silenced by the gate | 3 | 0 |
+| **false recall** | 1/5 (20%) | **5/5 (100%)** |
+| top-1 score when right, min / median | 0.559 / 0.678 | 0.791 / 0.857 |
+| top-1 when it must stay silent, median / max | 0.470 / 0.567 | 0.815 / 0.835 |
+| RU / EN / `hard` cases passed | 13/24 / 3/6 / 2/11 | 14/24 / 4/6 / 5/11 |
+| latency p50 / p95 / max | 59ms / 148ms / 194ms | 18ms / 37ms / 49ms |
+
+### What moved
+
+Ranking got better and got faster. Half the previously-unwinnable `hard` cases now pass (2/11 →
+5/11), the guitar note no longer beats the docker-logs note, and the gate stops silencing notes that
+already ranked first. The quantized e5 is also ~3x quicker than the fp32 MiniLM it replaces.
+
+### What got worse: the gate is now a no-op
+
+e5 packs every cosine into a narrow high band. Right-note scores start at 0.791; must-stay-silent
+scores reach 0.835. **The distributions still overlap, and now they overlap above the gate**, so
+0.55 admits everything and false recall goes from 1/5 to 5/5. The sweep:
+
+```
+gate 0.50–0.70: answered 18/25 (72%)  false recall 5/5
+gate 0.80:      answered 17/25 (68%)  false recall 4/5
+gate 0.90:      answered  0/25 ( 0%)  false recall 0/5
+```
+
+There is no value that keeps real recall and rejects made-up questions — same conclusion as before,
+now with a wider band and no room at all. `query_min_score` was left at 0.55 as instructed. **The
+recommendation is to leave it there and stop tuning it**: any number under ~0.79 is a no-op and
+anything above starts cutting real recall long before it stops the false ones. The fix is a margin
+gate (`top1 − top2 > δ`), next-steps item 3, which is now the top item.
+
+### The prefixes did not do the work
+
+A control run with both prefixes set to the empty string scored the **same** recall@1 (72%), a
+slightly better recall@3 (88%) and the same 5/5 false recall. So on this fixture the gain comes from
+the model, not from the `query:` / `passage:` split. The prefixes are kept because they are how e5
+was trained and the split is the right shape for the read path, but they are not worth defending on
+this evidence — a bigger fixture may say otherwise.
+
+### Stored vectors from the old model are now junk
+
+Cosine between a MiniLM vector and an e5 vector means nothing. Every row already in `notes` and in
+the vector memory table was written by the old model, so after this deploy they will score as noise
+against a new query. A live database needs every note and fact re-embedded before recall works at
+all. Filed as its own task.
+
 ## Next steps — ordered by value-to-risk; nothing here is a decision
 
 1. **Swap the embedder to `multilingual-e5-small` with `query:`/`passage:` prefixes.** One config