memory: record the recall topic veto's real price (V-496)

#496 asked to skip the veto when the question and the hit are in
different scripts, so an English question stops losing a Russian note.
Measured first: the fixture has no cross-language case, and en-hard-024
is an English question against an English note. Both proposed fixes are
no-ops.

What the veto actually does on the fixture, with the real embedder: it
costs en-hard-024 and buys ru-silent-029. Pass count is 22/32 either
way; false recall is 0/5 with it and 1/5 without. The two cases are one
lexical class, so no rule cheap enough for RecallAllowed separates them.

Accepts the loss and pins both sides in a test.

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

docs/evals/2026-08-03-recall-topic-veto.md

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+# Recall topic veto, what it costs and what it buys, 2026-08-03
+
+Vikunja #496. The task asked for a cross-language fix. Skip the topic veto in
+`memory.RecallAllowed` when the question and the hit are in different scripts.
+An English question would then stop losing a Russian note.
+
+No such case exists. No fixture case puts the question and its wanted note in
+different scripts. The case the task named is not one either.
+
+    en-hard-024
+      query  "what fixed the screen problem"
+      note   "the flicker went away once i swapped the display cable"
+
+Both are English. It is a paraphrase failure, not a language failure. A script
+test would not have changed a single case, and neither would a bilingual stem
+map.
+
+## What the veto is worth today
+
+Measured with the real embedder, multilingual-e5-small int8, gate 0.55, margin
+0.008. The first row is the veto as it ships. The second is `RecallAllowed`
+forced to true.
+
+| | cases passing | answered | false recall | silenced by gate |
+|---|---|---|---|---|
+| veto on | 22/32 | 17/27 | 0/5 | 2 |
+| veto off | 22/32 | 18/27 | 1/5 | 1 |
+
+The pass count does not move. The veto trades one true recall for one false one.
+It costs `en-hard-024` and it buys `ru-silent-029`:
+
+    ru-silent-029
+      query  "во сколько отходит поезд"
+      note   "погулял вдоль реки"        0.835, margin 0.019
+
+The second case counted as silenced by the gate is `ru-home-026` at margin
+0.001, which the margin gate stops. The veto has nothing to do with it.
+
+## Why no lexical rule separates the two
+
+`en-hard-024` and `ru-silent-029` are in the same lexical class. Both questions
+share zero content words with their hit, and neither carries a first-person
+marker. The scores sit on top of each other, 0.826 against 0.835, and so do the
+margins, 0.023 against 0.019. Only one thing separates them. A screen problem
+and a swapped display cable are the same event. A train and a river walk are
+not. The embedder scores that difference at nine thousandths.
+
+So the signal is semantic and the gate is lexical. Any rule cheap enough to sit
+in `RecallAllowed` and strong enough to recover `en-hard-024` also re-admits
+`ru-silent-029`, which puts false recall back to 1/5.
+
+One near-miss rule was tried on paper and rejected: let the veto pass when the
+hit itself is first person. It works on these two, because the English note says
+"i swapped" and the Russian note says only "погулял". It is backwards as a
+principle. A first-person note is exactly the personal note the veto keeps away
+from a world question. The rule would weaken the veto where it was designed to
+bite. It survives here only because Russian drops the pronoun.
+
+## Decision
+
+Accept the loss. `en-hard-024` stays silenced and false recall stays 0/5.
+
+The way out is a reranker, not a longer word list. Recall@3 is 85.2% against
+recall@1 at 70.4%, so the right note is usually in the returned set and ranked
+wrong. That is where the remaining points are, and it is not this task.