every turn persists its decision record, and the reversal is written down (V-629)

internal/decision kept a 25-turn ring and persisted nothing, on the argument
that a turn record is read minutes later or never. The owner reversed that on
06-08-2026: the routing heads cannot be fitted or calibrated without real
utterances, and V-631 measured that 9 of the 31 modes have no seed example at
all. docs/plans/21-persisting-the-routing-trace.md carries the reversal, and
CLAUDE.md now says which of its own sentences stopped being true.

cmd/mavend/routingtrace.go is a second sink beside the ring, which did not move:
the ring is still what /trace reads and still what a test with no store gets. A
failed insert is logged and swallowed, because a trace must never change what he
hears. traceSink keeps a nil store out of the interface, since a typed nil
pointer there would pass the nil check and die on the first turn.

Four fields the ring never carried: which reach the turn arrived on, whether
stage 0 answered before the classifier was consulted, which encoder body was
live (the same EmbedderID string the vector marker uses), and what the action
stage actually did.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0117tgnmbgZpHVV3XSNw8Qua

docs/plans/21-persisting-the-routing-trace.md

@@ -0,0 +1,60 @@
+# Plan: persist the routing trace
+
+**Owner's call, 06-08-2026. Vikunja #629, umbrella #628.**
+
+**Verdict: the per-turn decision record is now written to the database.** That reverses a
+written decision, which is the point of this file. It is not an incidental telemetry
+feature and must not be read as one.
+
+Last verified: 06-08-2026 @ 799cf55
+
+## What the old decision said
+
+`internal/decision` kept a 25-turn in-memory ring and persisted nothing. The argument was
+in `CLAUDE.md` and it was a good one. A turn record is read minutes after the turn or
+never, so a table that outlives the diagnosis buys nothing. His words did not belong in it.
+
+## Why it reversed
+
+V-546 replaces the generative router with classification heads on e5-small. Fitting
+prototypes and calibrating a distance both need real utterances. V-631 measured how few
+there are. Nine of the 31 modes in `internal/modes` have no seed example at all, and they
+are exactly the nine with no deterministic matcher. The seed corpus cannot supply them. A
+seed row is a phrase someone wrote for a matcher, not a thing he said. The 202 generated
+contrast pairs were tried and cost four points of fixture accuracy.
+
+So the choice was between no routing heads and a persisted trace. The owner chose the trace.
+
+## Retention, and why it is two answers
+
+**Raw trace: 14 days.** `routingTraceRetention` in `internal/store/routingtraces.go`. That
+is the life of a diagnosis with room for a weekend. The bound is an age and not a row
+count. The useful question is what she did this week, and a busy Tuesday must not push last
+Friday out.
+
+**A correction: indefinite.** The owner corrects a turn on `/chat` (V-630). The pair is then
+promoted out of the trace into a seed-shaped row and kept, because a label is not a
+transcript. What stays in `routing_traces` is the transcript. It expires on the same 14
+days as every other row, corrected or not.
+
+## What keeps it safe
+
+The utterance is stored in clear. A 384-dimension vector of a short sentence is
+substantially recoverable. Storing vectors instead would be a privacy claim we cannot
+support, and making it would be worse than staying silent.
+
+- **Nothing here leaves the box.** The rule that the owner's notes and facts are never
+  search input covers this table too. No query source reads it, and no upstream engine can.
+- **Retention is enforced on write.** `WriteRoutingTrace` prunes every 64th row, which is
+  hours at human rate.
+- **Deletion already exists.** `Store.Wipe` drops every table the database reports, so
+  `mavend -wipe -confirm-wipe` covers this one with no list to edit.
+- **The ring did not move.** It is still what `/trace` reads and still what a test with no
+  store gets. The table is a second sink beside it. A failed insert is logged and swallowed,
+  because a trace must never change what he hears.
+
+## What is not decided
+
+Whether some utterances must never be promoted into a durable label, no matter how badly
+they routed. That is a content rule and it belongs beside the personal boundary, not in the trace
+writer. Recorded here, left to the owner.