fix(recall): bind leftover covering to query month when tokens collapse

[sdntsng]

Summary

P21 is already on dest and main (36f39c2 / product fa915fe, 107/180). P22 is a net-positive skip-ingest 180 pin: 108/180 (0.600) on product SHA 9d50bad (pin docs 2287726).

Leftover covering for activity questions that name people and a month was collapsing to weak tokens (activity / together / plan). The rarest-token override then picked generic pep-talk (keep going and have fun) over a dated co-participant plan already in the leftover packet.

The product change is generic. It does not name LoCoMo, does not special-case painting vs kayaking, and does not expand looksWhenEventQuery.

Changes

• leftoverCoveringRareForQuery: when leftover tokens are weak-only after entity/calendar stripping, bind covering to the query month (or year if there is no month).
• leftoverCoverRarestTokens: never rarest-override on weak tokens such as activity.
• Test: dated September plan covers; pep-talk and undated kayaking do not.
• Pin: locomo-s0-diag-mh-135-p22-20260825.md. Cycle closeout section 2026-08-25 — P22.

Test plan

• gofmt -l clean on touched files
• go test ./internal/memory/ (includes new dated-plan leftover covering fixture)
• go vet ./internal/memory/ ./cmd/api ./cmd/worker
• Rebuild /tmp/brainy-api (BRAINY_RECALL_LLM=1). Live holds: yoga locations, destress pottery, Boston garage, Jon banker, McGee's, Ned, childhood items, Max, Thanksgiving, Toronto, basketball, chili+ring-toss, UK, Shadow, Gina internship, first-console, horseback, letter, Caroline biking, James girlfriend April 2022 — 0 hold fails. Gain: September paint plan is live on /recall (probe flagged kayaking leftover on items only; 180 harness is answer-mode).
• Skip-ingest 180 --run-prefix locomo-s0-diag-mh-135-p22 on frozen diag-mh-135: 108/180, flips +1 / −0 vs P21 (conv-49-q52). Temporal 25→26. READER 12→11.

Linear / tracking

• ENG-176 (MH / recall synthesis)
• ENG-168 (parent)

Risk / follow-ups

• Calendar restore only fires when leftover covering tokens collapse to weak-only. Queries that already have distinctive non-weak tokens (Boston, childhood items, when-event bind) held.
• Remaining mass after this READER join is still SH PROOF 20 / RETRIEVAL 29. 108/180 is not 162/180.
• Do not merge compiler-fishing S1–S5 compiler/answer/alias/KU (split from mixed S0 PR) #133.
• Auto smoke JSON/md/manifest stay uncommitted (secret scanner).
• Owner standing approval: FF dest and main after each net-positive 180 pin.