docs: n=1540 product-recall handoff for next-cycle planning

[sdntsng]

Summary

Temporary commit of a reviewer handoff for the in-flight n=1540 product /recall measurement on SHA bbe55f7 (PR #184 already on main/dev). No product behavior change.

The working tree on bbe55f7 was otherwise clean (n=1540 work was in /tmp and the live DB). This PR persists the handoff note plus local enqueue/score helpers so a planner can resume without reconstructing the pitfalls.

Changes

• docs/research/handover-n1540-agent-2026-09-11.md — operational truth: landed SHAs, P84/11.4% pins, live tenant locomo-n1540-bbe55f7, harness bugs (staging recall URL, FIFO extract, 8h search-settle), kill list, what the next plan must contain.
• evals/tools/n1540_preingest.py — enqueue all 10 LoCoMo convs with wait_jobs=False so extract can run per-subject in parallel.
• evals/tools/n1540_run_product_recall.sh — skip-ingest product /recall scorer; refuses a non-local product-recall base URL.

Test plan

• Working tree had no leftover-covering product diffs; this is docs + eval helpers only.
• gofmt -l . N/A (no Go).
• go vet ./... / go test ./... not required for this docs PR.
• Live n=1540 extract still draining on this VM (API :18200, 10 workers); score with the helper after extraction_jobs pending+in_progress hit 0.
• Cycle-closeout + README 11.4% replacement only after JSON exists.

Linear / tracking

Follow-on to PR #184 merge / main FF. No new Linear id.

Risk / follow-ups

• Handoff is not a pin. Published product /recall stays 11.4% until n=1540 JSON lands.
• Do not merge leftover-covering PRs S1–S5 compiler/answer/alias/KU (split from mixed S0 PR) #133/S0–S5 SOTA execution increments (stratified harness + compiler/answer/hop/LME) #131/fix(recall): instrument-purpose leftover covering over help flood #143/P29: demote single-token attended compiler echoes (ranking only) #145.
• Operator accepted listing n=1540 as true product scoring even if extract was partial on an earlier attempt; prefer drain-to-zero on this tenant.
• Do not commit /tmp/brainy_n1540.env (injected keys).