S8a: adaptive micro-window filter selection

Verdict

Observed in the fixture: micro-windows can serve as a bounded control plane as well as a data plane. A versioned selector receives one issue record and may emit only one allowlisted stage: exclude, run(auth-relevance), widen(issue-neighborhood), or escalate. The controller—not selector prose—executes that typed declaration.

Captured artifact: s8a-local-filter-selector-1000-pass-2026-08-09.json.

This is a fixture-backed experiment. Its cost units model relative work (selector=1, semantic filter =10); they are not dollars, tokens, or live-model latency.

Reproduce

go run ./cmd/microcontextdemo \
  -filter-selector-selfcheck -workers 16 \
  -filter-selector-output /tmp/filter-selector.json

go run ./cmd/microcontextdemo -verify-filter-selector /tmp/filter-selector.json

Witness

• 100 easy documentation records use exact field-level exclusion and remain model-free.
• 900 residual records receive selector micro-windows through 16 bounded workers.
• Routing confusion matrix: 972 correct exclusions, 26 correct semantic-filter routes, one correct group-widen route, one correct escalation, zero wrong decisions.
• The relation-dependent record widens to an issue neighborhood instead of guessing from its isolated record; the fixture error escalates instead of becoming a negative.
• Adaptive modeled work is 1,160 units versus 9,000 for deterministic-prefilter-plus-semantic residual processing and 10,000 for always-run, at the same zero-false-negative fixture target.
• An unchanged replay makes zero selector calls and reuses all 900 selector decisions.
• An undeclared stage such as an arbitrary shell request is denied by the catalog contract.

Interpretation

This proves the missing composition from the general operator note: a micro-window can decide which filter should run, whether context must widen, or whether work should escalate. It does not acquire tool authority and it does not hide uncertainty. Real endpoint economics and quality remain for the tuned-baseline program (#6033); read-only tool stages remain #6031.