docs(pm-dispatch): spec-semantic fable clause, native issue-typing + Bug-first tiebreaker, retire shift-end skill-suggestion list (#7971)

Closing consolidated skills batch (three maintainer rulings of 2026-08-12):

- Model tiering gains mandatory clause 2: cards altering the contract's
  accept/reject behavior or growing its public surface (the domain:spec
  semantic lane) dispatch at claude-fable-5, no downward discretion;
  spec-surface / spec-tooling / downstream-adaptation tiers explicitly
  unchanged. Criterion cites the existing adjudication boundary test and
  the one-package-three-seats split - no second copy.
- Triage duty: native issue types Bug/Feature/Task typed on every card by
  the triage seat as single authoritative producer; Bug without a named
  location or repro path does not enter pm:queue; no mass backfill. Three
  named consumers: adjudication routing, release-board type:Bug query,
  and the new Bug-first tiebreaker within ordinary queue items (a
  tiebreaker, not a priority ladder).
- Seat-exit checklist: the mandatory shift-end SKILL update-suggestion
  list is retired; shift-end reporting narrows to three classes (wrong or
  missing principle / mechanizable item / platform-fact row), default
  zero; lessons-learned prose is no longer admissible into skill texts.

Ratchet headroom 0: all additions offset in-place by compressing touched
sections whose operational detail already lives in references/ (seat-post
protocol, release board ops, cloud-card lessons, dispatch runbook).


Claude-Session: https://claude.ai/code/session_012Gg6rMAti8ZaueWb6BRsDn

Co-authored-by: Claude <noreply@anthropic.com>

Author: os-zhuang