docs: plan the worktree store, after two reviews and a planning interview

[REPPL]

Plans the worktree store: itd-2609091014076309 moves from drafts/ to planned/, together with its spec, spc-2609301811532881.

What changed

• Two adversarial reviews ran before the interview: one on design and feasibility, one on record discipline. Their findings are applied:
  • the belonging proof that prune deletes by
  • refusals for a locked worktree, the caller's own directory, and a live build lane
  • one store primitive shared with the build loop, so the intent now refines itd-2609201916151817
  • typed links corrected
• The planning interview's rulings are in the intent's ## Decisions:
  • the verb is abcd ahoy worktree add|list|prune
  • "merged" means the forge's pull-request state or patch-equivalence, and no forge is needed
  • a quiet unmerged worktree is surfaced with a dossier and removed only when named (--yes <name>), never forced
  • a reclaimed worktree's local tier is moved to ~/.abcd/notes/<root-sha>/<timestamp>-<name>/, redacted and with a manifest, and is never deleted
  • add is a host-run step on the plugin page
  • worktree directories are 0o700
  • exit codes are 0, 1 and 2
  • the product thinker accepted all 21 criteria
• The spec body carries the design, one line per criterion, seven steps, and the footprint.
• The brief's internals gain the store primitive.
• itd-148 keeps its mint-visibility criterion as peer awareness (Decision 5).
• The decomposition run is graded into the calibration note, and DECISIONS.md records the interview.

Checks

• make preflight is green on 536409e.
• abcd intent ready itd-2609091014076309 reports READY.

Records only, no code. The build follows once this lands.

Assisted-by: Claude:claude-opus-5-5