feat(devx): ratchet check:engine-double-contract's consumer-seam population (#9708) (#10502)

`SEAMS_DISCOVERED` fires at zero and never at one-fewer-than-yesterday, and
`REFUSES` iterates the discovered set — so a seam that LEAVES the set was
judged by nothing. Measured by ablation on the card: deleting the `remove()`
seam from packages/mcp/src/stdio-data-bridge.ts took the census down one and
left the script printing OK, exit 0.

The shape was chosen on a measurement rather than inherited from #9680: this
file's own scanAllSeams, unmodified, replayed over 58 daily trees of main
(2026-06-25..2026-08-21) found 3 membership changes — two moves and one
arrival — 2 refusal-state transitions SHARED_ONLY already governs, and 0
outright departures. One event a fortnight against a site of the
#4435/#5138/#5581/#7867 family silently ceasing to be judged.

- scripts/engine-double-contract.seams.json: the enumerated population, keyed
  (file, fn, verb) — not on the line, so an unrelated edit above a seam cannot
  churn it. Written by the same `--write` as the pinned ledger.
- SEAMS_RETAINED separates four loss worlds; `unrecognised` (the function is
  still declared and the scan no longer reads a seam in it) refuses the
  regeneration remedy the other three offer, because regenerating there would
  record a blind spot as intended.
- The seam list now prints on every run, green or red, and says the population
  is ratcheted rather than merely counted.


Claude-Session: https://claude.ai/code/session_01DdCnBGcHeufjrq7drTD3wt

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

Author: os-zhuang