[ExtraToast]

Summary

Composition now refuses a fragment written at a model version the toolkit cannot read, so a newer fragment can no longer compose with its new fields silently dropped.

• The range from chapter 40: a fragment at another major (either direction), or at a newer minor than the toolkit's, is E_SCHEMA_VERSION_MISMATCH. A patch difference never gates.
• A participant's own error: the Project is held at the fragment it last composed at, even when the digest didn't change, and dormancy doesn't exempt it. The issue body names the rule that fired, the fragment's reference and the version it was written at.
• The Platform document at such a version stops the run, and the message names the rule and the reference.
• Nothing readable left to hold at: if the fragment a Project would be held at, or the one a Rollback names, is itself unreadable, the run stops and names the Project and the fragment. Composing it would drop exactly the fields this check protects.
• The toolkit's model version follows releases: SCHEMA_VERSION carries x-release-please-version, and src/cli/main.ts is listed in extra-files, so release-please writes it beside package.json. chore(main): release 1.0.0 #631 writes 1.0.0 (the cut's Release-As), so nothing changes before 1.0.0.
• Docs: chapter 40's isolation paragraph, the REQ-050 row, and the code removed from the Slice 7: every refusal through check/, the pending codes included #204 pending list in lint-codes.

Decided here

• Ships in 1.0.0 (the maintainer, 2026-10-27). The composer that has to refuse a newer-minor fragment is the older toolkit, so 1.0.0 must carry the check itself.
• Chapter 40 changed meaning in one sentence (the maintainer, 2026-10-27). It used to say a toolkit that no participant's version accepts "holds every Project still and fails nothing". Holding a Project still without composing it would leave its consumers refused. So the run now stops instead, and the version rollout (republish before bumping the estate's pin) avoids it.
• Release-please sets the model version (the maintainer, 2026-10-27), rather than a constant nobody bumps.

Test plan

• npm run verify (2480 tests)
• Compose runs: newer minor, other major in both directions, older minor and other patch admitted, dormant participant, Platform document, unreadable fallback, unreadable Rollback, and the hint
• The CLI test asserts the lock against SCHEMA_VERSION, not a literal, so a 1.1.0 release PR stays green

Part of #195.
Closes #665

[github-actions]

Shape

bucket	files	additions	deletions
production code	2	+88	-20
tests	2	+176	-2
specification	1	+8	-3
documentation	1	+1	-1
tooling	2	+1	-1

Coverage

Baseline: main @ 30bc541.

metric	this branch	main	diff
statements	99.74%	99.74%	0.00
branches	98.57%	98.56%	+0.01
functions	100.00%	100.00%	0.00
lines	99.72%	99.72%	0.00

Lines this pull request changed: 23/23 covered (100.00%).