Document native block support boundaries and correct Accordion history

[noeltock]

Problem

Upstream block availability, headless validity, editable fields and real WordPress behaviour are separate support claims. The Accordion benchmark description also incorrectly attributed its first Core release to 7.1. Closes #119.

Solution

Correct the attribution to WordPress 6.9 and document the tested Tabs boundary plus explicit conditions for deferred coverage. Keep expected trees and measurements unchanged.

Behaviour	Read first	Proof
Accordion release attribution is accurate	dev/benchmarks/specs/accordion/expected.json	Core's 6.9 Field Guide and direct JSON comparison
Support claims match the route and observed evidence	docs/reference.md	Tabs proof in #120; compatibility investigation in #121
Deferred blocks remain deferred	docs/reference.md	Named destination/runtime and persistence requirements for each candidate

Diff

+37 −1 · 2 files · wording only

 Accordion expected.json intent description
- first Core release: WordPress 7.1
+ first Core release: WordPress 6.9
 docs/reference.md
+ intent validity / registered composition / editable fields / runtime evidence
+ tested Tabs page-content boundary
+ explicit promotion conditions for deferred native blocks

Testing & verification

Reviewed revision: 1e26f1a · Python 3, documentation/source review.

• python3 direct JSON comparison passed for accordion, faq-accordion and faq-rich against ff52333: expected trees unchanged; every non-description field in the changed fixture is identical. The FAQ descriptions refer to their target runtime, so they remain unchanged.
• git diff --check passed.
• WordPress 6.9 Field Guide explicitly lists the new Accordion block.
• Prove native Tabs assembly, editing and frontend persistence #120 and Prove generated-block compatibility across WordPress and Gutenberg #121 are merged with all CI green, including the shared WordPress browser proof. The compatibility suite passed on WordPress 7.1, 7.1.2 and 7.1.2 with Gutenberg 24.0.0 using identical ZIP bytes.

Exact-head CI passed on Node 20.19.0/22.13.0/24.0.0, package boundary and WordPress browser proof.

Not verified: no new model benchmark, score improvement, additional block implementation, manual acceptance or release. No new tests are needed for this wording-only change.

Risk / rollout

No runtime, schema, dependency or expected-tree change. Icon, Playlist, Breadcrumbs, Gallery Grid and future proposals retain their scoped qualification requirements.

Detection: compare support wording against the child receipts and run the JSON check. Rollback: revert this PR; no migration.