[chubes4]

Related issues

Fixes #3458.

How AI was used

Claude (via the Pi coding agent in a Roadie session) traced the root cause, wrote the change and tests, and ran the verification below on the Lab runner. A Homeboy cook attempt stopped at promotion (homeboy#16453, fixed after the installed release), so this was finalized outside Homeboy with the operator's authorization.

Proposed Changes

• Container inner content is always block markup (catalog.ts recurseInner). When no catalog pattern matches inside a callout, details or media-text, the inner HTML becomes the same html-fallback island an unmatched top-level element gets. It is no longer raw HTML, which the container's re-save discards.
• Callout groups keep the authored classes (paw-card, notice callout). They are no longer replaced with an is-style-<word> class that no theme registers.
• Canonicalize keeps content (wp/canonicalize.ts). If an invalid block's re-save would drop words or media sources it showed, the block is kept as written. serialize() emits an invalid block's original source, which is what the editor does until a person recovers it. The block is listed in FixResult.preservedBlocks and reported as an invalid_block_preserved warning, so the status is success_with_warnings.
• The 4 affected compose fixtures (generic-callout, generic-details, generic-media-text, sample-callout-div) are updated. Each new expected output canonicalizes with no validation issues.

Card contents now become a group containing an html island, not image/heading/paragraph blocks. Lowering the ordinary elements inside an island into real blocks belongs to the raw conversion path and is left for a follow-up. This PR removes the content loss.

Testing Instructions

cd packages/blocks-engine && pnpm typecheck && pnpm test

• src/__tests__/content-preservation.test.ts (20 tests) converts the issue's cards, a card grid, a callout, an accordion item and every compose fixture through convertReport on the real worker. It checks that the output keeps the input's words and media sources, and that none depend on the canonicalize guard. Guard cases cover a top-level group and a group nested in columns, plus a lossless invalid paragraph that is still fixed.

• Mutation check of the new tests plus the compose goldens (30 tests):

  Variant	Failing tests
  trunk	16
  catalog change reverted	13
  guard disabled	3
  raw inner HTML restored	12
  class replaced with is-style-card	2

• Full suite on Lab: 523 passed. 3 tests in 2 files fail identically on unmodified trunk in that checkout, because it has no pnpm build bundle and no php-transformer vendor/ (wp-runtime-bundle, associated-label-save-validity).

Pre-merge Checklist

• Tests added and failing on trunk
• Typecheck clean
• CI green