[wonjangcloud9]

Context: I've been using HyperFrames every day for the past two weeks to make Korean Shorts and long-form videos, and it's been great to work with. This PR is one of a batch of fixes for things I ran into along the way, so you'll see several PRs from me at once — sorry for the pile-up, and thanks for your patience. Each one is reproduced on current main, independent of the others, and can be reviewed, merged or closed on its own.

What

• skills/hyperframes/SKILL.md ("Keep it editable"): "Copy, brand colours and swappable media are variables (data-var-text, data-var-src, var(--id))." → "…are variables: declare each in data-composition-variables, then bind it (data-var-text, data-var-src, var(--id))."
• skills/hyperframes/references/format.md (Variables): the declare bullet names the attribute (data-composition-variables), the type list adds font and image (both in CompositionVariableType, missing here) and says a video or audio link is a string, and a new bullet says an undeclared bound id silently keeps its fallback (unknown_variable_binding) with a one-line declare-then-bind example.
• scripts/check-core-skills.mjs: hyperframes entry budget 7488 → 7552 B (+64 B, with the usual one-line reason). The entry was at 7481 B, so the new words did not fit otherwise.
• Regenerated skills-manifest.json; one test in coreSkillContent.test.ts.

Why

An agent following the SKILL.md line literally writes <h1 data-var-text="headline">Title</h1> and stops there. On main:

$ hyperframes check --no-cache --json
warning unknown_variable_binding  <h1> binds data-var-text="headline" but no variable "headline" is declared in data-composition-variables, so the binding will silently keep the authored fallback.

The lint catches it and its fix hint is right, but the skill sent the agent there: neither SKILL.md nor format.md's Variables section named the attribute (only the skeleton at the top of format.md shows it). With the declaration added, the same project checks clean (no unknown_variable_binding) and the snapshot shows the variable's default Hello instead of the authored Title.

Related work

No existing issue or PR. Lint rule from #2054 (declarative bindings).

How

Docs only, plus the budget bump. The example lives in format.md rather than SKILL.md to keep the entry within budget.

Test plan

• Reproduced on main (above); verified the documented declare-then-bind form on a real project: check has no unknown_variable_binding, snapshot at 1 s shows Hello.
• coreSkillContent.test.ts: new case asserts SKILL.md names `data-composition-variables` and format.md names `unknown_variable_binding`; fails on main's docs, passes here (15/15 in the file).
• node scripts/check-core-skills.mjs ✓ (7541 / 7552 B), node --test scripts/check-core-skills.test.mjs 12/12, bun scripts/lint-skills.ts no issues, check-skill-mirror OK, oxfmt/oxlint clean, manifest regenerated.
• Documentation updated (this is the documentation)
• Comments follow CONTRIBUTING.md "Comments"

Note for merging: this and the immediateRender: false skill PR both change the hyperframes hash in the generated skills-manifest.json; whichever lands second needs bun packages/cli/scripts/gen-skills-manifest.ts after rebasing. Nothing else overlaps.

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