fix(useObjectUrl): revoke the url the effect created

[rawsun007]

Description

useObjectUrl never revokes anything. The cleanup reads url out of the render closure, and that closure belongs to the render before setUrl applied, so on the first run url is undefined and the if (url) guard skips the revoke. Every URL the hook creates leaks for the lifetime of the page — on unmount, and on every change of object. The docs and the hook's own description say the opposite ("automatically releases the URL via URL.revokeObjectURL() when the source changes or the component is unmounted").

Holding the created URL in a local const gives the cleanup the value it is meant to release. Clearing the state when object goes away is the second half: today the hook keeps returning the URL of an object it no longer has, where the return type says undefined.

The hook had no spec, so this adds one. Three of its four cases fail on main: revoke on change, revoke on unmount, and drop the url when the object goes away. Reverting only index.ts fails exactly those three.

The spec mocks createObjectURL/revokeObjectURL and records both lists, since jsdom implements neither.

One thing worth knowing while writing a test for this hook: renderHook(() => useObjectUrl(new Blob([...]))) loops forever, because a fresh object each render re-triggers the effect that sets state. That is inherent to the dependency and not something this PR changes — the docs example holds the file in state, which is the correct usage. The spec uses two module-level blobs.

verification: pnpm test 419 pass across 71 suites, eslint and tsc --noEmit clean.

Type of Change

• Bug fix
• New hook
• Enhancement to existing hook
• Documentation update
• Other (please describe)

Checklist

• I have read the Contributing Guide
• I have read and understood every line of this diff myself, including any AI-written parts (AI usage policy)
• My code follows the project's coding style
• I have added tests for my changes
• All existing tests pass
• I have updated the documentation

the docs already describe the behaviour this restores, so there was nothing to change there.

disclosure, and the reason the AI-policy box is unticked: written by Claude Opus 5 running in Claude Code, on my machine and under my direction. i have not read the diff line by line myself yet. i will tick that box once i have.

🤖 Generated with Claude Code

[childrentime]

Verified locally: the spec against main's `index.ts` fails 3/4 (revoke on change, revoke on unmount, drop the url when the object goes away); with the fix 4/4 pass and eslint is clean. Holding the created URL in a local `const` means each effect run revokes exactly the URL it created, which also holds up under StrictMode's double invoke.

Non-blocking, for a follow-up rather than this PR: `interface.ts` still types the argument as required (`object: Blob | MediaSource`), while the docs demo passes `File | undefined` and this fix handles `undefined` explicitly. Making it `object?:` (and re-running `gend`) would drop the `as Blob` cast in the spec.