Fix video_thumbnail_animation undefined frame size and zoom 0

[11bit]

Two defects found while auditing the codebase for the same class of bug as #89.

1. video_thumbnail_animation could emit a literal undefined

build({ vta: { step: 10, delay: 100, frames: 5 } })
// before: "vta:10:100:5:undefined:undefined"

frame_width and frame_height were guarded with if (… !== undefined) and then interpolated into the template unconditionally, so omitting them produced a malformed URL with no error.

The docs list both as required (Default: 0:0:0:0:0, no (optional) marker) and the VideoThumbnailAnimation type declares them as required numbers, so they are now validated like step, delay and frames. TypeScript callers were already prevented from hitting this; vanilla-JS callers now get video_thumbnail_animation.frame_width is not a number instead of a broken URL. video_thumbnail_tile already handled its five numeric arguments this way.

2. zoom: 0 was silently dropped

getOpt used options.zoom || options.z, so a zoom of 0 fell through to undefined, test() returned false, and the option vanished from the URL without an error. The guard was also { min: 0 }, which would have accepted 0 had it ever been reached — while the docs state zoom values "must be greater than 0".

Now getOpt uses ??, test checks !== undefined, and the guard uses minEqual, so 0 is rejected for zoom, zoom_x and zoom_y.

Test-visible change: the error message for non-positive zoom values changes from can't be less than 0 to can't be less or equal than 0. Two existing assertions were updated accordingly — the only existing tests this PR modifies.

Verification

• tsc --noEmit clean, eslint src tests clean
• vitest run → 97 files / 1100 tests passing (5 new: missing frame_width, missing frame_height, zoom: 0 rejected, zoom_x: 0 rejected, test({ zoom: 0 }) truthy)

Related

Follows #89. A third finding from the same audit — falsy values skipping validation in ~9 modules — is a mechanical sweep and comes in a separate PR.

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https://claude.ai/code/session_01G8Aa3xeVUCaxKtQJDzZhMo