[Bug]: a malformed legacyEditor envelope crashes every clip edit with regions.filter is not a function

[EtienneLescot]

Summary

A project file whose legacyEditor envelope holds a non-array where an array is expected loads without complaint, then throws regions.filter is not a function on the first clip edit. Every clip delete / move / duplicate / source-range edit routes through the same unguarded function.

Cause

legacyEditorSchema is z.object({}).passthrough(), so zod validates nothing inside it — any shape survives loadProject.

mapAllRegionCollections (src/lib/ai-edition/document/timeline.ts:243-272) then assumes each envelope is an array and calls .filter() on it.

The migration path already knows better: upgradeV4DocumentToV5 (src/lib/ai-edition/schema/index.ts:577-582) guards these same fields with Array.isArray. The runtime path doesn't.

Reproduction

Hand-edit a project file (or load one written by an older/third-party build) so that:

{ "legacyEditor": { "speedRegions": "oops" } }

The project opens fine. Delete any clip → TypeError: regions.filter is not a function, and the editor is stuck until the file is repaired by hand.

Suggested fix

Mirror the guard the migration already uses:

const speedRegions = Array.isArray(legacy?.speedRegions)
  ? (legacy.speedRegions as StoredRegion[])
  : undefined;

…and likewise for cameraFullscreenRegions and the other envelopes.

Tightening legacyEditorSchema so the arrays are actually validated at load time would be the deeper fix — the passthrough is what lets a malformed document get this far — but the local guard is the cheap correct step and matches what upgradeV4DocumentToV5 already does.

Context

Found while reviewing #307, which changes a line inside this function's callback. Pre-existing and unrelated to that fix, so filing separately.