fix(studio): resolve cross-cutting SDK-cutover review findings

[vanceingalls]

Addresses the cross-cutting findings from the §3.0–§3.5 SDK-cutover stack review. The isolated keyframe-merge fix (#11 core) was folded into #1470 where it belongs; everything here is the shared/architectural set that can't be split without breaking intermediate builds.

Root causes fixed

• Two writers → one. Disabled the SDK persist queue (useSdkSession); Studio's writeProjectFile is the sole writer. Kills double-write, duplicate-on-write-throw, and the undo flush race.
• Stale in-memory SDK doc. forceReloadSdkSession() after every server-authoritative write (timeline delete/asset-drop/move-fallback, GSAP commitMutation, DOM server path, element delete) so a later SDK edit can't serialize the pre-write doc and revert it. Replaces the dead onDomEditPersisted hook.
• No-op detection. sdkCutover persist fns compare serialize() before/after; an unchanged dispatch (stale id, unsupported op) returns false → server fallback, no phantom undo entry. Subsumes the inconsistent getElement guards.
• batch() everywhere. All GSAP/timing/delete dispatches wrapped for atomic rollback on mid-op throw.
• Sub-composition guard. Central wrongCompositionFile check refuses edits whose targetPath ≠ the session's composition.
• @font-face preserved. Skip the SDK path when prepareContent is set (custom-font injection).
• skipRefresh / soft-reload honored. CutoverOptions.skipRefresh + a refresh hook that soft-reloads (preserves playhead via new extractGsapScriptText) and invalidates the panel cache — matching the server path.
• Stable sdkDeps. One memoized deps object shared by the 3 GSAP hooks (fixes the per-render debounce-flush regression; also collapses 3 duplicate interfaces).
• autoId clobber. addGsapAnimation skips the SDK path when an id was just server-assigned.

Known limitation (documented)

Server-fallback element delete does not GSAP-cascade like the SDK path (ponytail note + upgrade path in useElementLifecycleOps); the fallback only fires for elements absent from the SDK doc.

Verification

bun run build clean; sdkCutover 40/0, gsapWriter.acorn 22/0 (+ new sibling-preservation regression test); zero new failures vs baseline in the studio suite.

🤖 Generated with Claude Code

[vanceingalls]

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Learn more

• fix(studio): resolve cross-cutting SDK-cutover review findings #1471 👈 (View in Graphite)
• feat(studio): route GSAP keyframe add through SDK (§3.5 PR2) #1470
• feat(studio): route GSAP tween add/update/delete through SDK (§3.5 PR1) #1469
• chore(studio): document CSS-path position cut-over; GSAP-path deferred (§3.3) #1467
• feat(studio): route timeline trim/move through SDK setTiming (§3.2) #1466
• feat(studio): route element delete through SDK removeElement (§3.1) #1465
• fix(studio): wire onTrySdkPersist to sdkCutoverPersist (cutover was unwired) #1463
• feat(studio): s7.5 — make sdk cutover always-on, delete shadow scaffolding #1462
• fix(studio): force-reload sdk session after undo/redo bypasses suppress window #1460
• main

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