feat(sdk): stage 4 — canUndo/canRedo, removeElement GSAP cascade, override-set cleanup

[vanceingalls]

What

Stage 4 of the SDK — three features that complete the public history/editing API:

1. canUndo() / canRedo() on Composition — exposes the history module's existing state predicates on the public interface so hosts can enable/disable undo buttons without keeping their own patch counter.

2. removeElement GSAP cascade — when removing an element, its targeting GSAP animations are also removed from the script and the change is folded into the same forward/inverse patch pair. Undo restores both the element and its animations atomically.

3. Override-set orphan cleanup — after removing an element, its per-property override-set keys (hf-x.style.fontSize, hf-x.text, etc.) are purged. Keeps T3 serialized override-sets compact and avoids stale key replay on future session opens.

Also extracted selectorMatchesId / cascadeRemoveAnimations helpers to deduplicate the GSAP-target-matching pattern from handleSetTiming and reduce cognitive complexity.

Why

• canUndo/canRedo are needed for Studio toolbar state and any playground UI.
• Without the GSAP cascade, removing a composition element leaves dangling animation code in the script — those animations would run against a null target and generate console errors at runtime.
• Without override-set cleanup, a T3 session opened with stale property keys tries (harmlessly but wastefully) to apply styles to non-existent elements on every open.

Changes

File	Change
src/types.ts	Add canUndo(): boolean / canRedo(): boolean to Composition interface
src/session.ts	Implement canUndo/canRedo delegating to historyModule; add override-set orphan purge in _dispatch
src/engine/mutate.ts	handleRemoveElement GSAP cascade via new cascadeRemoveAnimations / selectorMatchesId helpers; same helpers used by handleSetTiming to eliminate duplication
src/session.test.ts	canUndo/canRedo lifecycle tests (6 cases); override-set orphan cleanup tests (2 cases)
src/engine/mutate.gsap.test.ts	removeElement GSAP cascade tests (5 cases)

Test plan

• bun run test in packages/sdk — 156 tests pass
• Remove an element with targeting GSAP tweens; verify script no longer references that element
• Undo the removal; verify element AND script are restored atomically
• comp.setStyle(id, ...) then comp.removeElement(id); verify getOverrides() shows no id.* keys
• comp.canUndo() returns false before mutations, true after, false after undo back to start

🤖 Generated with Claude Code

[vanceingalls]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• feat(sdk): stage 6 — sub-composition scoped ids (F9) #1434
• feat(sdk): stage 5 — export adapter factories from package root #1432
• docs(sdk-playground): accurate README with stage coverage and CanResult #1429
• feat(sdk): stage 4 — canUndo/canRedo, removeElement GSAP cascade, override-set cleanup #1431 👈 (View in Graphite)
• feat(sdk): can() returns CanResult; T4 dispatch-boundary tests #1426
• fix(sdk): fs adapter flush() tracks in-flight writes; add to T13 contract suite #1425
• feat(sdk): file-backed fs adapter + setTiming GSAP-script sync; add sdk-playground #1423
• refactor(core): swap studio-api read path from recast to acorn parser (T6e) #1392
• feat(core): parse-parity suite for acorn parser (T6d) #1370 : 1 other dependent PR (#1379 )
• feat(core): acorn GSAP write path — magic-string offset-splice (T6c) #1369
• feat(core): acorn GSAP read path with T6b differential corpus tests #1368
• main

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