refactor(studio): extract undo/redo + mix-save to src/undo.js (step 8)

[byrongamatos]

What

Step 8. Moves undo/redo + debounced mix-save out of main.js into src/undo.js:

• _pushUndo / _captureUndoNow (debounced vs immediate snapshots, §VI), _updateUndoButtons
• _applyRestoredMixState (re-applies a snapshot to the live audio graph + re-renders)
• _debounceSaveMix + _saveMixSettings (debounced server persist) + MAX_UNDO

_applyRestoredMixState imports the lower layers it drives (audio-graph _applyAllMixToLive/_getAudioCtx, viz _drawAllCursors, render _renderTracks) — one-way, no cycle. _saveMixSettings moved alongside its only caller (Codex preflight caught that leaving it behind = ReferenceError after the debounce). window.studioUndo/studioRedo stay in main and call the imported helpers. main.js 2076 → 2028.

Move-only, no behaviour change.

Tests

node --test 15/15, pytest 25/25. Codex preflight: 0 (after the _saveMixSettings fix).

Behavioral — on-device: change a mix control (persists after ~1s), undo/redo restores audio + UI, mix survives a reload.

Summary by CodeRabbit

• New Features
  • Added improved undo/redo support for mix changes, including smoother handling of continuous adjustments.
  • Mix settings are now saved more reliably after edits, with automatic delayed updates.
• Bug Fixes
  • Restored mix changes now reapply correctly and keep the on-screen controls in sync.
  • Undo/redo controls update properly after changes and restores.

[Copilot]

Pull request overview

This PR is part of the ongoing ES-module migration and refactors the Studio code by extracting undo/redo handling and the debounced server mix-save logic from src/main.js into a dedicated module src/undo.js, with the goal of keeping main.js smaller while preserving existing behavior.

Changes:

• Added src/undo.js containing undo/redo snapshot helpers, restored-state application, and debounced mix persistence.
• Updated src/main.js to import the extracted helpers and removed the inline implementations.
• Documented the refactor as “step 8” in CHANGELOG.md.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/undo.js	New module that owns undo/redo snapshot capture, restored-state application, and debounced mix-save persistence.
src/main.js	Switches to importing undo/mix-save helpers and removes the inlined implementations.
CHANGELOG.md	Adds an entry describing the step-8 extraction/refactor.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[coderabbitai]

Caution

Review failed

The pull request is closed.

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: f31a73b5-5fa5-44c1-95d8-ee091a0909b1

📥 Commits

Reviewing files that changed from the base of the PR and between f63c01a and 54bac45.

📒 Files selected for processing (3)

• CHANGELOG.md
• src/main.js
• src/undo.js

---

📝 Walkthrough

Walkthrough

Undo/redo snapshotting, restoration, undo-button UI updates, and debounced mix-settings persistence logic are extracted from src/main.js into a new src/undo.js module. main.js now imports these helpers instead of defining them. CHANGELOG.md documents this as a move-only change.

Changes

Undo/Redo Module Extraction

Layer / File(s)	Summary
Snapshot capture and stack management src/undo.js	Adds _pushUndo (debounced) and _captureUndoNow (immediate) functions that serialize mix state, deduplicate against last snapshot, enforce MAX_UNDO depth, clear redo stack, and update undo/redo button UI.
Snapshot restoration and mix persistence src/undo.js	Adds _applyRestoredMixState to restore a snapshot (re-render tracks, apply to live audio, trigger save, redraw cursors) and _debounceSaveMix/_saveMixSettings to POST mix settings to the server with a 1-second debounce.
main.js wiring src/main.js	Imports _pushUndo, _captureUndoNow, _applyRestoredMixState, _debounceSaveMix from ./undo.js and removes the corresponding previously in-file implementations, including MAX_UNDO and the old _saveMixSettings flow.
Changelog documentation CHANGELOG.md	Documents ES-module migration step 8 as a move-only extraction of undo/redo and mix-save logic to src/undo.js.

Estimated code review effort: 3 (Moderate) | ~25 minutes

Possibly related PRs

• got-feedBack/feedBack-plugin-studio#18: The extracted undo.js logic relies on S.undoStack/S.redoStack/S.mixState fields introduced by this state-container refactor.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/es-module-split-undo

---

_{Comment @coderabbitai help to get the list of available commands.}