feat(editor): loop snap modes — bar / grid / free + no-grid fallback

[ChrisBeWithYou]

Summary

The loop region was bar-snapped only — every drag ran through _barSpanForTimes — and looping was disabled entirely when the chart has no downbeats, which is the exact starting state of a song that wasn't recorded to a click. Transcribers need to loop a phrase before the tempo map exists, loop in subdivisions, and draw completely free loops.

• Bar / Grid / Free segmented control in the loop strip. Bar = whole-downbeat spans (the unchanged default — muscle memory preserved). Grid = loop edges snap through snapTime at the current snap subdivision, honoring the snap on/off toggle (snap off ⇒ behaves as Free — one coherent grid setting). Free = unsnapped.
• Shift-drag = temporary Free in any mode — resolved live each mousemove, so pressing/releasing Shift mid-gesture flips snapping without restarting the drag.
• No-grid fallback: with zero downbeats the strip stays enabled and forces Free ("Drag to set loop (free — no bar grid yet)") instead of showing "No bar grid available".
• Mode-aware relock: regions remember how they were drawn. TempoMapCmd/TempoGridCmd exec+rollback now relock bar/grid loops onto the changed grid (with an end-edge probe so a bar span whose end sits exactly on a new downbeat doesn't grow by a bar), while freely drawn loops are absolute seconds and never move.
• Grid/free regions label as a plain time range instead of a misleading "Bars X–Y"; the mode preference persists as an editor preference (localStorage, never the pack).
• Loop-in-3D verified unaffected: the highway A–B hand-off is seconds-based end to end, so free loops pass through unchanged.

Verification

• node --check screen.js clean
• New tests/loop_snap_modes.test.js — 10 cases via the @pure:loop-region block: bar-span legacy behavior + mode stamping, bar-degrades-to-free with no downbeats, grid snap-fn routing, free normalization/clamping, zero-width create, edge adjust per mode (no edge-crossing), mid-drag mode switch restamps
• All 26 JS test files pass (existing loop_region.test.js untouched and green)

🤖 Generated with Claude Code

https://claude.ai/code/session_01JEoFeTPSnz4NpwwCG52hnu

Summary by CodeRabbit

• New Features

  • Added loop strip snap mode controls (Bar / Grid / Free) with a persistent editor preference.
  • Shift-drag temporarily enables Free, with live snapping behavior flipping while the gesture is in progress.

• Bug Fixes

  • Improved handling when no bar grid/downbeats exist (loop strip remains available; “drag to set loop” stays forced to Free).
  • Mode-aware loop labels now show an accurate time range; tempo-map/tempo-grid edits re-lock Bar/Grid loops without moving Free loops.

• Tests

  • Added coverage for snap/edge-adjustment behavior, mid-drag mode switching, and undo/redo + 3D handoff mode preservation.

[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: 0934d3d6-309e-4bcd-86eb-d7b58700f2bc

📥 Commits

Reviewing files that changed from the base of the PR and between 8b95704 and 70a4291.

📒 Files selected for processing (6)

• CHANGELOG.md
• screen.html
• screen.js
• tests/loop_snap_modes.test.js
• tests/loop_undo_mode.test.js
• tests/pending_view.test.js

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📝 Walkthrough

Walkthrough

Adds three loop snap modes to the loop strip, with mode-aware loop math, persisted mode state, Shift-drag overrides, tempo-edit relocking, pending-view preservation, and test coverage.

Changes

Loop Snap Modes

Layer / File(s)	Summary
Pure loop region and edge-adjust helpers screen.js	Adds mode-aware _loopRegionForDragPure and _loopEdgeAdjustPure supporting bar, grid, and free snapping, storing region.mode.
Loop mode UI controls and rendering screen.html, screen.js	Adds Bar/Grid/Free buttons to the loop strip and updates loop strip rendering and label formatting for free-mode and gridless states.
Snap preference, live mode, and handoff state screen.js	Adds the persisted snap preference, Shift-driven live mode resolution, the global snap-mode setter, loop-mode button refresh, pending-view mode preservation, and loop region mode retention across the Loop-in-3D handoff.
Loop drag and resize wiring screen.js	Updates loop-strip mouse down and mouse move handling to use the live-resolved snap mode and the new pure helpers, and filters interactions on the mode controls from starting loop drags.
Tempo command relocking screen.js	Updates TempoGridCmd and TempoMapCmd to snapshot the prior loop selection, relock on exec after grid changes, and restore the exact saved selection on rollback.
Tests and changelog tests/loop_snap_modes.test.js, tests/loop_undo_mode.test.js, tests/pending_view.test.js, CHANGELOG.md	Adds tests for loop region creation, edge adjustment, tempo undo symmetry, and pending-view mode preservation, and expands the changelog entry for the new loop snap modes.

Estimated code review effort: 4 (Complex) | ~45 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main change: new loop snap modes with a no-grid fallback.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ 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/editor-loop-snap-modes

Warning

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screen.js

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[coderabbitai]

🧹 Nitpick comments (1)

screen.html (1)

133-135: 📐 Maintainability & Code Quality | 🔵 Trivial | 💤 Low value

Consider aria-pressed for the active mode button.

All three buttons share identical base classes with no built-in indicator of which mode is currently selected; this relies entirely on JS toggling classes at runtime (not shown in this batch). Using aria-pressed alongside the visual class toggle would make the active mode discoverable to assistive technology, independent of how the styling is implemented.

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@screen.html` around lines 133 - 135, Add an accessible active-state indicator
to the loop snap mode controls in the button group that uses
editorSetLoopSnapMode; the current selection is only conveyed visually via
runtime class changes. Update the Bar, Grid, and Free buttons to expose their
selected state with aria-pressed, and ensure the value is kept in sync with the
active mode wherever the UI updates the classes.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Nitpick comments:
In `@screen.html`:
- Around line 133-135: Add an accessible active-state indicator to the loop snap
mode controls in the button group that uses editorSetLoopSnapMode; the current
selection is only conveyed visually via runtime class changes. Update the Bar,
Grid, and Free buttons to expose their selected state with aria-pressed, and
ensure the value is kept in sync with the active mode wherever the UI updates
the classes.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 0ecce53f-eadb-491c-bb72-689530971c1c

📥 Commits

Reviewing files that changed from the base of the PR and between e067f25 and 43bc67b.

📒 Files selected for processing (4)

• CHANGELOG.md
• screen.html
• screen.js
• tests/loop_snap_modes.test.js