fix(editor): rigid group-move — snap once, move the whole selection

[ChrisBeWithYou]

What & why

Tester bug: "mass moving notes seem to have a limit, only a few of selected
notes get moved."

Root cause: the live move loop snapped each note's absolute time
independently (snapTime(origTime + dt) per note). With snap on (the default),
a small group drag quantised every note to its own nearest grid line — so only
the notes already near a line crossed it, the rest snapped back and appeared
not to move, and the selection's internal timing was silently destroyed.

How

• _groupTimeDeltaPure (@pure:group-time-delta) snaps the primary
  (grabbed) note's target once, takes that as the single group delta,
  applies it uniformly to every selected note, and clamps it so the earliest
  note can't cross t=0. The group moves rigidly, snaps as a unit, and keeps
  its internal spacing. snapFn is injected (pure/testable).
• onMouseDown records the grabbed note's time (primaryOrigTime); the move
  handler computes one snappedDt and applies origTimes[i] + snappedDt to
  every dragged note (keys + guitar-lane branches).
• DAW-style grid unlock: hold Alt while dragging to move free of the
  grid (verified against Ableton's Alt / Logic's off-grid step). Only the time
  grid is bypassed — vertical stays semitone/string-quantized.

Tests

tests/group_move_snap.test.js (6) — single-note snap unchanged, a group moves
by one rigid delta with spacing kept, the delta anchors on the grabbed note (not
note[0]), the t=0 clamp, snap-off raw delta, and the adversarial guards. All
fail on main. Full JS suite green (72/72).

Summary by CodeRabbit

• Bug Fixes

  • Fixed multi-note dragging with snap enabled so the entire selection applies one consistent, clamped time offset anchored on the grabbed note, preserving relative spacing.
  • Prevented grouped moves from looking partially unmoved or desynchronized, including correct behavior near the start of the timeline.
  • Added DAW-style grid unlock: hold Alt while dragging to move without grid snapping.

• Tests

  • Added automated coverage for grouped snap behavior, spacing preservation, clamping at t=0, and snap-off (no-snapping) moves.

[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: 6e763e69-d1ca-424a-933f-ff1c3e527484

📥 Commits

Reviewing files that changed from the base of the PR and between 5887b59 and e2fa980.

📒 Files selected for processing (3)

• CHANGELOG.md
• screen.js
• tests/group_move_snap.test.js

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📝 Walkthrough

Walkthrough

Adds group-move snapping that anchors on the grabbed note, applies one clamped delta to the whole selection, and supports Alt-drag to bypass grid snapping. Also adds tests and a changelog note.

Changes

Group time delta snapping fix

Layer / File(s)	Summary
Group time delta helper screen.js	Adds _groupTimeDeltaPure, a pure function that snaps a delta once using the primary/grabbed note as the anchor and clamps it so the earliest note cannot cross t=0.
Drag wiring for group snapping screen.js	Stores primaryOrigTime on drag state and replaces per-note time snapping in both move paths with one shared snappedDt, including Alt-key snap bypass.
Tests and changelog tests/group_move_snap.test.js, CHANGELOG.md	Adds tests for rigid group movement, anchoring, clamping, snap-off behavior, and edge cases; documents the fix and Alt-drag grid unlock.

Estimated code review effort: 3 (Moderate) | ~20 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: snapping once and moving the selection rigidly as a group.
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 fix/editor-group-move-snap

Warning

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screen.js

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