editorApplyOffset only shifts current arrangement - poisons dataset.applied for +Keys/+Drums imports

[mogul]

Restored from slopsmith/slopsmith-plugin-editor#56 — original issue, opened by @cambordas on 2026-06-14.
[restored-from: slopsmith/slopsmith-plugin-editor#56]

Bug: editorApplyOffset only shifts the current arrangement's notes

Steps to reproduce

1. Create a song from a GP file with two or more arrangements (e.g. Lead + Rhythm)
2. Apply an offset (e.g. +1s) via the offset toolbar while on the Lead arrangement
3. Switch to Rhythm - notes are still at the original position (not shifted)
4. Type 2 in the offset field to shift Rhythm -> dataset.applied is now 2
5. Open +Keys or +Drums and import

What happens

Audio:   |----♪----♪----♪----|
Lead:    |----♪----♪----♪----|  <- user applies offset +1 here
Rhythm:  |----♪----♪----♪----|  <- NOT shifted (still at original position)
         0    1    2    3

User switches to Rhythm, sees it's broken, types 2 to fix it:

Audio:   |----♪----♪----♪----|
Lead:    |----♪----♪----♪----|  ✓  (at +1)
Rhythm:  |----♪----♪----♪----|  ✓  (at +1, but dataset.applied is now 2)
         0    1    2    3

_effectiveAudioOffset() = S.offset + dataset.applied = 0 + 2 = 2

Next +Keys or +Drums import uses audio_offset=2 - lands 1s past everything else:

Audio:   |----♪----♪----♪----|
Lead:    |----♪----♪----♪----|  at +1
Rhythm:  |----♪----♪----♪----|  at +1
Keys:    |----♪----♪----♪----|       at +2  ✗
         0    1    2    3

Pattern: each arrangement the user manually fixes adds 1 to dataset.applied,
pushing every subsequent import 1s further off (+2, +3, +4 ...).

Root cause

editorApplyOffset shifts only S.arrangements[S.currentArr].notes.
Beats and sections are already shifted globally - notes were missing the all-arrangements loop.

Possible fix

-    const nn = notes();
-    for (const n of nn) n.time += delta;
+    for (const arr of S.arrangements) {
+        for (const n of (arr.notes || [])) n.time += delta;
+        for (const ch of (arr.chords || [])) {
+            ch.time += delta;
+            for (const cn of (ch.notes || [])) cn.time += delta;
+        }
+    }

All arrangements shift together in one apply - dataset.applied stays stable,
every subsequent +Keys / +Drums import gets the correct audio_offset.

[mogul]

@cambordas commented on 2026-06-14:

Confirmed on version 1.5.0 (commit 746f5f6).