fix(editor): don't leave the entry landing over a chart loaded via editSong

[byrongamatos]

Opening a song through the library card’s “Open in editor” action, or returning from the 3D highway’s “Edit region” button, could finish the load underneath a full-screen overlay that silently ate every canvas click.

The race

window.editSong navigates and loads in the same tick:

window.editSong = (filename) => {
    showScreen(plugin-editor);   // arms the landing timer
    loadCDLC(filename);            // still fetching when it fires
};

The screen activation arms _editorMaybeShowStartLanding on a setTimeout(…, 80) (and …, 120 when the screen is already active at init()). That function asks “is anything loaded?” only when it fires — so a load still fetching at +80 ms loses the race. And nothing ever took the landing down again: its own buttons were the only remove() call sites.

Why it wasn’t merely cosmetic

canvas.addEventListener(mousedown, onMouseDown);          // canvas
_globalListeners.add(document, mousemove, onMouseMove);   // document

mousemove fires straight through any overlay, so canvas.style.cursor still turns ew-resize over a note’s right edge. mousedown is bound to the canvas, so it is swallowed and the drag never starts. Cursor arms, nothing grabs — with a bg-black/70 scrim sitting there to explain it, if you happened to look.

Fix

Count loads in flight (_editorLoadsInFlight). A load in flight suppresses the landing; starting a load dismisses a landing already up.

A counter rather than a boolean because two loads can overlap — editSong twice, or a fast failure alongside a slow fetch — and the first to settle would otherwise clear a guard the second still needs held. Codex caught that on the first pass.

Verification

A headless harness drives the real flow (window.editSong on a 33 MB feedpak) and asserts both halves. It fails on main and passes here:

check	before	after
empty editor still offers the landing	PASS	PASS
no landing while a load is in flight	FAIL	PASS
no landing after the load completes	FAIL	PASS
elementFromPoint over a note	DIV#editor-start-landing	CANVAS#editor-canvas
canvas mousedown reaches onMouseDown	FAIL	PASS

The first row matters: it fails a “fix” that just deletes the landing.

node --test 88/88, npm run lint 0 errors (10 pre-existing warnings), Codex clean.

Not fixed here

The mousedown-on-canvas / mousemove-on-document asymmetry is the amplifier — any element above the canvas produces the same “cursor works, drag doesn’t” signature. Moving mousedown to document would change click-outside semantics, so it is left alone; the real defence is not leaving overlays around, which is what this PR does.

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes
  • Fixed an issue where opening a song could leave an invisible overlay on the canvas and block clicks.
  • Improved screen loading behavior so the landing overlay no longer appears while content is still loading, and it is dismissed when loading begins.

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ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 281448a and e362206.

📒 Files selected for processing (2)

• CHANGELOG.md
• src/main.js

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📝 Walkthrough

Walkthrough

Adds an _editorLoadsInFlight counter in src/main.js, incremented at the start of loadCDLC and decremented in a finally block, used to suppress _editorMaybeShowStartLanding() while a load is active. Updates CHANGELOG.md documenting the fixed overlay/click-swallowing race.

Changes

Landing Overlay Race Fix

Layer / File(s)	Summary
In-flight load tracking and landing guard src/main.js	loadCDLC increments _editorLoadsInFlight on entry and decrements it in a finally block; _editorMaybeShowStartLanding() returns early when loads are in flight, preventing the overlay from appearing during concurrent loads.
Changelog entry CHANGELOG.md	Documents the invisible overlay/click-swallowing bug and describes the fix suppressing/dismissing the landing during in-flight loads.

Estimated code review effort: 2 (Simple) | ~10 minutes

Sequence Diagram(s)

sequenceDiagram
  participant User
  participant editSong
  participant loadCDLC
  participant editorMaybeShowStartLanding

  User->>editSong: open song from library/highway
  editSong->>loadCDLC: loadCDLC(filename)
  loadCDLC->>loadCDLC: _editorLoadsInFlight++
  editSong->>editorMaybeShowStartLanding: showScreen triggers check
  editorMaybeShowStartLanding->>editorMaybeShowStartLanding: return early (loads in flight > 0)
  loadCDLC->>loadCDLC: finally: _editorLoadsInFlight--

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🚥 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 is clear and accurately summarizes the main fix: preventing the editor landing overlay from remaining over charts opened via editSong.
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.

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• Commit unit tests in branch fix/entry-landing-load-race

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src/main.js

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[Copilot]

Pull request overview

This PR fixes a race where the editor’s “start landing” overlay could remain on top of the canvas when a song is opened via window.editSong (or similar flows), preventing mousedown interactions from reaching the canvas.

Changes:

• Track in-flight editor loads via _editorLoadsInFlight and suppress showing the start landing while a load is running.
• Dismiss any existing start landing overlay when a load begins, ensuring it can’t persist over an active editor session.
• Document the issue and fix in CHANGELOG.md.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/main.js	Adds an in-flight load counter, removes the landing overlay on load start, and prevents landing display while loads are running.
CHANGELOG.md	Records the bug scenario and the behavioral change (landing suppressed during loads; dismissed on load start).

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