feat(editor): section completeness strip

[ChrisBeWithYou]

Summary

A thin band at the top of the lane area tints each section by whether the active arrangement has notes in it — an at-a-glance "where is this chart still empty" while working through a long song. It pairs naturally with the now-undoable sections in #104.

Ambient and neutral by design (per the charrette's gamification seat: descriptive, not a score): a gentle blue where there's content, a faint wash where there isn't — no percentage, no red, nothing to click. Drawn under the existing section lines/labels, so there's no layout change and no new chrome.

_sectionCoveragePure computes each section's [start, nextStart) span (the last section runs to the song duration, or open-ended when duration is unknown) with a half-open boundary rule — a note exactly on a boundary belongs to the later section. Sections are sorted defensively and non-finite start_times dropped.

Verification — held to the testing habits

This is a display feature, so there's no undoable command to round-trip; the habits that bite are adversarial inputs and proving the helper uses all its arguments.

• tests/section_coverage.test.js (8 cases) drive the real _sectionCoveragePure: per-span content detection, half-open boundaries (a note at t=4 lands in [4,8) not [0,4)), last-section-runs-to-duration, open-ended unknown-duration, sorted + dropped-NaN sections, a note before the first section counts for none, degenerate []/null/NaN no-ops.
• Proven to use both arguments: different note sets → different coverage; different duration moves the last span's end.
• node --check clean; all 26 JS test files pass.

🤖 Generated with Claude Code

https://claude.ai/code/session_01JEoFeTPSnz4NpwwCG52hnu

Summary by CodeRabbit

• New Features
  • Added a “completeness strip” to the top of the section lane to tint sections based on whether they contain notes.
• Bug Fixes
  • Improved coverage/tint accuracy using boundary-aware interval logic, including correct handling for the final section and unknown/zero duration.
  • Ensures the strip updates live during note moves and refreshes correctly after committed edits.
  • More resilient behavior for incomplete or invalid section timing inputs.
• Tests
  • Added coverage-math and memoization/invalidation tests to lock down interval semantics and rendering behavior.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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Reviewing files that changed from the base of the PR and between e860e89 and dc8431b.

📒 Files selected for processing (1)

• tests/section_coverage.test.js

🚧 Files skipped from review as they are similar to previous changes (1)

• tests/section_coverage.test.js

---

📝 Walkthrough

Walkthrough

This PR adds a section completeness strip in screen.js: section coverage is computed from active note times, cached across draws, rendered as a tinted lane band, and invalidated after committed edits. A new test suite covers the pure coverage logic and related source-level behavior, and CHANGELOG.md documents the feature.

Changes

Section Completeness Strip

Layer / File(s)	Summary
Coverage computation screen.js	Adds _sectionCoveragePure() and _currentNoteTimes() to derive per-section {start, end, hasContent} from section times and active note timestamps.
Memoized strip rendering screen.js	Adds _sectionCoverage() caching, draws the completeness tint bar in drawSections(), and bumps _coverageEditGen in _afterEdit() to invalidate cached coverage after edits.
Coverage tests tests/section_coverage.test.js	Adds a Node test suite that extracts the pure helper and checks interval semantics, sorting, invalid inputs, duplicate boundaries, memo usage, and edit invalidation.
Changelog entry CHANGELOG.md	Documents the new section completeness strip entry and references the test file.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Possibly related PRs

• got-feedBack/feedBack-plugin-editor#89: Both changes touch screen.js edit-history behavior and undoable command handling in the same area of the codebase.

🚥 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 and concisely summarizes the main editor UI change: adding a section completeness strip.
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-section-coverage

---

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[coderabbitai]

🧹 Nitpick comments (1)

screen.js (1)

1491-1514: 🚀 Performance & Scalability | 🔵 Trivial | 💤 Low value

Coverage recomputed from scratch every frame.

_currentNoteTimes() remaps all notes and _sectionCoveragePure re-scans note times per section on every drawSections() call. For charts with many notes/sections this repeats O(sections × notes) work per frame with no caching, though the early break on match keeps the common case cheap. Likely fine for typical chart sizes; consider memoizing/invalidating on note or section change only if profiling shows this is hot.

🤖 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.js` around lines 1491 - 1514, _currentNoteTimes() and drawSections()
recompute note times and section coverage from scratch on every render, so cache
the derived note-time list and section coverage instead of rescanning notes()
each frame. Add memoization or invalidation tied to the symbols that change the
inputs (notes(), S.sections, S.duration, and any arrangement edits), and have
drawSections() reuse the cached coverage so the hot path no longer does repeated
O(sections × notes) work.

🤖 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.js`:
- Around line 1491-1514: _currentNoteTimes() and drawSections() recompute note
times and section coverage from scratch on every render, so cache the derived
note-time list and section coverage instead of rescanning notes() each frame.
Add memoization or invalidation tied to the symbols that change the inputs
(notes(), S.sections, S.duration, and any arrangement edits), and have
drawSections() reuse the cached coverage so the hot path no longer does repeated
O(sections × notes) work.

---

ℹ️ Review info

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Configuration used: defaults

Review profile: CHILL

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Run ID: 23241ba4-6a22-4944-9e83-58eee4132d51

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📒 Files selected for processing (3)

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

[coderabbitai]

🧹 Nitpick comments (1)

tests/section_coverage.test.js (1)

123-135: 📐 Maintainability & Code Quality | 🔵 Trivial | ⚡ Quick win

Fixed 1200-char slice may not cover the full drawSections body.

Estimating the actual length of drawSections (per the line-range change details, lines 1547-1585), it's roughly ~1590 characters — longer than the 1200-char window sliced here. The negative assertion (drawSections must not call the O(N) pure helper directly every frame) currently only inspects the first ~1200 chars of the function, missing the tail (the section-label/dashed-line loop). A future stray _sectionCoveragePure( call placed later in the function wouldn't be caught by this guard.

Consider slicing up to the next top-level function boundary instead of a magic length:

♻️ Proposed fix

-    assert.ok(!/drawSections[\s\S]*?_sectionCoveragePure\(/.test(
-        src.slice(src.indexOf('function drawSections'), src.indexOf('function drawSections') + 1200)),
+    const fnStart = src.indexOf('function drawSections');
+    const nextFnStart = src.indexOf('\nfunction ', fnStart + 1);
+    const fnBody = src.slice(fnStart, nextFnStart === -1 ? undefined : nextFnStart);
+    assert.ok(!/_sectionCoveragePure\(/.test(fnBody),

🤖 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 `@tests/section_coverage.test.js` around lines 123 - 135, The negative
assertion in the drawSections coverage test uses a fixed 1200-character slice,
which can miss later calls to _sectionCoveragePure() inside the full
drawSections function. Update the test to slice or scope the search using a real
function boundary around drawSections (for example, from function drawSections
to the next top-level function) so the guard checks the entire body, while still
asserting that drawSections only uses _sectionCoverage() and not the pure helper
directly.

🤖 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 `@tests/section_coverage.test.js`:
- Around line 123-135: The negative assertion in the drawSections coverage test
uses a fixed 1200-character slice, which can miss later calls to
_sectionCoveragePure() inside the full drawSections function. Update the test to
slice or scope the search using a real function boundary around drawSections
(for example, from function drawSections to the next top-level function) so the
guard checks the entire body, while still asserting that drawSections only uses
_sectionCoverage() and not the pure helper directly.

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: e06aff58-ff65-43a4-9640-68cf6c690f6f

📥 Commits

Reviewing files that changed from the base of the PR and between 3c093ec and e860e89.

📒 Files selected for processing (2)

• screen.js
• tests/section_coverage.test.js