feat(editor): undoable part rename — kind-guarded display labels

[ChrisBeWithYou]

DAW-workspace 2.2b, first half (rename; drag-reorder is a separable follow-up). This was flagged "safe once §7 lands" — #101''s merge-not-rebuild save landed it: a rename no longer strips the manifest entry''s type/unknown keys, and sloppak sessions carry a stable id.

What

• ✏ button next to the arrangement selector (+ registry command renamePart) renames the current part through a new RenameArrangementCmd: full undo/redo, captured-index targeting (undo after an arrangement switch lands on the right part via the history''s per-arrangement tagging), selector text follows on both exec and rollback, and the stable manifest id never changes — so per-part view prefs and the manifest merge survive.
• The hard limit, enforced honestly: the NAME still drives kind inference — KEYS_PATTERN → piano roll + notation sidecar, /bass/i → 4-lane layout, /^drums/i → drum routing — so a rename that would change the inferred instrument is refused with an explanation (guitar→bass would silently re-lane a 6-string chart and strand notes on invisible strings). Cross-kind moves stay "add a new part". This constraint dissolves when arr.type fully replaces name inference (F9''s endgame).
• Duplicate names refused case-insensitively (the pack name discipline); empty/overlong refused; an exact no-op fails silently.

Tests

tests/rename_part.test.js (6): the kind table — including the anchored-KEYS_PATTERN nuance ("Electric Piano" is NOT a keys name by the layout rules, and the guard must mirror what routing would actually do) — the guard truth table (cross-kind reasons, dup/empty/overlong/no-op), and the real command round-tripped through EditHistory (exec/undo/redo, selector refresh, id stability, captured-index targeting). Full suite green except the pre-existing CRLF section_coverage failure (#116 fixes it).

Fresh region vs the open queue — the arrangement-selector toolbar cluster + one command class.

🤖 Generated with Claude Code

https://claude.ai/code/session_01JEoFeTPSnz4NpwwCG52hnu

Summary by CodeRabbit

• New Features

  • Added an undoable arrangement-part rename control to the editor top bar.
  • The rename option is available via the editor UI and is only shown when editing an arrangement.

• Bug Fixes

  • Renames preserve stable part identity and related view/merge behavior.
  • Invalid renames are prevented, including empty names, overly long names, case-insensitive duplicates, and renames that would change the inferred instrument type.

• Tests

  • Added automated coverage for rename validation, undo/redo behavior, and correct application to the targeted arrangement.

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Review details

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: fd1f2759-6fe3-4841-885e-640b2ac9f2cb

📥 Commits

Reviewing files that changed from the base of the PR and between b8eea3b and 0b4c561.

📒 Files selected for processing (3)

• CHANGELOG.md
• screen.html
• screen.js

📝 Walkthrough

Walkthrough

This PR adds undoable arrangement-part renaming. It wires a rename button and command into the editor, adds validation and kind-inference checks, implements undo/redo support, and includes tests plus changelog documentation.

Changes

Part Renaming Feature

Layer / File(s)	Summary
Rename command, validation logic, and command routing screen.js	Adds the renamePart command entry, routes it to window.editorRenameArrangement(), and implements rename validation, kind inference, and the undoable RenameArrangementCmd.
Rename button UI wiring screen.html, screen.js	Adds the hidden rename button and conditionally shows it when arrangements exist and a session is active.
Rename tests and changelog tests/rename_part.test.js, CHANGELOG.md	Adds tests for rename guards and undo/redo behavior, and documents the feature in the changelog.

Estimated code review effort: 3 (Moderate) | ~25 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: an undoable editor part rename with kind-guarded behavior.
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 unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/editor-rename-part

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