Fix #33520: Allow unhidden instruments in part scores

[officialasishkumar]

Resolves: #33520

Part-score Layout panel rows for instruments that do not yet exist in the current part score were initialized disabled, so the visibility control could not create and show them until another score change refreshed the row state. This keeps nonexistent master-part rows enabled and reuses the same enabled-state rule during score-change refresh, while existing rows still respect enabled shared parts.

Validation:

• git diff --check

• cmake -P /tmp/MuseScore/muse/buildscripts/ci/checkcodestyle/checkcodestyle.cmake src/instrumentsscene/qml/MuseScore/InstrumentsScene/internal

• I signed the CLA

• The title of the PR describes the problem it addresses

• Each commit's message describes its purpose and effects, and references the issue it resolves

• If changes are extensive, there is a sequence of easily reviewable commits

• The code in the PR follows the coding rules

• There are no unnecessary changes

• The code compiles and runs on my machine, preferably after each commit individually

• I created a unit test or vtest to verify the changes I made (if applicable)

[claude]

Claude Code Review

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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 81d6e24 and 3df6875.

📒 Files selected for processing (1)

• src/instrumentsscene/qml/MuseScore/InstrumentsScene/internal/parttreeitem.cpp

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📝 Walkthrough

Walkthrough

This PR refactors PartTreeItem to eliminate duplicated "enabled" state logic. A new internal helper isPartItemEnabled(const Part* part, bool partExists) centralizes the computation that was previously inlined in multiple places. The helper is called during init() and onScoreChanged() to determine whether a part tree item should be enabled based on part existence and shared-part status. Lines changed: +11/−4.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly describes the fix for issue #33520, focusing on allowing unhidden instruments in part scores, which matches the main problem being addressed.
Description check	✅ Passed	The description covers the issue being resolved, explains the problem and solution, and includes validation steps. However, the CLA checkbox and some testing checkboxes remain unchecked.
Linked Issues check	✅ Passed	The code changes successfully address issue #33520 by centralizing the enabled-state logic and applying it during initialization and score updates, allowing nonexistent instruments to be toggled visible without requiring a subsequent score change.
Out of Scope Changes check	✅ Passed	All changes are focused on fixing the enabled-state logic in PartTreeItem, directly addressing the linked issue with no extraneous modifications.

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🧪 Generate unit tests (beta)

• Create PR with unit tests

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