Issues

Fixes #2802

Proposed changes

This PR adds optional per-string tuning accidental preferences so alphaTab can preserve and render explicit sharp/flat choices such as F# and Gb.

• Adds optional TuningAccidentalMode[] support to the tuning model.
• Preserves tuning accidental preferences through alphaTex, Guitar Pro/GPIF, MusicXML, JSON, and exporters where supported by the format.
• Updates score-info and inline tuning rendering to use each string’s preference.
• Keeps existing behavior unchanged when no accidental mode is specified.
• Replaces an unsafe renderer argument spread with bounded iteration to prevent malformed GPIF tuning data from causing renderer exceptions.
• Adds importer, exporter, model, and visual regression coverage.

Related discussion: alphaTab discussion #2785

Root-cause analysis

Numeric tuning values did not preserve enharmonic spelling, and format-specific sharp/flat metadata was not consistently retained per string.

The renderer also used Math.max(...labels), allowing malformed GPIF tuning data with a large Pitches list to exceed the JavaScript argument limit. The fix preserves optional per-string modes and calculates widths iteratively, while retaining legacy behavior by default.

Checklist

• I consent that this change becomes part of alphaTab under its current or any future open source license
• This PR is linked to an accepted issue (see above)
• Changes are implemented
• New tests were added
• I have read AGENTS.md if an AI helped draft any part of this PR

AI authorship disclosure

• No AI agent authored any part of this PR (description, code, tests, or commit messages)
• An AI agent contributed to this PR. The AI-authored disclosure block
  (alphatab-ai-authored-v1) is present at the top of this body, and I have
  personally reviewed every change and can explain each one

Further details

• This is a breaking change
• This change will require update of the documentation/website