[Danielku15]

Note

AI-authored disclosure (alphatab-ai-authored-v1)

Portions of this content were authored by an AI agent. The agent has read
AGENTS.md and the human submitter accepts responsibility for
compliance with the rules in that document.

Issues

Fixes #2976

Proposed changes

The reported case (a whole rest in numbered notation) is already fixed on develop by #2990. One input still crashed with the same TypeError: Cannot read properties of null (reading 'beat') in every notation: dead-slapped beats of whole duration or longer, and beams made only of dead slaps (beam merge). Dead-slapped beats have no notes, but unlike rests they are not isRest, so the beaming bounds and beam drawing info dereferenced a missing highest/lowest note.

The beaming bounds and ensureBeamDrawingInfo now fall back to the beat itself when a helper has no notes. Branch order and the rest handling from #2990 are unchanged, and the unused, non-null-safe BeamingHelper.beatOfLowestNote/beatOfHighestNote getters are removed.

The new dead-slapped-beats test renders these inputs in all notations and checks there is no error and no NaN; it fails on develop. No existing reference changed (checked across the beaming-heavy visual suites).

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