feat(gp): continue tied notes (extend the held note's duration)

[PhysShell]

What

GP import fidelity, slice 2 (S3, ADR-0018): tied notes (NoteType::Tie) now continue the preceding note on their string instead of being dropped.

Before, a tie was skipped to LossReport, which truncated the held note's duration — a half-note written as two tied quarters imported as a single quarter plus a dropped note. Now the tie extends the most recent note on its string by the tie beat's duration, and an all-tie beat emits no event of its own (the held note carries the sound).

How (TDD: refactor → red → green)

• refactor — replace build_event_group (one beat → one group) with append_beat, which pushes onto the voice's group list and threads a VoiceAccum (groups + a per-string held-note map + loss). Behaviour unchanged; the dead-note characterization test moves to the new seam.
• test (red) — a struck note then a tie on the same string must yield one note of the summed duration; fails while ties are skipped (stray rest, original duration).
• feat (green) — extend_tie lengthens the held note; orphan ties (no preceding note on the string) remain a loss. Module loss note updated.

Notes

• Assumes a tie continues the immediately-preceding sound on its string (well-formed GP); a malformed orphan tie is reported, not silently mis-extended.

Checks

• cargo test --workspace green (502 tests; new tied_note_extends_previous_note_duration)
• cargo clippy --all-targets -- -D warnings clean; gp.rs rustfmt-clean

https://claude.ai/code/session_01TTUbGjzD8ysnVnCJnZJE95

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Generated by Claude Code

Summary by CodeRabbit

• Bug Fixes
  • Fixed handling of tied notes in Guitar Pro files to properly extend note durations.
  • Improved error reporting when encountering invalid ties without preceding notes.

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No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 18d9216b-f3f8-4fa3-8887-f443b528004f

📥 Commits

Reviewing files that changed from the base of the PR and between dc5509c and 5607ceb.

📒 Files selected for processing (1)

• core/src/gp.rs

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📝 Walkthrough

Walkthrough

Refactors GP beat processing in core/src/gp.rs to support tied notes. Introduces a VoiceAccum struct that threads per-voice mutable state (held-note map, event groups, loss report) through a new append_beat helper, replacing the previous build_event_group call. Ties extend the held note's duration instead of emitting a new event group; orphan ties record a loss.

Changes

GP Tied-Note Beat Processing

Layer / File(s)	Summary
VoiceAccum struct and build_gp_voice wiring core/src/gp.rs	Adds HashMap import, defines VoiceAccum bundling event_groups, held map, and loss, replaces the per-beat build_event_group call with append_beat, and adjusts the module-level doc comment on LossReport.
append_beat implementation with tie and held-note logic core/src/gp.rs	Implements append_beat: rest/empty beats push a rest group and return; normal/dead note beats iterate notes, convert pitches, collect TechniqueSpans, record atom_index in the held map, and record out-of-range losses. Unsupported notes record losses through the accumulator. All-tie beats emit no new EventGroup; otherwise atoms are wrapped into a single-note or chord group. Adds extend_tie which extends a held note's duration or records an orphan-tie loss.
Updated dead-note test and new tied-note test core/src/gp.rs	Adds HashMap import to the test module, updates the dead-note test to use append_beat/VoiceAccum, and adds a new test asserting that NoteType::Tie extends the prior note's duration without creating a new event group.

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~45 minutes

Possibly related PRs

• PhysShell/griff#51: Both PRs modify core/src/gp.rs beat/event-group handling — the retrieved PR changes dead-note mapping to NoteMark::DeadNote through map_gp_note_marks, the same technique-span path that this PR threads through append_beat.

Poem

🐰 A note rings out, its string still warm,
A tie arrives to stretch its form.
No new event — just longer sound!
In held the last-struck pitch is found.
The rabbit maps each beat with care,
Orphan ties? A loss declared.
hop 🎸

🚥 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 specifically describes the main feature: support for tied notes by extending held note duration, which is the primary change in the refactored beat processing logic.
Docstring Coverage	✅ Passed	Docstring coverage is 85.71% which is sufficient. The required threshold is 80.00%.
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.

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✨ 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 claude/gp-tied-notes

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