fix(core): exclude let_ring from the technical complexity axis (#75)

[PhysShell]

A playtest export of the DGD GPX showed a held let-ring section (phrase p5 — a sustained 8-note drone, one LetRing span over every note) scoring technical = 1.0, maximally technical, though letting notes ring on is a sustain instruction, not a playing demand.

What

structure::technique_share (the technical complexity axis = share of a track's notes carrying a per-note mark or sitting in a technique span) now excludes SpanTechnique::LetRing spans before deciding coverage. A let-ring-only phrase scores 0 on the axis instead of 1.0. let_ring still surfaces as a SwancoreTag/technique — only the difficulty axis stops counting it.

Scope / safety

• Only LetRing is reclassified. Palm-mute and other spans, and all per-note marks, are unchanged — the two existing technical-axis tests (both PalmMute) still pass.
• A note that both rings and carries a real technique still counts via that technique.
• Effect on the playtest export: p5 1.0 → 0; phrases mixing let_ring with slide/hammer (p1, p9) ease down to honest values.

TDD

red (d0eebb3) → green (852abfb) → docs (fd6535e). New technical_axis_ignores_a_passive_let_ring_span asserts a let-ring drone scores 0.

Verification

• cargo test --workspace green; cargo clippy --workspace --all-targets -- -D warnings clean; cargo fmt --all --check clean
• The active/passive judgement (only let_ring for now; a broader mark/span split deferred until the corpus motivates it) is recorded in decisions.log.

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https://claude.ai/code/session_01TTUbGjzD8ysnVnCJnZJE95

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Generated by Claude Code

Summary by CodeRabbit

• Bug Fixes

  • Let-ring sustain techniques no longer count toward technical difficulty scores, ensuring complexity measurements better reflect actual playing difficulty.

• Tests

  • Added validation test for let-ring exclusion from technical complexity calculations.

• Documentation

  • Updated decision log explaining let-ring complexity measurement changes.

[coderabbitai]

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: 2d65de82-5e0c-479c-9a3f-f11c0a48c808

📥 Commits

Reviewing files that changed from the base of the PR and between 4bec705 and fd6535e.

📒 Files selected for processing (3)

• core/src/structure.rs
• core/tests/structure.rs
• docs/decisions.log.md

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📝 Walkthrough

Walkthrough

SpanTechnique::LetRing is now imported in structure.rs and filtered out of the technique_share numerator so sustained let-ring spans no longer contribute to the technical axis of ComplexityProfile. A new test confirms the axis stays at 0.0 for a LetRing-only span, and a decisions-log entry records the exclusion rationale.

Changes

LetRing exclusion from technical complexity axis

Layer / File(s)	Summary
technique_share filter and regression test core/src/structure.rs, core/tests/structure.rs	Imports SpanTechnique, adds a filter excluding SpanTechnique::LetRing from the technical-share numerator, and adds a #[test] asserting measure_complexity(...).technical is 0.0 when the only span is a full-bar LetRing.
Decisions log entry docs/decisions.log.md	Appends a 2026-06-21 entry documenting that SpanTechnique::LetRing is excluded from the technical axis while remaining a valid technique and SwancoreTag.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~5 minutes

Possibly related PRs

• PhysShell/griff#87: Introduced SpanTechnique::LetRing with its model, serialization, and derivation plumbing — the direct prerequisite for this PR's exclusion logic in technique_share.

Poem

A rabbit strums and lets notes ring,
But ringing long's a passive thing!
No "technical" credit for drones that sustain —
The complexity axis must stay sane.
🐇🎸 Let ring, let ring, but don't complain!

🚥 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 accurately summarizes the main change: excluding let_ring from the technical complexity axis calculation, which is the core fix implemented across the codebase.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% 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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[PhysShell]

@codex review

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Codex Review: Didn't find any major issues. Can't wait for the next one!

Reviewed commit: fd6535e163

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