fix(generators): string-count-aware system defaults + bass shape guards (v0.1.12)

[ChrisBeWithYou]

Stacked on #5 (topbar host parity) — GitHub auto-retargets to virtuoso-dev when #5 merges. Review only this PR's diff.

What

Tester symptom: switching 6-string → 7/8-string guitar didn't add the extra strings to most exercises. Full audit verdict: design, not plumbing — string count/tuning reach every builder, but CAGED/Open deliberately anchor the top-six EADGBE subset (off = N-6; correct for CAGED itself — no method teaches an "8-string CAGED"), and caged was the universal beginner/session default. Renderers were innocent (they draw all N lanes).

Fix (guitar-pedagogy · bass-pedagogy · metal-idiom panel verdicts)

1. defaultFretboardSystem(instrument, count) — bass → position, guitar N>6 → 3nps (the extended-range scale system; tiles every string), guitar 6 → caged (unchanged). Explicit advanced-mode picks and rung-coded systems always win — a rung that teaches a CAGED shape stays a CAGED lesson. Wired into readConfig + buildSegmentConfig.
2. Instrument-first guards on every count-gated shape path (resolveCurrentShape, cagedShapeNotesForChord, templateFromShape, sweep wantShape). Kills a real latent pitch bug: a 6-string bass passes the old count-only >=6 guards, but CAGED templates bake EADGBE's G→B major 3rd — on an all-4ths bass the top two strings land a semitone flat. Only UI suppression protected it; programmatic configs (preset import, the new host sync) were exposed.

Deliberately NOT in this PR (panel-ratified, ROADMAP open thread)

• Extended-range CAGED window-continuation (opt-in; never a re-rooted box — extended-range players think top-6 box + low-string riff floor, per metal-idiom).
• bassRootGrip low-fifth downward reach (the "why own a 5-string" idiom).
• Drop-tuning single-finger s0+s1+s2 barre primitive.
• Sweeps/strum-grips/fingerstyle stay top-6 by design (now documented + guarded).

Verification

• New smoke-strings rows: (12) default routing — 8-string default = 3nps, run reaches s=0/s=1, no-unison holds, 6-string stays caged, explicit caged preserved; (13) bass never resolves a shape, a forced 6-string-bass caged sweep stays diatonic (traps the semitone-flat leak), 5-string scale plays the low-B string.
• Suite green; full run 16/19 — the 3 reds (backing-engine voice-leading row, progress, variation) fail identically on base; contained-verifier + level-gate-async flaked once under concurrency-4, green solo.

🤖 Generated with Claude Code

https://claude.ai/code/session_01MS2YFb6UUSwJVV6CmEa25i

[coderabbitai]

Important

Review skipped

Auto reviews are disabled on base/target branches other than the default branch.

Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 536872fb-c598-4661-b753-12dcdb42c902

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

Use the checkbox below for a quick retry:

• 🔍 Trigger review

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/string-count-aware-generation

---

_{Comment @coderabbitai help to get the list of available commands.}

[ChrisBeWithYou]

Landed on virtuoso-dev via the 2026-07-14 batch integration (v0.2.2), not a GitHub merge event — these branches predate the main→dev reconcile (Byron's Gold-rung #11 took the line to 0.2.x) and were rebased, so their head SHAs don't match the commits that reached dev. All content is verified present in dev (incl. #5's 62fc72e tuningMidis, cherry-picked as f0c78c6). Closing to avoid a duplicate re-merge; the work ships to main via the dev→main PR #4 line. — automated