`NamedForm.VerseChorus` is declared but `Form` never produces it; the spec's own verse–chorus example comes out `Unknown`

[matt-edmondson]

Plan reference

• Enum: https://github.com/ktsu-dev/Semantics/blob/7852eab73d673ab42ff1ad10cb1ad1124b8b0122/docs/superpowers/specs/2026-07-01-music-analysis-aggregate-design.md#L238-L241
• Example song map: https://github.com/ktsu-dev/Semantics/blob/7852eab73d673ab42ff1ad10cb1ad1124b8b0122/docs/superpowers/specs/2026-07-01-music-analysis-aggregate-design.md#L230-L233

enum NamedForm { ThirtyTwoBarAABA, TwelveBarBlues, VerseChorus, Binary, Ternary, Rondo, Strophic, ThroughComposed, Unknown }

Repetition and song-map semantics are expressed by repeating Section entries in order (e.g. Verse, Chorus, Verse, Chorus, Bridge, Chorus).

What exists today

• Semantics.Music/NamedForm.cs declares VerseChorus ("Verse-chorus form").
• Form.RecognizePattern (Semantics.Music/Form.cs ~L103-112) has no branch that returns it, and no test references it.
• Neither the spec nor the code records a deliberate deviation. Compare ChromaticKind.AugmentedSixth, whose doc explicitly marks it as reserved.

What's missing

• There is no recognition rule, so the spec's own example (Verse, Chorus, Verse, Chorus, Bridge, Chorus → ABABCB) comes out Unknown.
• The spec gives no letter pattern for this form. Recognition naturally keys on SectionType, which Form.Of has and Form.Parse(pattern) does not.

Acceptance criteria

• Form.Of returns VerseChorus when an arrangement alternates Verse and Chorus sections: at least two of each, with each verse followed by a chorus. Intro, PreChorus, Bridge and Outro sections around them are allowed. Pin down the exact rule in the XML doc.
• Form.Parse keeps letter-only recognition, and its doc states that it cannot produce VerseChorus (as with TwelveBarBlues).
• Tests:
  • The spec example yields VerseChorus.
  • An all-verse arrangement stays Strophic.
• If the form is not wanted after all, mark the member as reserved in its XML doc instead, as AugmentedSixth is.

Dependencies

None. #314 touches the same method but does not overlap with this.

[matt-edmondson]

Triage

• Category: Feature Request (a declared enum member that nothing produces)
• Priority: Low. Nothing returns wrong data. The spec's verse–chorus example classifies as Unknown, which is incomplete rather than wrong.
• Area / suggested assignment: Semantics.Music (Form.RecognizePattern, NamedForm).
• Duplicates: none. It touches the same method as Form.Of labels the 27th distinct section '[' so Form.Parse(form.ToString()) fails to round-trip #314 and Form.Of detects a 12-bar blues by counting chord events, not bars: 3 bars of quarter notes match and a real blues with held chords doesn't #317 but does not overlap with either, so batching the three Form changes would save churn.
• In progress: no open PR.

Suggested next step: decide whether to implement VerseChorus or mark it reserved, as AugmentedSixth is. If it is implemented, write the recognition rule in the XML doc first, since the spec gives no letter pattern for it.

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