Improve SongForge creative quality and exports

[WalksWithASwagger]

Context

SongForge is promising as a source-linked creative lane, but it should mature as a text-first workflow before any direct music-generation integration. This issue improves creative structure, export quality, and originality guardrails while keeping source notes visible.

Acceptance Criteria

• SongForge emits multiple structure variants with source notes and originality guardrails.
• Markdown/vault exports preserve lyric, spoken-word, prompt-pack, and source-note sections cleanly.
• Presentation docs describe SongForge as a source-linked text workflow, not direct music generation.
• Fixture tests pin the output structure.

Tests/Evals

• Add or update fixture tests around SongForge structure and markdown/vault export sections.
• Keep editorial/SongForge fixture evals passing without provider credentials.

Verification

• make test
• make eval-fixture
• git diff --check

Agent Instructions

Roadmap ID: wf-songforge-polish.

Work from whisperforge_core/songforge.py, export code, fixture tests, and docs/PRESENTATION-RUNBOOK-2026-05-19.md. Keep outputs original and source-linked. Use deterministic templates/fixtures for tests. Avoid adding new music-service dependencies.

Out of Scope

• No direct music-generation service calls.
• No new paid provider integration.
• No claim that SongForge produces final mastered audio.
• No broad UI redesign unrelated to SongForge review/export clarity.

Linear

Not linked yet. Source roadmap entries: ops/roadmap/features.json and docs/NEXT-ROUND-PLAN-2026-05-19.md.

[github-actions]

Agentic issue quality gate failed: missing sections: Context, Tests/Evals, Agent Instructions, Out of Scope; acceptance criteria must include markdown checkboxes

[github-actions]

Agentic dev loop started on branch codex/RUNBOOK-2026-improve-songforge-creative-quality-and-exports with provider noop.

[github-actions]

Agentic dev loop finished without opening a PR. Status: no-pr. Provider: noop.

[WalksWithASwagger]

Swarm lane completed in PR #56: #56

Verification: make lint, make test (283 passed), make eval-fixture, git diff --check. Ready for review/merge.