Step 6: FCPKitDSL create path

[leogdion]

What to build

Ship the FCPKitDSL product so authors can declare a Document, call export(version:), and get an FCPXML that soft-promotes shells, interns inline media, packs spine timing with transition overlap, and anchors via .anchor(lane:content:) — strong enough to reproduce the transitions and titles FeaturePairs after normalize.

Acceptance criteria

• FCPKitDSL product exists; core FCPKit stays a pure Codable layer for Diff/MediaTools
• Locked surface from the plan: Document, soft promotion, hidden primary spine, .anchor(lane:content:), inline media dedupe, export(version:) throws -> FCPXML
• Loud export failures for missing required values after defaults (including no default Gap.duration)
• DSL → encode → DTD validate → normalize → structural-equal at least transitions and titles FeaturePairs
• Opt-in hard failure for missing DTD tooling on the authoring path (e.g. FCPKIT_REQUIRE_DTD)
• MediaTools multicam builder remains on Codable (no forced migrate)
• swift test and schema-completeness at 0 remain green

Blocked by

• Step 5: Resources, document shells, ResourceRef #10 Step 5: Resources, document shells, ResourceRef

References

• Plan: docs/planning/v0.1.0-first-working-version.md
• ADR: docs/adr/0002-create-first-ordered-typed-model.md
• Worktrees: docs/planning/v0.1.0-worktree-plan.md