[Artifact Forest 2/9] Define canonical screenplay artifacts and capability truth

[szmyty]

Parent: #421
Depends on: #422 for exhaustive-forest semantics only; schema/design work may begin in parallel.

Outcome

Make screenplay structure a first-class static artifact domain instead of treating Fountain as an isolated format enum value.

Formats in initial scope

• Fountain
• Final Draft FDX
• Fade In
• Open Screenplay Format (OSF)
• normalized screenplay JSON/evidence form

Architecture

Define a provider-neutral renderflow.screenplay/v1 artifact/schema representing, where available:

• title-page metadata;
• scenes/headings;
• action;
• character cues;
• dialogue and parentheticals;
• transitions;
• lyrics;
• centered text;
• sections/synopses/notes where representable;
• dual-dialogue relationships;
• source order and stable element IDs;
• source-format extension data that cannot be normalized safely.

This intermediate is a conversion boundary, not a claim that every format round-trips perfectly.

Deliverables

• Add missing graph formats for FDX, FadeIn, OSF, and normalized screenplay JSON.
• Correct Fountain's current capability truth: detection/model support must be distinguished from executable conversion until providers land.
• Define loss profiles for each direction.
• Define screenplay validation/inspection evidence.
• Add tiny legal redistribution-safe fixtures for each format.
• Document exact representational gaps and round-trip limitations.

Acceptance criteria

• Fountain is no longer advertised as executable solely because Pandoc exists.
• FDX/FadeIn/OSF are represented as typed formats with accurate detect/profile/inspect/convert/generate states.
• The screenplay schema preserves ordered semantic structure and unknown/source-specific extensions honestly.
• Conversion loss can be expressed per edge/result.
• Fixtures prove parsing/serialization boundaries without relying on private scripts.
• No external provider is made mandatory for Renderflow core.

Non-goals

No PDF recovery, speech transcription, or comic-specific panel schema in this checkpoint.