GUI and docs emission: one file per controller plus index file

[gilesknap]

Parent

#351

What to build

GUI and docs emission produce a directory containing one file per controller plus an index file linking to them. The index uses pvi's format_index and is always emitted — even for one controller — so the file layout is stable as the number of controllers changes. Controllers appear in the index in the order they were declared in fastcs.yaml.

Scope:

• D4 GUI/docs file emission module: per-id files plus index file.
• GUI emission writes output_dir/{id}.bob per controller plus an index file via pvi.format_index.
• Docs emission mirrors GUI: one file per controller in the configured output directory.
• Declaration order from fastcs.yaml is preserved in the index layout.
• D4 ships with its own unit tests in this slice.
• Existing GUI test extended with an assertion that the index file is generated alongside per-controller files.
• Existing docs test extended analogously.
• Single transport-level options (title, output path, format) continue to apply to all controllers — per-controller GUI/docs overrides remain explicitly out of scope per the PRD.

User stories from #351 covered: 13, 14, 15, 23.

Acceptance criteria

• GUI emission writes output_dir/{id}.bob plus an index file for every configured controller
• Docs emission writes one file per controller plus an index file
• Index file is emitted even when only one controller is configured
• Controllers in the index appear in declaration order from fastcs.yaml
• D4 module has its own unit tests
• Existing GUI test asserts index file is generated alongside per-controller files
• Existing docs test asserts the same
• Full test suite stays green

Blocked by

• Multi-controller foundation end-to-end via REST transport #353