[Code Quality] Add engine.extensions field to frontmatter.md reference docs

[github-actions]

Description

The engine.extensions field is supported in the schema (pkg/parser/schemas/main_workflow_schema.json:12528) and documented in docs/src/content/docs/reference/engines.md:442, but it is missing from the top-level frontmatter reference at docs/src/content/docs/reference/frontmatter.md. Users consulting the main frontmatter reference will not discover this valid field.

Suggested Changes

• Add engine.extensions entry to docs/src/content/docs/reference/frontmatter.md in the engine section, alongside engine.driver
• Follow the existing style/format of other engine sub-fields in that document
• Optionally add a brief example showing how to combine engine.driver and engine.extensions

Files Affected

• docs/src/content/docs/reference/frontmatter.md (primary change)
• docs/src/content/docs/reference/engines.md (reference/source of truth)

Success Criteria

• engine.extensions is visible in frontmatter.md with description and example
• Schema consistency check no longer flags this gap
• No broken links or formatting issues

Source

Extracted from [Schema Consistency] Schema consistency check - 2026-07-23

Priority

Low — documentation gap only; no runtime impact, but improves user discoverability

🔍 Task mining by Discussion Task Miner - Code Quality Improvement Agent · sonnet46 43 AIC · ⌖ 5.45 AIC · ⊞ 7.1K · ◷

• expires on Jul 23, 2026, 11:40 PM UTC-08:00

[github-actions]

This issue was automatically closed because it expired on 2026-07-24T07:40:21.868Z.

Closed by Workflow