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

[github-actions]

Description

The engine.extensions field is fully supported in the schema (pkg/parser/schemas/main_workflow_schema.json:12517) and implemented at runtime (pkg/workflow/pi_engine.go:211,240). Specialized engine docs cover it (docs/src/content/docs/reference/engines.md:435-447), but the canonical frontmatter reference (docs/src/content/docs/reference/frontmatter.md) has an engine.driver section with no corresponding engine.extensions section.

Users reading the top-level frontmatter overview can miss this supported field entirely.

Suggested Changes

• Add an engine.extensions section to docs/src/content/docs/reference/frontmatter.md
• Include a brief description of the field, accepted values, and a link to the Pi engine docs for full details
• Ensure the section appears near other engine.* fields for discoverability

Files Affected

• docs/src/content/docs/reference/frontmatter.md

Success Criteria

• engine.extensions documented in the frontmatter reference
• Section includes example usage and links to Pi engine details
• Users reading frontmatter.md can discover the field without needing to read engine-specific docs first

Source

Extracted from Schema Consistency Check discussion 47210 (Critical Issue 3)

Priority

Low — documentation gap only, estimated effort 30min

🔍 Task mining by Discussion Task Miner - Code Quality Improvement Agent · sonnet46 76.4 AIC · ⌖ 5.54 AIC · ⊞ 7.1K · ◷

• expires on Jul 23, 2026, 5:19 AM UTC-08:00

[github-actions]

This issue was automatically closed because it expired on 2026-07-23T13:19:36.212Z.

Closed by Workflow