feat(claudecode): add first-class subagent frontmatter fields

[dyoshikawa]

Summary

Follow up Claude Code upstream updates by promoting the full set of subagent frontmatter fields documented at https://code.claude.com/docs/en/sub-agents to first-class, validated fields on ClaudecodeSubagentFrontmatterSchema.

Previously the schema only modeled name, description, model, tools, permissionMode, and skills. The remaining fields still round-tripped via z.looseObject passthrough, so this is a schema-completeness/validation improvement (type checking + documentation), not a data-loss fix.

Changes

• src/features/subagents/claudecode-subagent.ts: extended ClaudecodeSubagentFrontmatterSchema (kept z.looseObject) with optional first-class fields:
  • disallowedTools (string or array, mirroring tools)
  • maxTurns (number)
  • color, memory, effort, isolation (plain strings for forward-compat)
  • background (boolean)
  • initialPrompt (string)
  • mcpServers and hooks accepted loosely as z.unknown() — nested schemas are deferred to a follow-up.
• src/features/subagents/claudecode-subagent.test.ts: added tests asserting the new fields validate, round-trip through the claudecode: section (generate + import), and reject invalid types (maxTurns: "x", background: "yes").
• docs/reference/file-formats.md (+ auto-synced skills/rulesync/file-formats.md): enumerated the new fields in the claudecode: subagent example with inline comments.
• cspell.json: added xhigh (a documented effort enum value).

No rules-processor.ts additionalConvention change is needed (Claude Code subagents are native, not simulated). The new fields apply identically to project and global scope, so no scope-specific work. The README support matrix already shows Claude Code subagents as supported — no matrix change.

Note on deferred fields

mcpServers and hooks are accepted loosely (z.unknown()) for now so they round-trip without data loss; dedicated nested schemas are intentionally deferred to a follow-up.

Verification

pnpm cicheck is fully green (format, oxlint, typecheck, 6426 tests, sync-skill-docs, cspell, secretlint).

Closes #1878

🤖 Generated with Claude Code

[dyoshikawa]

@dyoshikawa Thank you!