feat(codexcli): add PostCompact hook event and preserve prompt frontmatter

[dyoshikawa]

Summary

Follow up on Codex CLI upstream updates from issue #1879.

Part A — PostCompact hook event

Codex CLI documents a PostCompact hook event that runs after Codex compacts the conversation, with the matcher applied to the trigger (manual / auto). This is distinct from the already-supported PreCompact.

• Added postCompact to the canonical HookEvent union.
• Added postCompact to CODEXCLI_HOOK_EVENTS (after preCompact).
• Added postCompact: "PostCompact" to CANONICAL_TO_CODEXCLI_EVENT_NAMES; the reverse map is derived automatically. No other tool documents this event, so no other tool map was touched.
• The hooks processor and codexcli-hooks.ts read these constants generically, so no further wiring was needed.

Part B — preserve description / argument-hint on Codex CLI custom prompts (fully implemented)

Codex custom prompts support description: and argument-hint: frontmatter, which the adapter previously discarded on both generate and import. The adapter now models its frontmatter with z.looseObject (consistent with claudecode-command.ts), reads these fields in fromFile, re-emits them in fromRulesyncCommand, and round-trips description (canonical) and argument-hint (under the codexcli section) in toRulesyncCommand. Prompts without metadata stay as plain Markdown bodies (no empty frontmatter is emitted).

Files changed

• src/types/hooks.ts — add postCompact event + Codex CLI mapping
• src/types/hooks.test.ts — Codex CLI event-naming + map-completeness tests
• src/features/hooks/codexcli-hooks.test.ts — postCompact ⇄ PostCompact round-trip tests
• src/features/commands/codexcli-command.ts — frontmatter support for description / argument-hint
• src/features/commands/codexcli-command.test.ts — frontmatter round-trip tests
• docs/reference/file-formats.md — postCompact matrix row (Codex CLI only) + codexcli command frontmatter example
• skills/rulesync/file-formats.md — auto-synced from docs/

Validation evidence

• PostCompact hook event: https://developers.openai.com/codex/hooks
• Custom-prompt frontmatter (description / argument-hint): https://developers.openai.com/codex/custom-prompts

Checks

pnpm cicheck is fully green: format, oxlint, typecheck, 6409 tests passing, skill-docs sync, cspell, secretlint all clean.

Closes #1879

Related issue: #1879

🤖 Generated with Claude Code

[dyoshikawa]

@dyoshikawa Thank you!