feat: add Codex plugin distribution support

[yangchuansheng]

Summary

Adds Codex plugin distribution support for Marketing Skills while keeping the existing root skills/** directory as the single skill source.

Codex plugin support

• Adds .codex-plugin/plugin.json with plugin identity, interface metadata, starter prompts, and ./skills/ discovery.
• Adds .agents/plugins/marketplace.json for repo-local Codex marketplace testing.
• Adds distribution/platforms.json to record Codex, Claude Code, npx skills, and generic importer support claims.

Validation and CI

• Adds scripts/validate-codex-plugin.mjs to validate Codex manifest, marketplace, platform registry, asset paths, skill count, and Claude manifest parity.
• Validates all platform registry entries and required platform IDs so support claims stay covered by CI.
• Adds .github/workflows/validate-plugin.yml to run plugin metadata validation and npx plugins discover in CI.
• Updates the existing skill sync workflow and script so Codex metadata stays aligned with skill count and version changes.

Docs and repo guidance

• Updates README installation docs with npx plugins add ... --target codex and plugin distribution notes.
• Updates AGENTS.md with Codex plugin structure and verification commands.
• Allows only .agents/plugins/marketplace.json through .gitignore while preserving .agents/ as an install-artifact ignore path.

Test Coverage

Metadata and documentation only. No application code paths changed.

Pre-Landing Review

Pre-Landing Review: No unresolved issues.

Auto-fixed during review:

• .github/scripts/sync-skills.js now updates skill counts in both marketing skills and agent skills descriptions.
• scripts/validate-codex-plugin.mjs now validates all required platform registry entries and common platform fields.

Design Review

No frontend files changed. Design review skipped.

Eval Results

No prompt-related application files changed. Evals skipped.

Scope Drift

Scope Check: CLEAN

Intent: add Codex plugin support modeled after labring/sealos-skills.

Delivered: Codex plugin manifest, repo marketplace, platform registry, validation script, CI workflow, sync maintenance, and README/AGENTS guidance.

Plan Completion

No plan file detected.

Verification Results

• node scripts/validate-codex-plugin.mjs passed: marketing-skills (43 skills)
• ./validate-skills.sh passed: 43/43 skills valid
• npx plugins discover . --remote --target codex found marketing-skills with 43 skills
• go run github.com/rhysd/actionlint/cmd/actionlint@latest .github/workflows/sync-skills.yml .github/workflows/validate-plugin.yml passed
• git diff --check $(git merge-base origin/main HEAD) passed
• python3 -m json.tool passed for plugin and distribution JSON files

TODOS

No TODO file exists in this repo. No TODO items completed in this PR.

Test plan

• Validate Codex plugin metadata
• Validate all Agent Skills
• Verify Codex plugin discovery
• Lint GitHub Actions workflows
• Check diff whitespace

🤖 Generated with OpenAI Codex