Summary

• set CONTEXT_MODE_PLATFORM=codex in the Codex plugin MCP manifest
• document the same env for the manual Codex fallback config
• add a manifest regression test so the Codex MCP server stays aligned with hook wrappers

Why

On Windows machines with both Claude Code and Codex installed, context-mode can otherwise fall through config-dir detection and pick claude-code because ~/.claude exists before ~/.codex. The Codex hook wrappers already set CONTEXT_MODE_PLATFORM=codex; this makes the plugin MCP server get the same platform signal.

This keeps Codex plugin storage and doctor output under ~/.codex/context-mode instead of accidentally falling back to Claude storage before client/platform metadata is available.

Validation

• npx vitest run tests/plugins/codex-manifest.test.ts --reporter=dot
• npx vitest run tests/core/cli.test.ts tests/plugins/codex-manifest.test.ts tests/adapters/detect.test.ts --reporter=dot
• npx vitest run tests/core/server.test.ts -t "getDefaultSessionDir|ctx_doctor reports storage|Storage sessions" --reporter=dot
• npm run typecheck
• git diff --check

Manual Codex check on Windows:

• Codex CLI: codex-cli 0.133.0
• installed a temporary local Codex marketplace/plugin containing the updated .codex-plugin/mcp.json
• codex mcp get context-mode-env-test showed CONTEXT_MODE_PLATFORM attached to the MCP server env, confirming Codex consumes this manifest field in the actual plugin registration path