Problem

Refs @Tomodad's Codex marketplace reports in #45:

• Beta testers wanted — 15 platforms × 3 operating systems #45 (comment)
• Beta testers wanted — 15 platforms × 3 operating systems #45 (comment)

The Codex marketplace MCP manifest does not set default_tools_approval_mode, so context-mode MCP calls can enter Codex's approval/auto-review path before the tool runs. In the reported setup that path failed with a 503 before MCP execution.

Fix

Add default_tools_approval_mode: "approve" to .codex-plugin/mcp.json so Codex marketplace installs match the previously working manual MCP config behavior.

Also adds a regression test for the Codex plugin manifest.

Validation

• pnpm exec vitest run tests/core/cli.test.ts -t "Codex plugin MCP manifest"
• pnpm exec vitest run tests/core/cli.test.ts
• pnpm run build
• Manual E2E: temp CODEX_HOME, no manual [mcp_servers.context-mode], installed the patched plugin through a Codex plugin path, then ran codex exec and confirmed ctx_stats completed through the context-mode MCP server on v1.0.151.
• Control E2E: removing the field made the same tool call fall into the approval path and fail before result on my machine.

I could not reproduce the reporter's exact 503 locally; that looks provider/proxy-path-specific. This change avoids the approval/auto-review path for context-mode marketplace tools.

Separate note: I also found a Windows install blocker where codex plugin add context-mode@context-mode can fail with missing plugin.json because plugins/context-mode is a symlink to ... I kept that out of this PR because it is a separate install-path issue.