fix(windows): avoid unspawnable Deep Scan launchers

[kmbroai]

Summary

• Normalize CODEX_CLI_PATH at the nested Deep Scan MCP environment boundary.
• On Windows, preserve explicit direct executables while rejecting extensionless npm shims, .cmd shims that require a shell, and protected WindowsApps binaries.
• Fall back to the existing resolveCodexCommand() platform-binary resolver instead of adding another launcher resolver.

Root cause

Deep Scan workers inherit CODEX_CLI_PATH through the plugin MCP environment. Before this change, any non-empty value bypassed the canonical npm platform-binary resolver. On Windows that value can be the extensionless npm shim or a protected MSIX WindowsApps executable; CodexExec passes it directly to child_process.spawn without a shell, which can fail with spawn EPERM even when the installed @openai/codex platform package contains a valid executable.

This keeps case-insensitive Windows environment propagation intact, preserves explicit spawnable .exe / .com launchers, and uses the existing bundled platform executable when the inherited value cannot be launched.

Related: CLI-18410, codex#35872.

Validation

• bun test tests-ts/runtime.test.ts --test-name-pattern 'bundled Codex through|explicit Codex executable override|spawnable Windows' — 3 passed
• pnpm run types
• pnpm run build
• pnpm run format
• pnpm pack --pack-destination ../../dist
• pnpm run test:package — validated the installed package and a nested worker without global codex
• Native prepublish review gate: 3 independent passes plus verifier; 0 findings

The full runtime.test.ts module was also attempted, but this host reports / and /home as UID 65534, so 24 unrelated trusted-owner tests fail closed. The launcher-focused tests and package smoke pass without weakening those checks.