feat(mcp): make sync opt-in and address review

Opt-in (mcpSyncEnabled, default OFF; routes 403 until on). Review fixes:
- codex TOML read/validated with smol-toml: CRLF, inline tables and
  command-less tables no longer yield a duplicate [mcp_servers.x]; the new
  text is re-parsed before writing
- null-prototype tables and own-key checks; unsafe names ignored at every level
- servers switched off in their own CLI (codex/opencode/antigravity) are not copied
- only CLIs that are installed or already have a config file take part
- files receiving env/headers are left 0600; symlinked configs are written through
- one apply at a time (409), unique tmp files cleaned on failure, failed status
- routes set real HTTP status codes; api-reference section; format type single-sourced

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

docs/cli-registry.md

@@ -251,9 +251,9 @@ A module-level const freezes at first import, and the failure is asymmetric: a C
 
 ## MCP server sync
 
-`capabilities.mcpConfig` (`{ path, format }`, `path` relative to the home directory) names the file a CLI keeps its user-level MCP server list in and the dialect it is written in. `src/mcp-sync.ts` reads that list from every ENABLED CLI that declares one and adds any server a CLI is missing from the others; `GET`/`POST /api/mcp-sync` and Settings → Agents & CLIs → MCP servers drive it. Declared today for claude, gemini, codex, opencode and antigravity; every format was checked against what the CLI's own `mcp add` writes, except opencode's (documented, not installed to check). A CLI with no entry (pi, grok, omp, deepseek) is not guessed at: it is listed as `unsupported` in the result when enabled. Adding one is a registry entry plus a small adapter in `mcp-sync.ts`, and a verified fixture in `test/mcp-sync.test.ts`.
+`capabilities.mcpConfig` (`{ path, format }`, `path` relative to the home directory) names the file a CLI keeps its user-level MCP server list in and the dialect it is written in. `src/mcp-sync.ts` reads that list from every ENABLED CLI that declares one, and that is installed or already has the file (a CLI that is neither is reported `absent`, never created), and adds any server a CLI is missing from the others. It writes other tools' own config, so it is **opt-in**: `mcpSyncEnabled` (synced, default OFF) gates `GET`/`POST /api/mcp-sync` (403 while off) and the Settings → Agents & CLIs → MCP servers controls. Declared today for claude, gemini, codex, opencode and antigravity; every format was checked against what the CLI's own `mcp add` writes, except opencode's (documented, not installed to check). A CLI with no entry (pi, grok, omp, deepseek) is not guessed at: it is listed as `unsupported` in the result when enabled. Adding one is a registry entry plus a small adapter in `mcp-sync.ts`, and a verified fixture in `test/mcp-sync.test.ts`.
 
-Three rules the module keeps and the tests pin: it only ADDS (an existing server is never edited or removed, a same-name difference is reported as a conflict), it never writes a file it could not parse (opencode JSONC with comments), and its result carries server names only, never env values or headers. The schema restricts `path` to a home-relative path without `..`, since sync writes to it.
+The rules the module keeps and the tests pin: it only ADDS (a name already defined, in any shape, is never edited or removed; a same-name difference is reported as a conflict); a server switched off in its own CLI is not copied; it never writes a file it could not parse (opencode JSONC with comments, a TOML file with a duplicate table) and re-parses the new text before writing; codex TOML is read with a real parser (`smol-toml`), so CRLF files and inline tables are handled; names such as `__proto__` are ignored and every table keyed by an untrusted name has no prototype; a symlinked config is written through, not replaced; a file that receives `env`/`headers` is left `0600`; only one apply runs at a time; and its result carries server names only, never env values or headers. The schema restricts `path` to a home-relative path without `..`, since sync writes to it.
 
 ## See also