[I] bug(mcp): tools whose input schema carries `$schema` cannot be published as Client Capabilities [maka]

["jsiu93 (via GitHub)" <gi...@apache.org>]

jsiu93 opened a new issue, #3559:
URL: https://github.com/apache/maka/issues/3559

   ### What happened
   
   `maka runtime-host capability-provider serve` fails before publishing a single tool when an MCP server advertises input schemas with a root `$schema` annotation. The descriptor is copied into the Client Capability frame unchanged, and the protocol's strict keyword allowlist rejects it:
   
   ```text
   Runtime Host capability provider stopped: Unsupported Client Capability tool schema keyword
   CapabilityProviderPublicationError: Unsupported Client Capability tool schema keyword
   [exit=1]
   ```
   
   This hits most servers built with the TypeScript SDK. `@modelcontextprotocol/sdk` converts Zod input schemas in `server/zod-json-schema-compat.js` with `zod-to-json-schema` (Zod v3) or `z.toJSONSchema` (Zod v4), and both emit a root `$schema` by default. A direct `tools/list` from XcodeBuildMCP 2.7.0 had `$schema` on 44 of 44 tools, and it was the only keyword outside the allowlist in any of them; an earlier probe through `mcp_router` saw the same on 31 of 31 tools. Python FastMCP servers generally do not emit it.
   
   `$schema` and `$comment` are annotations with no validation meaning. Expected: the provider publishes these tools; the allowlist can stay strict for everything else.
   
   ### How to reproduce
   
   1. Start a fresh Runtime Host with a loopback WebSocket listener and issue a capability-provider credential (supply it through `MAKA_RUNTIME_HOST_ACCESS_CREDENTIAL`).
   2. Point an MCP config at any TypeScript SDK server, for example:
   
   ```json
   {
     "version": 2,
     "mcpServers": {
       "xcodebuildmcp": {
         "command": "bunx",
         "args": ["xcodebuildmcp", "mcp"]
       }
     }
   }
   ```
   
   3. Run:
   
   ```sh
   maka runtime-host capability-provider serve \
     --url ws://127.0.0.1:47633/runtime-host \
     --mcp-config ./mcp.json \
     --expected-root "$ROOT_ID" \
     --client-identity ./capability-provider-identity.json
   ```
   
   4. The provider exits 1 with the error above and publishes nothing.
   
   Unit reproduction: an MCP manager test against a stdio fixture whose tool schema carries a root `$schema`, a nested `$schema` under `properties`, a `$comment`, and an `$id`. On `origin/main` the descriptor still contains all three annotations.
   
   ### Environment
   
   - Maka version or commit: 0.1.11 dev build; confirmed on `origin/main` at `6ada6b546`
   - OS and version: macOS 26.6.1 (25G76), arm64
   - Surface: CLI capability provider and Runtime Host
   - Node.js v22.22.2, npm 10.9.7
   - MCP server: XcodeBuildMCP 2.7.0 (TypeScript SDK)
   
   ### Logs, screenshots, or additional context
   
   Census of the captured XcodeBuildMCP `tools/list`, recursing through the allowlisted child positions:
   
   ```text
   tools=44
   root_$schema=44
   unsupported_keywords={"$schema":44}
   ```
   
   I have a fix that strips `$schema` and `$comment` at MCP discovery and leaves the validator untouched; PR to follow.
   


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Re: [I] bug(mcp): tools whose input schema carries `$schema` cannot be published as Client Capabilities [maka]

["Astro-Han (via GitHub)" <gi...@apache.org>]

Astro-Han closed issue #3559: bug(mcp): tools whose input schema carries `$schema` cannot be published as Client Capabilities
URL: https://github.com/apache/maka/issues/3559


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