[rupesh-kumar-sah]

Summary

When an unknown tool was requested, BazaarMcpServer threw an unhandled Error, causing the JSON-RPC transport to fail with a protocol fault (-32603 Internal error) instead of an MCP CallToolResult with isError: true.

This PR replaces the raw exception with a structured ERR_UNKNOWN_TOOL error response that lists valid tool names (bazaar_search, paid_call) and length-bounds the untrusted input name.

Changes

• Added ERR_UNKNOWN_TOOL to MCP_ERROR_CODES in src/mcp/codes.ts.
• Exported VALID_TOOL_NAMES in src/mcp/server.ts.
• Bounded and sanitized unknown tool names to 64 characters without control characters.
• Returned createErrorResponse('ERR_UNKNOWN_TOOL', ...) in CallToolRequestSchema handler.
• Added unit tests in tests/mcp.test.ts verifying error shape, valid tool list inclusion, and length bounding.

Closes #415

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[Miracle656]

Merged to main as 8cc184e.

An unknown tool name threw, so the SDK surfaced a JSON-RPC transport error and the calling agent got nothing to branch on — which is exactly what #415 describes. It now answers with ERR_UNKNOWN_TOOL, the offending name, and the list of tools that do exist.

Listing the valid tools in the reason is the detail I'd single out. A model that guessed a tool name can correct itself straight from the response instead of needing another round trip to ListTools. That turns an error into something recoverable rather than just well-formed.

One fix on merge. tests/mcp.test.ts already had unknown tool > rejects instead of returning a best-effort result, asserting the old throw — and its own comment described the missing error code as the problem:

// The handler throws, so the SDK surfaces this as a JSON-RPC error rather
// than a structured McpErrorResponse — the agent gets no error code.
await expect(callTool('bazaar_refund')).rejects.toThrow('Unknown tool: bazaar_refund');

So that test was pinning the bug you were fixing. I inverted the assertion rather than deleting it — it now checks isError, the ERR_UNKNOWN_TOOL code, and that the reason names the tool — and left a comment saying why it flipped. Worth catching this yourself next time: when a fix makes an existing test fail, check whether the test was documenting the old behaviour before assuming your change is wrong.

For your awareness: #561 implements the same issue. #415 is assigned to you, so yours is the one I reviewed and merged; I'll note the duplication there.

Lens: 116 files, 1,428 tests passing, typecheck clean.