[BUG] Figma MCP tool calls fail with SSE JSON parse error on long responses (desktop app, Code tab)

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Figma MCP tool calls fail with an SSE JSON parse error when the response payload is large, in a Code-tab session of the Claude desktop app.

Calling get_metadata or get_design_context on a Figma node whose response exceeds roughly 20KB consistently fails with:

Failed to parse SSE message: 1 validation error for union[JSONRPCRequest,JSONRPCNotification,JSONRPCResponse,JSONRPCError]
Invalid JSON: EOF while parsing a string at line 1 column XXXXX [type=json_invalid]

Observed byte offsets across multiple calls, on different nodes and different tools: 20068, 19989, 19952, 19878, 19439 — all clustering around ~20KB regardless of node size or tool used. This held both before and after updating the desktop app to the latest version.

get_screenshot on the same nodes works fine (its response is short). The same Figma file/nodes also work correctly when queried from the regular Claude chat tab (not Code), suggesting the SSE client used in Code-tab sessions fails to reassemble/parse larger multi-chunk messages while the chat-tab client does.

Reconnecting the Figma connector does not help — session_connectors_status reports it as "connected" (40 tools) both before and after the failures, so this isn't a dropped-connection issue.

What Should Happen?

Figma MCP calls with large JSON/XML responses (get_metadata, get_design_context) should complete successfully in Code-tab sessions, the same way they do in the regular chat tab.

Error Messages/Logs

Failed to parse SSE message: 1 validation error for union[JSONRPCRequest,JSONRPCNotification,JSONRPCResponse,JSONRPCError]
  Invalid JSON: EOF while parsing a string at line 1 column 19439 [type=json_invalid]
    For further information visit https://errors.pydantic.dev/2.12/v/json_invalid

Steps to Reproduce

1. Open a Code-tab session in the Claude desktop app with the Figma MCP connector connected.
2. Open any Figma design file and pick a node whose subtree is non-trivial (a few dozen layers is enough).
3. Call the Figma MCP tool get_metadata (or get_design_context) with that node's fileKey/nodeId.
4. The call fails immediately with the SSE parse error above instead of returning the metadata/design context.

Additional observations:

• get_screenshot on the same node succeeds (its response is short, just a URL).
• The exact same fileKey/nodeId works fine when queried through the regular Claude chat tab (not Code) using what appears to be the same Figma connector.
• Reconnecting the Figma connector does not help; session_connectors_status reports it as "connected" throughout.
• Reproduced consistently across 5 separate calls, 3 different Figma nodes, and 2 different tools (get_metadata, get_design_context), both before and after updating the desktop app to the latest version.

Claude Model

Sonnet (default)

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

2.1.284 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Other

Additional Information

Claude desktop app (embedded terminal panel), not an external terminal

Additionally, the Figma connector status check (session_connectors_status) reports the Figma MCP server as "connected" with 40 tools available, both before and after the failures — ruling out a dropped/failed connection as the cause.

The same file/nodes were successfully queried via get_screenshot (short response) in the same session, confirming the connector itself is reachable and functioning; only large JSON/XML payloads (get_metadata, get_design_context) fail to parse.