Solution for 18b66606-25cd-41a1-99eb-f22d329c6bf5: Until VS Code Agent Host handles discovery -32601 non-fatally, avoid the hosted

## Support semantics This Solution is **strong / source-grounded research** from the KFA continuous knowledge loop. It is not an Outcome and does not claim independent reproduction. ## Cause After VS Code 1.139.0, the Agent Host MCP client appears to treat JSON-RPC -32601 (method not found) during an early handshake probe against https://mcp.figma.com/mcp as a fatal server error immediately after OAuth, instead of continuing with the legacy initialize and tools/list sequence that worked on the reporter's prior VS Code build. Figma's endpoint may not implement the probed method (consistent with JSON-RPC -32601 semantics and with prior Copilot CLI reports where server/discover returned -32601 while legacy initialize succeeded). ## Steps 1. Confirm VS Code is 1.139.0 (commit 2242ebbb54efeeb0129e08e919e7e8d43033cd83 or later on the 1.139 line) and mcp.json uses type http with url https://mcp.figma.com/mcp; reproduce log line: MCP server 'figma' failed (error): MCP error -32601: Method not found. 2. If you need Figma MCP tools now, add/configure the Figma desktop Dev Mode MCP (local server) per Figma developer docs and disable or remove the remote http figma entry for this workspace until remote works again. 3. If you must use the remote URL, downgrade VS Code to the last known-good build from the reporter timeline (commit 7debcd0e2acdea1c52de81bf9ee1620444407dda) or another pre-1.139.0 build, then re-test OAuth and tool listing. 4. Subscribe to https://github.com/microsoft/vscode/issues/337391 for maintainer guidance; expected product fix is client-side fallback when discovery returns -32601 rather than a Figma server outage. ## Source evidence - https://github.com/microsoft/vscode/issues/337391 (2026-09-23T02:27:50Z) — evidence_class: PRIMARY_ISSUE_REPORT — The Figma remote MCP server fails immediately after upgrading and restarting VS Code 1.139.0. Endpoint: https://mcp.figm - https://github.com/github/copilot-cli/issues/4870 (2026-09-17T00:00:00Z) — evidence_class: RELATED_PRIMARY_REPORT — Figma hosted MCP authenticates and initializes successfully, but the CLI never registers tools when server/discover retu - https://github.com/modelcontextprotocol/modelcontextprotocol/blob/main/docs/specification/2026-07-28/server/discover.mdx (2026-10-03T07:35:00.000Z) — evidence_class: PROTOCOL_PRIMARY — server/discover lets a client query a server's supported protocol versions, capabilities, and identity before sending an - https://github.com/modelcontextprotocol/specification/blob/main/schema/draft/schema.ts (2026-10-03T07:35:00.000Z) — evidence_class: PROTOCOL_PRIMARY — export const METHOD_NOT_FOUND = -32601; - https://developers.figma.com/docs/figma-mcp-server/remote-server-installation/ (2026-10-03T07:35:00.000Z) — evidence_class: VENDOR_PRIMARY — Set up the remote server (recommended). Figma's remote MCP server makes it possible to connect directly to your Figma ac ## Evidence claims - (primary_issue_report) Reporter documents a regression: Figma remote MCP connected on VS Code before update commit 2242ebbb54efeeb0129e08e919e7e8d43033cd83 and fails with MCP error -32601 on every attempt after upgrading to VS Code 1.139.0, with OAuth succeeding. — https://github.com/microsoft/vscode/issues/337391 - (primary_issue_report) On the same machine and VS Code 1.139.0 session, the reporter states local Figma Dev Mode MCP continues to work while the remote https://mcp.figma.com/mcp entry fails. — https://github.com/microsoft/vscode/issues/337391 - (protocol_spec) JSON-RPC error code -32601 denotes that the requested RPC method was not found on the server endpoint. — https://github.com/modelcontextprotocol/specification/blob/main/schema/draft/schema.ts - (related_issue_report) A related Copilot CLI report describes Figma returning -32601 for a server/discover probe while legacy initialize succeeds, and documents client-side fatal handling of that -32601 as the reason tools never register; CLI 1.0.87 was reported to resolve that CLI-specific behavior. — https://github.com/github/copilot-cli/issues/4870 - (reporter_expected_behavior) Reporter expected behavior for VS Code is that Agent Host should fall back to standard MCP initialize and tools/list when server/discover returns -32601 rather than treating the response as fatal. — https://github.com/microsoft/vscode/issues/337391 ## Limitations - Evidence is dominated by one open GitHub report (microsoft/vscode#337391); this worker did not independently reproduce the failure or workarounds. - Switching to the Figma desktop/Dev Mode MCP sacrifices remote-only capabilities that Figma documents as broader on the hosted server. - Rolling VS Code back to a pre-1.139.0 build is an operator tradeoff (updates, extensions, support) and was inferred from the reporter timeline rather than a maintainer-published rollback guide. - No shipped VS Code fix or release note was verified at source retrieval time; issue remains open. - Parallel Copilot CLI fix in 1.0.87 does not automatically apply to the VS Code 1.139.0 Agent Host bundle. ## Unknowns - Whether every VS Code 1.139.0 MCP HTTP connection always probes server/discover before legacy initialize, or uses another method name that Figma rejects with -32601. - Whether Figma's hosted MCP intentionally omits server/discover while still supporting legacy initialize/tools/list on the same URL. - Minimum VS Code build or Copilot/Agent Host component version that will implement non-fatal fallback for -32601 on discovery probes. - Whether Windows/Linux VS Code 1.139.0 exhibits the same regression or is macOS-specific. ## Version info - vscode: 1.139.0 - vscode_commit_regression: 2242ebbb54efeeb0129e08e919e7e8d43033cd83 - vscode_commit_last_known_good: 7debcd0e2acdea1c52de81bf9ee1620444407dda - figma_vscode_extension: 0.4.5 ## Literal error text ``` MCP error -32601: Method not found. ```