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refactor(mcp): simplify proxy with SDK transports

@abir-taheerchecks n/achecks…abir/rework-proxy → main3 files · +489 −659review: @sarahsimionescuupdated 1mo ago

▸Description · 1 noise

Replaced manual JSON-RPC parsing, protocol version tracking, and request ID remapping with the MCP SDK's built-in transport wiring (StreamableHttpProxy)
Fixed elicitation (server→client requests): upstream messages like elicitation/create were silently dropped because send() was called without relatedRequestId. Now tracks in-flight client request IDs and routes server→client messages to the correct POST response SSE stream.
Deferred upstream SSE start: client.start() was being called eagerly before the upstream session existed (pre-initialize). Now deferred until notifications/initialized.
Added Redis message brokering (mcp-proxy-downstream:v1:{sessionId}): upstream→client messages are published to Redis as backup for cross-instance delivery in serverless. Messages are replayed on session restore or GET SSE reconnection.
Reduced proxy.ts from ~900 to ~560 lines and streamable-http-proxy.ts from 164 to ~180 lines (with new routing + Redis logic)
Preserved all auth (Bearer JWT/opaque, consumer key), SSRF prevention, Redis session persistence, upstream timeout/unauthorized handling, and structured logging

Verify MCP connections work end-to-end with Claude, Cursor, and other OAuth clients
Verify elicitation prompts work: trigger a tool that requires permissions gate → client should see the elicitation/create prompt and be able to respond
Verify session persistence across serverless cold starts (Redis restore path)
Verify upstream 401 handling evicts cached sessions and forces re-auth
Verify SSRF allowlist still blocks non-backend upstream URLs
Verify consumer API key auth path still works
Verify Redis downstream messages are delivered on reconnection

🤖 Generated with Claude Code

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