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Forward passthrough MCP requests of moved workspaces to v2 #2388

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Merged
RhysSullivan merged 1 commit into from
Oct 25, 2026
Merged

Forward passthrough MCP requests of moved workspaces to v2 #2388

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5 changes: 5 additions & 0 deletions .changeset/v2-forward-passthrough.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
---
"@executor-js/cloud": patch
---

Executor Cloud forwards MCP requests that use `mode=passthrough` for a workspace that has moved to Executor v2, instead of refusing them. v2 serves its own tools for them.
15 changes: 6 additions & 9 deletions apps/cloud/src/mcp/v2-forward.ts
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Expand Up @@ -20,7 +20,7 @@
// ---------------------------------------------------------------------------

import { jsonRpcErrorBody, UNAVAILABLE_RETRY_AFTER_SECONDS } from "@executor-js/host-mcp";
import { readElicitationMode, readToolMode } from "@executor-js/cloudflare/mcp/do-headers";
import { readElicitationMode } from "@executor-js/cloudflare/mcp/do-headers";
import { EXECUTOR_ORG_SELECTOR_HEADER } from "@executor-js/sdk/shared";

import type { MovedToV2 } from "./moved-to-v2";
Expand Down Expand Up @@ -105,7 +105,11 @@ export const toolkitConnectionId = async (
return `v1-${hex(digest).slice(0, 40)}`;
};

/** v2's MCP endpoint for a request: only the elicitation mode and toolkit connection carry over. */
/**
* v2's MCP endpoint for a request: only the elicitation mode and toolkit
* connection carry over. v1's tool mode (`mode=passthrough`) does not: v2
* serves its own tools for every request.
*/
export const buildV2Url = (origin: string, request: Request, connection?: string): URL => {
const url = new URL("/mcp", origin);
const mode = readElicitationMode(request);
Expand Down Expand Up @@ -169,9 +173,6 @@ export const relayV2Response = (
});
};

export const PASSTHROUGH_MOVED_MESSAGE =
"This workspace has moved to Executor v2, which has no passthrough mode. Remove mode=passthrough from the MCP URL.";

export const TOOLKIT_NOT_FOUND_MESSAGE = "Toolkit not found";

/** The bindings forwarding needs; absent in workers that do not forward. */
Expand Down Expand Up @@ -217,10 +218,6 @@ export const forwardToV2 = async (
): Promise<Response> => {
const log = deps.log ?? defaultLog;

if (readToolMode(request) === "passthrough") {
return jsonRpcErrorBody(400, -32600, PASSTHROUGH_MOVED_MESSAGE);
}

const { V2_MCP: binding, V2_MCP_ORIGIN: origin, V2_MCP_FORWARD_SECRET: secret } = env;
if (!binding || !origin || !secret) {
log({ event: "mcp_v2_forward_unconfigured", hasBinding: !!binding, hasOrigin: !!origin });
Expand Down
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