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fix: simplify MCP STDIO reconnection by closing client before reconnect #11887

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fix: simplify MCP STDIO reconnection by closing client before reconnect #11887

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871b7c5
fix: simplify MCP STDIO reconnection by closing client before reconnect
yaruchyo Mar 26, 2026
cf55775
fix: resolve MCP reconnection 'Already connected to a transport' error
yaruchyo Mar 26, 2026
db3d590
fix: preserve Client instance on reconnect, fallback to fresh Client …
yaruchyo Mar 26, 2026
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60 changes: 30 additions & 30 deletions core/context/mcp/MCPConnection.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -85,7 +85,13 @@ class MCPConnection {
// Don't construct transport in constructor to avoid blocking
this.transport = {} as Transport; // Will be set in connectClient

this.client = new Client(
this.client = this.createClient();

this.abortController = new AbortController();
}

private createClient(): Client {
return new Client(
{
name: "continue-client",
version: "1.0.0",
Expand All @@ -94,8 +100,24 @@ class MCPConnection {
capabilities: {},
},
);
}

this.abortController = new AbortController();
private async connectTransport(transport: Transport): Promise<void> {
try {
await this.client.close();
await this.client.connect(transport, {});
} catch (error) {
if (
error instanceof Error &&
error.message.startsWith("Already connected")
) {
this.client = this.createClient();
await this.client.connect(transport, {});
} else {
throw error;
}
}
this.transport = transport;
}

async disconnect(disable = false) {
Expand Down Expand Up @@ -218,40 +240,20 @@ Org-level secrets can only be used for MCP by Background Agents (https://docs.co
const transport = await this.constructStdioTransport(
this.options,
);
try {
await this.client.connect(transport, {});
this.transport = transport;
} catch (error) {
// Allow the case where for whatever reason is already connected
if (
error instanceof Error &&
error.message.startsWith(
"StdioClientTransport already started",
)
) {
await this.client.close();
await this.client.connect(transport);
this.transport = transport;
} else {
throw error;
}
}
await this.connectTransport(transport);
} else {
// SSE/HTTP: if type isn't explicit: try http and fall back to sse
if (this.options.type === "sse") {
const transport = this.constructSseTransport(this.options);
await this.client.connect(transport, {});
this.transport = transport;
await this.connectTransport(transport);
} else if (this.options.type === "streamable-http") {
const transport = this.constructHttpTransport(this.options);
await this.client.connect(transport, {});
this.transport = transport;
await this.connectTransport(transport);
} else if (this.options.type === "websocket") {
const transport = this.constructWebsocketTransport(
this.options,
);
await this.client.connect(transport, {});
this.transport = transport;
await this.connectTransport(transport);
} else if (this.options.type) {
throw new Error(
`Unsupported transport type: ${this.options.type}`,
Expand All @@ -262,16 +264,14 @@ Org-level secrets can only be used for MCP by Background Agents (https://docs.co
...this.options,
type: "streamable-http",
});
await this.client.connect(transport, {});
this.transport = transport;
await this.connectTransport(transport);
} catch (e) {
try {
const transport = this.constructSseTransport({
...this.options,
type: "sse",
});
await this.client.connect(transport, {});
this.transport = transport;
await this.connectTransport(transport);
} catch (e) {
throw new Error(
`MCP config with URL and no type specified failed both SSE and HTTP connection: ${e instanceof Error ? e.message : String(e)}`,
Expand Down
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