Allow disabling MCP config filtering

src/CodexAcpClient.ts

@@ -326,21 +326,23 @@ export class CodexAcpClient {
             return configWithWorkspaceRoots;
         }
 
-        // Deduplicates new servers against existing config to prevent Codex from deep-merging
-        // incompatible field types (e.g., mixing url and stdio schemas).
-        const existingNames = await this.getConfigMcpServerNames(projectPath);
         const requestedServers = mcpServers.map(mcp => ({
             name: sanitizeMcpServerName(mcp.name),
             server: mcp,
         }));
-        const uniqueServers = requestedServers.filter(mcp => !existingNames.has(mcp.name));
-        if (uniqueServers.length === 0) {
+        let serversToConfigure = requestedServers;
+        if (shouldDeduplicateMcpConflicts()) {
+            // Prevents Codex from deep-merging incompatible field types, such as url and stdio schemas.
+            const existingNames = await this.getConfigMcpServerNames(projectPath);
+            serversToConfigure = requestedServers.filter(mcp => !existingNames.has(mcp.name));
+        }
+        if (serversToConfigure.length === 0) {
             return configWithWorkspaceRoots;
         }
 
         return {
             ...configWithWorkspaceRoots,
-            "mcp_servers": Object.fromEntries(uniqueServers.map(mcp => [mcp.name, this.createMcpSeverConfig(mcp.server)])),
+            "mcp_servers": Object.fromEntries(serversToConfigure.map(mcp => [mcp.name, this.createMcpSeverConfig(mcp.server)])),
         };
     }
 
@@ -735,6 +737,11 @@ function formatUriAsLink(name: string | null | undefined, uri: string): string {
     return uri;
 }
 
+function shouldDeduplicateMcpConflicts(): boolean {
+    const disabledByEnv = process.env["DISABLE_MCP_CONFIG_FILTERING"] === "true";
+    return !disabledByEnv;
+}
+
 interface GatewayConfig {
     modelProvider: string;
     config: {

src/__tests__/CodexACPAgent/mcp-config-merge.test.ts

@@ -35,6 +35,7 @@ url = "https://example.com/mcp"
     });
 
     afterEach(() => {
+        vi.unstubAllEnvs();
         removeDirectoryWithRetry(codexHome);
     });
 
@@ -66,4 +67,24 @@ url = "https://example.com/mcp"
         expect(transportDump).contain("Configured MCP servers:");
         expect(transportDump).contain("- shared-mcp");
     });
+
+    it('should not filter the conflicting ACP MCP when config filtering is disabled', async () => {
+        vi.stubEnv("DISABLE_MCP_CONFIG_FILTERING", "true");
+        const codexAcpAgent = fixture.getCodexAcpAgent();
+        await codexAcpAgent.initialize({protocolVersion: 1});
+
+        fixture.getCodexAcpClient().authRequired = vi.fn().mockResolvedValue(false);
+
+        const conflictingMcp: McpServerStdio = {
+            name: "shared-mcp",
+            command: "./node_modules/.bin/mcp-hello-world",
+            args: ["example"],
+            env: [{name: "example", value: "example"}],
+        };
+
+        await expect(codexAcpAgent.newSession({
+            cwd: "",
+            mcpServers: [conflictingMcp],
+        })).rejects.toThrow("url is not supported for stdio");
+    });
 });