fix(desktop): check the backend's launch id before sending the bootstrap token#21102

@@ -548,24 +577,50 @@ export const runBackendProcess = Effect.fn("runBackendProcess")(function* (
   // the initial readiness budget while the backend is about to come up moments
   // later; a one-shot probe left the app stuck on "Connecting to WSL…" forever
   // even though the backend kept running and became healthy.
-  const probeReadiness = Effect.fn("desktop.backendProcess.probeReadiness")(() =>
-    waitForHttpReady({
+  //
+  // Any HTTP answer is not enough: the port scan ran before this backend
+  // bound, so another server can be answering there by now. Only a server that
+  // echoes this launch's id counts as ready.
+  const portTaken = yield* Ref.make(false);
+  const probeReadiness = Effect.fn("desktop.backendProcess.probeReadiness")(function* () {
+    const answered = yield* waitForHttpReady({
       executablePath: options.executablePath,
       entryPath: options.entryPath,
       cwd: options.cwd,
       httpBaseUrl: options.httpBaseUrl,
       timeout: options.readinessTimeout ?? DEFAULT_BACKEND_READINESS_TIMEOUT,
     }).pipe(
-      Effect.flatMap(() => options.onReady?.() ?? Effect.void),
       Effect.as(true),
       Effect.catchTags({
         BackendReadinessTimeoutError: (error) =>
           (options.onReadinessFailure?.(error) ?? Effect.void).pipe(Effect.as(false)),
       }),
-    ),
-  );
+    );
+    if (!answered) {
+      return false;
+    }

@@ -96,25 +112,44 @@ export const make = Effect.gen(function* () {
         if (!credential) {
           return yield* new DesktopLocalEnvironmentAuthBackendNotConfiguredError();
         }
-        const session = yield* bootstrapRemoteBearerSession({
-          httpBaseUrl: config.httpBaseUrl.href,
-          credential,
-          clientMetadata: {
-            label: "T3 Code Desktop",
-            deviceType: "desktop",
-          },
+        // Readiness already checked this, but the exchange can run much later,
+        // after another server has taken the port. Every attempt checks again;
+        // the check and the POST are still two separate requests.
+        const session = yield* DesktopBackendManager.checkBackendOwnership({
+          httpBaseUrl: config.httpBaseUrl,
+          desktopLaunchId: config.bootstrap.desktopLaunchId,
         }).pipe(
+          Effect.mapError((cause) => new OwnershipCheckUnavailableError({ cause })),
+          Effect.flatMap(
+            Effect.fnUntraced(function* (ownership) {
+              if (ownership === "foreign") {
+                return yield* new DesktopLocalEnvironmentAuthForeignServerError({
+                  port: config.bootstrap.port,
+                });
+              }
+              return yield* bootstrapRemoteBearerSession({
+                httpBaseUrl: config.httpBaseUrl.href,
+                credential,
+                clientMetadata: {
+                  label: "T3 Code Desktop",
+                  deviceType: "desktop",
+                },
+              });
+            }),
+          ),
           Effect.provideService(HttpClient.HttpClient, httpClient),
           Effect.retry({
-            while: isTransientBearerBootstrapError,
+            while: (error) =>
+              error._tag === "OwnershipCheckUnavailableError" ||
+              (error._tag !== "DesktopLocalEnvironmentAuthForeignServerError" &&
+                isTransientBearerBootstrapError(error)),
             schedule: Schedule.spaced(BOOTSTRAP_TRANSIENT_RETRY_INTERVAL),
           }),
           Effect.timeout(BOOTSTRAP_TRANSIENT_RETRY_TIMEOUT),
-          Effect.mapError(
-            (cause) =>
-              new DesktopLocalEnvironmentAuthSessionBootstrapError({
-                cause,
-              }),
+          Effect.mapError((cause) =>
+            cause._tag === "DesktopLocalEnvironmentAuthForeignServerError"
+              ? cause
+              : new DesktopLocalEnvironmentAuthSessionBootstrapError({ cause }),