diff --git a/apps/desktop/scripts/dev-electron.mjs b/apps/desktop/scripts/dev-electron.mjs
index 8938763a3730..01ff2f984526 100644
--- a/apps/desktop/scripts/dev-electron.mjs
+++ b/apps/desktop/scripts/dev-electron.mjs
@@ -9,7 +9,7 @@ import {
   resolveElectronLaunchCommand,
 } from "./electron-launcher.mjs";
 import { acquireRunnerRecord, releaseRunnerRecord } from "./dev-runner-control.mjs";
-import { createCrashLoopBreaker } from "./dev-runner-guards.mjs";
+import { createCrashLoopBreaker, devAppPattern, devBackendPattern } from "./dev-runner-guards.mjs";
 import { waitForResources } from "./wait-for-resources.mjs";
 
 const devServerUrl = process.env.VITE_DEV_SERVER_URL?.trim();
@@ -49,6 +49,8 @@ const watchedDirectories = [
   { directory: "../server/dist", files: new Set(["bin.mjs"]) },
 ];
 const forcedShutdownTimeoutMs = 1_500;
+const backendShutdownTimeoutMs = 4_000;
+const backendPollIntervalMs = 100;
 const restartDebounceMs = 120;
 const childTreeGracePeriodMs = 1_200;
 const orphanCheckIntervalMs = 1_000;
@@ -124,16 +126,34 @@ function cleanupStaleDevApps() {
     return;
   }
 
-  const escapedDesktopDir = desktopDir.replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
-  NodeChildProcess.spawnSync(
-    "pkill",
-    ["-f", "--", `(^| )--t3code-dev-root=${escapedDesktopDir}( |$)`],
-    {
+  NodeChildProcess.spawnSync("pkill", ["-f", "--", devAppPattern(desktopDir)], {
+    stdio: "ignore",
+  });
+}
+
+// pkill and pgrep exit 0 only when the pattern matched a process.
+function matchDevBackends(command, args) {
+  return (
+    NodeChildProcess.spawnSync(command, [...args, "-f", "--", devBackendPattern(desktopDir)], {
       stdio: "ignore",
-    },
+    }).status === 0
   );
 }
 
+async function stopStaleDevBackends() {
+  if (hostPlatform === "win32" || !matchDevBackends("pkill", ["-TERM"])) {
+    return;
+  }
+
+  for (let waited = 0; waited < backendShutdownTimeoutMs; waited += backendPollIntervalMs) {
+    await new Promise((resolve) => setTimeout(resolve, backendPollIntervalMs));
+    if (!matchDevBackends("pgrep", [])) {
+      return;
+    }
+  }
+  matchDevBackends("pkill", ["-KILL"]);
+}
+
 function startApp() {
   if (shuttingDown || currentApp !== null) {
     return;
@@ -194,6 +214,8 @@ function restartAfterFailure(app) {
 async function stopApp() {
   const app = currentApp;
   if (!app) {
+    // A crashed Electron is already gone, but its backend may still hold the T3 home.
+    await stopStaleDevBackends();
     return;
   }
 
@@ -228,6 +250,7 @@ async function stopApp() {
       finish();
     }, forcedShutdownTimeoutMs).unref();
   });
+  await stopStaleDevBackends();
 }
 
 function scheduleRestart() {
@@ -316,6 +339,7 @@ const orphanCheck = setInterval(() => {
 
 startWatchers();
 cleanupStaleDevApps();
+await stopStaleDevBackends();
 startApp();
 
 process.once("SIGINT", () => {
diff --git a/apps/desktop/scripts/dev-runner-guards.mjs b/apps/desktop/scripts/dev-runner-guards.mjs
index feec05dc04ec..5b9ebc814eab 100644
--- a/apps/desktop/scripts/dev-runner-guards.mjs
+++ b/apps/desktop/scripts/dev-runner-guards.mjs
@@ -1,5 +1,22 @@
+import * as NodePath from "node:path";
+
 const RUNNER_SCRIPT_NAME = "dev-electron.mjs";
 
+const escapeRegExp = (text) => text.replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
+
+// `pkill -f` patterns for the Electron apps a runner launches from one checkout.
+export function devAppPattern(desktopDir) {
+  return `(^| )--t3code-dev-root=${escapeRegExp(desktopDir)}( |$)`;
+}
+
+// The backend Electron spawns carries no dev-root tag and is the runner's grandchild, so neither
+// the tag nor `pkill -P` reaches it once its Electron parent is gone. A hung one keeps the T3
+// home's ownership lock and every later start fails with ServerAlreadyRunningError.
+export function devBackendPattern(desktopDir) {
+  const serverEntry = NodePath.join(NodePath.dirname(desktopDir), "server", "dist", "bin.mjs");
+  return `(^| )${escapeRegExp(serverEntry)} --bootstrap-fd( |$)`;
+}
+
 export function parseRunnerRecord(text) {
   let parsed;
   try {
diff --git a/apps/desktop/scripts/dev-runner-guards.test.mjs b/apps/desktop/scripts/dev-runner-guards.test.mjs
index 3e75a05f4e93..2695625869e6 100644
--- a/apps/desktop/scripts/dev-runner-guards.test.mjs
+++ b/apps/desktop/scripts/dev-runner-guards.test.mjs
@@ -3,6 +3,7 @@ import { assert, describe, it } from "vite-plus/test";
 import {
   createCrashLoopBreaker,
   decideTakeover,
+  devBackendPattern,
   isVerifiedRunner,
   parseRunnerRecord,
 } from "./dev-runner-guards.mjs";
@@ -92,3 +93,20 @@ describe("crash loop breaker", () => {
     assert.isTrue(breaker.recordAbnormalExit(4_000).tripped);
   });
 });
+
+describe("dev process patterns", () => {
+  const matches = (pattern, command) => new RegExp(pattern).test(command);
+  const electron =
+    "/work/a/apps/desktop/.electron-runtime/T3 Code (Dev).app/Contents/MacOS/Electron";
+
+  it("matches the orphaned backend of this checkout only", () => {
+    const pattern = devBackendPattern(desktopDir);
+    assert.isTrue(
+      matches(pattern, `${electron} /work/a/apps/server/dist/bin.mjs --bootstrap-fd 3`),
+    );
+    assert.isFalse(
+      matches(pattern, `${electron} /work/b/apps/server/dist/bin.mjs --bootstrap-fd 3`),
+    );
+    assert.isFalse(matches(pattern, "node /work/a/apps/server/dist/bin.mjs serve"));
+  });
+});
diff --git a/apps/desktop/scripts/electron-launcher.test.mjs b/apps/desktop/scripts/electron-launcher.test.mjs
index dd88bf2e47b5..3bb48f15b55a 100644
--- a/apps/desktop/scripts/electron-launcher.test.mjs
+++ b/apps/desktop/scripts/electron-launcher.test.mjs
@@ -7,6 +7,8 @@ import * as NodeVM from "node:vm";
 
 import { assert, describe, it } from "vite-plus/test";
 
+import { devAppPattern, devBackendPattern } from "./dev-runner-guards.mjs";
+
 import {
   makeDevelopmentEnvironmentScript,
   makeDevelopmentLauncherScript,
@@ -129,7 +131,9 @@ async function startupCleanupPattern(desktopDir) {
       NodeChildProcess: {
         execFileSync: () => undefined,
         spawnSync: (command, args) => {
-          if (command === "pkill" && args.includes("-f")) pattern = args.at(-1);
+          // The dev-root cleanup signals first; later backend cleanup must find nothing to stop.
+          if (command === "pkill" && args.includes("-f")) pattern ??= args.at(-1);
+          return { status: 1 };
         },
         spawn: () => new NodeEvents.EventEmitter(),
       },
@@ -139,6 +143,8 @@ async function startupCleanupPattern(desktopDir) {
       desktopDir,
       acquireRunnerRecord: async () => ({ claimed: true, stoppedPids: [] }),
       releaseRunnerRecord: () => undefined,
+      devAppPattern,
+      devBackendPattern,
       createCrashLoopBreaker: () => ({
         recordAbnormalExit: () => ({ tripped: false }),
         rearm: () => undefined,