Prevent diff-heavy task renderer crash loops

apps/code/src/main/index.ts

@@ -101,6 +101,10 @@ import {
 import { isMacosPackagedUnsafeBundleLocation } from "./utils/macos-packaged-install-guard";
 import { installMainFetchLogging } from "./utils/network-fetch-logger";
 import { installRendererNetworkLogging } from "./utils/network-webrequest-logger";
+import {
+  RendererCrashRecovery,
+  toSafeRendererUrl,
+} from "./utils/renderer-crash-recovery";
 import { createWindow } from "./window";
 
 type FileWatcherEventsByKind = {
@@ -167,19 +171,10 @@ const RECOVERABLE_RENDER_REASONS = new Set([
 ]);
 const CRASH_LOOP_WINDOW_MS = 30_000;
 const CRASH_LOOP_THRESHOLD = 3;
-const recentCrashTimestamps: number[] = [];
-
-function isCrashLoop(): boolean {
-  const now = Date.now();
-  while (
-    recentCrashTimestamps.length > 0 &&
-    now - recentCrashTimestamps[0] > CRASH_LOOP_WINDOW_MS
-  ) {
-    recentCrashTimestamps.shift();
-  }
-  recentCrashTimestamps.push(now);
-  return recentCrashTimestamps.length >= CRASH_LOOP_THRESHOLD;
-}
+const rendererCrashRecovery = new RendererCrashRecovery({
+  crashLoopThreshold: CRASH_LOOP_THRESHOLD,
+  crashLoopWindowMs: CRASH_LOOP_WINDOW_MS,
+});
 
 function crashDiagnostics() {
   return {
@@ -211,9 +206,10 @@ app.on("render-process-gone", (_event, webContents, details) => {
   posthogNodeAnalytics.flush().catch(() => {});
 
   if (RECOVERABLE_RENDER_REASONS.has(details.reason)) {
-    if (isCrashLoop()) {
+    const recoveryAction = rendererCrashRecovery.nextAction();
+    if (recoveryAction === "stop") {
       log.error("Crash loop detected, stopping auto-recovery", {
-        crashesInWindow: recentCrashTimestamps.length,
+        crashesInWindow: rendererCrashRecovery.recentCrashCount,
         windowMs: CRASH_LOOP_WINDOW_MS,
       });
       return;
@@ -226,8 +222,16 @@ app.on("render-process-gone", (_event, webContents, details) => {
     }
     setImmediate(() => {
       if (win.isDestroyed()) return;
-      log.info("Reloading webContents");
-      win.webContents.reload();
+      if (recoveryAction === "reset-route") {
+        const safeUrl = toSafeRendererUrl(win.webContents.getURL());
+        log.info("Reloading renderer without the crashing route", { safeUrl });
+        void win.loadURL(safeUrl).catch((error) => {
+          log.error("Failed to load renderer recovery URL", { error });
+        });
+      } else {
+        log.info("Reloading webContents");
+        win.webContents.reload();
+      }
       log.info("Bringing window to foreground");
       win.show();
       win.moveTop();

apps/code/src/main/utils/renderer-crash-recovery.test.ts

@@ -0,0 +1,38 @@
+import { describe, expect, it } from "vitest";
+import {
+  RendererCrashRecovery,
+  toSafeRendererUrl,
+} from "./renderer-crash-recovery";
+
+describe("RendererCrashRecovery", () => {
+  it("escapes the crashing route before stopping automatic recovery", () => {
+    const recovery = new RendererCrashRecovery({
+      crashLoopThreshold: 3,
+      crashLoopWindowMs: 30_000,
+    });
+
+    expect(recovery.nextAction(0)).toBe("reload");
+    expect(recovery.nextAction(13_000)).toBe("reset-route");
+    expect(recovery.nextAction(20_000)).toBe("stop");
+  });
+
+  it("starts with a normal reload after the crash window expires", () => {
+    const recovery = new RendererCrashRecovery({
+      crashLoopThreshold: 3,
+      crashLoopWindowMs: 30_000,
+    });
+
+    expect(recovery.nextAction(0)).toBe("reload");
+    expect(recovery.nextAction(31_000)).toBe("reload");
+  });
+});
+
+describe("toSafeRendererUrl", () => {
+  it("removes the route while preserving the renderer entrypoint", () => {
+    expect(
+      toSafeRendererUrl(
+        "file:///Applications/PostHog%20Code.app/index.html#/website/site/tasks/task",
+      ),
+    ).toBe("file:///Applications/PostHog%20Code.app/index.html");
+  });
+});

apps/code/src/main/utils/renderer-crash-recovery.ts

@@ -0,0 +1,37 @@
+export type RendererCrashRecoveryAction = "reload" | "reset-route" | "stop";
+
+type RendererCrashRecoveryOptions = {
+  crashLoopThreshold: number;
+  crashLoopWindowMs: number;
+};
+
+export class RendererCrashRecovery {
+  private readonly recentCrashTimestamps: number[] = [];
+
+  constructor(private readonly options: RendererCrashRecoveryOptions) {}
+
+  nextAction(now = Date.now()): RendererCrashRecoveryAction {
+    while (
+      this.recentCrashTimestamps.length > 0 &&
+      now - this.recentCrashTimestamps[0] > this.options.crashLoopWindowMs
+    ) {
+      this.recentCrashTimestamps.shift();
+    }
+
+    this.recentCrashTimestamps.push(now);
+    if (this.recentCrashTimestamps.length >= this.options.crashLoopThreshold) {
+      return "stop";
+    }
+    return this.recentCrashTimestamps.length === 1 ? "reload" : "reset-route";
+  }
+
+  get recentCrashCount(): number {
+    return this.recentCrashTimestamps.length;
+  }
+}
+
+export function toSafeRendererUrl(rendererUrl: string): string {
+  const url = new URL(rendererUrl);
+  url.hash = "";
+  return url.toString();
+}

packages/ui/src/features/sessions/components/ConversationView.tsx

@@ -40,6 +40,7 @@ import {
   type VirtualizedListHandle,
 } from "@posthog/ui/features/sessions/components/VirtualizedList";
 import { CHAT_CONTENT_MAX_WIDTH } from "@posthog/ui/features/sessions/constants";
+import { createConversationDiffPoolOptions } from "@posthog/ui/features/sessions/conversationDiffPoolOptions";
 import { DIFFS_HIGHLIGHTER_OPTIONS } from "@posthog/ui/features/sessions/diffHighlighterOptions";
 import { useContextUsage } from "@posthog/ui/features/sessions/hooks/useContextUsage";
 import { useConversationItems } from "@posthog/ui/features/sessions/hooks/useConversationItems";
@@ -102,14 +103,7 @@ export function ConversationView({
 }: ConversationViewProps) {
   const diffWorkerFactory = useService<DiffWorkerFactory>(DIFF_WORKER_FACTORY);
   const diffsPoolOptions = useMemo(
-    () => ({
-      workerFactory: () => diffWorkerFactory(),
-      totalASTLRUCacheSize: 200,
-      // Each pooled highlighter worker is a full V8 isolate with shiki
-      // grammars loaded (~40MB RSS); the library default of 8 costs hundreds
-      // of MB for parallelism conversation diffs don't need.
-      poolSize: 2,
-    }),
+    () => createConversationDiffPoolOptions(diffWorkerFactory),
     [diffWorkerFactory],
   );
 

packages/ui/src/features/sessions/components/chat-thread/ChatThread.tsx

@@ -61,6 +61,7 @@ import {
 import { SessionUpdateView } from "@posthog/ui/features/sessions/components/session-update/SessionUpdateView";
 import { UserShellExecuteView } from "@posthog/ui/features/sessions/components/session-update/UserShellExecuteView";
 import { CHAT_CONTENT_MAX_WIDTH } from "@posthog/ui/features/sessions/constants";
+import { createConversationDiffPoolOptions } from "@posthog/ui/features/sessions/conversationDiffPoolOptions";
 import { DIFFS_HIGHLIGHTER_OPTIONS } from "@posthog/ui/features/sessions/diffHighlighterOptions";
 import { useConversationItems } from "@posthog/ui/features/sessions/hooks/useConversationItems";
 import {
@@ -990,10 +991,7 @@ export function ChatThread({
 }: ConversationViewProps) {
   const diffWorkerFactory = useService<DiffWorkerFactory>(DIFF_WORKER_FACTORY);
   const diffsPoolOptions = useMemo(
-    () => ({
-      workerFactory: () => diffWorkerFactory(),
-      totalASTLRUCacheSize: 200,
-    }),
+    () => createConversationDiffPoolOptions(diffWorkerFactory),
     [diffWorkerFactory],
   );
 

packages/ui/src/features/sessions/conversationDiffPoolOptions.test.ts

@@ -0,0 +1,15 @@
+import { describe, expect, it, vi } from "vitest";
+import { createConversationDiffPoolOptions } from "./conversationDiffPoolOptions";
+
+describe("createConversationDiffPoolOptions", () => {
+  it("limits syntax-highlighting workers for diff-heavy conversations", () => {
+    const worker = {} as Worker;
+    const diffWorkerFactory = vi.fn(() => worker);
+    const options = createConversationDiffPoolOptions(diffWorkerFactory);
+
+    expect(options.poolSize).toBe(2);
+    expect(options.totalASTLRUCacheSize).toBe(200);
+    expect(options.workerFactory()).toBe(worker);
+    expect(diffWorkerFactory).toHaveBeenCalledOnce();
+  });
+});

packages/ui/src/features/sessions/conversationDiffPoolOptions.ts

@@ -0,0 +1,11 @@
+import type { DiffWorkerFactory } from "@posthog/ui/shell/diffWorkerHost";
+
+export function createConversationDiffPoolOptions(
+  diffWorkerFactory: DiffWorkerFactory,
+) {
+  return {
+    workerFactory: () => diffWorkerFactory(),
+    totalASTLRUCacheSize: 200,
+    poolSize: 2,
+  };
+}