🤖 Fix init display bug - restore defensive checks

The cleanup removed necessary defensive checks, causing crashes when
init-output or init-end arrive without init-start (can happen during
replay or out-of-order events). Restored graceful handling.

Added TDD test to prevent regression.

Generated with `cmux`

Author: ammar-agent

src/utils/messages/StreamingMessageAggregator.init.test.ts

@@ -0,0 +1,76 @@
+import { StreamingMessageAggregator } from "./StreamingMessageAggregator";
+
+interface InitDisplayedMessage {
+  type: "workspace-init";
+  status: "running" | "success" | "error";
+  lines: string[];
+  exitCode: number | null;
+}
+
+describe("Init display after cleanup changes", () => {
+  it("should display init messages correctly", () => {
+    const aggregator = new StreamingMessageAggregator();
+
+    // Simulate init start
+    aggregator.handleMessage({
+      type: "init-start",
+      hookPath: "/test/.cmux/init",
+      timestamp: Date.now(),
+    });
+
+    let messages = aggregator.getDisplayedMessages();
+    expect(messages).toHaveLength(1);
+    expect(messages[0].type).toBe("workspace-init");
+    expect((messages[0] as InitDisplayedMessage).status).toBe("running");
+
+    // Simulate init output
+    aggregator.handleMessage({
+      type: "init-output",
+      line: "Installing dependencies...",
+      timestamp: Date.now(),
+      isError: false,
+    });
+
+    messages = aggregator.getDisplayedMessages();
+    expect(messages).toHaveLength(1);
+    expect((messages[0] as InitDisplayedMessage).lines).toContain("Installing dependencies...");
+
+    // Simulate init end
+    aggregator.handleMessage({
+      type: "init-end",
+      exitCode: 0,
+      timestamp: Date.now(),
+    });
+
+    messages = aggregator.getDisplayedMessages();
+    expect(messages).toHaveLength(1);
+    expect((messages[0] as InitDisplayedMessage).status).toBe("success");
+    expect((messages[0] as InitDisplayedMessage).exitCode).toBe(0);
+  });
+
+  it("should handle init-output without init-start (defensive)", () => {
+    const aggregator = new StreamingMessageAggregator();
+
+    // This might crash with non-null assertion if initState is null
+    expect(() => {
+      aggregator.handleMessage({
+        type: "init-output",
+        line: "Some output",
+        timestamp: Date.now(),
+        isError: false,
+      });
+    }).not.toThrow();
+  });
+
+  it("should handle init-end without init-start (defensive)", () => {
+    const aggregator = new StreamingMessageAggregator();
+
+    expect(() => {
+      aggregator.handleMessage({
+        type: "init-end",
+        exitCode: 0,
+        timestamp: Date.now(),
+      });
+    }).not.toThrow();
+  });
+});

src/utils/messages/StreamingMessageAggregator.ts

@@ -511,15 +511,17 @@ export class StreamingMessageAggregator {
     }
 
     if (isInitOutput(data)) {
+      if (!this.initState) return; // Defensive: shouldn't happen but handle gracefully
       const line = data.isError ? `ERROR: ${data.line}` : data.line;
-      this.initState!.lines.push(line.trimEnd());
+      this.initState.lines.push(line.trimEnd());
       this.invalidateCache();
       return;
     }
 
     if (isInitEnd(data)) {
-      this.initState!.exitCode = data.exitCode;
-      this.initState!.status = data.exitCode === 0 ? "success" : "error";
+      if (!this.initState) return; // Defensive: shouldn't happen but handle gracefully
+      this.initState.exitCode = data.exitCode;
+      this.initState.status = data.exitCode === 0 ? "success" : "error";
       this.invalidateCache();
       return;
     }