fix(app): truncate agent sender attribution to one line (#8092)

Constrain the sender label to the message width so long agent names do not wrap above received messages. Keep the line limit opt-in on Button and cover compact chat widths with a real-browser regression.

packages/app/e2e/browser/turn-collapse.spec.ts

@@ -203,6 +203,47 @@ test("received messages show their sender and open that agent", async ({ page })
   }
 });
 
+test("long sender attribution stays on one line in compact chat", async ({ page }, testInfo) => {
+  await page.setViewportSize({ width: 390, height: 844 });
+  await page.addInitScript(() =>
+    localStorage.setItem("@paseo:app-settings", JSON.stringify({ theme: "dark" })),
+  );
+  const recipient = await seedMockAgentWorkspace({
+    repoPrefix: "compact-attribution-",
+    title: "Implementation",
+  });
+  try {
+    const title = "Reviewer checking the compact chat timeline and sender attribution";
+    const sender = await recipient.client.createAgent({
+      provider: "codex",
+      cwd: recipient.cwd,
+      workspaceId: recipient.workspaceId,
+      title,
+      model: "gpt-6.1-sol",
+      modeId: "full-access",
+    });
+    await recipient.client.sendAgentMessage(
+      recipient.agentId,
+      "The sender label stays on one line, even when the agent has a long name.",
+      { sourceAgentId: sender.id },
+    );
+    await openAgentRoute(page, recipient);
+    await expectComposerVisible(page);
+    const attribution = page.getByRole("button", { name: `Sent by ${title}`, exact: true });
+    await expect(attribution).toBeVisible();
+    await expectSenderTruncatedWithinMessage(attribution, title);
+    await expectSenderAlignedWithBubble(attribution);
+    await attribution.scrollIntoViewIfNeeded();
+    await page.screenshot({ path: testInfo.outputPath("sender-compact-390.png") });
+    await page.setViewportSize({ width: 320, height: 740 });
+    await expectSenderTruncatedWithinMessage(attribution, title);
+    await expectSenderAlignedWithBubble(attribution);
+    await page.screenshot({ path: testInfo.outputPath("sender-compact-320.png") });
+  } finally {
+    await recipient.cleanup();
+  }
+});
+
 interface MessagePreviewWatch {
   /** Frames after the watch started on which the fade or "Show more" control was missing. */
   framesWithoutClip: number[];
@@ -316,6 +357,20 @@ test("opening a turn keeps the received message above it clipped on every frame"
   }
 });
 
+async function expectSenderTruncatedWithinMessage(attribution: Locator, title: string) {
+  const label = attribution.getByText(`Sent by ${title}`, { exact: true });
+  await expect(label).toHaveCSS("white-space", "nowrap");
+  await expect(label).toHaveCSS("text-overflow", "ellipsis");
+  const bounds = await label.evaluate((element) => ({
+    textWidth: element.scrollWidth,
+    visibleWidth: element.clientWidth,
+    right: element.getBoundingClientRect().right,
+    viewportWidth: document.documentElement.clientWidth,
+  }));
+  expect(bounds.textWidth).toBeGreaterThan(bounds.visibleWidth);
+  expect(bounds.right).toBeLessThanOrEqual(bounds.viewportWidth);
+}
+
 async function expectSenderAlignedWithBubble(attribution: Locator) {
   const edges = await attribution.evaluate((button) => {
     const bubble = button.nextElementSibling;

packages/app/src/components/ui/button.tsx

@@ -168,6 +168,7 @@ export function Button({
   trailing,
   style,
   textStyle,
+  numberOfLines,
   disabled,
   loading = false,
   accessibilityRole,
@@ -182,6 +183,7 @@ export function Button({
     trailing?: ReactNode;
     style?: StyleProp<ViewStyle>;
     textStyle?: StyleProp<TextStyle>;
+    numberOfLines?: number;
     loading?: boolean;
   }
 >) {
@@ -277,7 +279,11 @@ export function Button({
         iconSize={buttonIconSize[size]}
         uniProps={resolveIconMapping()}
       />
-      {children != null ? <Text style={resolvedTextStyle}>{children}</Text> : null}
+      {children != null ? (
+        <Text numberOfLines={numberOfLines} style={resolvedTextStyle}>
+          {children}
+        </Text>
+      ) : null}
       {trailing}
     </Pressable>
   );

packages/app/src/components/user-message/index.tsx

@@ -80,6 +80,8 @@ export function MessageSender({
       size="sm"
       leftIcon={renderProviderIcon}
       style={styles.sender}
+      textStyle={styles.senderText}
+      numberOfLines={1}
       disabled={!host}
       onPress={openSender}
     >
@@ -90,7 +92,8 @@ export function MessageSender({
 
 const styles = StyleSheet.create((theme) => ({
   body: { flexShrink: 0 },
-  sender: { paddingRight: 0, borderRightWidth: 0 },
+  sender: { paddingRight: 0, borderRightWidth: 0, maxWidth: "100%" },
+  senderText: { flexShrink: 1 },
   toggle: { alignSelf: "flex-start", paddingHorizontal: 0, minHeight: 0, borderWidth: 0 },
   expandedToggle: { marginTop: theme.spacing[2] },
   fade: { position: "absolute", bottom: 0, left: 0, right: 0, height: theme.spacing[12] },