fix(ui): stabilize task loading and live feeds (#13095)

Coordinate initial conversation reveal, preserve message identity and reading anchors during live updates, and bound transcript reads with recoverable retries. Cover desktop/mobile navigation and rich task loading with actual-route browser tests.

Verified all Linux CI gates, 5,575 local UI tests, eight layout browser scenarios, and recorded native Codex walkthroughs. Greptile: 5/5; all review findings resolved.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

ui/src/components/transcript/read-transcript-request.ts

@@ -0,0 +1,35 @@
+export const TRANSCRIPT_REQUEST_TIMEOUT_MS = 15_000;
+
+/** Bound history reads, including body consumption, and release coalesced GETs
+ * on timeout so Retry starts a fresh request. Late responses cannot commit. */
+export function readTranscriptRequest<T>(request: (signal: AbortSignal) => Promise<T>, signal: AbortSignal): Promise<T> {
+  if (signal.aborted) return Promise.reject(new DOMException("History read cancelled", "AbortError"));
+  return new Promise<T>((resolve, reject) => {
+    const controller = new AbortController();
+    let settled = false;
+    const finish = (complete: () => void) => {
+      if (settled) return;
+      settled = true;
+      window.clearTimeout(timer);
+      signal.removeEventListener("abort", onAbort);
+      complete();
+    };
+    const onAbort = () => {
+      finish(() => reject(new DOMException("History read cancelled", "AbortError")));
+      controller.abort();
+    };
+    const timer = window.setTimeout(() => {
+      finish(() => reject(new Error("Run history took too long to load. Retry to load it.")));
+      controller.abort();
+    }, TRANSCRIPT_REQUEST_TIMEOUT_MS);
+    signal.addEventListener("abort", onAbort, { once: true });
+    try {
+      request(controller.signal).then(
+        (value) => finish(() => resolve(value)),
+        (error) => finish(() => reject(error)),
+      );
+    } catch (error) {
+      finish(() => reject(error));
+    }
+  });
+}