fix(webui): clear stale 'Reasoning...' indicator before large-chat re-render

tests/test_webui_snapshot_ordering.py

@@ -0,0 +1,100 @@
+"""Regression tests for the Web UI snapshot-application ordering.
+
+Root cause (2026-08-02): after a WebSocket reconnect mid-turn, the frontend
+receives a snapshot whose log version advanced while disconnected. In
+``applySnapshot`` the cheap agent-state fields (progress indicator, paused
+flag, notifications) were applied only AFTER ``await setMessages(...)``.
+For large chats the message re-render can take a very long time, so a stale
+"A0: Reasoning..." indicator stayed on screen — making an idle, finished
+agent look like it was still working — until the render backlog drained.
+
+The fix sequences the cheap state updates before the render await. These
+tests pin that ordering in ``webui/index.js``.
+"""
+
+import sys
+from pathlib import Path
+
+PROJECT_ROOT = Path(__file__).resolve().parents[1]
+if str(PROJECT_ROOT) not in sys.path:
+    sys.path.insert(0, str(PROJECT_ROOT))
+
+
+def _load_apply_snapshot_body() -> str:
+    js = (PROJECT_ROOT / "webui" / "index.js").read_text(encoding="utf-8")
+    start = js.find("export async function applySnapshot(")
+    assert start != -1, "applySnapshot function not found in webui/index.js"
+    # Skip the parameter list first (its `options = {}` default would fool a
+    # naive brace counter), then brace-count the body to its matching close.
+    paren_open = js.find("(", start)
+    depth = 0
+    pos = paren_open
+    while pos < len(js):
+        char = js[pos]
+        if char == "(":
+            depth += 1
+        elif char == ")":
+            depth -= 1
+            if depth == 0:
+                break
+        pos += 1
+    body_start = js.find("{", pos)
+    assert body_start != -1, "applySnapshot body opening brace not found"
+    depth = 0
+    for pos in range(body_start, len(js)):
+        char = js[pos]
+        if char == "{":
+            depth += 1
+        elif char == "}":
+            depth -= 1
+            if depth == 0:
+                return js[start : pos + 1]
+    raise AssertionError("applySnapshot body is unbalanced in webui/index.js")
+
+
+def test_apply_snapshot_updates_progress_before_render():
+    body = _load_apply_snapshot_body()
+    progress_pos = body.find("updateProgress(snapshot.log_progress")
+    render_pos = body.find("await setMessages(modelGateStore")
+    assert progress_pos != -1, "updateProgress call not found in applySnapshot"
+    assert render_pos != -1, "setMessages render call not found in applySnapshot"
+    assert progress_pos < render_pos, (
+        "updateProgress must run before `await setMessages(...)` so the "
+        "progress indicator cannot go stale behind a slow re-render"
+    )
+
+
+def test_apply_snapshot_updates_paused_before_render():
+    body = _load_apply_snapshot_body()
+    paused_pos = body.find("inputStore.paused = snapshot.paused")
+    render_pos = body.find("await setMessages(modelGateStore")
+    assert paused_pos != -1, "paused assignment not found in applySnapshot"
+    assert render_pos != -1, "setMessages render call not found in applySnapshot"
+    assert paused_pos < render_pos, (
+        "inputStore.paused must run before `await setMessages(...)` so the "
+        "paused state cannot go stale behind a slow re-render"
+    )
+
+
+def test_apply_snapshot_updates_notifications_before_render():
+    body = _load_apply_snapshot_body()
+    notif_pos = body.find("notificationStore.updateFromPoll(snapshot)")
+    render_pos = body.find("await setMessages(modelGateStore")
+    assert notif_pos != -1, "notification update not found in applySnapshot"
+    assert render_pos != -1, "setMessages render call not found in applySnapshot"
+    assert notif_pos < render_pos, (
+        "notifications must update before `await setMessages(...)` so they "
+        "cannot be delayed by a slow re-render"
+    )
+
+
+def test_apply_snapshot_keeps_log_cursors_after_render():
+    """Cursor updates must stay after the render block: if the render throws,
+    the next poll must retry the same log version instead of skipping it."""
+    body = _load_apply_snapshot_body()
+    render_pos = body.find("await setMessages(modelGateStore")
+    cursor_pos = body.find("lastLogVersion = snapshot.log_version")
+    assert render_pos != -1 and cursor_pos != -1
+    assert cursor_pos > render_pos, (
+        "lastLogVersion must only advance after setMessages succeeds"
+    )

webui/index.js

@@ -408,6 +408,19 @@ export async function applySnapshot(snapshot, options = {}) {
     lastLogGuid = snapshot.log_guid;
   }
 
+  // Apply cheap agent-state fields BEFORE the potentially expensive message
+  // render below. After a reconnect, a large chat log can take a long time to
+  // re-render; sequencing these behind `await setMessages(...)` leaves a stale
+  // "Reasoning..."/paused indicator on screen until the render backlog drains,
+  // making an idle agent look like it is still working.
+  updateProgress(snapshot.log_progress, snapshot.log_progress_active);
+
+  // Update notifications from snapshot
+  notificationStore.updateFromPoll(snapshot);
+
+  // set ui model vars from backend
+  inputStore.paused = snapshot.paused;
+
   if (lastLogVersion != snapshot.log_version) {
     updated = true;
     if (snapshot.logs?.[0]?.no === 0) {
@@ -420,14 +433,6 @@ export async function applySnapshot(snapshot, options = {}) {
   lastLogVersion = snapshot.log_version;
   lastLogGuid = snapshot.log_guid;
 
-  updateProgress(snapshot.log_progress, snapshot.log_progress_active);
-
-  // Update notifications from snapshot
-  notificationStore.updateFromPoll(snapshot);
-
-  // set ui model vars from backend
-  inputStore.paused = snapshot.paused;
-
   // Optional: treat snapshot application as proof of connectivity (poll path)
   if (touchConnectionStatus) {
     setConnectionStatus(true);