fix(client): реальный обрыв SSE → reconnect-лесенка, не терминальный error (#488)

Браузерный QA поймал баг, который юнит-тесты пропускали из-за вакуумной SDK-формы.

Премиса (подтверждена по ai@6.0.207 AbstractChat.makeRequest, catch ~13763): при
сетевом дропе SDK ставит isError=true БЕЗУСЛОВНО, а isError=true → isDisconnect=true
ставится РЯДОМ (только для fetch/network TypeError). Т.е. реальный обрыв ВСЕГДА
даёт { isError:true, isDisconnect:true }; форма { isDisconnect:true, isError:false }
SDK'ом НЕ эмитится.

Баг: в onFinish проверка `if (isError) return` стояла РАНЬШЕ ветки isDisconnect →
реальный дроп уходил в терминальный error-баннер, а FINISH_DISCONNECT (единственный
вход в reconnect-лесенку) не диспатчился НИКОГДА. Сценарии 1/2 (commit 2 «обрыв до
первого кадра» и commit 3 «два обрыва») в браузере не работали.

Фикс: маршрутизация по disconnect ПЕРВЫМ: isDisconnect → FINISH_DISCONNECT
(reconnect); НЕ-disconnect error (isError && !isDisconnect, напр. провайдерский 500)
→ FINISH_ERROR (терминал); затем isAbort; затем clean. Порядок веток supersede-
блока тоже disconnect-first (для консистентности; там всё равно всё дропается I1).

Инварианты сохранены: epoch-штамп turnEpochRef на всех FINISH_*; honor-in-stopping
в редьюсере честит ЛЮБОЙ финиш в фазе stopping → на пути Stop дроп-финиш уходит в
idle, а не в ложный reconnect (новый тест). F1 supersede-drop чужого поколения цел.

Тесты сделаны НЕ вакуумными: дроп подаётся реальной формой { isError:true,
isDisconnect:true }, терминальная ошибка — { isError:true, isDisconnect:false }.
MUTATION-VERIFY: багованный isError-first порядок → 6 reconnect-тестов краснеют
(нет баннера «reconnecting»); с фиксом зелены. Полный ai-chat 35 файлов / 377 / 0.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/client/src/features/ai-chat/components/chat-thread.test.tsx

@@ -248,14 +248,15 @@ describe("ChatThread — send now", () => {
     startLocalStreamWithRun();
     fireEvent.click(screen.getByTestId("queue-btn"));
     fireEvent.click(screen.getByLabelText("Send now")); // -> superseding, aborts A
-    // A ends via isDisconnect (the server CAS closed it). The OLD overlap bug would
-    // route the LIVE new run into a false reconnect banner.
+    // A ends via a REAL network drop { isError:true, isDisconnect:true } (the server
+    // CAS closed it). The OLD overlap bug would route the LIVE new run into a false
+    // reconnect banner.
     await act(async () => {
       h.state.onFinish?.({
         message: { id: "a1", role: "assistant", parts: [{ type: "text", text: "x" }] },
         isAbort: false,
         isDisconnect: true,
-        isError: false,
+        isError: true,
       });
       await Promise.resolve();
     });
@@ -328,6 +329,23 @@ describe("ChatThread — send now", () => {
     expect(screen.getAllByLabelText("Remove queued message")).toHaveLength(1);
   });
 
+  it("Stop then a REAL network-drop finish exits to idle (honor-in-stopping), NOT a false reconnect", () => {
+    // Regression for the disconnect-first reorder: on the STOP path, even a drop-
+    // form finish { isError:true, isDisconnect:true } arriving in `stopping` must be
+    // HONORED (reducer) and exit to idle — it must NOT enter the reconnect ladder.
+    startLocalStreamWithRun(); // live local stream, autonomous
+    fireEvent.click(screen.getByLabelText("Stop")); // STOP_REQUESTED -> stopping
+    act(() => {
+      h.state.onFinish?.({
+        message: { id: "a1", role: "assistant", parts: [] },
+        isAbort: false,
+        isDisconnect: true,
+        isError: true,
+      });
+    });
+    expect(screen.queryByText(/reconnecting/i)).toBeNull();
+  });
+
   it("Send now is HIDDEN while observing a resumed run and VISIBLE on a local stream", () => {
     // Resumed (mount attach) -> observer -> hidden.
     renderThread({ autonomousRunsEnabled: true, initialRows: streamingTail() });
@@ -419,15 +437,18 @@ describe("ChatThread — turn-end decision (onFinish)", () => {
     expect(screen.getByText("Response stopped.")).toBeTruthy();
   });
 
-  it("ENDS — keeps the queue on a disconnect (non-autonomous) and shows the notice", () => {
-    finishWith({ isDisconnect: true });
+  it("ENDS — keeps the queue on a REAL disconnect (non-autonomous) and shows the notice", () => {
+    // Real SDK drop form: { isError:true, isDisconnect:true }. With the buggy
+    // isError-first order this would fall to the terminal error branch (no notice).
+    finishWith({ isDisconnect: true, isError: true });
     expect(h.state.sendMessage).not.toHaveBeenCalled();
     expect(
       screen.getByText("Connection lost — the answer was interrupted."),
     ).toBeTruthy();
   });
 
-  it("ENDS — keeps the queue on a stream error (no notice)", () => {
+  it("ENDS — keeps the queue on a NON-disconnect stream error (no notice)", () => {
+    // A provider error is { isError:true, isDisconnect:false } — terminal.
     finishWith({ isError: true });
     expect(h.state.sendMessage).not.toHaveBeenCalled();
     expect(screen.queryByText("Response stopped.")).toBeNull();
@@ -437,7 +458,7 @@ describe("ChatThread — turn-end decision (onFinish)", () => {
     for (const flags of [
       {},
       { isAbort: true },
-      { isDisconnect: true },
+      { isDisconnect: true, isError: true },
       { isError: true },
     ]) {
       cleanup();
@@ -787,13 +808,18 @@ describe("ChatThread — live reconnect + stalled", () => {
     cleanup();
   });
 
+  // A REAL live SSE drop. ai@6.0.207 emits BOTH { isError:true, isDisconnect:true }
+  // for a network TypeError — NOT the { isError:false } form the old tests fed. This
+  // is the form browser QA hit; with the buggy isError-first routing these tests go
+  // red (a real drop would surface the terminal error banner, not the reconnect
+  // ladder). MUTATION-VERIFY of the disconnect-first fix.
   function disconnect(message: unknown = liveMsg) {
     act(() => {
       h.state.onFinish?.({
         message,
         isAbort: false,
         isDisconnect: true,
-        isError: false,
+        isError: true,
       });
     });
   }

apps/client/src/features/ai-chat/components/chat-thread.tsx

@@ -626,10 +626,13 @@ export default function ChatThread({
         machineRef.current.phase.name === "superseding" &&
         pendingSupersedeTextRef.current !== null
       ) {
-        if (isError) dispatch({ type: "FINISH_ERROR", kind: "stream", epoch: stampEpoch });
-        else if (isAbort) dispatch({ type: "FINISH_ABORT", epoch: stampEpoch });
-        else if (isDisconnect)
+        // Disconnect-first (see the routing note below): a real drop is
+        // { isError:true, isDisconnect:true }. All of these are dropped by I1 here
+        // (superseding bumped the epoch) — the order only mirrors the main routing.
+        if (isDisconnect)
           dispatch({ type: "FINISH_DISCONNECT", hasVisibleContent: msgHasVisible, epoch: stampEpoch });
+        else if (isError) dispatch({ type: "FINISH_ERROR", kind: "stream", epoch: stampEpoch });
+        else if (isAbort) dispatch({ type: "FINISH_ABORT", epoch: stampEpoch });
         else dispatch({ type: "FINISH_CLEAN", epoch: stampEpoch });
         const text = pendingSupersedeTextRef.current;
         pendingSupersedeTextRef.current = null;
@@ -642,18 +645,14 @@ export default function ChatThread({
         return;
       }
 
-      if (isError) {
-        dispatch({ type: "FINISH_ERROR", kind: "stream", epoch: stampEpoch });
-        setStopNotice(null);
-        return;
-      }
-      if (isAbort) {
-        // A user Stop / an interrupt abort finished. The FSM stopping/idle exit is
-        // by DATA (this terminal outcome, I4).
-        dispatch({ type: "FINISH_ABORT", epoch: stampEpoch });
-        setStopNotice("manual");
-        return;
-      }
+      // #488 (browser QA): route DISCONNECT FIRST. In ai@6.0.207 a real network drop
+      // yields BOTH `{ isError:true, isDisconnect:true }` — the SDK sets `isError`
+      // unconditionally in its catch and `isDisconnect` only ALONGSIDE it (for a
+      // fetch/network TypeError). Checking `isError` first therefore sent EVERY real
+      // drop to the terminal error banner and NEVER entered the reconnect ladder
+      // (`FINISH_DISCONNECT` is its only entry). A disconnect — the detached run
+      // keeps executing server-side — must win; only a NON-disconnect error (a
+      // provider 500, `{ isError:true, isDisconnect:false }`) is terminal.
       if (isDisconnect) {
         if (wasObserver) {
           // A resumed/attached OBSERVER stream dropped. Recover via the degraded
@@ -722,6 +721,19 @@ export default function ChatThread({
         }
         return;
       }
+      // A NON-disconnect stream error (a provider 500 etc.) -> terminal error banner.
+      if (isError) {
+        dispatch({ type: "FINISH_ERROR", kind: "stream", epoch: stampEpoch });
+        setStopNotice(null);
+        return;
+      }
+      if (isAbort) {
+        // A user Stop / an interrupt abort finished. The FSM stopping/idle exit is
+        // by DATA (this terminal outcome, I4 — honored in `stopping` by the reducer).
+        dispatch({ type: "FINISH_ABORT", epoch: stampEpoch });
+        setStopNotice("manual");
+        return;
+      }
       // Clean finish.
       if (wasObserver) {
         if (mountedRef.current) {