fix(studio): 回放视图加一个无条件「停止」（Esc 同效），并让「文件一帧都不出」直接报错而不是一直等

- What: `ToolbarWidget` 新增 `set_reset_role("reset"/"stop")`，回放视图把轨道第二个按钮变成「停止」；
  `StudioMainWindow._stop_replay_activity()` 一次停掉回放（play_timer）与「从视频重算」通道（worker），
  并清掉三维面板上的重算画面，状态栏说明"已停止了什么"；`_on_reset`/`_on_stop_shortcut`(Esc) 按角色路由；
  `_start_playback`/`_pause_playback` 结束时调用 `_update_run_enabled()`，让停止按钮在有东西可停时才可用；
  两个采集 worker 新增 `FILE_FIRST_FRAME_TIMEOUT_S=10s`：文件源一帧都没出来就报错结束会话
  （原先 `saw_frame` 为假时 EOF 分支永不执行，循环空转到天荒地老、窗口一直停在"连接中"）。
- Why: 用户报告"视频播放完之后无法再次按回放，卡住了"，并建议加手动停止。复现得到两种状态：
  ① 普通回放播到末尾后再按回放**是可以**重新从头播的（探针实测 0.967→0→0.371，计时器在跑），
  不是这条路径的问题；② 「从视频重算」通道跑文件时，工作线程可能既不出帧也不结束
  （实测：1.5 s 的合成视频跑 25 s，packets=0 且 is_running=True），于是界面永远停在运行/连接状态，
  操作者看到"卡住"。所以既给一个无论什么状态都能按的停止，也让"读不出帧"变成一条明确的错误。
- Verification: 新增/更新用例：`test_worker_frame_rate.py` 的"文件一帧都不出→error+消息"（缩短时限跑，
  真实 worker）；`test_ui_smoke.py` 三项：回放视图的停止按钮（播放中可用、按下停回放、重算中停下重算、
  无事可停时说明）、Esc 同样能停、实时视图仍是「重置」；apps/studio 全量通过；shared 全量通过；
  ui_check 583 项 0 失败（新增回放停止的 5 项检查，并给"场景已加载却仍在显示消息"那条加了诊断细节，
  它此前偶发失败过一次、这次跑通）。
- Not in this change: 普通回放"播到末尾→再按回放"的路径（实测正常，未改）；让回放直接播放"非记录"的视频
  （仍走「从视频重算」）；`_recompute_running` 与 worker 真实状态的进一步合并（现在停止按钮同时看两者）。

apps/studio/src/orisys_studio/app_window.py

@@ -1033,6 +1033,9 @@ class StudioMainWindow(QMainWindow):
         self._play_timer.start()
         self.toolbar.set_run_checked(True)
         self.toolbar.refresh_labels()
+        # The stop button appears with the playback: one place decides what the rail
+        # offers, so it is told here rather than kept in step in two places.
+        self._update_run_enabled()
 
     def _pause_playback(self) -> None:
         if self._play_timer.isActive():
@@ -1040,6 +1043,7 @@ class StudioMainWindow(QMainWindow):
         if self.toolbar.btn_run.isChecked():
             self.toolbar.set_run_checked(False)
             self.toolbar.refresh_labels()
+        self._update_run_enabled()
 
     def _on_play_tick(self) -> None:
         """Advance the playhead from the wall clock, not from the tick count."""
@@ -1486,8 +1490,10 @@ class StudioMainWindow(QMainWindow):
         self._pause_playback()
         self.toolbar.set_source_view("replay" if preset == "replay" else "live")
         # The rail's primary button is this view's main action: acquire while
-        # measuring, play back while replaying.
+        # measuring, play back while replaying; and the second button is that view's
+        # own reset — or, in the replay view, an unconditional stop.
         self.toolbar.set_run_role("playback" if preset == "replay" else "acquire")
+        self.toolbar.set_reset_role("stop" if preset == "replay" else "reset")
         self._apply_panel_visibility()
         if apply_sizes and preset in VIEW_SPLITTER_SIZES:
             self.content_splitter.setSizes(self._splitter_sizes_for(preset))
@@ -1529,6 +1535,14 @@ class StudioMainWindow(QMainWindow):
                 reason = t("toolbar.playback_disabled")
             self.toolbar.set_run_tooltip_reason(reason)
             self.toolbar.set_run_enabled(loaded or self._play_timer.isActive())
+            # The stop button is offered whenever there is something to stop; the
+            # operator must never have to guess whether that is the case.
+            if self.toolbar.reset_role() == "stop":
+                self.toolbar.set_reset_enabled(
+                    self._play_timer.isActive()
+                    or self._recompute_running
+                    or self._session_active
+                )
             self.toolbar.set_record_enabled(
                 self._running or self.recorder.is_recording
             )
@@ -2272,7 +2286,16 @@ class StudioMainWindow(QMainWindow):
         self.toolbar.btn_run.setChecked(not self.toolbar.btn_run.isChecked())
 
     def _on_stop_shortcut(self) -> None:
-        """Esc must always be able to cancel a session, even a stuck connect."""
+        """Esc must always be able to cancel a session, even a stuck connect.
+
+        In the replay view it is the same escape hatch as the rail's 停止 button: a
+        replay or a recompute pass that will not stop by itself has to be stoppable
+        from the keyboard.
+        """
+        if self.toolbar.run_role() == "playback":
+            if self._play_timer.isActive() or self._session_active:
+                self._stop_replay_activity()
+            return
         if not self._session_active:
             return
         self._stop_run(reason="user_stop")
@@ -2576,7 +2599,36 @@ class StudioMainWindow(QMainWindow):
         else:
             self.statusBar().showMessage(t("status.run_stopped"))
 
+    def _stop_replay_activity(self) -> None:
+        """Stop whatever the replay view is doing. The operator's escape hatch.
+
+        Two different things can be running there — plain playback of the recorded
+        timeline, and a recompute pass over the video — and the person in front of the
+        screen should not have to work out which one is stuck before they can stop it.
+        So this stops both, clears a recomputed 3D picture, and says what it stopped.
+        Safe to press when nothing is running (it says so rather than doing nothing
+        silently, which is what made a stuck state feel stuck).
+        """
+        stopped: list[str] = []
+        if self._recompute_running or self._session_active:
+            self._stop_run(reason="user_stop")
+            stopped.append(t("toolbar.stopped_pass"))
+        if self._play_timer.isActive():
+            self._pause_playback()
+            stopped.append(t("toolbar.stopped_playback"))
+        self.mesh3d_panel.show_reference_only()
+        self._update_run_enabled()
+        if stopped:
+            self._notify(t("toolbar.stopped", what=", ".join(stopped)))
+        else:
+            self._notify(t("toolbar.nothing_to_stop"))
+
     def _on_reset(self) -> None:
+        if self.toolbar.reset_role() == "stop":
+            # In the replay view that button is the operator's way out of a replay or
+            # a recompute pass, whatever state the transport is in.
+            self._stop_replay_activity()
+            return
         if self._session_phase != "running" or self._active_worker is None:
             return
         try:

apps/studio/src/orisys_studio/ui/toolbar.py

@@ -107,6 +107,7 @@ class ToolbarWidget(QWidget):
         self._video_path = ""
         #: ``acquire`` while measuring, ``playback`` while replaying a recording.
         self._run_role = "acquire"
+        self._reset_role = "reset"
 
         outer = QVBoxLayout(self)
         outer.setContentsMargins(2, 2, 2, 2)
@@ -387,6 +388,34 @@ class ToolbarWidget(QWidget):
     def run_role(self) -> str:
         return self._run_role
 
+    def set_reset_role(self, role: str) -> None:
+        """What the second rail button does: zero the tracker, or stop the replay.
+
+        The replay view needs a *stop* the operator can always reach. The transport
+        button is a play/pause toggle, which is ambiguous precisely when something is
+        wrong (is it playing? is a recompute pass running?), so the second button —
+        disabled in that view otherwise — becomes an unconditional stop instead of a
+        second thing to reason about.
+        """
+        wanted = "stop" if str(role) == "stop" else "reset"
+        if wanted == self._reset_role:
+            return
+        self._reset_role = wanted
+        if wanted == "reset":
+            self.btn_reset.setEnabled(False)
+        self._refresh_reset_label()
+
+    def reset_role(self) -> str:
+        return self._reset_role
+
+    def _refresh_reset_label(self) -> None:
+        if self._reset_role == "stop":
+            self.btn_reset.setText(t("toolbar.stop_playback"))
+            self.btn_reset.setToolTip(t("toolbar.stop_playback_tip"))
+            return
+        self.btn_reset.setText(t("toolbar.reset"))
+        self.btn_reset.setToolTip("")
+
     def source_view(self) -> str:
         return self._source_view
 
@@ -686,7 +715,7 @@ class ToolbarWidget(QWidget):
         self.btn_use_camera.setText(t("toolbar.use_camera"))
         self.btn_replay_video.setText(t("toolbar.choose_video"))
         self.refresh_labels()
-        self.btn_reset.setText(t("toolbar.reset"))
+        self._refresh_reset_label()
         self.units_label.setText(t("toolbar.units"))
         self.units_combo.setItemText(0, t("toolbar.units_newton"))
         self.units_combo.setItemText(1, t("toolbar.units_raw"))