Serve replay playback from a cached analysis result

Replay re-ran the SDK chain on every seek; Part A's pass stores the flow
samples once. Opening a recording now reuses a compatible result or runs the
pass behind a progress/cancel surface, and one cursor with two modes
(recorded CSV, analysed) feeds the charts, the 2D canvas and the 3D pane by
frame id. A threshold, colour or idle-dot change redraws from the stored
frames and writes nothing; a cancelled pass is reported and never played.

Verified: apps/studio/tests 440 items / 0 failed / 18 skipped (15 new, no
existing assertion changed); shared 417 / 0 / 1; autocal 358.

apps/studio/config/locales/en_US.json

@@ -155,7 +155,8 @@
     "units_newton": "Newton",
     "units_raw": "Raw",
     "settings": "Settings",
-    "settings_tip": "Show or hide the unit, record-mode and preview controls"
+    "settings_tip": "Show or hide the unit, record-mode and preview controls",
+    "stopped_analysis": "analysis"
   },
   "units": {
     "newton_short": "N",
@@ -218,7 +219,10 @@
     "mesh3d_rejected": "The 3D scene was refused: {message}\nOnly the 3D view is affected; measuring, recording and the charts work as usual.",
     "mesh3d_unavailable_gl_reason": "3D is not available on this machine: {reason}\nMeasuring, recording and the charts work as usual.",
     "mesh3d_settings_tip": "3D display settings (view, housing, colour scale, frame rate)",
-    "mesh3d_reset_tip": "Reset view: back to the framing the scene itself uses"
+    "mesh3d_reset_tip": "Reset view: back to the framing the scene itself uses",
+    "analysis_pipeline": "Analysis result (one finished pass)",
+    "analysis_pipeline_tip": "This frame's arrows come from a stored analysis result rather than a chain running now; changing the threshold only changes which stored samples count as active.",
+    "analysis_empty": "the analysis result holds no frame here"
   },
   "chart": {
     "fn": "FN",
@@ -278,7 +282,16 @@
     "warn_config_missing": "no config hash was recorded, so recomputation cannot be verified",
     "warn_rows_skipped": "some unparsable CSV rows were skipped",
     "warn_frames_dropped": "frames were lost to a full queue; only their index rows remain (shown as \"not recorded\")",
-    "warn_out_of_order": "this recording was written by an older version: its rows are not in time order, so the replay re-sorts them and window edges may differ"
+    "warn_out_of_order": "this recording was written by an older version: its rows are not in time order, so the replay re-sorts them and window edges may differ",
+    "analysis_empty": "this analysis result holds no frame to show",
+    "analysis_unreadable": "this frame cannot be read ({error})",
+    "analysis_complete": "replaying from the analysis result: {frames} frames, cursor on signal time (the recording's own frames.csv)",
+    "analysis_reused": "an analysis result was already stored and is being replayed: {frames} frames",
+    "analysis_failed": "the analysis did not finish ({reason}): playback is not served. Re-run it, or turn 「从视频重算」 off to read the recorded forces.csv",
+    "analysis_cancelled": "the analysis was cancelled: no complete result was written, so no playback is served",
+    "analysis_no_source": "this recording has no video segment to analyse",
+    "analysis_busy": "an analysis is already running: wait for it, or cancel it",
+    "analysis_grid_mismatch": "the current display settings moved the sample grid ({keys}); the stored candidate locations cannot serve it, so the replay keeps drawing the result's own grid"
   },
   "record": {
     "label": "Record",
@@ -497,6 +510,27 @@
     "severity_info": "Note",
     "severity_warning": "Warning",
     "severity_error": "Error",
-    "stats": "shown {displayed} · display drops {dropped} · compose {compose} ms · paint {paint} ms"
+    "stats": "shown {displayed} · display drops {dropped} · compose {compose} ms · paint {paint} ms",
+    "source_analysis": "Analysis result: one finished pass, read by frame",
+    "source_analysis_tip": "The picture comes from a stored analysis result: the chain has already run and its output is on disk, so scrubbing and playing are file reads. Changing a threshold or a colour does not recompute."
+  },
+  "analysis": {
+    "title": "Analysing the recording",
+    "subtitle": "once only: scrubbing, playing and stepping afterwards are reads",
+    "stage_open": "open chain",
+    "stage_frames": "frame by frame",
+    "stage_write": "write result",
+    "frames": "{written} / {expected} frames",
+    "segment": "segment {index} / {count}",
+    "elapsed": "{seconds:.1f} s elapsed",
+    "cancel": "Cancel",
+    "cancelling": "Cancelling…",
+    "cancel_tip": "Cancel this pass: the frames already written stay, but the result is marked incomplete and is never played back as if it were whole",
+    "reused": "a stored result is already there — nothing to recompute",
+    "complete": "analysis finished: {frames} frames in {seconds:.1f} s",
+    "cancelled": "analysis cancelled ({frames} frames written; the result is marked incomplete)",
+    "failed": "analysis failed: {reason}",
+    "incomplete": "the result is incomplete: {reason}",
+    "blocked": "a session is running: stop it before analysing"
   }
 }