perf(vegas): report the frame rate when it is worth reporting

Two Vegas telemetry lines were 37% of a running rig's entire log volume:
"Vegas FPS" every five seconds and "Scroll progress" on its own five-second
timer, 712 lines in half an hour, every one a journal write to an SD card.

The FPS line is the interesting one, because almost none of it was news.
Measured over two hours on that rig: 1410 samples, 98.5% of them within 10%
of target. What the other 1.5% contained was a reading of 8.6fps against a
target of 60 -- a real stall, sitting invisible inside 1389 lines that read
"59.6".

So it now reports at INFO when the frame rate falls short of target, when it
recovers from a shortfall, and on a five-minute heartbeat so a healthy
marquee still shows a pulse. Everything else drops to debug.

Replaying the same two hours of real samples through the committed logic:
1410 -> 53 INFO lines, a 96% reduction, and all 21 degraded samples are
retained, worst reading included. The signal survives; the wall of "fine"
does not.

Scroll progress is demoted outright. It reports how far along a marquee is,
which is what you turn debug on to watch, not something an operator needs in
the journal on a device that scrolls all day.

543 vegas and scroll tests pass.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01STMbQE4YctTacQXfbYqKuW

src/common/scroll_helper.py

@@ -328,7 +328,11 @@ class ScrollHelper:
             elapsed_time = current_time - (self.scroll_start_time or current_time)
             # The image already includes display_width padding, so we only need total_scroll_width
             required_total_distance = self.total_scroll_width
-            self.logger.info(
+            # Progress telemetry, emitted every few seconds for the whole of
+            # every scroll. It says how far along a marquee is, which is what
+            # you turn debug on to watch and not something an operator needs
+            # in the journal on a device that scrolls all day.
+            self.logger.debug(
                 "Scroll progress: elapsed=%.2fs, target=%.2fs, total_scrolled=%.0f/%d px (%.1f%%)",
                 elapsed_time,
                 self.calculated_duration,

src/vegas_mode/coordinator.py

@@ -31,6 +31,14 @@ if TYPE_CHECKING:
 logger = logging.getLogger(__name__)
 
 
+#: A frame rate this close to target is not news; below it is.
+_FPS_HEALTHY_FRACTION = 0.9
+
+#: A healthy marquee still reports this often, so silence means stopped
+#: rather than fine.
+_FPS_HEARTBEAT_INTERVAL = 300.0
+
+
 def _percentile(ordered: List[float], fraction: float) -> float:
     """Nearest-rank percentile of an already-sorted list.
 
@@ -395,7 +403,9 @@ class VegasModeCoordinator:
             duration = self.render_pipeline.get_dynamic_duration()
         start_time = time.time()
         frame_count = 0
-        fps_log_interval = 5.0  # Log FPS every 5 seconds
+        fps_log_interval = 5.0  # Sample FPS every 5 seconds
+        last_fps_health_log = 0.0   # last INFO-level report
+        was_degraded = False        # so the recovery is reported too
         last_fps_log_time = start_time
         fps_frame_count = 0
         # A mean hides stutter completely. At 120fps a five-second window is
@@ -448,16 +458,36 @@ class VegasModeCoordinator:
             frame_count += 1
             fps_frame_count += 1
 
-            # Periodic FPS logging
+            # Periodic FPS logging. Reported at INFO only when the frame rate
+            # is actually worth an operator's attention -- a shortfall against
+            # target, or the recovery from one -- with a slow heartbeat so a
+            # healthy marquee still shows a pulse.
+            #
+            # Measured over two hours on a running rig: 1410 samples, 98.5%
+            # of them within 10% of target. The 1.5% that were not included a
+            # reading of 8.6fps against a target of 60 -- a real stall, and
+            # completely invisible inside 1389 lines reading "59.6".
             current_time = time.time()
             if current_time - last_fps_log_time >= fps_log_interval:
                 fps = fps_frame_count / (current_time - last_fps_log_time)
                 p99 = _percentile(sorted(frame_times), 0.99)
-                logger.info(
-                    "Vegas FPS: %.1f (target: %d, frames: %d) p99 %.1fms worst %.1fms",
-                    fps, self.vegas_config.target_fps, fps_frame_count,
-                    p99 * 1000.0, frame_worst * 1000.0
-                )
+                target = self.vegas_config.target_fps
+                degraded = target > 0 and fps < target * _FPS_HEALTHY_FRACTION
+                due = current_time - last_fps_health_log >= _FPS_HEARTBEAT_INTERVAL
+                if degraded or was_degraded or due:
+                    logger.info(
+                        "Vegas FPS: %.1f (target: %d, frames: %d) p99 %.1fms worst %.1fms",
+                        fps, target, fps_frame_count,
+                        p99 * 1000.0, frame_worst * 1000.0
+                    )
+                    last_fps_health_log = current_time
+                else:
+                    logger.debug(
+                        "Vegas FPS: %.1f (target: %d, frames: %d) p99 %.1fms worst %.1fms",
+                        fps, target, fps_frame_count,
+                        p99 * 1000.0, frame_worst * 1000.0
+                    )
+                was_degraded = degraded
                 last_fps_log_time = current_time
                 fps_frame_count = 0
                 frame_worst = 0.0