fix: integrate 04b trim into pipeline + no-regression guard

- run_pipeline.sh: add stage 04b after frame extract
- 04b_trim_water.py: skip trim if after_pct < before_pct (no-regression guard)
- 05_inference.py: add --offload_to_cpu + --ply_conf_threshold flags

Recovers 4 degraded segments on Lepradet mission (AUV213/GX020030,
AUV212/GX010094, AUV212/GX019861, AUV210/GX029818).

pipeline/run_pipeline.sh

@@ -42,6 +42,13 @@ echo "--- Stage 04: frame extract ---" | tee -a "${RUN_LOG_DIR}/run.log"
 python3 "${PIPELINE_DIR}/04_frame_extract.py" --mission "${MISSION}" \
     2>&1 | tee -a "${RUN_LOG_DIR}/stage04.log" "${RUN_LOG_DIR}/run.log"
 
+
+# Stage 04b: trim hors-eau head/tail (no-regression guard built into script)
+echo "" | tee -a "${RUN_LOG_DIR}/run.log"
+echo "--- Stage 04b: trim hors-eau head/tail ---" | tee -a "${RUN_LOG_DIR}/run.log"
+python3 "${PIPELINE_DIR}/04b_trim_water.py" --mission "${MISSION}" \
+    2>&1 | tee -a "${RUN_LOG_DIR}/stage04b.log" "${RUN_LOG_DIR}/run.log"
+
 # Stage 05: inference (sequential, one segment at a time)
 echo "" | tee -a "${RUN_LOG_DIR}/run.log"
 echo "--- Stage 05: inference ---" | tee -a "${RUN_LOG_DIR}/run.log"

pipeline/stages/04b_trim_water.py

@@ -289,6 +289,18 @@ def process_segment(mission_name: str, auv_id: str, segment: str,
     # Re-QC if not dry-run and something was trimmed (or always to keep metrics fresh)
     after_agg = None
     if not dry_run and (head > 0 or tail > 0):
+        # No-regression guard: compute expected post-trim pct before deleting frames
+        remaining_paths_check = sorted(frames_dir.glob("frame_*.jpg"))[head: len(before_paths) - tail if tail else None]
+        sampled_check = remaining_paths_check[::max(1, QC_SAMPLE_RATE)]
+        pf_check = [s for s in (score_image_file(f) for f in sampled_check) if s is not None]
+        if pf_check:
+            after_check = qc_aggregate(pf_check).get("bottom_visible_pct", 0)
+            before_pct = result.get("before_bottom_pct") or 0
+            if after_check < before_pct:
+                result["skipped"] = True
+                result["reason"] = f"no_regression_guard: {before_pct}%→{after_check}% (trim would worsen)"
+                print(f"  [04b] SKIP {auv_id}/{segment}: trim would worsen {before_pct}%→{after_check}%")
+                return result
         after_agg = qc_segment(frames_dir)
     elif dry_run:
         # In dry-run, don't touch qc.json; compute aggregate from remaining slice in-memory

pipeline/stages/05_inference.py

@@ -158,7 +158,7 @@ def run_inference(frames_dir: Path, worker_key: str, mission_name: str,
         f"--overlap_size 16 "
         f"--save_ply {ply_remote} "
         f"--save_poses {npz_remote} "
-        f"--use_sdpa "
+        f"--use_sdpa " f"--offload_to_cpu " f"--ply_conf_threshold 1.5 "
         f"2>&1"
     )