dashboard — preview thumbnail par job

dispatcher scp frame_*.jpg (premiere apres trim head) vers
/var/lib/cosma-qc/thumbnails/job_N.jpg a la fin de do_extract.

Endpoint GET /jobs/{id}/thumbnail serve via FileResponse. Template:
<img class=thumb src=jobs/N/thumbnail> si has_thumbnail. 48x27 px,
object-fit cover.

Backfill manuel des jobs deja done (9, 12, 13, 16, 19) via scp direct.

app/main.py

@@ -167,6 +167,7 @@ def _build_acquisitions():
         d["gp_label"] = gp_label.get((j["acquisition_id"], j["auv"], j["gopro_serial"]), "?")
         d["video_duration_fmt"] = _fmt_dur(int(j["video_duration_s"] or 0)) if (j["video_duration_s"] or 0) > 0 else "—"
         d["trimmed_total"] = (j["trimmed_head"] or 0) + (j["trimmed_tail"] or 0)
+        d["has_thumbnail"] = (DB_PATH.parent / "thumbnails" / f"job_{j['id']}.jpg").exists()
         # Only expose a native viser link when port is listening. Probed on render via TCP check.
         d["native_viser_url"] = None  # filled below
         by_acq.setdefault(j["acquisition_id"], []).append(d)
@@ -392,6 +393,16 @@ async def view_job(job_id: int):
     return {"url": f"http://{worker['host']}:{port}"}
 
 
+@app.get("/jobs/{job_id}/thumbnail")
+async def job_thumbnail(job_id: int):
+    """Serve the cached thumbnail the dispatcher scp'd after trimming out-of-water frames."""
+    from fastapi.responses import FileResponse
+    thumb = DB_PATH.parent / "thumbnails" / f"job_{job_id}.jpg"
+    if not thumb.exists():
+        raise HTTPException(404, "no thumbnail yet")
+    return FileResponse(thumb, media_type="image/jpeg")
+
+
 @app.post("/jobs/{job_id}/live")
 async def live_job(job_id: int):
     """Return the URL of demo.py's native viser (PointCloudViewer with camera frustums,

app/static/style.css

@@ -127,3 +127,5 @@ code { background: rgba(255,255,255,0.05); padding: 0 0.25rem; border-radius: 3p
 .job-item .viser-link:hover { background: var(--accent, #4a9); color: white; }
 .job-item.skipped { opacity: 0.55; }
 .job-item.skipped .label { font-style: italic; }
+
+.job-item .thumb { width: 48px; height: 27px; object-fit: cover; border-radius: 3px; margin-right: 4px; }

app/templates/_jobs_table.html

@@ -18,6 +18,7 @@
             {% else %}<span class="sq">■</span>{% endif %}
           </span>
           <span class="label">
+            {% if j.has_thumbnail %}<img class="thumb" src="jobs/{{ j.id }}/thumbnail" alt="" loading="lazy">{% endif %}
             <span class="job-id">#{{ j.id }}</span>
             <span class="auv-gp" title="{{ j.gopro_serial }}">{{ j.auv }} {{ j.gp_label }}</span>
             <span class="seg">{{ j.segment_label }}</span>

scripts/dispatcher.py

@@ -379,6 +379,25 @@ def do_extract(job: sqlite3.Row, worker: dict) -> str:
         print(f"  ↳ job #{job['id']}: only {remaining} underwater frames (<{min_frames}) — marking skipped")
         set_status(job["id"], status="skipped", error=f"too short: {remaining} underwater frames")
         raise RuntimeError("skipped_short")
+    # Copy the first kept frame back to the dashboard host as a thumbnail so the UI can show
+    # what the job actually sees. Mid-point would be better but first is cheap and on disk now.
+    thumb_dir = DB_PATH.parent / "thumbnails"
+    thumb_dir.mkdir(exist_ok=True)
+    thumb_local = thumb_dir / f"job_{job['id']}.jpg"
+    subprocess.run(
+        ["scp", "-o", "BatchMode=yes",
+         f"{worker['ssh_alias']}:{frames_dir}/frame_*.jpg", str(thumb_local)],
+        capture_output=True, timeout=30,
+    )  # globbing only picks 1 on the remote side via shell expansion
+    # If glob scp is empty, try first explicit by listing
+    if not thumb_local.exists() or thumb_local.stat().st_size == 0:
+        rc, out, _ = ssh(worker["ssh_alias"], f"ls {shlex.quote(frames_dir)}/frame_*.jpg 2>/dev/null | head -1")
+        first = out.strip()
+        if first:
+            subprocess.run(
+                ["scp", "-o", "BatchMode=yes", f"{worker['ssh_alias']}:{first}", str(thumb_local)],
+                capture_output=True, timeout=30,
+            )
     # Trim once per job so LVM thin pool on the host actually reclaims the freed blocks.
     ssh(worker["ssh_alias"], "sudo fstrim / 2>/dev/null || fstrim / 2>/dev/null", timeout=60)
     return frames_dir