dispatcher — stitch passthrough pour acquisition 1 seul PLY

Quand un seul PLY est disponible (1 segment, 1 caméra), aucun alignement
n'est nécessaire. On copie directement le PLY en output et on marque la
stitch done plutôt qu'error. Cross-AUV est quand même tenté si conditions remplies.

scripts/dispatcher.py

@@ -296,13 +296,24 @@ def run_one_stitch(stitch: sqlite3.Row):
                 rows = []
             ply_paths = [r["output_ply"] for r in rows if r["output_ply"]]
 
-    if len(ply_paths) < 2:
+    if len(ply_paths) == 0:
         set_stitch_status(stitch_id, status="error",
-                          error=f"Pas assez de PLY disponibles ({len(ply_paths)})",
+                          error="Aucun PLY disponible",
                           finished_at=_now_iso())
         return
 
     out_ply = f"{worker['frames_dir']}/stitch_{stitch_id}.ply"
+
+    # Single PLY — no alignment needed, pass through directly.
+    if len(ply_paths) == 1:
+        rc, _, err = ssh(worker["ssh_alias"], f"cp {shlex.quote(ply_paths[0])} {shlex.quote(out_ply)}")
+        if rc != 0:
+            set_stitch_status(stitch_id, status="error", error=f"cp failed: {err[:200]}", finished_at=_now_iso())
+            return
+        set_stitch_status(stitch_id, status="done", output_ply=out_ply, finished_at=_now_iso())
+        print(f"  → stitch #{stitch_id} passthrough (1 PLY) → {out_ply}")
+        _maybe_create_cross_auv_stitch(stitch_id)
+        return
     deploy_stitch_script(worker)
 
     cmd = (