recondition_masklets` encoded memory is overwritten by `_tracker_update_memories

[amier2775]

Bug Description

In sam3/model/sam3_video_base.py, the memory encoded during reconditioning is
immediately overwritten, making reconditioning ineffective at the memory level.

Root Cause

In run_tracker_update_planning_phase, the execution order is:

1. _recondition_masklets() (line ~727) — calls add_new_mask() +
   propagate_in_video_preflight(run_mem_encoder=True), encoding detector masks
   into output_dict[frame_idx]["maskmem_features"]
2. _tracker_update_memories() (line ~757) — re-runs memory encoder using
   tracker_low_res_masks_global (the original tracker masks, unchanged by
   reconditioning), and overwrites the same maskmem_features for the same
   frame_idx

The overwrite happens here in _tracker_update_memories:

output_dict[storage_key][frame_idx]["maskmem_features"] = local_maskmem_features
output_dict[storage_key][frame_idx]["maskmem_pos_enc"] = [...]

Since tracker_low_res_masks_global is never updated with the reconditioned detector
masks, the memory encoder in step 2 encodes the old tracker masks, discarding the
detector mask memory from step 1.

Impact

• Reconditioned detector masks are correctly used for output (via
  _execute_tracker_update_phase), but their memory is lost
• Subsequent frames attend to memory encoded from old tracker masks, not the
  corrected detector masks
• Both periodic (recondition_every_nth_frame) and IoU-based reconditioning are
  affected

Suggested Fix

Update tracker_low_res_masks_global with reconditioned detector masks before calling
_tracker_update_memories(), so a single memory encoding pass uses the correct
masks:

Before _tracker_update_memories, replace masks for reconditioned objects

if reconditioned_obj_ids:
    for trk_obj_id in reconditioned_obj_ids:
        det_idx = trk_id_to_max_iou_high_conf_det.get(trk_obj_id)
        if det_idx is None:
            continue
        trk_idx = np.where(tracker_metadata_prev["obj_ids_all_gpu"] ==
trk_obj_id)[0].item()
        tracker_low_res_masks_global[trk_idx] = det_out["mask"][det_idx]

Then remove run_mem_encoder=True from _recondition_masklets

Affected Versions

Verified present from Initial commit (a13e358) through latest (2e0009e v3 code).