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+    "spline/spline_fit.json": "1447d06033aef8a695483ebe1fa9cd15f4036f0e66c80028257fba96cf9c5d25",
+    "spline/spline_init.json": "4bb3a888f0ebf238522423ac5e25d5b700225db8a9a346f09f348736d04b7b89",
+    "spline/witness.json": "2e2b05643b7d4b5b27fa363133a00d709afe07cf7bec6b77fdc6a54ed0232924",
+    "steps/colors.json": "355eac997ce111ffac41ff17c67442bda249ab4c7ecf461d358910c3d25374d7",
+    "steps/diagnose-depth.json": "5b365bf12f3911e0793100e7b1cf27651274aa34eb3d64e8964e315d3a28ec11",
+    "steps/fit.json": "34024d577db0e41cff9501a202f224251ddb21897009fb8d0f701a9fa281cff1",
+    "steps/hybrid.json": "df5f67fc1b1c3bdc3f774113a8c56ab6eb99b433699ae9afbc00aa321547a0af",
+    "steps/inputs.json": "a19ef8186e9d3908129d76cd4ba616e5dc492577b9e5bc254b6548bb98c7ecb5",
+    "steps/review.json": "936ab1f8758247b91b31410da12d372636409edfd109429dd61eedbc81062f86",
+    "steps/tube.json": "eea23375710e29c982028d50ea243016c486d827cd035c7e78ec209d4a33dcb0",
+    "tube/geometry.npz": "cd15ecc7c9c9f0d325909e4c163290e3e91787125a9b27561f442d7059d92862",
+    "tube/shape_prior.glb": "bc674f33899a26c8c73819745e35f58700a5c890aa6cae21adb3808b0e8b3485",
+    "tube/triangle_areas.npz": "ca83380396645b5921951f62ed30798c3b4da4229bb1aafee20cc86a083aeeeb",
+    "tube/tube.ply": "b8b4f0ad74e18c4b281c7f8441087052d1ef084cb7e87558e9ad8e680cbcc5c6",
+    "tube/tube_checks.json": "77c3aec85bf619cdd253452947885e2991045f37fa5521a83091b0335c813218"
+  }
+}
\ No newline at end of file
diff --git a/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_colors.log b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_colors.log
new file mode 100644
index 0000000000000000000000000000000000000000..7e71f2636647b1b06ffa7f12983277baec1269d9
--- /dev/null
+++ b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_colors.log
@@ -0,0 +1 @@
+colors: ok -> /mnt/data2/magna/belt_perception_shared/phystwin_model_corpus_expansion/lab/session_20260921_233045_819927/window_anchor0256-0546/accepted_input_preparation_c6a_v1/prior_chain_m18_lowcurvature_v1/steps/colors.json
diff --git a/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_colors_argv.json b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_colors_argv.json
new file mode 100644
index 0000000000000000000000000000000000000000..04baa502a1e968967a7232a9ca01f8424cbf0f8f
--- /dev/null
+++ b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_colors_argv.json
@@ -0,0 +1,11 @@
+{
+  "argv": [
+    "/mnt/data0/magna/belt_perception_wt_c6a_lab_input_preparation_20261027/.venv/bin/python",
+    "-B",
+    "/mnt/data0/magna/belt_perception_wt_c6a_lab_input_preparation_20261027/scripts/real_rgbd_appearance_spline_prior.py",
+    "colors",
+    "--run",
+    "/mnt/data2/magna/belt_perception_shared/phystwin_model_corpus_expansion/lab/session_20260921_233045_819927/window_anchor0256-0546/accepted_input_preparation_c6a_v1/prior_chain_m18_lowcurvature_v1"
+  ],
+  "started_utc": "2026-10-28T22:10:27.214011+00:00"
+}
\ No newline at end of file
diff --git a/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_colors_result.json b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_colors_result.json
new file mode 100644
index 0000000000000000000000000000000000000000..3799f9b613e2fa562bb571ee7d0543920dd198ef
--- /dev/null
+++ b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_colors_result.json
@@ -0,0 +1,4 @@
+{
+  "returncode": 0,
+  "elapsed_s": 9.80495451799652
+}
diff --git a/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_fit.log b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_fit.log
new file mode 100644
index 0000000000000000000000000000000000000000..61db133e9f0ee71649b2b605c36ea68e681721a7
--- /dev/null
+++ b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_fit.log
@@ -0,0 +1,43 @@
+compiling!
+compiling!
+compiling!
+compiling!
+compiling!
+compiling!
+compiling!
+compiling!
+compiling!
+compiling!
+compiling!
+compiling!
+compiling!
+compiling!
+compiling!
+compiling!
+compiling!
+compiling!
+compiling!
+compiling!
+compiling!
+compiling!
+compiling!
+compiling!
+compiling!
+compiling!
+compiling!
+compiling!
+compiling!
+compiling!
+compiling!
+compiling!
+compiling!
+compiling!
+compiling!
+compiling!
+compiling!
+compiling!
+compiling!
+compiling!
+compiling!
+compiling!
+fit: ok -> /mnt/data2/magna/belt_perception_shared/phystwin_model_corpus_expansion/lab/session_20260921_233045_819927/window_anchor0256-0546/accepted_input_preparation_c6a_v1/prior_chain_m18_lowcurvature_v1/steps/fit.json
diff --git a/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_fit_argv.json b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_fit_argv.json
new file mode 100644
index 0000000000000000000000000000000000000000..0c0c1f816765070897856cee09939fd625427f9f
--- /dev/null
+++ b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_fit_argv.json
@@ -0,0 +1,23 @@
+{
+  "argv": [
+    "/mnt/data0/magna/belt_perception_wt_c6a_lab_input_preparation_20261027/.venv/bin/python",
+    "-B",
+    "/mnt/data0/magna/belt_perception_wt_c6a_lab_input_preparation_20261027/scripts/real_rgbd_appearance_spline_prior.py",
+    "fit",
+    "--run",
+    "/mnt/data2/magna/belt_perception_shared/phystwin_model_corpus_expansion/lab/session_20260921_233045_819927/window_anchor0256-0546/accepted_input_preparation_c6a_v1/prior_chain_m18_lowcurvature_v1",
+    "--outlier-filter",
+    "statistical:20:2.0",
+    "--max-rounds",
+    "400",
+    "--reprojection-weight",
+    "4",
+    "--baseline-run",
+    "/mnt/data2/magna/belt_perception_shared/phystwin_model_corpus_expansion/lab/session_20260921_233045_819927/window_anchor0256-0546/accepted_input_preparation_c6a_v1/prior_chain_v1",
+    "--chain-curvature-weight",
+    "5e-9",
+    "--chain-control-count",
+    "18"
+  ],
+  "started_utc": "2026-10-28T22:03:10.077563+00:00"
+}
\ No newline at end of file
diff --git a/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_fit_result.json b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_fit_result.json
new file mode 100644
index 0000000000000000000000000000000000000000..3515b4672d420d78fb9a79abde6ef099be962c72
--- /dev/null
+++ b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_fit_result.json
@@ -0,0 +1,4 @@
+{
+  "returncode": 0,
+  "elapsed_s": 312.6585516320047
+}
diff --git a/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_hybrid.log b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_hybrid.log
new file mode 100644
index 0000000000000000000000000000000000000000..a23b162cf49077121acd7f141b504c6e74bb86de
--- /dev/null
+++ b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_hybrid.log
@@ -0,0 +1 @@
+hybrid: ok -> /mnt/data2/magna/belt_perception_shared/phystwin_model_corpus_expansion/lab/session_20260921_233045_819927/window_anchor0256-0546/accepted_input_preparation_c6a_v1/prior_chain_m18_lowcurvature_v1/steps/hybrid.json
diff --git a/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_hybrid_argv.json b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_hybrid_argv.json
new file mode 100644
index 0000000000000000000000000000000000000000..a9f0d0f09761268418e77f54a1ab251476a3d2a4
--- /dev/null
+++ b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_hybrid_argv.json
@@ -0,0 +1,11 @@
+{
+  "argv": [
+    "/mnt/data0/magna/belt_perception_wt_c6a_lab_input_preparation_20261027/.venv/bin/python",
+    "-B",
+    "/mnt/data0/magna/belt_perception_wt_c6a_lab_input_preparation_20261027/scripts/real_rgbd_appearance_spline_prior.py",
+    "hybrid",
+    "--run",
+    "/mnt/data2/magna/belt_perception_shared/phystwin_model_corpus_expansion/lab/session_20260921_233045_819927/window_anchor0256-0546/accepted_input_preparation_c6a_v1/prior_chain_m18_lowcurvature_v1"
+  ],
+  "started_utc": "2026-10-28T22:10:37.019150+00:00"
+}
\ No newline at end of file
diff --git a/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_hybrid_result.json b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_hybrid_result.json
new file mode 100644
index 0000000000000000000000000000000000000000..f78cb017b345ee905ed088f26014f877f21dca9e
--- /dev/null
+++ b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_hybrid_result.json
@@ -0,0 +1,4 @@
+{
+  "returncode": 0,
+  "elapsed_s": 32.505380379006965
+}
diff --git a/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_manifest.log b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_manifest.log
new file mode 100644
index 0000000000000000000000000000000000000000..5dcbd2104d3f8b4b5dbd6b48d927e6ab2d5827ad
--- /dev/null
+++ b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_manifest.log
@@ -0,0 +1 @@
+/mnt/data2/magna/belt_perception_shared/phystwin_model_corpus_expansion/lab/session_20260921_233045_819927/window_anchor0256-0546/accepted_input_preparation_c6a_v1/prior_chain_m18_lowcurvature_v1/manifest.json
diff --git a/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_manifest_argv.json b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_manifest_argv.json
new file mode 100644
index 0000000000000000000000000000000000000000..9f397a88191534833fcd63345ee21714e1bbfa95
--- /dev/null
+++ b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_manifest_argv.json
@@ -0,0 +1,11 @@
+{
+  "argv": [
+    "/mnt/data0/magna/belt_perception_wt_c6a_lab_input_preparation_20261027/.venv/bin/python",
+    "-B",
+    "/mnt/data0/magna/belt_perception_wt_c6a_lab_input_preparation_20261027/scripts/real_rgbd_appearance_spline_prior.py",
+    "manifest",
+    "--run",
+    "/mnt/data2/magna/belt_perception_shared/phystwin_model_corpus_expansion/lab/session_20260921_233045_819927/window_anchor0256-0546/accepted_input_preparation_c6a_v1/prior_chain_m18_lowcurvature_v1"
+  ],
+  "started_utc": "2026-10-28T22:11:27.350569+00:00"
+}
\ No newline at end of file
diff --git a/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_manifest_result.json b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_manifest_result.json
new file mode 100644
index 0000000000000000000000000000000000000000..a501688259886f444f080a20895e2a83ed11dda4
--- /dev/null
+++ b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_manifest_result.json
@@ -0,0 +1,4 @@
+{
+  "returncode": 0,
+  "elapsed_s": 13.853932117010118
+}
diff --git a/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_review.log b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_review.log
new file mode 100644
index 0000000000000000000000000000000000000000..3e8e949a892c5352d1347a83369c09a7dc45bf10
--- /dev/null
+++ b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_review.log
@@ -0,0 +1 @@
+review: ok -> /mnt/data2/magna/belt_perception_shared/phystwin_model_corpus_expansion/lab/session_20260921_233045_819927/window_anchor0256-0546/accepted_input_preparation_c6a_v1/prior_chain_m18_lowcurvature_v1/steps/review.json
diff --git a/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_review_argv.json b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_review_argv.json
new file mode 100644
index 0000000000000000000000000000000000000000..1150ae759f64fa7bf5872b857fd1ca81df9555f4
--- /dev/null
+++ b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_review_argv.json
@@ -0,0 +1,11 @@
+{
+  "argv": [
+    "/mnt/data0/magna/belt_perception_wt_c6a_lab_input_preparation_20261027/.venv/bin/python",
+    "-B",
+    "/mnt/data0/magna/belt_perception_wt_c6a_lab_input_preparation_20261027/scripts/real_rgbd_appearance_spline_prior.py",
+    "review",
+    "--run",
+    "/mnt/data2/magna/belt_perception_shared/phystwin_model_corpus_expansion/lab/session_20260921_233045_819927/window_anchor0256-0546/accepted_input_preparation_c6a_v1/prior_chain_m18_lowcurvature_v1"
+  ],
+  "started_utc": "2026-10-28T22:11:09.524759+00:00"
+}
\ No newline at end of file
diff --git a/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_review_result.json b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_review_result.json
new file mode 100644
index 0000000000000000000000000000000000000000..f21efcfaf9341b3ff0c95e03dab3e3e80a7becc4
--- /dev/null
+++ b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_review_result.json
@@ -0,0 +1,4 @@
+{
+  "returncode": 0,
+  "elapsed_s": 17.825640156006557
+}
diff --git a/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_tube.log b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_tube.log
new file mode 100644
index 0000000000000000000000000000000000000000..18a35812176c96d267fc884c3708f55e2b630e87
--- /dev/null
+++ b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_tube.log
@@ -0,0 +1 @@
+tube: ok -> /mnt/data2/magna/belt_perception_shared/phystwin_model_corpus_expansion/lab/session_20260921_233045_819927/window_anchor0256-0546/accepted_input_preparation_c6a_v1/prior_chain_m18_lowcurvature_v1/steps/tube.json
diff --git a/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_tube_argv.json b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_tube_argv.json
new file mode 100644
index 0000000000000000000000000000000000000000..11102466a122063f3ddf0857d763c13217aa03fd
--- /dev/null
+++ b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_tube_argv.json
@@ -0,0 +1,11 @@
+{
+  "argv": [
+    "/mnt/data0/magna/belt_perception_wt_c6a_lab_input_preparation_20261027/.venv/bin/python",
+    "-B",
+    "/mnt/data0/magna/belt_perception_wt_c6a_lab_input_preparation_20261027/scripts/real_rgbd_appearance_spline_prior.py",
+    "tube",
+    "--run",
+    "/mnt/data2/magna/belt_perception_shared/phystwin_model_corpus_expansion/lab/session_20260921_233045_819927/window_anchor0256-0546/accepted_input_preparation_c6a_v1/prior_chain_m18_lowcurvature_v1"
+  ],
+  "started_utc": "2026-10-28T22:08:22.736874+00:00"
+}
\ No newline at end of file
diff --git a/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_tube_result.json b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_tube_result.json
new file mode 100644
index 0000000000000000000000000000000000000000..a1f60a451a9463c5e0f55e7722a90351be095d71
--- /dev/null
+++ b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_tube_result.json
@@ -0,0 +1,4 @@
+{
+  "returncode": 0,
+  "elapsed_s": 124.47691196101368
+}
diff --git a/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/rerun/appearance_spline_prior.rrd b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/rerun/appearance_spline_prior.rrd
new file mode 100644
index 0000000000000000000000000000000000000000..deb760ed865320ef291c32d0ee70c19618061f7d
--- /dev/null
+++ b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/rerun/appearance_spline_prior.rrd
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:0f909388144796bfd2b3b0b94ba69fca7dd8c3bbb924f0395c669b057474819e
+size 26134260
diff --git a/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/reused_inputs.json b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/reused_inputs.json
new file mode 100644
index 0000000000000000000000000000000000000000..6acd08d62d7079e298a728af6f68b65619338c89
--- /dev/null
+++ b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/reused_inputs.json
@@ -0,0 +1,43 @@
+{
+  "source_run": "/mnt/data2/magna/belt_perception_shared/phystwin_model_corpus_expansion/lab/session_20260921_233045_819927/window_anchor0256-0546/accepted_input_preparation_c6a_v1/prior_chain_v1",
+  "files": [
+    "inputs/reference_views.json",
+    "inputs/observed_cloud.npz",
+    "inputs/depth_offset_diagnostic.json",
+    "gaussian_data/session_20260921_233045_819927/mask_0.png",
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+    "gaussian_data/session_20260921_233045_819927/2.png",
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+    "gaussian_data/session_20260921_233045_819927/mask_human_0.png",
+    "gaussian_data/session_20260921_233045_819927/3_depth.npy",
+    "gaussian_data/session_20260921_233045_819927/interp_poses.pkl",
+    "gaussian_data/session_20260921_233045_819927/observation.ply",
+    "gaussian_data/session_20260921_233045_819927/1_depth.npy",
+    "gaussian_data/session_20260921_233045_819927/mask_1.png",
+    "gaussian_data/session_20260921_233045_819927/1.png",
+    "gaussian_data/session_20260921_233045_819927/mask_human_2.png",
+    "gaussian_data/session_20260921_233045_819927/3.png",
+    "spline/filter.json",
+    "spline/filter_removed.npz",
+    "spline/filtered_cloud.npz",
+    "steps/inputs.json",
+    "steps/diagnose-depth.json"
+  ],
+  "requested_fit": {
+    "owner_text": "Use 18 controls and curvature 5e-9",
+    "question_item_id": "[\"request_user_input_async\",\"call_a0e9fa3be9d24527b644d22e28b0859a\",0]",
+    "recorded_utc": "2026-10-28T22:03:09.899460+00:00",
+    "control_count": 18,
+    "lambda_curvature_cost": 5e-09,
+    "settings_source": "233248 variant B",
+    "scope": "Prepare a separate233045 prior using18controls and curvature5e-9; preserve baseline and all other scientific settings. This is not prior acceptance.",
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+  },
+  "action": "Exact copies of27 true observation/filter/step inputs; derived shape_prior.glb is generated by the new colors stage."
+}
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+{"loss": 5.7054683566093445e-05, "components": {"distance": 2.43807789956918e-05, "curvature": 1.916789784672801e-07, "arclength": 3.3035778557177764e-08, "mask_reprojection_2d": 3.2449188438476995e-05}, "grad_norm": 9.133969433605671e-05, "arclength_m": 0.585574746131897, "arclength_bound_active_within_1mm": true, "max_curvature_per_m": 32.09360885620117, "curvature_p50_p90_per_m": [11.833191394805908, 27.98315544128418], "curvature_above_max_fraction": 0.552, "mean_distance_m": 0.00749255351546465, "max_distance_m": 0.016013795509934425, "beyond_2delta_fraction": 0.16239654694491742, "at_cap_fraction": 0.0, "per_view": [{"view": 0, "count": 6305, "median_m": 0.008462566882371902, "p90_m": 0.012568965554237366, "max_m": 0.016013795509934425, "beyond_2delta_fraction": 0.3370340999206979, "at_cap_fraction": 0.0}, {"view": 1, "count": 6623, "median_m": 0.005789372604340315, "p90_m": 0.00846491064876318, "max_m": 0.01196344755589962, "beyond_2delta_fraction": 0.01162615129095576, "at_cap_fraction": 0.0}, {"view": 2, "count": 7409, "median_m": 0.007865439169108868, "p90_m": 0.010451062396168708, "max_m": 0.01335628516972065, "beyond_2delta_fraction": 0.13888513969496558, "at_cap_fraction": 0.0}, {"view": 3, "count": 4916, "median_m": 0.008147876244038343, "p90_m": 0.010634738020598888, "max_m": 0.01547787431627512, "beyond_2delta_fraction": 0.17697314890154597, "at_cap_fraction": 0.0}], "round": 1, "relative_loss_change": 0.9871013016921988}
diff --git a/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/spline/spline_fit.json b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/spline/spline_fit.json
new file mode 100644
index 0000000000000000000000000000000000000000..5ef7f57c7b976c91a4be4c519e383ff946a29df4
--- /dev/null
+++ b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/spline/spline_fit.json
@@ -0,0 +1,98 @@
+{
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\ No newline at end of file
diff --git a/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/spline/witness.json b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/spline/witness.json
new file mode 100644
index 0000000000000000000000000000000000000000..cdf84dcfc7ce7357f39204bcc0743a4fac2b66da
--- /dev/null
+++ b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/spline/witness.json
@@ -0,0 +1,26 @@
+{
+  "source": "synthetic rounded trapezoid, four retained RP2 camera centres",
+  "control_count": 18,
+  "curvature_weight": 5e-09,
+  "seed": 5,
+  "noise_sigma_m": 0.0015,
+  "points": 288,
+  "tube_radius_m": 0.00475,
+  "truth_arclength_m": 0.5839999999999999,
+  "truth_corner_curvature_per_m": 100.0,
+  "fit_arclength_m": 0.5848261713981628,
+  "mean_centerline_distance_to_truth_m": 0.0033057606075813984,
+  "max_centerline_distance_to_truth_m": 0.00574637227071573,
+  "corner_truth_to_fit_mean_max_m": [
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+  "fit_curvature_nearest_corners_p50_max_per_m": [
+    49.564300537109375,
+    123.19891357421875
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+  "rounds": 1,
+  "stop": "gradient_tolerance"
+}
\ No newline at end of file
diff --git a/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/steps/colors.json b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/steps/colors.json
new file mode 100644
index 0000000000000000000000000000000000000000..ac83e380391d13029656489717829cc5cc1e3bf3
--- /dev/null
+++ b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/steps/colors.json
@@ -0,0 +1,67 @@
+{
+  "status": "ok",
+  "settings": {
+    "depth_tolerance_m": 0.025
+  },
+  "outputs": {
+    "rule": "native sRGB/255, cosine weighted over mask/depth/first-hit visible views",
+    "two_sided": false,
+    "depth_tolerance_m": 0.025,
+    "first_hit_tolerance_m": 0.0002,
+    "per_view": [
+      {
+        "view": 0,
+        "serial": "12540311",
+        "observed_vertices": 656,
+        "projected_inside": 1728,
+        "first_hit": 914
+      },
+      {
+        "view": 1,
+        "serial": "12933256",
+        "observed_vertices": 720,
+        "projected_inside": 1728,
+        "first_hit": 913
+      },
+      {
+        "view": 2,
+        "serial": "17736741",
+        "observed_vertices": 706,
+        "projected_inside": 1728,
+        "first_hit": 918
+      },
+      {
+        "view": 3,
+        "serial": "23007103",
+        "observed_vertices": 756,
+        "projected_inside": 1728,
+        "first_hit": 930
+      }
+    ],
+    "observed_vertices": 1201,
+    "filled_vertices": 527,
+    "fill_color_rgb": [
+      0.2063746900559351,
+      0.1692619234299968,
+      0.15709957824017537
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+    "glb_roundtrip": {
+      "float32_positions_exact": true,
+      "vertex_colors_exact": true,
+      "uv_count": 0,
+      "vertex_reordered_on_open3d_load": true
+    },
+    "files": {
+      "colors/vertex_colors.npz": "26544cfddfd79d39272c9baf2c9c8e5b7a1aa4a8a22ec9096154a5d5f2de9e0e",
+      "colors/color_summary.json": "1815056fb39076ada8a08aad5c67d421010d07fad81312bbba8fb4a3ab984941",
+      "tube/shape_prior.glb": "bc674f33899a26c8c73819745e35f58700a5c890aa6cae21adb3808b0e8b3485",
+      "tube/tube.ply": "b8b4f0ad74e18c4b281c7f8441087052d1ef084cb7e87558e9ad8e680cbcc5c6",
+      "gaussian_data/session_20260921_233045_819927/shape_prior.glb": "bc674f33899a26c8c73819745e35f58700a5c890aa6cae21adb3808b0e8b3485"
+    }
+  },
+  "code": {
+    "commit": "d1d2f1381470138dfbb3c58d448e53bfed1e0d7e",
+    "u_pin": "81c718790a37e5e0102eb77af2c6edd34a9db25f"
+  },
+  "wall_time_s": 1.1453757286071777
+}
\ No newline at end of file
diff --git a/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/steps/fit.json b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/steps/fit.json
new file mode 100644
index 0000000000000000000000000000000000000000..ff6653eda3bbd4298d64d088e10845070cce5638
--- /dev/null
+++ b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/steps/fit.json
@@ -0,0 +1,215 @@
+{
+  "status": "ok",
+  "settings": {
+    "object": {
+      "name": "bike_chain",
+      "representation": "tube",
+      "fitter_source": "scripts/chain_state_estimation.py loss/solver literals",
+      "dimension_source": "owner approximate 9.5 mm diameter (corpus Q2, 2026-10-25)",
+      "radius_m": 0.00475,
+      "ribbon_width_m": null,
+      "step_t": 0.125,
+      "step_angle_deg": 30,
+      "u_resolution": null,
+      "overlap_rule": "surface_intersection",
+      "twist_penalty": null
+    },
+    "max_rounds": 400,
+    "control_count": 18,
+    "relative_loss_tolerance": 1e-07,
+    "reprojection": {
+      "weight": 4.0,
+      "direction": "visible mask pixels to projected centerline",
+      "ribbon_twist_stage": null,
+      "mask": "accepted object outside hand/occluder union",
+      "view_aggregation": "equal view means",
+      "distance": "metric image plane using per-view median visible belt depth and fx/fy",
+      "samples": 360,
+      "huber_delta_m": 0.005,
+      "smooth_cap_m": 0.035,
+      "baseline_run": "/mnt/data2/magna/belt_perception_shared/phystwin_model_corpus_expansion/lab/session_20260921_233045_819927/window_anchor0256-0546/accepted_input_preparation_c6a_v1/prior_chain_v1"
+    },
+    "loss_config": {
+      "eval_distances": true,
+      "max_saturation_distance": 0.035,
+      "distance_huber_delta": 0.005,
+      "eval_curvature_cost": true,
+      "num_eval_reg_points": 250,
+      "lambda_curvature_cost": 5e-09,
+      "max_curvature": 10.0,
+      "curvature_huber_delta": 30.0,
+      "max_saturation_curvature": 80.0,
+      "eval_curvilinear_energy": false,
+      "lambda_curvilinear_energy": 0.001,
+      "eval_length_constraint": true,
+      "lambda_length_constraint": 0.1,
+      "arclength_bounds": [
+        0.5830000042915344,
+        0.5849999785423279
+      ]
+    },
+    "solver_config": {
+      "solver_type": "lbfgs",
+      "linesearch_type": "zoom",
+      "max_linesearch_steps": 10,
+      "grad_norm_tolerance": 0.0001,
+      "max_iter": 25
+    },
+    "ribbon_twist_refinement": null
+  },
+  "outputs": {
+    "filter": {
+      "method": "Open3D.remove_statistical_outlier",
+      "nb_neighbors": 20,
+      "std_ratio": 2.0,
+      "input_count": 26278,
+      "kept_count": 25253,
+      "removed_count": 1025,
+      "per_view": [
+        {
+          "view": 0,
+          "input": 6485,
+          "kept": 6305,
+          "removed": 180,
+          "live_20_0.05_kept": 4606,
+          "no_filter_kept": 6485
+        },
+        {
+          "view": 1,
+          "input": 7095,
+          "kept": 6623,
+          "removed": 472,
+          "live_20_0.05_kept": 3663,
+          "no_filter_kept": 7095
+        },
+        {
+          "view": 2,
+          "input": 7626,
+          "kept": 7409,
+          "removed": 217,
+          "live_20_0.05_kept": 5361,
+          "no_filter_kept": 7626
+        },
+        {
+          "view": 3,
+          "input": 5072,
+          "kept": 4916,
+          "removed": 156,
+          "live_20_0.05_kept": 2537,
+          "no_filter_kept": 5072
+        }
+      ]
+    },
+    "rounds": 1,
+    "stop": "gradient_tolerance",
+    "final": {
+      "loss": 5.7054683566093445e-05,
+      "components": {
+        "distance": 2.43807789956918e-05,
+        "curvature": 1.916789784672801e-07,
+        "arclength": 3.3035778557177764e-08,
+        "mask_reprojection_2d": 3.2449188438476995e-05
+      },
+      "grad_norm": 9.133969433605671e-05,
+      "arclength_m": 0.585574746131897,
+      "arclength_bound_active_within_1mm": true,
+      "max_curvature_per_m": 32.09360885620117,
+      "curvature_p50_p90_per_m": [
+        11.833191394805908,
+        27.98315544128418
+      ],
+      "curvature_above_max_fraction": 0.552,
+      "mean_distance_m": 0.00749255351546465,
+      "max_distance_m": 0.016013795509934425,
+      "beyond_2delta_fraction": 0.16239654694491742,
+      "at_cap_fraction": 0.0,
+      "per_view": [
+        {
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+          "count": 6305,
+          "median_m": 0.008462566882371902,
+          "p90_m": 0.012568965554237366,
+          "max_m": 0.016013795509934425,
+          "beyond_2delta_fraction": 0.3370340999206979,
+          "at_cap_fraction": 0.0
+        },
+        {
+          "view": 1,
+          "count": 6623,
+          "median_m": 0.005789372604340315,
+          "p90_m": 0.00846491064876318,
+          "max_m": 0.01196344755589962,
+          "beyond_2delta_fraction": 0.01162615129095576,
+          "at_cap_fraction": 0.0
+        },
+        {
+          "view": 2,
+          "count": 7409,
+          "median_m": 0.007865439169108868,
+          "p90_m": 0.010451062396168708,
+          "max_m": 0.01335628516972065,
+          "beyond_2delta_fraction": 0.13888513969496558,
+          "at_cap_fraction": 0.0
+        },
+        {
+          "view": 3,
+          "count": 4916,
+          "median_m": 0.008147876244038343,
+          "p90_m": 0.010634738020598888,
+          "max_m": 0.01547787431627512,
+          "beyond_2delta_fraction": 0.17697314890154597,
+          "at_cap_fraction": 0.0
+        }
+      ],
+      "round": 1,
+      "relative_loss_change": 0.9871013016921988
+    },
+    "deterministic": true,
+    "partial_view_witness": {
+      "source": "synthetic rounded trapezoid, four retained RP2 camera centres",
+      "control_count": 18,
+      "curvature_weight": 5e-09,
+      "seed": 5,
+      "noise_sigma_m": 0.0015,
+      "points": 288,
+      "tube_radius_m": 0.00475,
+      "truth_arclength_m": 0.5839999999999999,
+      "truth_corner_curvature_per_m": 100.0,
+      "fit_arclength_m": 0.5848261713981628,
+      "mean_centerline_distance_to_truth_m": 0.0033057606075813984,
+      "max_centerline_distance_to_truth_m": 0.00574637227071573,
+      "corner_truth_to_fit_mean_max_m": [
+        0.0034471907212280492,
+        0.004112132806429916
+      ],
+      "straight_truth_to_fit_mean_m": 0.0032905154061825467,
+      "fit_max_curvature_per_m": 123.19891357421875,
+      "fit_curvature_nearest_corners_p50_max_per_m": [
+        49.564300537109375,
+        123.19891357421875
+      ],
+      "rounds": 1,
+      "stop": "gradient_tolerance"
+    },
+    "files": {
+      "spline/reprojection_residuals.npz": "db9abb57322446b740e12f3110d591fc6adf4202ce5ac365f5a6080c4ce16e45",
+      "spline/residuals.npz": "104e8ddb927f270231c908e26b7376baeb250ca0d40666b6637afa924bfe127f",
+      "spline/filtered_cloud.npz": "b6ea191c915aeedd5bca0de57c95adc7e33de26e3f933748fc2770c7a27d056c",
+      "spline/spline_init.json": "4bb3a888f0ebf238522423ac5e25d5b700225db8a9a346f09f348736d04b7b89",
+      "spline/determinism.json": "773d1a02e2924f0d7df2d5d0011979c4e408678ebfdb9633a8348b9788132683",
+      "spline/filter.json": "ed8ad36a695023cc0a6caf46cd046cfda732d7fe6277b48e7f8c18d920ab1dc1",
+      "spline/witness.json": "2e2b05643b7d4b5b27fa363133a00d709afe07cf7bec6b77fdc6a54ed0232924",
+      "spline/filter_removed.npz": "dbe5d8f81c1c941ff98416d4133b541e4692467f01490f56d753f38da0bef6e1",
+      "spline/spline_fit.json": "1447d06033aef8a695483ebe1fa9cd15f4036f0e66c80028257fba96cf9c5d25",
+      "spline/reprojection_comparison.json": "96dd1ecc886fa5a993c745caf615d3a8726de4a4155dd28fe74f18c61da0c886",
+      "spline/rounds.jsonl": "9347186bb2683e1622fe5da000eb0627522f6881cff6cdffc6ed6a328091e694",
+      "spline/init_ellipse.json": "c494971b08e2c055d366fb9aeb8a59e644cbc6f814538890d610e0cde605431c",
+      "spline/reprojection.json": "620ec0c2cf34ed208da0277d8c98e80f0c6477817448363752c06baffc94d55b"
+    }
+  },
+  "code": {
+    "commit": "d1d2f1381470138dfbb3c58d448e53bfed1e0d7e",
+    "u_pin": "81c718790a37e5e0102eb77af2c6edd34a9db25f"
+  },
+  "wall_time_s": 20.815335273742676
+}
\ No newline at end of file
diff --git a/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/steps/hybrid.json b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/steps/hybrid.json
new file mode 100644
index 0000000000000000000000000000000000000000..147cdd9e7d7689f176d68f84b8b42f2156e244d6
--- /dev/null
+++ b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/steps/hybrid.json
@@ -0,0 +1,24 @@
+{
+  "status": "ok",
+  "settings": {
+    "u_pin": "81c718790a37e5e0102eb77af2c6edd34a9db25f",
+    "numpy_seed": 0,
+    "points_per_triangle": 30
+  },
+  "outputs": {
+    "counts": {
+      "observed": 25253,
+      "mesh": 103680,
+      "total": 128933,
+      "mesh_to_observed": 4.105650813764702
+    },
+    "files": {
+      "hybrid/populations.npz": "41016b710691adb01b9c5e214077774f9ae0a2696bb2f0253e1249233fd14494"
+    }
+  },
+  "code": {
+    "commit": "d1d2f1381470138dfbb3c58d448e53bfed1e0d7e",
+    "u_pin": "81c718790a37e5e0102eb77af2c6edd34a9db25f"
+  },
+  "wall_time_s": 0.8177316188812256
+}
\ No newline at end of file
diff --git a/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/steps/review.json b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/steps/review.json
new file mode 100644
index 0000000000000000000000000000000000000000..e684a2475469ef06dc4436c53764ac8e1b2d7415
--- /dev/null
+++ b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/steps/review.json
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+    "historical_sha256": null,
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\ No newline at end of file
diff --git a/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/steps/tube.json b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/steps/tube.json
new file mode 100644
index 0000000000000000000000000000000000000000..43137b55b35378b13bec1c8c96aa612352c1d812
--- /dev/null
+++ b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/steps/tube.json
@@ -0,0 +1,63 @@
+{
+  "status": "ok",
+  "settings": {
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+    "step_t": 0.125,
+    "step_angle_deg": 30
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+  "outputs": {
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+      "watertight": true,
+      "components": 1,
+      "winding_consistent": true,
+      "signed_volume_m3": 3.9607764826905275e-05,
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+      "confirmed_intersecting_pairs": [],
+      "passed": true,
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+    "triangle_count": 3456,
+    "files": {
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+}
\ No newline at end of file
diff --git a/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/tube/geometry.npz b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/tube/geometry.npz
new file mode 100644
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diff --git a/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/tube/triangle_areas.npz b/sessions/session_20260921_233045_819927/preprocessing/chain-prior-m18-lowcurvature-v1/native/tube/triangle_areas.npz
new file mode 100644
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