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+    "steps/colors.json": "79dfa32b59d071f13a373d69a8f08291657a7cb79fc2bf8f69c5afed5d596a38",
+    "steps/diagnose-depth.json": "1623cbe7cd56d5931017999562c131d5c9ac9ccd1f0d9276a63c289ff591736e",
+    "steps/fit.json": "e1261496f315a9b6ab3ea913452ce3242f38b65869a856dbf0e92b6370516b3d",
+    "steps/hybrid.json": "9795438bb12d3a7f27b1bfc3d1f32cbdb1e235bfbfc4d87f84b2b35d39e65c64",
+    "steps/inputs.json": "a642fd3f354dec88337aa9da882f7415d7f766104fb5c9e635f9eac9abd485fe",
+    "steps/review.json": "822147ef281cb8bfb2aca8d054bee38b54c2ade42a25187cc0c8c2a5ec8b4387",
+    "steps/tube.json": "dbf051b16ebd7d2ac80f6037123fe489f53c45ff3ab6b4208e4ca0c7c24bc678",
+    "tube/geometry.npz": "12c9a533bff1a5a9fa45161bea4f6775c76aafe82ace7c5ceaafcde99d69250e",
+    "tube/shape_prior.glb": "6684bd8b1a51a67bc36b716fdd41cc0ad017a5b38be32c22936b4d2df016194f",
+    "tube/triangle_areas.npz": "e9bd729c84feb8d572e2da7b33e7aa87c6ca25e1ae9b624b906cb70aa9731899",
+    "tube/tube.ply": "d5ac60a97990278dce254b01fbc88c7168d046d15a2a206ccfd93cad6747312e",
+    "tube/tube_checks.json": "9303db164117d89eaa1406141d1c5d4661f70304680da93868e00ee8c7331929"
+  }
+}
\ No newline at end of file
diff --git a/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_colors.log b/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_colors.log
new file mode 100644
index 0000000000000000000000000000000000000000..9c3b2c242cb07069a518fce463086d7f4310a95d
--- /dev/null
+++ b/sessions/session_20260921_233144_367389/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_233144_367389/window_anchor0268-0673/accepted_input_preparation_c6a_v1/prior_chain_m18_lowcurvature_v1/steps/colors.json
diff --git a/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_colors_argv.json b/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_colors_argv.json
new file mode 100644
index 0000000000000000000000000000000000000000..1a32ca9bfaf2a13181b8fc9e3abefbebefcb26b6
--- /dev/null
+++ b/sessions/session_20260921_233144_367389/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_233144_367389/window_anchor0268-0673/accepted_input_preparation_c6a_v1/prior_chain_m18_lowcurvature_v1"
+  ],
+  "started_utc": "2026-10-28T22:10:34.418464+00:00"
+}
\ No newline at end of file
diff --git a/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_colors_result.json b/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_colors_result.json
new file mode 100644
index 0000000000000000000000000000000000000000..dccae93fb048f5835d745de37eb11f2c90b259c9
--- /dev/null
+++ b/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_colors_result.json
@@ -0,0 +1,4 @@
+{
+  "returncode": 0,
+  "elapsed_s": 32.876061360002495
+}
diff --git a/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_fit.log b/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_fit.log
new file mode 100644
index 0000000000000000000000000000000000000000..48f6c18482aad83739d3d4b57d93f382579730e2
--- /dev/null
+++ b/sessions/session_20260921_233144_367389/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_233144_367389/window_anchor0268-0673/accepted_input_preparation_c6a_v1/prior_chain_m18_lowcurvature_v1/steps/fit.json
diff --git a/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_fit_argv.json b/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_fit_argv.json
new file mode 100644
index 0000000000000000000000000000000000000000..5f848d9c071b90bb4c38337b11d5181eb4c4f173
--- /dev/null
+++ b/sessions/session_20260921_233144_367389/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_233144_367389/window_anchor0268-0673/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_233144_367389/window_anchor0268-0673/accepted_input_preparation_c6a_v1/prior_chain_v1",
+    "--chain-curvature-weight",
+    "5e-9",
+    "--chain-control-count",
+    "18"
+  ],
+  "started_utc": "2026-10-28T22:07:04.736859+00:00"
+}
\ No newline at end of file
diff --git a/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_fit_result.json b/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_fit_result.json
new file mode 100644
index 0000000000000000000000000000000000000000..3c46e6ef105f53a64cac8fde86f7e05a3c477230
--- /dev/null
+++ b/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_fit_result.json
@@ -0,0 +1,4 @@
+{
+  "returncode": 0,
+  "elapsed_s": 184.04458521200286
+}
diff --git a/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_hybrid.log b/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_hybrid.log
new file mode 100644
index 0000000000000000000000000000000000000000..9c004a5b0d752134e0b5839f1d9b060b90e05985
--- /dev/null
+++ b/sessions/session_20260921_233144_367389/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_233144_367389/window_anchor0268-0673/accepted_input_preparation_c6a_v1/prior_chain_m18_lowcurvature_v1/steps/hybrid.json
diff --git a/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_hybrid_argv.json b/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_hybrid_argv.json
new file mode 100644
index 0000000000000000000000000000000000000000..392d9eb84f254f399d88cf2504ddf1ebd49b82a9
--- /dev/null
+++ b/sessions/session_20260921_233144_367389/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_233144_367389/window_anchor0268-0673/accepted_input_preparation_c6a_v1/prior_chain_m18_lowcurvature_v1"
+  ],
+  "started_utc": "2026-10-28T22:11:07.294716+00:00"
+}
\ No newline at end of file
diff --git a/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_hybrid_result.json b/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_hybrid_result.json
new file mode 100644
index 0000000000000000000000000000000000000000..1efb6459f4eeee6e5f9969afa64b442f96c25b4b
--- /dev/null
+++ b/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_hybrid_result.json
@@ -0,0 +1,4 @@
+{
+  "returncode": 0,
+  "elapsed_s": 7.612649925009464
+}
diff --git a/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_manifest.log b/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_manifest.log
new file mode 100644
index 0000000000000000000000000000000000000000..00ee82efc8dfdc0de55461e33b41cd1e4ce08a7c
--- /dev/null
+++ b/sessions/session_20260921_233144_367389/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_233144_367389/window_anchor0268-0673/accepted_input_preparation_c6a_v1/prior_chain_m18_lowcurvature_v1/manifest.json
diff --git a/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_manifest_argv.json b/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_manifest_argv.json
new file mode 100644
index 0000000000000000000000000000000000000000..2d08f8c14679d256b177e04a843cc360855414ec
--- /dev/null
+++ b/sessions/session_20260921_233144_367389/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_233144_367389/window_anchor0268-0673/accepted_input_preparation_c6a_v1/prior_chain_m18_lowcurvature_v1"
+  ],
+  "started_utc": "2026-10-28T22:11:39.872053+00:00"
+}
\ No newline at end of file
diff --git a/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_manifest_result.json b/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_manifest_result.json
new file mode 100644
index 0000000000000000000000000000000000000000..fc5e7a74df7853fa31c1431b298f1a4985bdf7b5
--- /dev/null
+++ b/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_manifest_result.json
@@ -0,0 +1,4 @@
+{
+  "returncode": 0,
+  "elapsed_s": 6.891923165996559
+}
diff --git a/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_review.log b/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_review.log
new file mode 100644
index 0000000000000000000000000000000000000000..d6caf703422a5b754f0d96161ab76b6255a0fbb9
--- /dev/null
+++ b/sessions/session_20260921_233144_367389/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_233144_367389/window_anchor0268-0673/accepted_input_preparation_c6a_v1/prior_chain_m18_lowcurvature_v1/steps/review.json
diff --git a/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_review_argv.json b/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_review_argv.json
new file mode 100644
index 0000000000000000000000000000000000000000..707c17163edf4515b47e08a81bf8cb38bf756b23
--- /dev/null
+++ b/sessions/session_20260921_233144_367389/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_233144_367389/window_anchor0268-0673/accepted_input_preparation_c6a_v1/prior_chain_m18_lowcurvature_v1"
+  ],
+  "started_utc": "2026-10-28T22:11:14.907860+00:00"
+}
\ No newline at end of file
diff --git a/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_review_result.json b/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_review_result.json
new file mode 100644
index 0000000000000000000000000000000000000000..3edd4d5c178d8b5269ac8af50bf5111c4d690c73
--- /dev/null
+++ b/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_review_result.json
@@ -0,0 +1,4 @@
+{
+  "returncode": 0,
+  "elapsed_s": 24.963562548000482
+}
diff --git a/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_tube.log b/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_tube.log
new file mode 100644
index 0000000000000000000000000000000000000000..a1bfab2f11141b970aba41533f35a232f4fc67d2
--- /dev/null
+++ b/sessions/session_20260921_233144_367389/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_233144_367389/window_anchor0268-0673/accepted_input_preparation_c6a_v1/prior_chain_m18_lowcurvature_v1/steps/tube.json
diff --git a/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_tube_argv.json b/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_tube_argv.json
new file mode 100644
index 0000000000000000000000000000000000000000..3dd65c8b8b541b06fa9d7c6e0671453e21d5ced7
--- /dev/null
+++ b/sessions/session_20260921_233144_367389/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_233144_367389/window_anchor0268-0673/accepted_input_preparation_c6a_v1/prior_chain_m18_lowcurvature_v1"
+  ],
+  "started_utc": "2026-10-28T22:10:08.782098+00:00"
+}
\ No newline at end of file
diff --git a/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_tube_result.json b/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_tube_result.json
new file mode 100644
index 0000000000000000000000000000000000000000..7b13ba50fd1110a03c74ffddb84498bab617a582
--- /dev/null
+++ b/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/owner_refit_tube_result.json
@@ -0,0 +1,4 @@
+{
+  "returncode": 0,
+  "elapsed_s": 25.636197654996067
+}
diff --git a/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/rerun/appearance_spline_prior.rrd b/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/rerun/appearance_spline_prior.rrd
new file mode 100644
index 0000000000000000000000000000000000000000..c5852d21e888da195781bb1be13c8c9af714274c
--- /dev/null
+++ b/sessions/session_20260921_233144_367389/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 sha256:2694cde81fda7f9510e43e71f07d9f7f95545318edc5b51c3d556b4ff2fd9897
+size 26230243
diff --git a/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/reused_inputs.json b/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/reused_inputs.json
new file mode 100644
index 0000000000000000000000000000000000000000..d14bc2706e57e7cf47b63ccfd1f3091075504026
--- /dev/null
+++ b/sessions/session_20260921_233144_367389/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_233144_367389/window_anchor0268-0673/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_233144_367389/mask_0.png",
+    "gaussian_data/session_20260921_233144_367389/mask_human_3.png",
+    "gaussian_data/session_20260921_233144_367389/mask_human_1.png",
+    "gaussian_data/session_20260921_233144_367389/0.png",
+    "gaussian_data/session_20260921_233144_367389/mask_3.png",
+    "gaussian_data/session_20260921_233144_367389/camera_meta.pkl",
+    "gaussian_data/session_20260921_233144_367389/2.png",
+    "gaussian_data/session_20260921_233144_367389/2_depth.npy",
+    "gaussian_data/session_20260921_233144_367389/mask_2.png",
+    "gaussian_data/session_20260921_233144_367389/0_depth.npy",
+    "gaussian_data/session_20260921_233144_367389/mask_human_0.png",
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+    "spline/filtered_cloud.npz",
+    "steps/inputs.json",
+    "steps/diagnose-depth.json"
+  ],
+  "requested_fit": {
+    "owner_text": "Use 18 controls and 5e-9 for both",
+    "question_item_id": "[\"request_user_input_async\",\"call_4f3ca5db567e45e7a0e793e0329a9bf9\",0]",
+    "recorded_utc": "2026-10-28T22:07:04.693454+00:00",
+    "control_count": 18,
+    "lambda_curvature_cost": 5e-09,
+    "settings_source": "233248 variant B",
+    "scope": "Prepare233144 with18controls and curvature5e-9; all other current C2 settings unchanged. Individual prior review and acceptance remain separate.",
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+  "action": "Exact copies of27 true observation/filter/step inputs. Baseline had completed before owner decision; derived GLB is generated by the new colors stage."
+}
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diff --git a/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/steps/colors.json b/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/steps/colors.json
new file mode 100644
index 0000000000000000000000000000000000000000..8c3d197deb1479379d54af97b09aceb659066380
--- /dev/null
+++ b/sessions/session_20260921_233144_367389/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": [
+      {
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+        "serial": "12540311",
+        "observed_vertices": 625,
+        "projected_inside": 1728,
+        "first_hit": 925
+      },
+      {
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+        "serial": "12933256",
+        "observed_vertices": 678,
+        "projected_inside": 1728,
+        "first_hit": 900
+      },
+      {
+        "view": 2,
+        "serial": "17736741",
+        "observed_vertices": 637,
+        "projected_inside": 1728,
+        "first_hit": 919
+      },
+      {
+        "view": 3,
+        "serial": "23007103",
+        "observed_vertices": 733,
+        "projected_inside": 1728,
+        "first_hit": 914
+      }
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+    "observed_vertices": 1147,
+    "filled_vertices": 581,
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+      "float32_positions_exact": true,
+      "vertex_colors_exact": true,
+      "uv_count": 0,
+      "vertex_reordered_on_open3d_load": true
+    },
+    "files": {
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+      "colors/color_summary.json": "26a66302071986512b6d008ac62f7e9b34581cd1abffdca722bed036fae39080",
+      "tube/shape_prior.glb": "6684bd8b1a51a67bc36b716fdd41cc0ad017a5b38be32c22936b4d2df016194f",
+      "tube/tube.ply": "d5ac60a97990278dce254b01fbc88c7168d046d15a2a206ccfd93cad6747312e",
+      "gaussian_data/session_20260921_233144_367389/shape_prior.glb": "6684bd8b1a51a67bc36b716fdd41cc0ad017a5b38be32c22936b4d2df016194f"
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+  },
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+    "u_pin": "81c718790a37e5e0102eb77af2c6edd34a9db25f"
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+}
\ No newline at end of file
diff --git a/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/steps/fit.json b/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/steps/fit.json
new file mode 100644
index 0000000000000000000000000000000000000000..c8f3a292c3f664a3718dfd8b0278438222c0d294
--- /dev/null
+++ b/sessions/session_20260921_233144_367389/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_233144_367389/window_anchor0268-0673/accepted_input_preparation_c6a_v1/prior_chain_v1"
+    },
+    "loss_config": {
+      "eval_distances": true,
+      "max_saturation_distance": 0.035,
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+      "lambda_curvature_cost": 5e-09,
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+      "arclength_bounds": [
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+    },
+    "solver_config": {
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+      "grad_norm_tolerance": 0.0001,
+      "max_iter": 25
+    },
+    "ribbon_twist_refinement": null
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+  "outputs": {
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+      "std_ratio": 2.0,
+      "input_count": 27239,
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+      "per_view": [
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+          "removed": 165,
+          "live_20_0.05_kept": 6121,
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+        },
+        {
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+          "input": 6875,
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+          "live_20_0.05_kept": 3896,
+          "no_filter_kept": 6875
+        },
+        {
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+          "input": 6954,
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+          "removed": 171,
+          "live_20_0.05_kept": 4963,
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+        },
+        {
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+        {
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+        {
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+          "count": 4519,
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+          "at_cap_fraction": 0.0
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+      "round": 1,
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+    "deterministic": true,
+    "partial_view_witness": {
+      "source": "synthetic rounded trapezoid, four retained RP2 camera centres",
+      "control_count": 18,
+      "curvature_weight": 5e-09,
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+      "points": 288,
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+      "fit_curvature_nearest_corners_p50_max_per_m": [
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+        123.24449920654297
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+      "stop": "gradient_tolerance"
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+      "spline/rounds.jsonl": "a1dacca4ea7a924588f3b9713279c4834a7a8809e38b13c8334200e93a87dcd5",
+      "spline/init_ellipse.json": "ca18195cdf76514f76c5e7f0c278c3a0d05584929738ac154d92ae7adf5064a9",
+      "spline/reprojection.json": "a2423fa09343e404bf108c2411ed62da67f3dd7477679ebf3d9855e99fe12223"
+    }
+  },
+  "code": {
+    "commit": "d1d2f1381470138dfbb3c58d448e53bfed1e0d7e",
+    "u_pin": "81c718790a37e5e0102eb77af2c6edd34a9db25f"
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+}
\ No newline at end of file
diff --git a/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/steps/hybrid.json b/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/steps/hybrid.json
new file mode 100644
index 0000000000000000000000000000000000000000..7383d35623a5da6776b78ab03f553e75e1cf9e15
--- /dev/null
+++ b/sessions/session_20260921_233144_367389/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": 26339,
+      "mesh": 103680,
+      "total": 130019,
+      "mesh_to_observed": 3.936368123315236
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+    "files": {
+      "hybrid/populations.npz": "65f063b7c9787fe557c2c27fbe86a94948a07c97907becfdd317ae34a263b4e4"
+    }
+  },
+  "code": {
+    "commit": "d1d2f1381470138dfbb3c58d448e53bfed1e0d7e",
+    "u_pin": "81c718790a37e5e0102eb77af2c6edd34a9db25f"
+  },
+  "wall_time_s": 0.8134143352508545
+}
\ No newline at end of file
diff --git a/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/steps/review.json b/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/steps/review.json
new file mode 100644
index 0000000000000000000000000000000000000000..a572b26a58c72cab814392180d6ac842a36095b7
--- /dev/null
+++ b/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/steps/review.json
@@ -0,0 +1,65 @@
+{
+  "status": "ok",
+  "settings": {
+    "historical_prior": null,
+    "historical_sha256": null,
+    "baseline_fit": null
+  },
+  "outputs": {
+    "review_files": 52,
+    "files": {
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+      "review/tube/silhouette_3_with_masks.png": "b38a97f74d80d6761ca85419dbf3656ff7628e5e291cefdfe41444b404a22c1e",
+      "review/tube/silhouette_2_with_masks.png": "5a49a03fc38cd918f65e1a34f88e45138c91a59d0920e5e6595f9f6237b9fcb6",
+      "review/tube/check_table.json": "9303db164117d89eaa1406141d1c5d4661f70304680da93868e00ee8c7331929",
+      "review/tube/orbit.mp4": "f98f4eebebcd33cfb05740d6af4a122d9119e337dca1162c570998c1eca2b933",
+      "review/tube/silhouette_3_unmasked.png": "aa7b017c20076d1e8fd0038f43fe55628ccbc2a5497ba63e5c02b9239ede1ca9",
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+      "review/inputs/depth_offset.png": "7edb01fd88acec7901cfca283e6cd548231b5faf1bb38bf5ff71588411ef2320",
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diff --git a/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/steps/tube.json b/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/steps/tube.json
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+++ b/sessions/session_20260921_233144_367389/preprocessing/chain-prior-m18-lowcurvature-v1/native/steps/tube.json
@@ -0,0 +1,63 @@
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