experiment: replay captured candidates and run focused frozen probes

experiments/plateau_diagnostic_README.md

@@ -135,3 +135,46 @@ Check a completed endpoint with
 This gates strict recorded solver convergence and all eight finite virial errors
 at 1e-5, while reporting local field errors separately. See
 `check_plateau_physics_README.md` for the exit codes and interpretation limits.
+
+## Pressure obstruction and shape curvature (September 17)
+
+These switches belong only to this experiment executable; no production model or
+solver options are added.
+
+`--capture-iterations 2,7,11` copies the selected zero-based Newton iteration's
+physical/normalized base, residual, and exact first-trial candidate from observer
+spans into `capture_N/`. It reconstructs the normalized direction as
+`(candidate - base) / first_trial_alpha`. `capture.txt` records the step, observed
+rejection, reconstruction error, and a heuristic subtraction-roundoff scale.
+This is not a direct copy of the solver's internal correction. Prefer an onset
+capture whose first step is large for derivative measurements; retain the exact
+candidate for unambiguous replay even when a late direction loses digits.
+No operator or preconditioner is evaluated from the observer, and no accepted
+state is changed. Compare non-timing trajectory columns and final-state hashes
+against the control to verify that capture is observational.
+
+A focused frozen investigation bypasses both cold Krylov solves:
+
+```sh
+./cmake-build-release-homebrew/plateau_diagnostic \
+  --index 1 --angular-momentum 0.1 --no-central --max-newton 0 \
+  --probe-state /absolute/path/to/capture_2/physical_base.txt \
+  --probe-direction /absolute/path/to/capture_2/normalized_direction.txt \
+  --replay-candidate /absolute/path/to/capture_2/normalized_candidate.txt \
+  --pressure-probe --shape-curvature \
+  --output /absolute/path/to/new-focused-results
+```
+
+The state input is physical; direction and candidate inputs are normalized in the
+same recorded normalization. Mesh, model, field layout, and scaling must match the
+capture. If a sibling `normalized_base.txt` exists, its agreement with the newly
+normalized physical base is checked before probing. This check is not a complete
+model fingerprint. The runner hashes each explicit input plus every text/CSV/JSON
+output, including nested capture files. Exact replay logs root rejection reason,
+stage and EOS code; the EOS code has meaning only for thermodynamic rejections.
+
+`frozen_input_checks.csv` records the current F, Jp+F defect, captured normalization
+agreement, and final restoration error. The two methodology notes describe the
+pressure-bound crossings and common-step vector Taylor decomposition. Every
+candidate remains uncommitted. The flags may be used separately to limit work.
+These are diagnostic outcomes, not new equilibrium-convergence or virial claims.