docs: use fixed MITC4 reference tolerance

docs/io-definitions/linear-static-mitc4-shell-io.md

@@ -36,7 +36,8 @@ The user approved the following I/O-specific decisions on `2026-08-12`:
    retaining the existing common metadata, nodal-result, diagnostic, CLI, and
    failure-atomicity conventions.
 
-The approved requirements fix the drilling rule and B33 mixed displacement tolerance.
+The approved requirements fix the drilling rule and the MITC4 fixed absolute
+displacement tolerance `1.0e-5`.
 Drilling calibration/output, `NR-O03`, `NR-O04`, bundle-administration metadata, and
 an expanded reference portfolio are outside this contract.
 
@@ -514,22 +515,21 @@ Before tolerance evaluation:
 Only `U1/U2/U3` affect pass/fail. `UR1/UR2/UR3` are always compared and reported but
 can emit only an approved deterministic nonblocking warning.
 
-For each model, step/frame, quantity, and component group:
+For every matched displacement row:
 
 ```text
-reference_scale_c = max(abs(reference_value_i))
-row_tolerance_c = 1e-9 + 1e-6 * reference_scale_c
-row_pass = abs(fesa_value-reference_value) <= row_tolerance_c
+row_tolerance = 1.0e-5
+row_pass = abs(fesa_value-reference_value) <= row_tolerance
 ```
 
-Reference scale uses finite Abaqus values only. A zero scale makes the relative term
-zero. No reference or result value is zero-clamped and no row-specific relative
-denominator replaces the component scale. The formula is the approved B33 rule:
-the `1e-9` floor is in the user-consistent length unit for U and dimensionless for UR.
-U exceedance fails; UR exceedance emits a deterministic warning only.
+The `1.0e-5` value is in the user-consistent length unit for U and dimensionless for
+UR. No reference or result value is zero-clamped and neither component scale nor a
+row-specific denominator changes the fixed value. A reference scale may remain in the
+report as diagnostic information only. U exceedance fails; UR exceedance emits a
+deterministic warning only. The separate B33 mixed tolerance is unchanged.
 
 The report records every U/UR row, blocking/nonblocking decision, absolute error,
-component-scale normalized error, RMS error, displacement/rotation vector-norm
+fixed-tolerance-normalized error, RMS error, displacement/rotation vector-norm
 error, worst source row/component, and every UR warning.
 
 ## 8. CLI and Diagnostics Contract
@@ -615,7 +615,7 @@ physics review, or release status follows from approval of this document alone.
 | `031-038` | source-independent MITC4 identity, fixed drilling stabilization and full-integration policy; no drilling output | Implementation Planning tests |
 | `039-048` | additive HDF5 v0 paths, mandatory quantities, location identity, atomic output | Reference Model and Implementation Planning |
 | `049-057` | diagnostic/schema hooks and required verification-metric/physical-energy evidence | Numerical Review and planning |
-| `058-064` | normalized U/UR rows, exact B33 tolerance, blocking/warning behavior, report inventory | Reference Verification |
+| `058-064` | normalized U/UR rows, fixed absolute `1.0e-5`, blocking/warning behavior, report inventory | Reference Verification |
 | `065-072` | exact current S4 paths, S4R reference non-consumption, immutability and displacement-only gate | Reference Model |
 
 ## 11. Open Issues and Downstream Handoff
@@ -623,8 +623,8 @@ physics review, or release status follows from approval of this document alone.
 ### 11.1 Numerical Review boundary
 
 No I/O-owned calibration value remains open. Numerical Review shall verify the exact
-fixed drilling rule, basic geometry predicates, required HDF5 inventory, and B33
-tolerance mapping. Drilling calibration/energy output, `NR-O03`, `NR-O04`, bundle
+fixed drilling rule, basic geometry predicates, required HDF5 inventory, and fixed
+absolute MITC4 tolerance mapping. Drilling calibration/energy output, `NR-O03`, `NR-O04`, bundle
 administration and reference-portfolio expansion are removed scope.
 
 ### 11.2 Reference Model Agent
@@ -632,7 +632,7 @@ administration and reference-portfolio expansion are removed scope.
 - Write `docs/reference-models/linear-static-mitc4-shell-reference-models.md` using
   this exact keyword/HDF5/reference-row contract.
 - Record only the two exact existing input/displacement pairs, comparison components,
-  HDF5 projection, source-row identity, B33 tolerance and immutability rule.
+  HDF5 projection, source-row identity, fixed absolute MITC4 tolerance and immutability rule.
 - Treat reaction/stress artifacts as nonblocking review evidence and do not create
   location-equivalence claims absent from this contract.