modify tolerance policy

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

@@ -36,8 +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 the MITC4 fixed absolute
-displacement tolerance `1.0e-5`.
+The approved requirements fix the drilling rule and the project-wide common
+family-scale reference tolerance.
 Drilling calibration/output, `NR-O03`, `NR-O04`, bundle-administration metadata, and
 an expanded reference portfolio are outside this contract.
 
@@ -515,22 +515,31 @@ 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 every matched displacement row:
+Matched U rows form one blocking translation family and matched UR rows form one warning-only
+rotation family. For each family:
 
 ```text
-row_tolerance = 1.0e-5
-row_pass = abs(fesa_value-reference_value) <= row_tolerance
+S = max(abs(reference_value_i))
+error_i = abs(fesa_value_i-reference_value_i)
+near_zero_band = 0.01*S
+
+if abs(reference_value_i) <= near_zero_band:
+    row_pass = error_i <= near_zero_band
+else:
+    row_pass = error_i/abs(reference_value_i) <= 0.05
+
+relative_rms = sqrt(mean(error_i^2))/S
+family_pass = all(row_pass) and relative_rms <= 0.01
 ```
 
-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.
+Reference values alone define `S`; values are not zero-clamped or omitted and there is no
+independent absolute-error gate. A zero-scale family passes only if every FESA value is exactly
+zero, otherwise it fails without emitting NaN/Inf. U row or RMS exceedance fails; the same UR
+exceedance emits a deterministic warning only.
 
-The report records every U/UR row, blocking/nonblocking decision, absolute error,
-fixed-tolerance-normalized error, RMS error, displacement/rotation vector-norm
-error, worst source row/component, and every UR warning.
+The report records every U/UR row, blocking/nonblocking decision, family scale,
+near-zero branch, absolute and applicable row-relative error, scale-relative RMS,
+worst source row/component, and every UR warning.
 
 ## 8. CLI and Diagnostics Contract
 
@@ -615,7 +624,7 @@ 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, fixed absolute `1.0e-5`, blocking/warning behavior, report inventory | Reference Verification |
+| `058-064` | common-policy U/UR families, 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 +632,8 @@ 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 fixed
-absolute MITC4 tolerance mapping. Drilling calibration/energy output, `NR-O03`, `NR-O04`, bundle
+fixed drilling rule, basic geometry predicates, required HDF5 inventory, and common
+family-scale row/RMS 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 +641,7 @@ administration and reference-portfolio expansion are removed scope.
 - Write `docs/linear-static-mitc4-shell/reference-model.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, fixed absolute MITC4 tolerance and immutability rule.
+  HDF5 projection, source-row identity, common family-scale tolerance and immutability rule.
 - Treat reaction/stress artifacts as nonblocking review evidence and do not create
   location-equivalence claims absent from this contract.