Prove cast validation and exact-size metadata inference

[joshlf]

Specify metadata_for_exact_size and validate_cast_and_convert_metadata
against independent layout calculations. Prove exact representability,
greatest-fitting metadata, alignment-before-size error priority and the
complete prefix or suffix result.

Add Rust assertion harnesses comparing the full optional metadata and cast
outcomes with remainder-based checked arithmetic. Keep address-addition
bounds and the zero-stride panic exclusion visible in their domains.
Outcome examples cover unattainable sizes and intentional panic separately
from checks of the specification's meaning.

Agent-authored-by: AI agent acting on joshlf's behalf

---

• 　  Prove record construction against independent Rust references #3846
• 　  Prove selected cast plans preserve size without metadata overflow #3845
• 　  Prove CastPlan selection and unchecked metadata arithmetic #3844
• 👉 Prove cast validation and exact-size metadata inference #3843
• 　  Prove allocation-size preparation and tail containment #3842
• 　  Prove CastUnsized's production layout acceptance gate #3841
• 　  Prove the numerical bounds used by split operations #3840
• 　  Prove advancement and padding-sequence decisions #3839
• 　  Prove DstLayout padding and field extension #3838
• 　  Prove unit and usize PointerMetadata operations #3837
• 　  Prove trailing sizes, padding and capacity including overflow #3836
• 　  Prove primitive DstLayout constructors #3835
• 　  Add an independent Rust reference for nested DST sizes #3834
• 　  Specify rounding encodings as alignment and phase #3833
• 　  Relate recursive record layout to normalized size formulas #3832
• 　  Prove normalized trailing-size and capacity formulas #3831
• 　  Reuse Aeneas rules for views and indexed loops #3830
• 　  Prove least padding and greatest aligned predecessors #3829
• 　  Test total and partial Aeneas contract semantics #3828
• 　  Verify Boolean and NonZeroUsize candidate predicates #3852
• 　  Verify the byte writers used by IntoBytes #3851
• 　  Prove U16 and U32 byte-order reads, writes and updates #3827
• 　  Prove guarded Boolean conversion and byte copying #3849
• 　  Reject unsupported execution effects before Aeneas lowering #3848
• 　  Check Rust specs against golden and live Aeneas models #3826
• 　  Separate cast plans from pointer reconstruction #3825
• 　  Move cast_from into layout/cast_from.rs #3824
• 　  Share Rust layout and byte models in anneal/lean #3823
• 　  Update Anneal to Aeneas ca282ec and Lean 4.31 #3822

Latest Update: v8 — Compare vs v7

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v6			vs v5	vs v4	vs v3	vs v2	vs v1	vs Base
v5				vs v4	vs v3	vs v2	vs v1	vs Base
v4					vs v3	vs v2	vs v1	vs Base
v3						vs v2	vs v1	vs Base
v2							vs v1	vs Base
v1								vs Base

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[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-08T10:26:36.539554Z	9a256bd	PR opened
🔒 Security Review	✅ Completed 2026-10-08T10:25:45.509910Z	9a256bd	PR opened

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Codecov Report

❌ Patch coverage is 0% with 85 lines in your changes missing coverage. Please review.
✅ Project coverage is 51.42%. Comparing base (8044666) to head (16e3d62).

Files with missing lines	Patch %	Lines
zerocopy/src/layout/tail_checks.rs	0.00%	85 Missing ⚠️

Additional details and impacted files

@@                          Coverage Diff                          @@
##           G6adazbpusq7dy2xngdcyapzjy47q6llm    #3843      +/-   ##
=====================================================================
- Coverage                              52.51%   51.42%   -1.09%     
=====================================================================
  Files                                     30       30              
  Lines                                   4380     4465      +85     
=====================================================================
- Hits                                    2300     2296       -4     
- Misses                                  2080     2169      +89     

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