Prove CastUnsized's production layout acceptance gate

[joshlf]

Move the numerical decision used by CastUnsized's associated constant into
an extracted helper. Preserve sized casts' size-only comparison and require
accepted slice-DST casts to retain alignment, physical tail offset and the
complete size sequence.

Prove that decision and a Rust assertion harness comparing independent
checked sizes, including overflow and zero-sized tails. A rejected DST
comparison need not establish that its size sequences differ. Pointer
construction and validity remain outside these numerical claims.

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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[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 2026-10-08T10:25:21.395836Z	029004d	PR opened
🔒 Security Review	✅ Completed 2026-10-08T10:27:41.290859Z	029004d	PR opened

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Codecov Report

❌ Patch coverage is 0% with 47 lines in your changes missing coverage. Please review.
✅ Project coverage is 53.43%. Comparing base (8b0dc59) to head (867db38).

Files with missing lines	Patch %	Lines
zerocopy/src/pointer/mod.rs	0.00%	47 Missing ⚠️

Additional details and impacted files

@@                          Coverage Diff                          @@
##           Gytt7syk4w4f52xlmszabgwlaiofsu7p6    #3841      +/-   ##
=====================================================================
- Coverage                              54.02%   53.43%   -0.60%     
=====================================================================
  Files                                     27       27              
  Lines                                   4235     4282      +47     
=====================================================================
  Hits                                    2288     2288              
- Misses                                  1947     1994      +47     

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