Move pointer cast implementation into its own source file

[joshlf]

Move the inline cast_from module to layout/cast_from.rs without changing its
implementation. Use layout/mod.rs as the root of the resulting multi-file
module, and update existing source-path references.

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

---

• 　  Prove record construction against independent Rust references #3744
• 　  Prove cast metadata composition against reference sizes #3777
• 　  Prove numerical cast plan selection and metadata conversion #3776
• 　  Prove cast validation and exact metadata inference #3755
• 　  Prove allocation size preparation and tail containment #3790
• 　  Prove the concrete CastUnsized layout gate #3789
• 　  Prove split lengths and non-overlapping numerical regions #3788
• 　  Prove byte advancement and padding sequence queries #3754
• 　  Prove normalized layout padding and field extension #3753
• 　  Prove concrete pointer metadata operations #3787
• 　  Prove exact trailing sizes, padding and capacity #3752
• 　  Prove primitive layout constructors with recursive mathematical models #3751
• 　  Compare nested DST sizes with a recursive Rust oracle #3749
• 　  Model alignment and phase encoding as a bounded mathematical pair #3747
• 　  Refine recursive record semantics into normalized layouts #3743
• 　  Prove trailing-layout normalization and capacity arithmetic #3742
• 　  Reuse Aeneas specifications for views and indexed loops #3745
• 　  Strengthen arithmetic specifications and prove arithmetic corollaries #3746
• 　  Check native total and partial Aeneas specifications #3739
• 　  Prove unsigned byte-order reads, writes and updates #3800
• 　  Verify doc-owned specifications over recursive mathematical models #3738
• 　  Separate numerical cast planning from typed pointer projection #3774
• 👉 Move pointer cast implementation into its own source file #3773
• 　  Share Rust mathematical models across Anneal frontends #3799

Latest Update: v9 — Compare vs v8

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Version	v8	v7	v6	v5	v4	v3	v2	v1	Base
v9	v8	v7	v6	v5	v4	v3	v2	v1	Base
v8		v7	v6	v5	v4	v3	v2	v1	Base
v7			v6	v5	v4	v3	v2	v1	Base
v6				v5	v4	v3	v2	v1	Base
v5					v4	v3	v2	v1	Base
v4						v3	v2	v1	Base
v3							v2	v1	Base
v2								v1	Base
v1									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 2026-10-05T15:31:42.061030Z	7c15a27	PR opened
🔒 Security Review	✅ Completed 2026-10-05T15:33:37.844824Z	7c15a27	PR opened

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 95.23810% with 1 line in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (Gluzscumtqii4zeryhevzpymev2ojqng@ae3acb5). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
zerocopy/src/layout/cast_from.rs	95.23%	1 Missing ⚠️

Additional details and impacted files

@@                         Coverage Diff                         @@
##             Gluzscumtqii4zeryhevzpymev2ojqng    #3773   +/-   ##
===================================================================
  Coverage                                    ?   92.94%           
===================================================================
  Files                                       ?       17           
  Lines                                       ?     2466           
  Branches                                    ?        0           
===================================================================
  Hits                                        ?     2292           
  Misses                                      ?      174           
  Partials                                    ?        0           

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[chatgpt-codex-connector]

Add the extracted cast module to the audit scope

Following the source catalog's explicit audit-unit assignment now scopes the layout/proof shard to src/layout/mod.rs but omits src/layout/cast_from.rs, even though that new file contains the entire unsafe pointer-cast implementation and the catalog specifically assigns the known layout::cast_from proof obligations to this shard. This can cause the current open-world audit to skip the implementation it is meant to assess; update unit 8 to include the extracted file (or the whole src/layout/ directory).

AGENTS.md reference: zerocopy/AGENTS.md:L33-L34

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