Thread Windows metadata targets through sessions

[evawong-oai]

Summary

1. Threads Windows protected metadata targets through reusable Windows sandbox sessions.
2. Keeps session wiring separate from direct exec wiring.

Why

1. Session based commands are a different entry point from direct exec and need the same protected metadata decisions.
2. Splitting this PR lets reviewers inspect session lifecycle wiring without also reviewing target planning or enforcement logic.

Stack Relation

This PR is part 7 of 21 in the Windows protected metadata stack.

1. PR 20889 Add Windows metadata adapter target type
2. PR 20890 Add Windows metadata setup target type
3. PR 20891 Add Windows metadata enforcement guard
4. PR 21030 Plan Windows metadata targets from filesystem policy
5. PR 21031 Thread Windows metadata targets through setup request
6. PR 21032 Pass Windows metadata targets to direct exec
7. PR 21033 Thread Windows metadata targets through sessions
8. PR 21035 Enforce Windows protected metadata targets
9. PR 21036 Deny Windows protected metadata symlink targets
10. PR 21037 Use Windows metadata targets in debug sandbox
11. PR 21038 Allow Windows sandbox Git signal pipes
12. PR 21039 Add Windows legacy Git read root helpers
13. PR 21040 Grant Windows legacy Git read roots
14. PR 21041 Inject Git safe directory for Windows legacy sandbox
15. PR 21042 Test Windows runtime metadata target preparation
16. PR 21043 Document Windows metadata request boundary
17. PR 21172 Add Windows missing metadata monitor runtime
18. PR 21173 Wire Windows metadata monitor through sandbox exits
19. PR 21174 Add Windows missing metadata deny sentinel
20. PR 21175 Wire missing Windows metadata to deny sentinel
21. PR 21184 Use direct deny ACLs for Windows metadata sentinels

Validation

1. Stack head local format and Rust tests passed on 95ef124d6194bd2126c11928cb3973214f9ac63a.
2. Azure Windows VM 56 case validation is running on 95ef124d6194bd2126c11928cb3973214f9ac63a.