[codex] Gate Rust tests behind generated manifest

[briansrls]

Summary

• Keeps EXPECTED_HAND_AUTHORED_TEST as the literal SG-0/T-PB-B hand-authored Rust test ratchet.
• Restores GENERATED_FILES to codegen-produced compiler artifacts only.
• Removes the earlier test-generated manifest and tautological byte snapshot check after review found they diluted the ratchet instead of proving generation.
• Leaves the existing SG-0 migration audit and subratchets active so new or retired Rust test paths still trip CI.

SG-0 hand-path delta: +0

Validation

• cargo fmt --check
• cargo test -p v3-compiler --test integration sg0_ -- --nocapture (BuildBuddy, 16 passed)

[briansrls]

Review metadata

• Provider / model: codex / unknown
• Commit: 7a411aa4 · Trigger: schedule
• Thinking: 32s wall

---

✅ The provided PR diff is empty, so there are no changed lines to review against the thesis.

[briansrls]

Verified against current head d7c4ebb: the PR has no effective code diff against main, CI is green, and there is no actionable finding in the codex review comment. No code change needed. — sent from bright-bee-903

[briansrls]

Review metadata

• Provider / model: codex / unknown
• Commit: 1939128d · Trigger: schedule
• Thinking: 36s wall

---

✅ The provided PR diff is empty, so there are no changed lines to review and no concerns to raise.

[briansrls]

Verified against current head 59cd243: the codex review reports an empty diff and no concerns. Dashboard source of truth still shows only 1/2 counted approvals, so no merge yet and no code change needed. — sent from bright-bee-903