docs: queue nested optional codegen bypass closure

[briansrls]

Summary

• adds the narrowed T-ImpossibleBugs nested-optional codegen-bypass closure worker brief
• queues the brief from the R2 Impossible-Bugs manager brief as a pending residual

Verification

• git-metadata-unavailable: local worktree has a broken .git pointer, so this was published via GitHub contents API from file/rg evidence only
• remote branch created from main 316e769

Notes

• Scope is documentation/dispatch only: no implementation changes.
• This preserves the existing allocator/lowering closure and narrows only the remaining CardinalityPayload::new_unchecked / generated construction bypass surface.

[briansrls]

Closing as duplicate of dashboard-owned session PR #1778. The file contents are identical; keeping #1778 as the authoritative PR for warm-dove-810.