fix(auip): bind pending preparation to active work

[Lucas1479]

Summary

• compile an explicit request to join a still-running deliverable into Host-grounded AUIP preparation
• suppress a duplicate Work start while preserving independent Work clauses
• revalidate frozen active Attempt identity against the current Session roster and reserve launch on the original WorkItem

Regression coverage

• reproduces 你能接入他吗？我想和你一起玩 while the game WorkItem is still running and has no Artifact
• verifies an erroneous execute project proposal cannot create a second WorkItem
• verifies unrelated independent Work is not absorbed
• verifies the preparation callback receives the original WorkItem and keeps the Ledger at one WorkItem

Validation

• python -m ruff check core/chat_runtime.py server/auip_control_decision.py server/auip_launch.py tests/test_auip_control_decision.py tests/test_auip_launch.py
• 101 passed — AUIP control, launch, action-existence, and delegate dispatch
• 55 passed — cross-axis assembly, runtime control, amend intent, WorkItem continuity, and export

[Lucas1479]

Maintainer self-review complete: no blocking findings. The change binds an explicit AUIP engage/preparation request to the already-active, subsuming WorkItem by carrying frozen Attempt identity and revalidating it against the Host session roster before launch. It does not add keyword routing or a second intent classifier, suppresses only duplicate work-start proposals, and preserves the independent-work path. Local validation on the rebased head: Ruff passed; 101 AUIP/control/dispatch tests, 56 cross-axis/runtime/amend/continuity/export tests, and 49 compound-authority/workspace tests passed. Required build and cpu-model-less checks are green on head 5bc7a7f. Admin merge bypass is used only for the unavailable external approval requirement.