Preserve completed async results after interrupted responses

[fitchmultz]

Fix

Keep completed tool results in the automatic recovery handoff when the assistant response that started them errors or is interrupted. Native asynchronous tools may already have finished before that response fails. Returning early discarded their results even though Pi still projects them.

The fix removes that early return and uses the existing call/result matching. No new state, policy, or dependencies.

Verification

• Reproduced with the real fork SDK and scripted native async provider responses; the tool executed once, but its receipt disappeared from the fresh request.
• Added regression cases for overflow recovery, interruption, and output-length stops. All three fail on the original code.
• All 27 native tests pass with the fix on the installed fork 0.87.1.
• Updated the existing truncated-call check to require the projected error receipt to remain explicitly labeled not executed, while still excluding the older batch. This matches Pi's projected result and the existing recovery contract.
• git diff --check passes.
• CI checks the pinned fork, types, unit/rendering tests, source integration, and official-host refusal.