test(server): isolate #26671 to TUI client-side event filter

prompt_async forks publish GlobalBus events with the correct
directory/workspace (proving Effect.forkIn preserves InstanceRef per
#26586). The TUI's useEvent filter, however, returns early in the
workspace branch when event.workspace is undefined, never falling through
to directory matching. Two tests document the boundary: the live request
asserts the publishing path is correct, the synthetic filter test pins
the dropped-event shape so the fix can flip a single branch.

https://claude.ai/code/session_011VwDFG5W32dnu1qnT3SGr1