tls-budget asyncpipe exits before Darwin sampling and yields zero-root profile #8050

Failure

The Darwin TLS budget's asyncpipe subject exits before sampling begins, so its budget result is vacuous-red rather than a measurement:

Exact evidence: run 31736187608 / tls-budget job 94568276080, head 3381e1b89048592cfc91f3d4a43349c6e7c16015.

The uploaded asyncpipe.sample is only 69 lines with an empty call graph: zero root samples, zero _tlv_get_addr, and zero distinct Perry runtime symbols. The gate correctly rejects it. In the same job, interp.sample is a positive control with 48,508 report lines and 4,848 root samples, so /usr/bin/sample and tls_budget_check.py are functioning.

Mechanism

scripts/tls_budget_gate.sh starts the subject and then waits a fixed one second before invoking sample. The current asyncpipe binary completes during that sleep. This is a workload-lifetime/attachment bug; changing the percentage threshold cannot repair it.

Acceptance

• Make the representative asyncpipe subject remain live long enough for the sampler without changing its deterministic correctness result or removing its async/Map/Set/template-literal coverage.
• Retain the minimum root-sample, runtime-symbol, direct_tsd, and claimed-site liveness requirements.
• Validate locally on Darwin with a nonempty call graph and sufficient samples; interp remains a positive control.
• A deliberately short-lived subject must still be rejected rather than silently passing.

Refs #7966.