diag(net): harden paired worker capture and split observer timing

Keep the observer diagnostic-only and opt-in. Preserve native boundary
parentage through task destruction, bound startup/shutdown coordination,
and fail closed after bounded native resume retries. Separate the copied
stack/resume window from post-resume processing, with exact local PDB
provisioning and a bounded executable-only symbol cache.

Local forced-stale capture is an instrumentation proof, not a field
mechanism verdict. No PR, remedy, rollout, or staging authorization.

Co-authored by: todlando