[ga-gap][unit] std.runtime.seam: unit map for 621 unreferenced extern defs

Summary

std/runtime/seam.li exports 674 extern defs; only 53 are named in li-tests/**/*.li. 621 lack unit coverage or ga-waiver.

Partial suites today: net_trusted, container_trusted, httpd, async, runtime.

Suggested fix

1. Inventory by subdomain (net/epoll/httpd/proxy/tls/container/math-rt).
2. Per-subdomain compile/policy fixtures + edge outcomes (bad fd, hangup, empty buffer).
3. Waive only with owner + expiry where execution requires root/net privilege (integration lane).

north_star_fit: scientific computing / HPC / AI — proof pillar via std lib surface; PH-IO-4/5/7, PH-7e, WP0.

Audit: data/ga-audits/lic-unit.md (ga_unit_auditor worker c2ab15d5, 2026-07-15).