FABRIC-3.8.md: design for real concurrency; stop the serialized DoE campaign

The per-ISA amd64 campaign (12345 3 S" amd64" DOE) was stopped ~49 min in,
zero trials complete: its harness drives workers by synchronous VM-EXEC on
Hera's stack, so the concurrency factor counted resident VMs while execution
stayed serialized. Tracing further showed the v2.1.0 reshuffle stops short of
real concurrency: kernel-Hermes never publishes eligibility (no mark_work in
sk_hermes_send_one), the switch trampoline is still the Stage-2 placeholder,
delivery to passive VMs still goes through the idle pump, only Tripod/WIREBIND
VMs are switch participants, and the stack-ownership gate is a single global.

FABRIC-3.8.md records the gap analysis and a staged A-I design, each stage its
own commit and 3-arch acceptance. FABRIC-3.md SXXXV.16 points to it. Logs and
extracted CSVs from today's boots and the stopped run are kept as audit
artifacts.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

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