F10 isr_unblock_for_io breadcrumb diagnostic

[ryanbreen]

Summary

• add seven AHCI ring breadcrumbs inside scheduler::isr_unblock_for_io(tid)
• encode UNBLOCK_PER_SGI target CPU in slot_mask and document the choice
• run 5x Parallels sweep and append the F10 investigation verdict

Validation

• cargo build --release --target aarch64-breenix.json -Z build-std=core,alloc -Z build-std-features=compiler-builtins-mem -p kernel --bin kernel-aarch64
• grep -E '^(warning|error)' /tmp/f10-aarch64-build-final.log produced no output
• git diff --check
• 5x ./run.sh --parallels --test 60 under logs/breenix-parallels-cpu0/f10-isr-unblock/run{1..5}/

Verdict

Primary F11 direction: audit SGI delivery. Runs 1 and 3 stopped after UNBLOCK_PER_SGI; run 2 stopped after UNBLOCK_AFTER_CPU, so wake-buffer push remains a secondary candidate.