Move the mmap/mmio grant-arena cursors off Task into the per-address-space object
(scheduler aspace_refs, exposed via aspaceMmapNextPtr/aspaceDeviceMapNextPtr), so
sibling threads in one address space hand out disjoint grants. systemMmap reserves
a range under a brief lock then maps per page under a short-held lock (not the
whole grant): the big lock runs with interrupts disabled, so pinning it across a
multi-MiB memset+map froze other cores. Guard the runtime heap's rawAlloc/rawFree
with a Thread.Mutex, gated on !single_threaded so ordinary binaries compile it out.
thread-test gains an alloc mode: 4 threads x 500 alloc/fill/verify/free cycles;
any overlap between concurrent allocations is caught by the pattern check.
Also fix the affinity guardrail: its 3-billion-iteration busy-loop had
codegen-dependent wall-time (adding a function to tests.zig swung it ~4s -> ~63s
and timed it out). Reworked to wait on the wall clock instead.
Gate thread-alloc PASS (3x); full guardrail 23/23 green; build + host tests clean.
daniel
8259678f0a