FABRIC.md: item 4.5b complete -- TimeTrustState.ticks fixed, three-arch verified

Marks 4.5b done with the verification record (three log dirs, all reaching
[Hera] ok> at unchanged -O0). Routine artifacts from this session's
three-arch runs: capsules/BLOCK_MAP.md, disk/artemis.img, DOE CSVs, QEMU
serial logs.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

FABRIC.md

@@ -5454,7 +5454,7 @@ document and committing that amendment as its own item.*
   > No other ISR-reachable global state was found beyond what's listed above, on any of the
   > three architectures.
 
-- [ ] **4.5b — Fix every hazard 4.5a found.** Depends on 4.5a. Code fix, no optimization
+- [x] **4.5b — Fix every hazard 4.5a found.** Depends on 4.5a. Code fix, no optimization
   flags touched yet. `TimeTrustState.ticks` is the one already-confirmed instance — mark it
   `volatile`, or fold it into the existing `g_pending_counter`/`g_pending_valid`-style
   ISR→mainline handoff pattern already used elsewhere in `heartbeat.c`, whichever fits the
@@ -5466,6 +5466,18 @@ document and committing that amendment as its own item.*
   is now safe).
   *Refs:* 4.5, 4.5a.
 
+  > **Done 2026-08-11.** 4.5a found exactly one hazard, so this fixes exactly one field:
+  > `TimeTrustState.ticks` (`include/starkernel/timer.h:90`) marked `volatile` in place,
+  > rather than folded into the `g_pending_counter` handoff — `ticks` is a simple monotonic
+  > counter with a single ISR writer and no derived-state computation on the mainline side
+  > (unlike `window`/`variance`/`trust`, which genuinely need `heartbeat_service()`'s
+  > deferred-processing pattern), so a direct `volatile` on the one hazardous field is the
+  > narrower fix and leaves the struct's other fields — which don't need it — unaffected.
+  > Three-arch acceptance boot clean at unchanged `-O0`: amd64 `logs/20260811-100623/`,
+  > aarch64 `logs/20260811-100724/`, riscv64 `logs/20260811-100825/`, all reaching
+  > `[Hera] ok>`. This proves no regression, not that optimization is safe yet — that's
+  > 4.5e's job once 4.5c/4.5d actually turn it on.
+
 - [ ] **4.5c — Decide and record the target optimization flags.** Design-only, no code.
   Depends on 4.5b (deciding flags before the known hazard is fixed is premature). Candidates
   to weigh, not yet chosen: matching the hosted/StarForth ladder's