feat(scheduler-sim-decision-trace): hook the host pre-filter, host scan and satisfaction check

Task 3.3: the pre-filter records selection mismatches and internal
errors as host verdicts, a scan stopped by an error marks the position
as a scan error, and unsatisfy_() hands every checked row to the current
record. Iterator and check results are unchanged.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/scheduler/include/sched/trace.h

@@ -94,8 +94,10 @@ typedef struct xce_sched_trace_rec_s xce_sched_trace_rec_t;
  * effects and argument evaluation included) runs only while `core` (an
  * xce_sched_core_t*) has a record under construction in trace_rec, so a
  * hook costs one pointer test when nothing is traced, and nothing else.
- * Only the allocator thread sets trace_rec, so hooks are placed only on
- * that thread. One statement: safe in an unbraced if/else.
+ * Only the allocator thread sets trace_rec. A hooked function called from
+ * another thread (the sim thread's reconciliation reaches unsatisfy_)
+ * sees NULL there, because the allocator clears trace_rec before it hands
+ * each decision back. One statement: safe in an unbraced if/else.
  */
 #define SCHED_TRACE(core, call)                                                \
     do {                                                                       \