feat(scheduler-sim-decision-trace): trace record model foundation

Task 1.3: trace types and constants, per-record arena, job selection
matching, no-decision record finishing; empty capture module; both
sources scanned by the core isolation test with a no-stdio check.

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

src/scheduler/testsuite/meson.build

@@ -234,6 +234,13 @@ sched_core_isolation_test = executable(
              '-DXCE_CORE_CLOCK_C_PATH="'
              + (meson.current_source_dir() / '..' / 'src' / 'core_clock.c')
              + '"',
+             '-DXCE_SCHED_TRACE_C_PATH="'
+             + (meson.current_source_dir() / '..' / 'src' / 'sched_trace.c')
+             + '"',
+             '-DXCE_SCHED_TRACE_CAPTURE_C_PATH="'
+             + (meson.current_source_dir() / '..' / 'src'
+                / 'sched_trace_capture.c')
+             + '"',
              '-DXCE_CORE_LIB_PATH="'
              + sched_core_isolation_lib.full_path()
              + '"'],
@@ -2509,3 +2516,18 @@ test('scheduler repl trace baseline test',
      sched_repl_trace_baseline_test, suite: 'scheduler',
      env: ['ASAN_OPTIONS=detect_leaks=0'],
      depends: scheduler)
+
+# scheduler-sim-decision-trace task 1.3: decision trace record model
+# (src/sched_trace.c) unit tests -- selection matching, record header and
+# per-record arena copying and size, record finishing. Links only the model
+# source; libxce supplies the jobid helpers.
+sched_trace_model_test = executable(
+    'sched_trace_model_test',
+    ['test_trace_model.c', '../src/sched_trace.c'],
+    include_directories:[incdir],
+    dependencies: [scheduler_test_deps],
+    install: false)
+
+test('scheduler trace model test',
+     sched_trace_model_test, suite: 'scheduler',
+     env: ['ASAN_OPTIONS=detect_leaks=0'])