feat(scheduler-core): enforce simulation isolation (task 11.3)

Three-layer regression guard (test_sim_isolation.c) proving sim.h/sim.c/
sim_loop.c hold no controller-facing client/cluster-config/capnp-socket
state: source-text scan, struct-body field scan, and nm(1) link-time
undefined-symbol audit of a new isolated sched_sim_isolation_lib target.

src/scheduler/testsuite/meson.build

@@ -501,6 +501,40 @@ sched_sim_event_loop_test = executable(
     dependencies: [scheduler_test_deps],
     install: false)
 
+# Regression guard for task 11.3's Observable (scheduler-core spec, Req 5 AC
+# 17, "Simulation isolation"): "a build-time or structural check confirms no
+# controller-facing symbol is reachable from the simulation driver's compiled
+# object", plus the AC's own "confirmed by the struct definition itself, not
+# runtime checks alone" clause. Same source-text-scan + nm(1) link-time-proof
+# genre as sched_core_isolation_test above, PLUS a third, narrower structural
+# layer scanning ONLY xce_sched_sim_driver_t's own struct body text for
+# forbidden field types -- see the test's own header comment for why a
+# comment-stripping pass is required first (sim.h's own boundary doc comment
+# legitimately names xcecli_ctx_t/xce_cluster_config_t in prose). link_with
+# establishes the build-order dependency on sched_sim_isolation_lib (parent
+# meson.build -- sim.c AND sim_loop.c compiled together, isolated from the
+# rest of the scheduler); XCE_SIM_*_PATH bake in absolute paths the same way
+# XCE_CORE_*_PATH does above.
+sched_sim_isolation_test = executable(
+    'sched_sim_isolation_test',
+    ['test_sim_isolation.c'],
+    include_directories:[incdir],
+    dependencies: [scheduler_test_deps],
+    link_with: [sched_sim_isolation_lib],
+    c_args: ['-DXCE_SIM_H_PATH="'
+             + (meson.current_source_dir() / '..' / 'include' / 'sim.h')
+             + '"',
+             '-DXCE_SIM_C_PATH="'
+             + (meson.current_source_dir() / '..' / 'src' / 'sim.c')
+             + '"',
+             '-DXCE_SIM_LOOP_C_PATH="'
+             + (meson.current_source_dir() / '..' / 'src' / 'sim_loop.c')
+             + '"',
+             '-DXCE_SIM_LIB_PATH="'
+             + sched_sim_isolation_lib.full_path()
+             + '"'],
+    install: false)
+
 # Register as meson tests so `meson test --suite scheduler` runs them all.
 # detect_leaks=0 matches the suite convention (fixtures are not torn down).
 test('scheduler test', scheduler_test, suite: 'scheduler',
@@ -576,3 +610,6 @@ test('scheduler sim startup test',
 test('scheduler sim event loop test',
      sched_sim_event_loop_test, suite: 'scheduler',
      env: ['ASAN_OPTIONS=detect_leaks=0'])
+test('scheduler sim isolation test',
+     sched_sim_isolation_test, suite: 'scheduler',
+     env: ['ASAN_OPTIONS=detect_leaks=0'])