fix(scheduler): sim mode picker never learns about the initial snapshot's own jobs/queues (bug-1567)

xce_scheduler -i -s <replay>: WARN "failed to resolve job picker
plugin (rc=-2)" on load, and every job already present in the
replay file's INITIAL snapshot stayed PEND forever -- never even
reached the picker, let alone got dispatched.

Root cause: sched_sim_driver_start() (sim.c) loads the initial
snapshot via xce_sched_core_load_snapshot() BEFORE any picker
plugin is registered (sim.h's own documented "Known scope
boundary" -- only the picker's NAME is threaded through from the
ReplayHeader). sched_resolve_job_picker() therefore always returns
-ENOENT there, and xce_sched_core_load_snapshot()'s own
picker-rebuild walk (on_queue_update/on_job_push per queue/job) is
silently skipped. The real builtin_fcfs picker only gets registered
moments later in sched_sim_driver_run() -- but nothing then replayed
that rebuild walk, so any job/queue from the INITIAL snapshot (as
opposed to one arriving later via a ReplayEvent, which correctly
reaches the picker through xce_core_push_events()'s own picker!=NULL
check) was permanently invisible to next_job().

Fixed by a new file, sim_picker.c: sim_bootstrap_picker() (replacing
sim_loop.c's sim_register_default_picker(), moved out because
sim_loop.c was already at its own documented 800-line "zero
line-budget headroom" cap) registers the picker AND then replays the
missed rebuild walk against it. Wired into scheduler_srcs,
sched_sim_isolation_lib, and all 9 white-box test TUs that #include
sim_loop.c directly.

New regression test (test_sim_event_loop.c): a job baked into a
fixture's INITIAL snapshot (not a ReplayEvent) now gets a live PEND
decision. RED confirmed by temporarily no-op'ing the rebuild walk
(test failed as expected), GREEN with the real fix. Full scheduler
suite green (41/41, excluding the pre-existing unrelated bug-1560).

Note: sim mode still never DISPATCHes (only PENDs) -- that is a
separate, intentionally out-of-scope gap (real resource-matching
allocation belongs to the not-yet-designed scheduler-allocation
spec), not addressed here.

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

src/scheduler/meson.build

@@ -16,6 +16,7 @@ scheduler_srcs = [
   'src/recording_session.c',
   'src/sim.c',
   'src/sim_loop.c',
+  'src/sim_picker.c',
   'src/sim_verify.c',
   'src/sim_record.c',
   'src/repl.c',
@@ -82,23 +83,28 @@ sched_core_isolation_lib = static_library(
 # the simulation driver's own files, consumed by
 # testsuite/test_sim_isolation.c to prove at build time that
 # sim.c/sim_loop.c/sim_record.c/repl.c/repl_break.c/repl_info.c/
-# repl_params.c reference zero controller-facing symbols (client/netio/
-# xceapi/delay/idgen). All files are compiled together into ONE archive --
-# task 11.2 added sim_loop.c as a sibling file to task 11.1's sim.c, task
-# 11.5 added sim_record.c as a third, task 12.1 added repl.c as a fourth,
-# task 12.2 added repl_break.c/repl_info.c as a fifth/sixth (task 12.2's
-# own 800-line-cap split of repl.c's breakpoint/state-inspection logic --
-# repl_internal.h's own "Why a split at all" section has the full
-# rationale), and task 12.3 adds repl_params.c as a seventh (the same
-# split, extended again for `snapshot`/`set`); covering only a subset of
-# them would repeat core.c's own siblings' (core_events.c/core_session.c/
-# core_clock.c) never-mechanically-covered gap for the sim driver. Same
-# "compiling to an object is enough, no real linking needed" rationale as
-# sched_core_isolation_lib above.
+# repl_params.c/sim_picker.c reference zero controller-facing symbols
+# (client/netio/xceapi/delay/idgen). All files are compiled together into
+# ONE archive -- task 11.2 added sim_loop.c as a sibling file to task
+# 11.1's sim.c, task 11.5 added sim_record.c as a third, task 12.1 added
+# repl.c as a fourth, task 12.2 added repl_break.c/repl_info.c as a
+# fifth/sixth (task 12.2's own 800-line-cap split of repl.c's
+# breakpoint/state-inspection logic -- repl_internal.h's own "Why a split
+# at all" section has the full rationale), task 12.3 added repl_params.c
+# as a seventh (the same split, extended again for `snapshot`/`set`), and
+# bug-1567's fix added sim_picker.c as an eighth (sim_loop.c's own
+# "zero line-budget headroom" -- same reason its siblings above exist --
+# so the fix's picker-registration + post-load picker-rebuild-walk logic
+# lives here instead of growing sim_loop.c past its cap); covering only a
+# subset of them would repeat core.c's own siblings' (core_events.c/
+# core_session.c/core_clock.c) never-mechanically-covered gap for the sim
+# driver. Same "compiling to an object is enough, no real linking needed"
+# rationale as sched_core_isolation_lib above.
 sched_sim_isolation_lib = static_library(
     'sched_sim_isolation',
-    ['src/sim.c', 'src/sim_loop.c', 'src/sim_record.c', 'src/repl.c',
-     'src/repl_break.c', 'src/repl_info.c', 'src/repl_params.c'],
+    ['src/sim.c', 'src/sim_loop.c', 'src/sim_picker.c', 'src/sim_record.c',
+     'src/repl.c', 'src/repl_break.c', 'src/repl_info.c',
+     'src/repl_params.c'],
     include_directories: incdir,
     dependencies: scheduler_deps,
     install: false)