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>

.kiro/specs/scheduler-sim-decision-trace/tasks.md

@@ -22,7 +22,7 @@
   - Done when every existing REPL test and the 1.1 baseline test pass unchanged under ASAN, and the helpers can be called from other REPL files.
   - _Requirements: 7.7_
 
-- [ ] 1.3 Build the trace record model foundation, test first
+- [x] 1.3 Build the trace record model foundation, test first
   - Define these types: record, settings snapshot, verdict kinds, record kinds, path, no-plan and position-end. Define these constants: line bound (default 1000, range 50 to 100000) and outcome hosts (50).
   - The per-record arena copies every string and number, so a record never points into scheduler memory. The record reports its own byte size, and freeing a NULL record is a no-op.
   - Job selection matching covers all jobs, a plain job, an array element, and every element of an array (including elements created later).
@@ -337,3 +337,6 @@
 
 ## Implementation Notes
 - 1.1: build dir is src/xce.build. Baseline test sched_repl_trace_baseline_test runs the built xce_scheduler (depends: scheduler); regenerate fixtures with XCE_REPL_BASELINE_REGEN=1 (script.txt is hand-written). Fixture sends the license value as a RESVALS_FULL event because shared resvals in the snapshot are dropped on load (bug-1923). sim_output.replay has no session decisions (set output switches files before session 1 is finalized); decisions are covered by set_output.replay and sim_verify.txt.
+- 1.3: `sched_trace_ctl_wants` whole-array selectors match elements only, not the bare key. A bare id in `trace on job <id>` can't be told apart from an array base for a job that doesn't exist yet, so 4.3's parser must emit both `{key,false}` and `{key,true}`, or the matcher must also accept `jobid == key`.
+- 1.3: design's record header lists a "file tag", but `xce_sched_trace_ctl_t` has no such field; the 4.2/4.6 store/emit tasks must set it or drop it explicitly.
+- 1.3: trace sources (sched_trace.c, sched_trace_capture.c) may not include <stdio.h> (core isolation test); capture copies raw strings/numbers and leaves formatting to the renderer.