docs(scheduler): list the decision-trace sources in the component guide

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

src/scheduler/CLAUDE.md

@@ -16,6 +16,15 @@ C-based job scheduling engine with a plugin architecture. Determines job-to-node
 - **Replay/recording** — `recording.c`/`recording_events.c`/`recording_session.c` (live capture) and `sim.c`/`sim_loop.c` (simulation-side decode) do the actual capnp encode/decode of the `.replay` binary stream (`src/schema/controller.capnp`); `snapshot.c`/`snapshot_wire.c`/`snapshot_load.c` only populate/consume the plain in-memory `sched_snapshot_data_t` struct that `recording.c`'s `write_snapshot_entry()` then serializes — no capnp or file I/O lives in the snapshot files themselves. Controlled via `OPCode_schedAdmin` (`src/controller/cluster.c`) and `xceadmin scheduler record start|stop|status` / `scheduler dump <FILE>`.
 - **Interactive REPL** (`repl.c`/`repl_break.c`/`repl_info.c`/`repl_params.c`, `--interactive`) — single-step/breakpoint/state-inspection/snapshot-capture control over the simulation driver; drives the exact same `sched_sim_driver_run()` as batch `--sim`, gated only by `sim->interactive`, so REPL and batch runs are decision-equivalent by construction (`test_repl_equivalence.c`).
 
+- **Decision trace** (`scheduler-sim-decision-trace`, simulator REPL only) — `include/sched/trace.h` is the public interface and the `SCHED_TRACE(core, call)` hook macro, which evaluates `call` only while `core->trace_rec` is set; live never sets it, so hooks cost one pointer test. The sources are split to stay under the line cap:
+  - `sched_trace.c`: the record, its arena, the entry sequence and line budget, and requirement/plan/check entries.
+  - `sched_trace_scan.c`: positions, host verdicts and rows, summary tallies, rollback, commit and search end.
+  - `sched_trace_capture.c`: copies selection facts, cluster-wide limits, check rows and attempt reasons out of scheduler state.
+  - `sched_trace_outcome.c`: dispatch and pend outcomes, and reconstructed-dispatch records.
+  - `sched_trace_internal.h`: helpers shared between those files (`sti_` prefix).
+
+  None of them may use stdio, file I/O or logging, and none belongs in `sched_core_isolation_lib`; `test_core_isolation.c` scans all five. Every white-box test that `#include`s a hooked source (resource, host_iter, alloc_runner, scheduler, sched_election, driver) must also `#include` the four trace `.c` files, exactly once.
+
 Links against `libxce` from `src/lib/`. Full design/requirements: `.kiro/specs/scheduler-core/`.
 
 ## Conventions