feat(scheduler-sim-decision-trace): hook resource-requirement branching

Task 3.2: single requirements, top-level compounds, alternatives and
members push their path level and record one begin and one end; member
failures record the members not tried, merge failures and skipped
alternatives are separate entries, the chosen alternative or all-failed
is recorded, and each compound attempt's reasons are captured before the
job's stored reason is replaced. Scheduling results are unchanged.

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

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

@@ -138,7 +138,7 @@
   - _Boundary: TraceHooks (allocator loop)_
   - _Depends: 2.1, 2.3_
 
-- [ ] 3.2 Hook resource-requirement branching (P)
+- [x] 3.2 Hook resource-requirement branching (P)
   - Single, top-level compound, each alternative and each member push their path level and record exactly one begin and one end.
   - The begin carries task counts and requested resources for single requirements and members, and the member count for containers.
   - A member that fails or errors records the number of members not tried. A merge failure after a member is a separate entry.
@@ -361,3 +361,4 @@
 - 2.3: the outcome capture functions are `sched_trace_capture_dispatch`, `sched_trace_capture_pend` and `sched_trace_rec_reconstructed`, declared in trace.h; 3.x and 5.3 call them. Limit charges are classified by the limit flag or a `limit=` prefix and resolved via glimits (shared) or the worker's hlimits (host, worker looked up by host name). An unresolved charge has `limited_res == NULL`, which is the raw-number fallback. Shared pend entries carry host "" and are treated as host-less. For 4.1: limit totals over omitted hosts have a scope without the host, and a NULL host name yields the scope "h=". Follow-up (low): capture's `key_find`/`vget` on resmgr/workers run without the RTTI read lock that `sched_get_worker` takes. That is safe while the sim runs in lock-step; the 2.4 split may wrap them.
 - 2.4: the trace sources are now sched_trace.c (record, arena, entries, budget, requirement/plan/check), sched_trace_scan.c (positions, host verdicts/rows, tallies, rollback, commit, search end), sched_trace_capture.c, sched_trace_outcome.c (dispatch, pend, reconstructed) and sched_trace_internal.h (12 shared `sti_` helpers). Every target that compiles one trace .c file needs all four. Later tasks that extend the trace must keep each file under 800 lines and add new files to the core isolation scan.
 - 3.1: allocator-loop hooks live in `sched_allocator()` (sched_election.c), with helpers `sched_trace_push_no_decision()` and `sched_trace_attach()`. Selection is captured at job lookup, before election, so NO_SCHEDOBJ still has its selection; cluster-wide limits are captured after election. The position counter (`ctl->position`) is not SCHED_TRACE-gated (it creates the record) and counts only real pops. `sched_sim_isolation_lib` stays without the trace sources (unresolved references in a static archive are harmless); 5.1 decides whether to add them. `core->decisions` holds 5 items, so trace-only decisions take FIFO slots and cannot reorder real ones.
+- 3.2: requirement-branch hooks are in scheduler.c (`sched_make_allocation`, `sched_make_alter_allocation`, `sched_make_compound_alloc_`). The alternatives after the chosen one are not stored as entries; 4.1 renders "alternatives i+1..n not tried" from the alt_result (i,n). A merge failure stores an ATTEMPT_REASONS entry with ncodes==0. A failing single requirement records no attempt reasons; its pend outcome carries them. A single job with a NULL resreq stores its begin as a container with 0 members before returning -EINVAL, and 4.1 must tolerate that.