fix(scheduler-sim-decision-trace): render an unset pend main reason as none

The pend outcome printed 'main reason: code 0' for every pend the
allocator builds, because 0 (libxce's 'no main reason set') fell through
to the unknown-code fallback. Found by the 6.1 end-to-end review.

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

src/scheduler/src/repl_trace_render_outcome.c

@@ -248,9 +248,12 @@ static void put_pend(FILE* f, const sched_trace_pend_out_t* p)
         return;
     }
 
+    /* 0 is libxce's "no main reason set" (preason.c), not a code */
     rtr_indent(f, 2);
     fprintf(f, "main reason: %s\n",
-            rtr_reason_name(r->main_reason, buf, sizeof(buf)));
+            (r->main_reason == 0)
+                ? "none"
+                : rtr_reason_name(r->main_reason, buf, sizeof(buf)));
 
     /* entries tied to no host (a shared resource carries host "") */
     for (k = 0; (r->host_based_reasons != NULL) && (k < r->nhost_reasons);

src/scheduler/testsuite/test_repl_trace_e2e.c

@@ -338,6 +338,7 @@ static void test_step_mode_full_all_jobs_and_file_copy(void)
              "\n    cluster-wide check failed; no placement plans tried\n",
              "\n  single requirement not satisfied\n",
              "\n  outcome: PEND\n",
+             "\n    main reason: none\n",
              "\n    resource license: NO_RESOURCE\n",
              "\n    resource limit=cluster_slots: NO_RESOURCE\n");
     TEST_ASSERT_NULL(strstr(b, "plan 1"));
@@ -362,7 +363,7 @@ static void test_step_mode_full_all_jobs_and_file_copy(void)
              "\n  alternative 2/2 not satisfied\n",
              "\n  no alternative chosen: none of the 2 alternatives was "
              "satisfied\n",
-             "\n  outcome: PEND\n");
+             "\n  outcome: PEND\n", "\n    main reason: none\n");
     free(b);
 
     /* 105, session 5: per-host shortfall rows next to limit rows, the

src/scheduler/testsuite/test_trace_render.c

@@ -865,6 +865,42 @@ static void test_pend_outcome_null_entries(void)
     sched_trace_rec_free(rec);
 }
 
+/* A pend whose set carries no main reason (0, preason.c's "none set"), as
+ * every pend the allocator builds from per-host and per-resource reasons
+ * does: the line says none instead of a bare code. */
+static void test_pend_outcome_without_main_reason(void)
+{
+    xce_sched_trace_rec_t* rec;
+    xce_res_reason_t       rr     = { "license", "", PREASON_NO_RESOURCE };
+    xce_res_reason_t*      rrp[1] = { &rr };
+    xce_job_preason_t      jr;
+    char*                  out;
+
+    rec = new_rec(XCE_TRACE_LEVEL_FULL, XCE_TRACE_LINE_BOUND_DEFAULT,
+                  XCE_TRACE_REC_DECISION);
+    TEST_ASSERT_NOT_NULL(rec);
+    set_selection(rec);
+    set_glimits(rec, 0, NULL, NULL);
+
+    memset(&jr, 0, sizeof(jr));
+    jr.nres_reasons      = 1;
+    jr.res_based_reasons = rrp;
+    rec->outcome      = SCHED_TRACE_OUTCOME_PEND;
+    rec->pend.reasons = &jr; /* read only by the renderer */
+
+    out = render(rec, XCE_REPL_UNITS_RAW);
+    assert_golden(
+        "[trace] job 1-2-1000-42  session 7  position 3  level full\n"
+        SEL_LINE NO_LIMITS_LINE
+        "  outcome: PEND\n"
+        "    main reason: none\n"
+        "    resource license: NO_RESOURCE\n",
+        out);
+    free(out);
+    rec->pend.reasons = NULL;
+    sched_trace_rec_free(rec);
+}
+
 /* ---- no-decision and reconstructed records (2.4, 2.5) ------------------- */
 
 static void test_no_decision_not_found(void)
@@ -1277,6 +1313,7 @@ int main(void)
     RUN_TEST(test_dispatch_outcome_cap);
     RUN_TEST(test_pend_outcome);
     RUN_TEST(test_pend_outcome_null_entries);
+    RUN_TEST(test_pend_outcome_without_main_reason);
     RUN_TEST(test_no_decision_not_found);
     RUN_TEST(test_no_decision_no_schedobj);
     RUN_TEST(test_no_decision_internal_error_keeps_hierarchy);