fix(test): stop budget-env poisoning from the backpressure test

cbm_mem_init is init-once (guarded by g_initialized), so the
backpressure test's setenv(CBM_MEM_BUDGET_MB=1) + re-init 'restore'
was a silent no-op: whichever init ran first fixed the budget for the
whole process. In the full runner this test's init won, locking a 1 MB
budget that leaked into every later budget consumer —
mem_over_budget_low_rss red on every platform, and all subsequent
pipeline tests silently running with backpressure permanently engaged.

Add cbm_mem_set_budget_for_tests(): writes the budget directly without
touching the init guard. The test now saves the caller-visible budget,
sets 1 MB via the hook, and restores before asserting. Env dance
removed.

Signed-off-by: Martin Vogel <martin.vogel.tech@gmail.com>

Author: DeusData

src/foundation/mem.c

@@ -234,6 +234,10 @@ size_t cbm_mem_budget(void) {
     return g_budget;
 }
 
+void cbm_mem_set_budget_for_tests(size_t bytes) {
+    g_budget = bytes;
+}
+
 bool cbm_mem_over_budget(void) {
     size_t rss = cbm_mem_rss();
     check_pressure(rss);

src/foundation/mem.h

@@ -29,6 +29,15 @@ size_t cbm_mem_peak_rss(void);
 /* Total budget in bytes. */
 size_t cbm_mem_budget(void);
 
+/* TEST HOOK: overwrite the budget directly, bypassing cbm_mem_init's
+ * init-once guard (a setenv+re-init dance in tests is a silent no-op once
+ * some earlier init won the guard — the poisoned budget then leaks into
+ * every later budget consumer in the process). Does NOT flip the init
+ * guard: a later cbm_mem_init still initializes normally. Callers must
+ * save cbm_mem_budget() first and restore it before their assertions.
+ * Never call from production code. */
+void cbm_mem_set_budget_for_tests(size_t bytes);
+
 /* Returns true if current RSS exceeds the budget. */
 bool cbm_mem_over_budget(void);
 

tests/test_pipeline.c

@@ -6577,9 +6577,16 @@ TEST(pipeline_backpressure_futile_nap_disengages) {
         fclose(f);
     }
 
-    /* 1 MB budget: over-budget on every pull, unreclaimable by napping. */
-    cbm_setenv("CBM_MEM_BUDGET_MB", "1", 1);
-    cbm_mem_init(0);
+    /* 1 MB budget: over-budget on every pull, unreclaimable by napping.
+     * Set via the test hook, NOT setenv + cbm_mem_init: the init-once guard
+     * makes any re-init keep whatever budget the FIRST in-process init
+     * computed. The old env dance either failed to apply the 1 MB budget
+     * (some earlier test's init won the guard) or applied it permanently
+     * (this test's init won) — the "restore" re-init was then a silent
+     * no-op and the 1 MB budget leaked into every later budget consumer
+     * in the runner (mem_over_budget_low_rss went red suite-order-wide). */
+    size_t saved_budget = cbm_mem_budget();
+    cbm_mem_set_budget_for_tests((size_t)1024 * 1024);
     ASSERT_TRUE(cbm_mem_budget() > 0);
     ASSERT_TRUE(cbm_mem_over_budget());
 
@@ -6589,9 +6596,8 @@ TEST(pipeline_backpressure_futile_nap_disengages) {
     int rc = cbm_pipeline_run(p);
     long cycles = cbm_pp_bp_nap_cycles();
 
-    /* Restore the tests' default budget-off state BEFORE asserting. */
-    cbm_unsetenv("CBM_MEM_BUDGET_MB");
-    cbm_mem_init(0);
+    /* Restore the caller-visible budget BEFORE asserting. */
+    cbm_mem_set_budget_for_tests(saved_budget);
     cbm_pipeline_free(p);
     teardown_test_repo();