Make parallel suite wait for runners

Author: IyeOnline

changelog/unreleased/synchronized-parallel-suite-batches.md

@@ -0,0 +1,26 @@
+---
+title: Reliable parallel suite startup ordering
+type: bugfix
+authors:
+  - IyeOnline
+  - codex
+created: 2026-06-02T13:19:12.043532Z
+---
+
+Parallel suites now preserve suite member startup order more reliably, making
+publisher/subscriber and other interdependent pipeline suites less prone to
+startup races.
+
+Use the existing `suite.mode: parallel` configuration:
+
+```yaml
+suite:
+  name: pipeline-suite
+  mode: parallel
+  min_jobs: 2
+```
+
+When enough jobs are available for the whole suite, the harness still runs
+members concurrently, but it submits later suite members first so earlier
+members can establish subscriptions before dependent publishers start sending
+events.

src/tenzir_test/run.py

@@ -433,6 +433,8 @@ def is_valid(self) -> bool:
 
 @dataclasses.dataclass(slots=True)
 class SuiteQueueState:
+    """Track pending parallel suites that should reserve slots before other work."""
+
     pending_items: int = 0
 
 
@@ -5369,7 +5371,8 @@ def _run_suite_parallel(
                 max_workers=reserved_workers,
                 thread_name_prefix="suite",
             ) as executor:
-                for index, test_item in enumerate(tests, start=1):
+                indexed_tests = list(enumerate(tests, start=1))
+                for index, test_item in reversed(indexed_tests):
                     if interrupt_requested():
                         interrupted = True
                         break