perf: run all background build/merge/rsync subprocesses at nice 19

bincio/serve/tasks.py

@@ -51,6 +51,8 @@ def _job_finish(job_id: str) -> None:
 _rebuild_lock = threading.Lock()
 _site_rebuild_event = threading.Event()
 
+_low_priority = {"preexec_fn": lambda: os.nice(19)}
+
 
 def _site_rebuild_worker() -> None:
     """Single background thread: debounced Astro build + rsync after uploads.
@@ -76,6 +78,7 @@ def _site_rebuild_worker() -> None:
                  "--site-dir", _site_dir],
                 capture_output=True,
                 text=True,
+                **_low_priority,
             )
             if result.returncode != 0:
                 log.error("site-rebuild: build failed (rc=%d):\n%s\n%s",
@@ -89,6 +92,7 @@ def _site_rebuild_worker() -> None:
                  f"{_site_dir}/dist/", _webroot + "/"],
                 capture_output=True,
                 text=True,
+                **_low_priority,
             )
             if rsync.returncode != 0:
                 log.error("site-rebuild: rsync failed (rc=%d):\n%s\n%s",
@@ -138,6 +142,7 @@ def _trigger_rebuild(handle: str) -> None:
                      "--no-build"],
                     capture_output=True,
                     text=True,
+                    **_low_priority,
                 )
                 if result.returncode != 0:
                     log.error("rebuild[%s]: merge failed (rc=%d):\n%s\n%s",