fix: resolve the pipeline output dir once

Every step runs from the repository root, but the lock and the purge of
stale packs read --output-dir from the caller's directory. Started from
scripts/, the run locked and purged scripts/dist/ and wrote to dist/,
leaving the stale packs there. The directory is now made absolute before
the lock, dist/ at the root by default.

scripts/pipeline.py

@@ -92,6 +92,19 @@ class StepResults(dict):
 # Steps that report without failing the run.
 NON_BLOCKING = frozenset({"check_buildbot"})
 
+def _output_dir(typed: str | None) -> str:
+    """The pack directory as an absolute path.
+
+    Every step runs from the repository root, while the lock and the purge
+    of stale packs ran here, against the caller's directory: started from
+    scripts/, the run locked and purged scripts/dist/ and wrote its packs to
+    dist/. A directory the caller typed is read from where they typed it.
+    """
+    if typed is None:
+        return str(Path(__file__).resolve().parent.parent / "dist")
+    return str(Path(typed).resolve())
+
+
 def run(cmd: list[str], label: str) -> tuple[bool, str]:
     """Run a command, echoing its output as it comes. Returns (success, output).
 
@@ -425,7 +438,8 @@ def main() -> None:
         "assets already in .cache/large/"
     )
     parser.add_argument(
-        "--output-dir", default="dist", help="Pack output directory (default: dist/)"
+        "--output-dir",
+        help="Pack output directory (default: dist/ at the repository root)",
     )
     parser.add_argument("--target", "-t", help="Hardware target (e.g., switch, rpi4)")
     parser.add_argument(
@@ -455,6 +469,7 @@ def main() -> None:
     )
     args = parser.parse_args()
     _refuse_unapplied_flags(parser, args)
+    args.output_dir = _output_dir(args.output_dir)
 
     # A second run on the same output directory is refused before any work:
     # the database rebuild alone takes minutes, and the reader holding the

tests/test_audit_regressions.py

@@ -5975,5 +5975,25 @@ class ErrorsGoToStderr(unittest.TestCase):
             self.assertGreater(seen, 0, script)
 
 
+class PipelineOutputDirIsTheOneItWrites(unittest.TestCase):
+    """Started from scripts/, the pipeline locked and purged scripts/dist/
+    while every step, run from the repository root, wrote to dist/."""
+
+    def test_the_default_is_the_root_dist_wherever_the_run_starts(self):
+        previous = os.getcwd()
+        self.addCleanup(os.chdir, previous)
+        os.chdir(ROOT / "scripts")
+        self.assertEqual(pipeline._output_dir(None), str(ROOT / "dist"))
+        self.assertEqual(pipeline._output_dir("out"), str(ROOT / "scripts" / "out"))
+
+    def test_main_resolves_it_before_the_lock(self):
+        source = (ROOT / "scripts" / "pipeline.py").read_text(encoding="utf-8")
+        body = source[source.index("def main("):]
+        self.assertLess(
+            body.index("args.output_dir = _output_dir(args.output_dir)"),
+            body.index("hold_artifact_lock(args.output_dir)"),
+        )
+
+
 if __name__ == "__main__":
     unittest.main()