Fix trace reuse and packaged model assets

trace_formatter/trace_io.py

@@ -0,0 +1,33 @@
+from __future__ import annotations
+
+import subprocess
+from contextlib import contextmanager
+from pathlib import Path
+from typing import Iterator, TextIO
+
+
+@contextmanager
+def open_trace_text(path: str | Path) -> Iterator[TextIO]:
+    resolved = Path(path)
+    if resolved.suffix == ".zst":
+        proc = subprocess.Popen(
+            ["zstdcat", str(resolved)],
+            stdout=subprocess.PIPE,
+            stderr=subprocess.PIPE,
+            text=True,
+            encoding="utf-8",
+        )
+        if proc.stdout is None:
+            raise RuntimeError(f"Failed to stream {resolved}")
+        try:
+            yield proc.stdout
+        finally:
+            proc.stdout.close()
+            stderr = proc.stderr.read() if proc.stderr else ""
+            return_code = proc.wait()
+            if return_code != 0:
+                raise RuntimeError(f"zstdcat failed for {resolved}: {stderr.strip()}")
+        return
+
+    with resolved.open("r", encoding="utf-8") as handle:
+        yield handle