fix: resolve review budget feedback

pilot/review/opencode_runtime.py

@@ -1,6 +1,7 @@
 """Isolated opencode process runtime."""
 
 import os
+import selectors
 import subprocess
 import time
 
@@ -130,6 +131,8 @@ def _run_process(
             cmd, cwd=cwd, env=env, capture_output=True, text=True,
             stdin=subprocess.DEVNULL, timeout=timeout,
         )
+    if runner not in (None, subprocess.run):
+        raise ValueError("custom runners are unsupported for budgeted streaming")
     existing_reason = budget_state.reason()
     if existing_reason:
         budget_state.cap_reason = existing_reason
@@ -142,9 +145,27 @@ def _run_process(
     previous = {"steps": 0, "total": 0, "output": 0, "cost": 0.0}
     cap_reason = ""
     started = time.monotonic()
+    selector = selectors.DefaultSelector()
     try:
         assert proc.stdout is not None
-        for line in proc.stdout:
+        selector.register(proc.stdout, selectors.EVENT_READ)
+        while selector.get_map():
+            remaining = budget.max_duration_seconds - (time.monotonic() - started)
+            if remaining <= 0:
+                cap_reason = "max_duration_seconds"
+                budget_state.cap_reason = cap_reason
+                proc.terminate()
+                break
+            events = selector.select(timeout=remaining)
+            if not events:
+                cap_reason = "max_duration_seconds"
+                budget_state.cap_reason = cap_reason
+                proc.terminate()
+                break
+            line = proc.stdout.readline()
+            if not line:
+                selector.unregister(proc.stdout)
+                break
             output.append(line)
             _, usage = parse_events("".join(output))
             if usage:
@@ -180,6 +201,7 @@ def _run_process(
             proc.kill()
             proc.wait()
     finally:
+        selector.close()
         if proc.stdout:
             proc.stdout.close()
     stderr = proc.stderr.read() if proc.stderr else ""