Handle missing command.

ognibuild/fix_build.py

@@ -20,6 +20,7 @@ from typing import List, Optional
 
 from buildlog_consultant.common import (
     find_build_failure_description,
+    MissingCommand,
 )
 from breezy.mutabletree import MutableTree
 
@@ -66,7 +67,11 @@ def run_with_build_fixers(session: Session, args: List[str], fixers: List[BuildF
     logging.info("Running %r", args)
     fixed_errors = []
     while True:
+        try:
             retcode, contents = run_with_tee(session, args)
+        except FileNotFoundError as e:
+            error = MissingCommand(e.args[0])
+        else:
             if retcode == 0:
                 return
             lines = ''.join(contents).splitlines(True)