The 9P monkey's chunked read check allows a live file that changed between its two reads

Seed 131 flagged a command pane's tag: the whole read said `running`, the
chunked read on the same open said `exit 0`. A tag is live, not frozen at
the open, and the command ended between the reads, so this was a false
alarm that did not reproduce on replay. A mismatch now counts only when a
third, whole read still differs from the chunks. Seeds 131, 133 and 134 at
3000 steps each run clean.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

1 files changed, 4 insertions, 1 deletions

diff --git a/test/monkey9p.py b/test/monkey9p.py
index fd8c80fa..87e386b3 100644
--- a/test/monkey9p.py
+++ b/test/monkey9p.py
@@ -1616,7 +1616,10 @@ def chunked_equals_whole(ctx, res):
             whole_n, chunk_n = dir_names(whole), dir_names(chunked)
             if whole_n != chunk_n:
                 return f'{path}: whole {whole_n} != chunked({size}) {chunk_n}'
-        elif whole != chunked:
+        elif whole != chunked and w.read_all(fid) != chunked:
+            # A live file (a tag says `running`, then `exit 0`) may change
+            # between the two reads: only chunks that no whole read matches,
+            # read again, are a chunking fault.
             return f'{path}: whole {whole[:200]!r} != chunked({size}) {chunked[:200]!r}'
     finally:
         w.clunk(fid)