diff -u in a command pane names its files though the terminal turned the tab before each timestamp into blanks

A `---`/`+++` path was cut at the tab before diff -u's timestamp. Run in
a command pane, the terminal had turned that tab into blanks, so the name
took the timestamp with it and a look at a changed line opened nothing.
The name is now also cut where blanks run up to a timestamp, either GNU
diff's `2026-09-30 10:00:00...` or ctime's `Wed Sep 30 10:00:00 2026`. One
blank is enough, since a tab can expand to a single blank, and the stamp
is strict, so a name with blanks and no stamp after them stays whole.
Tested on the parsed text and, in fs.py, on real `diff -u` output in a
command pane, where a look at `+TWO` opens the new file.

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

1 files changed, 19 insertions, 0 deletions

diff --git a/test/fs.py b/test/fs.py
index 80bee07f..9392ffb7 100644
--- a/test/fs.py
+++ b/test/fs.py
@@ -381,6 +381,25 @@ def discovery(binary, embedded=False):
             # Through a mount both read as EINVAL; the log says which and why.
             assert f'err {scratch} addr: no match for regexp\n'.encode() in client.read('/log')
             client.remove(f'/pane/{scratch}')
+            # Real `diff -u` in a command pane: the terminal turns the tab
+            # before each timestamp into blanks, and a look at a changed line
+            # still opens the new file at it.
+            (root / 'diff-old.txt').write_text('one\ntwo\nthree\n')
+            (root / 'diff-new.txt').write_text('one\nTWO\nthree\n')
+            seen = client.read('/log').decode().count('\nexit ')
+            client.write('/exec', b'diff -u diff-old.txt diff-new.txt\n')
+            deadline = time.monotonic() + 10
+            while client.read('/log').decode().count('\nexit ') <= seen:
+                assert time.monotonic() < deadline, 'diff -u never ended'
+                time.sleep(.05)
+            ran = [row.split()[0] for row in client.read('/index').decode().splitlines() if row.split()[1] == 'term']
+            shown = client.read(f'/pane/{ran[-1]}/body').decode()
+            assert '+++ diff-new.txt' in shown and '\t' not in shown, shown
+            client.write(f'/pane/{ran[-1]}/look', b'+TWO\n')
+            opened = [row for row in client.read('/index').decode().splitlines() if row.split()[3] == f'{root}/diff-new.txt']
+            assert len(opened) == 1, client.read('/index')
+            client.remove(f'/pane/{opened[0].split()[0]}')
+            client.remove(f'/pane/{ran[-1]}')
             # A Save makes the directories its file goes in, whatever names
             # it: the pane's own name or Save's path.
             # `~` is home (this session's HOME, the test's root) wherever a