Fix expect() timeout never firing while the stream keeps producing output

[CarlosFelipeOR]

Close #2

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Description of Changes

expect() only evaluated its deadline inside the except TimeoutError: branch, which is reached only when read() sees no data for 0.1s. With a stream that never goes quiet that branch is never taken, so timeleft reaches 0 and the loop spins indefinitely.

The deadline is now checked on every iteration: search first, so a match that just arrived still wins, then check the deadline, then read. The timeout block is moved unchanged, so expect_timeout=True still returns instead of raising.

Verified with the reproducer from #2:

case	before	after
timeout, quiet stream	3.0s	3.0s
timeout, continuous stream	never fires	3.8s
match, quiet stream	ok	ok
match, continuous stream	ok	ok

The continuous-stream case overshoots slightly (3.8s for timeout=3) because the regex search over the accumulated buffer runs before the deadline check. That ordering is deliberate — checking first would discard a match that had just arrived.

[CarlosFelipeOR]

I have read the CLA Document and I hereby sign the CLA

[vzakaznikov]

The solution does not seem to be correct. Try changing

TestFlows-uExpect/testflows/uexpect/uexpect.py

Line 221 in b7ddbd3

while timeleft >= 0:

to just ">" so that the 0 value will cause an exception.

[vzakaznikov]

Actually, the read(timeout=0) is treated as non-blocking so if data is there it will read. So expect with timeout=0 should do the same, try only once if data is read and matched then no exception otherwise raise.

[CarlosFelipeOR]

Done. expect() now attempts exactly one read before the deadline can fire, so expect(timeout=0) matches when the data is already there and raises otherwise. read() is untouched, so read(timeout=0) stays non-blocking.

Behaviour matrix used to verify it, generated by Claude Opus 5: test_matrix.py

python3 test_matrix.py <path-to-checkout> — 8/8 on this branch. On b7ddbd3 two cases hang; on the previous commit the two timeout=0 cases fail.

@vzakaznikov could you review it again?