The resize handler painted synchronously via commit() but left the commit
scheduler's pending trailing throttle timer armed. If an update was sitting
in that timer, it fired a second doCommit() right after the resize paint —
and because shouldClearTerminalForFrame clears whenever the previous frame
overflowed the viewport, the second commit emitted a duplicate clearTerminal.
Cancel the pending trailing commit before the synchronous paint; the paint
already reflects the current tree, so the pending commit is redundant.
Regression test (test-first) in throttle.sequential.test.tsx reproduces the
double-clear (2 clears) and verifies the fix (1 clear). Closes#26 (item 1).
Yunfei He
f3bb5f268a