Output slow for 1/2 second, then fast

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### Windows Terminal version

1.25.2604.02003 (preview) (1.25.923.0) and the previous 1.25 preview

### Windows build number

10.0.26200.8037 (25H2)

### Other Software

TCC shell; v36

### Steps to reproduce

N.B., I have many versions of TCC and WT 1.25, WT 1.24, and WT 1.23 (Store install). I can **only** observe this behavior with WT 1.25 and the newest TCC (v36, now in public beta).

First, wait a while (an hour, several hours, overnight?). When this behavior begins varies and it doesn't seem to have anything to with what **I** do. Then do any of these: press [up] for command history recall, paste into a command line, run a command.

### Expected Behavior

Normal output

### Actual Behavior

If I press [up] a recalled command appears on the command line **slowly**; there's no delay, the characters just stream slowly across the screen. If the recalled command is long enough, after about 1/2 second of slowness, it becomes fast, as usual.

If I paste to a command line the pasted characters appear slowly. If the pasted data is long enough, after about 1/2 second of slowness, it becomes fast, as usual.

If I execute, for example, DIR, the initial output (about 1/2 second, several lines) is slow, thereafter fast.

If I press and hold [up] the result is much like executing DIR ... as I go through the command history output is slow for about 1/2 sec (several lines), then fast.

Once this behavior starts all of the above happen and in several weeks of investigating I haven't found a way to stop it. I must emphasize, there are no outright delays, just slow output followed by normally fast output.

I new instance of the shell (replacing the old one) started with TCC's EXEC command (same ConPty I believe) inherits this problem.

Start by reproducing the slow initial output with Windows Terminal 1.25 and TCC v36 after an extended idle period, then compare the same actions in Windows Terminal 1.24 and 1.23. Check command recall, paste, and DIR output separately; done means identifying and correcting the initial half-second slow rendering without changing normal output speed.

Written by the indexing model from the issue text.