Modified F1-F4, Alt+] and Alt+Shift+P typed before a terminal takes input are still dropped without a notice #2708

Follow-up to #2689.

Before a terminal takes input (input-ready), a key the held draft cannot hold is now told as "Not sent". A few real keys still produce the same bytes as a report xterm sends by itself, so the filter in retainTyped (src/lib/useTerminalMount.ts) treats them as xterm's and drops them without a notice:

• Shift+F3 sends ESC [1;2R and Ctrl+F3 sends ESC [1;5R. Both look like a cursor-position report.
• Alt+] sends ESC ], which looks like the start of an OSC color report.
• Alt+Shift+P sends ESC P, which looks like the start of a DECRQSS reply.

Repro. Run scripts/terminal-early-keys-demo-regression.ts with input-ready held back, then press Shift+F3. No input frame is sent, nothing goes to the draft, and no notice appears. This was reproduced by the review of #2689.

Not a regression. Main drops every such key silently. #2689 makes most of them visible and leaves these few as they were.

Possible fix. Decide by whether the user or xterm produced the input, not by the bytes. One way is a flag set from the terminal's keydown/keypress listeners (like the existing typedChord and commandBackspace hooks). Add a Shift+F3 or Alt+] case to the regression script.