Apply findings from /simplify-code 3-agent review:
1. Extract _install_paired() inner helper — the Ctrl, Alt, and Shift
sections all repeated the same mok+csiu sequence generation pattern
(~30 lines of duplication). Now each section builds a dict and
delegates to _install_paired(modifier, mapping).
2. Replace 10 hardcoded Ctrl+digit lines with a loop matching the
Ctrl+letter pattern above it.
3. Fix misleading comment: claimed 'Ctrl+0 doesn't produce a control
byte' but chr(ord('0') & 0x1F) = 0x10 = ControlP. The code was
correct (maps directly to Keys.Control0..9); only the comment was
wrong.
4. Add comment explaining why Shift+letter maps both lowercase and
uppercase codepoints (some terminals send the already-shifted
codepoint with modifier=2).
5. Test fixture: snapshot/restore ANSI_SEQUENCES in teardown so 294
mappings don't leak into sibling test files (global mutable state).
kshitij
2be183142c