The KiCad s-expression parser rejects raw newline and carriage-return
characters inside quoted string literals — a multi-line text annotation
written through `add_text` produced a `.kicad_sch` file that eeschema
silently tolerated but `kicad-cli sch ...` refused with "Failed to load
schematic." The escape pass only handled backslashes and double quotes.
Add `\\n` → `\\\\n` and `\\r` → `\\\\r` to the same escape chain. Order
matters: backslashes are escaped first so we don't double-escape our
own escapes.
A new regression test (`test_escapes_newlines_in_multiline_text`)
checks both that the resulting quoted string literal contains no raw
newline characters and that the file round-trips cleanly through the
sexpdata parser.
End-to-end smoke: a 4-line annotation written through the patched
add_text now passes `kicad-cli sch erc` (exit 0) where the previous
behaviour failed parse.
Note: the same escape gap exists in `_make_hierarchical_label_text`
and `_make_sheet_pin_text` for unescaped quotes/newlines in the user-
supplied text. Not fixed here to keep this PR scoped to the documented
add_text bug; happy to fold it in if a reviewer prefers.
09ec6aaeb5