In @Parser/action_helpers.c:
- Around line 1295-1392: unicodewriter_write_line currently writes trailing
backslash+newline sequences verbatim for non-raw d-strings, causing newline
suppression to be ignored; modify unicodewriter_write_line to, when is_raw is
false, detect a final "\\\n" at the end of the provided segment and drop the
backslash and newline before writing (so non-raw d-strings and the dedent logic
in _PyPegen_dedent_string_part preserve line-continuation behavior), while
leaving the raw path unchanged (the early is_raw short-circuit should still
bypass this trimming).

In @Parser/string_parser.c:
- Line 284: Update the comment that currently reads "checks the prefix is
consistant." to fix the typo by changing "consistant" to "consistent" so the
comment reads "checks the prefix is consistent." This change is in the comment
string present in Parser/string_parser.c.
- Around line 337-344: The code passes raw=1 to _PyPegen_decode_string in the
non-raw branch so escapes are not processed and also fails to discard the
PyUnicodeWriter on the error return; change the call to
_PyPegen_decode_string(p, 0, line_start, line_end - line_start, token) (or use
the existing is_raw false variable) so escape sequences are handled, and on the
error path before returning NULL call PyUnicodeWriter_Discard(w) to free writer
state (ensure you still Py_XDECREF(line) as currently done).
- Around line 280-292: The code reads endline[0] without ensuring indent_len>0
which can read past the buffer for cases like d"""\nfoo\n"""; add an early check
for indent_len == 0 before computing indent_char/endline loop and raise a syntax
error using RAISE_ERROR_KNOWN_LOCATION (use PyExc_SyntaxError or equivalent)
with the same token position info (token->end_lineno, token->end_col_offset
offsets) and a message like "d-strings require trailing indentation to determine
dedent level" so the function returns NULL instead of reading out-of-bounds.

In `@Parser/action_helpers.c`:
- Around line 1475-1517: After creating temp_bytes via PyBytesWriter_Finish,
check the return value of _PyArena_AddPyObject(p->arena, temp_bytes); if it
fails (non-zero) then DECREF/clean up temp_bytes (e.g., Py_DECREF(temp_bytes) or
PyBytesWriter_Discard equivalent) and return NULL instead of proceeding to use
temp_bytes; ensure you only call PyBytes_AsString(temp_bytes) after a successful
_PyArena_AddPyObject to avoid leaking temp_bytes on arena insertion failure and
to propagate the existing exception.

In `@Parser/string_parser.c`:
- Line 392: Rename the local variable _prev_call_invald to _prev_call_invalid in
Parser/string_parser.c and update all its usages (the assignments/reads
currently referencing _prev_call_invald around the earlier usages) so they
reference _prev_call_invalid instead (also update the declaration "int
_prev_call_invald = p->call_invalid_rules;" and every subsequent use at the
three places noted).
- Around line 269-290: The inner loop in Parser/string_parser.c that compares
s[i] to indent (inside the for (; s < end; lineno++) block) can read past the
buffer when the remaining bytes are shorter than indent_len; modify the loop in
the function to check bounds (ensure s + i < end) before accessing s[i] and
break/handle as a short-line case, and also guard the subsequent check that uses
s[i] after the loop (the `if (s[i] == '\n')` branch) so it only runs when i <
remaining_length; on short lines call the same error/empty-line handling path
(using PyBytesWriter_Discard, RAISE_ERROR_KNOWN_LOCATION, or writing the newline
via PyBytesWriter_WriteBytes) as appropriate.

In `@Parser/action_helpers.c`:
- Around line 1295-1311: The bug is that unicodewriter_write_line calls
_PyPegen_decode_string with a hardcoded raw=1, preventing escape processing for
non-raw strings; update the call in unicodewriter_write_line to pass the correct
raw flag (use 0 or the is_raw variable) instead of 1 so escapes (e.g.
backslash-newline) are decoded; ensure the call to
_PyPegen_decode_string(line_start, line_end - line_start, token) uses the proper
raw parameter consistent with is_raw.

In `@Parser/lexer/lexer.c`:
- Around line 483-485: The parser's prefix validation misses the incompatible
combination of byte and dedent prefixes: add a check that if saw_b && saw_d then
call RETURN_SYNTAX_ERROR("b", "d") (place it alongside the existing saw_b &&
saw_f / saw_b && saw_t checks in the same validation function), and update the
nearby comment that lists unsupported prefix combos to include "bd" so the
supported/incompatible list accurately reflects this case; reference the boolean
flags saw_b and saw_d and the macro/function RETURN_SYNTAX_ERROR to locate where
to insert the check and update the comment.

In `@Parser/action_helpers.c`:
- Around line 1365-1377: The code reads line_start[i] after the
indentation-match loop without ensuring the pointer is still within bounds; add
a guard after the loop to ensure (line_start + i) < end before any dereference.
Specifically, in the block containing variables line_start, end, i, indent_len
and the calls to PyUnicodeWriter_WriteChar, insert a check like if (line_start +
i >= end) break; (or otherwise handle end-of-buffer) before testing
line_start[i] == '\0' or '\n' so you never read past end.