Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@crates/compiler/src/lib.rs`:
- Around line 986-1025: The helper parenthesized_param_message currently only
inspects the current physical line, missing multiline cases; update it to scan
backwards from line_start through previous lines to find a preceding "def " or
"lambda" token and then evaluate parenthesis depth across that full span.
Specifically, for "def " (use def_idx search but on the concatenated slice from
the found def position to the error start) walk characters from that def
position counting '(' and ')' to determine if the error position is inside the
function parameter list (return the CPython message if inside), and for "lambda"
search backwards similarly to find a lambda token without a ':' between it and
the error (consider spanning newlines). Keep the existing return messages and
reuse parenthesized_param_message, but replace single-line checks with these
backward-scanning, depth-aware checks so multiline parameter lists are detected.
- Around line 1397-1419: chunk_has_bare_assignment currently treats any
alphanumeric LHS as an identifier; update it to reject literals/keywords by
first checking the trimmed lhs start and exact content: ensure lhs is non-empty
and its first byte is ASCII alphabetic or b'_' (reject if it starts with a
digit, quote, '(' '[' '{', etc.), then ensure the whole lhs matches the
identifier shape (bytes().all(...) as you already do) and is not one of the
Python literal/keyword tokens like "True", "False", or "None" (use a small
static set and compare lhs.eq_ignore_ascii_case or exact match as appropriate).
Return false for those cases so chunk_has_bare_assignment only returns true for
real identifiers.
- Around line 1682-1698: The current is_in_case_pattern only checks the current
line for a "case " header so it misses multi-line case headers; change the logic
to scan backwards from range.start() to find the nearest preceding non-empty
line whose trimmed start begins with "case " (use the existing start and
line_start variables as anchors) and treat the location as being in a case
pattern if such a "case " header exists with indentation (case_indent) less than
the current line and there is no '=' token between the header start and the
range.start(); update the code around is_in_case_pattern, keeping references to
start, line_start, rest, and case_indent, to iterate previous lines (instead of
only checking source[line_start..]) and ensure multiline headers are recognized
before falling back to the match-search logic.

---

Nitpick comments:
In `@crates/codegen/src/compile.rs`:
- Around line 4718-4729: Extract the duplicated "__debug__" type-parameter check
into a new helper on the compiler impl (e.g. fn
validate_type_params_no_debug(&self, type_params: Option<&ast::TypeParams>) ->
CompileResult<()>) that iterates params.type_params, extracts the name from
ast::TypeParam variants, and returns
Err(self.error(CodegenErrorType::Assign("__debug__"))) if a name equals
"__debug__", otherwise Ok(()). Replace the duplicated validation blocks in the
function compilation path and the class compilation path with a single call to
this helper, keeping existing types (ast::TypeParams, CompileResult) and error
construction unchanged.