ISSUE-005: Include positional-only parameters in argument capture

- Fix `on_py_start` to include positional-only parameters by selecting
  `co_posonlyargcount + co_argcount` names from `co_varnames` for the
  positional slice.
- Keep existing handling for `*args`, keyword-only, and `**kwargs` intact.
- Rationale: `co_argcount` counts only pos-or-keyword parameters; omitting
  `co_posonlyargcount` dropped names before `/` (PEP 570). This patch ensures
  complete positional argument coverage and aligns with CPython ordering.
- Validation: Python tests already cover this via
  `test_all_argument_kinds_recorded_on_py_start` which asserts presence of
  `p` from `def g(p, /, q, *args, r, **kwargs)`. The fix satisfies that check.

Implementation notes:
- No new public API; minimal, focused change in `runtime_tracer.rs`.
- Followed repo rules to avoid unnecessary code and changes.

Author: tzanko-matev

codetracer-python-recorder/src/runtime_tracer.rs

@@ -158,7 +158,9 @@ impl Tracer for RuntimeTracer {
 
                 // Argument names come from co_varnames in the order defined by CPython:
                 // [positional (pos-only + pos-or-kw)] [+ varargs] [+ kw-only] [+ kwargs]
-                let argcount = code.arg_count(py)? as usize; // includes pos-only + pos-or-kw
+                // Note: `co_argcount` includes only pos-or-keyword parameters.
+                // Positional-only parameters are reported separately via `co_posonlyargcount`.
+                let argcount = code.arg_count(py)? as usize; // pos-or-keyword only
                 let posonly: usize = code
                     .as_bound(py)
                     .getattr("co_posonlyargcount")?
@@ -177,7 +179,8 @@ impl Tracer for RuntimeTracer {
 
                 // 1) Positional parameters (pos-only + pos-or-kw)
                 let mut idx = 0usize;
-                let take_n = std::cmp::min(argcount, varnames.len());
+                let total_positional = posonly.saturating_add(argcount);
+                let take_n = std::cmp::min(total_positional, varnames.len());
                 for name in varnames.iter().take(take_n) {
                     match locals.get_item(name) {
                         Ok(val) => {

issues.md

@@ -63,9 +63,10 @@ to preserve structure.
 Partially done
 
 Implemented varargs (`*args`), keyword-only, and kwargs (`**kwargs`) capture.
-Positional-only parameters are read (`co_posonlyargcount`) but not yet included
-in the positional slice, so they are currently omitted. Follow-up: include
-`posonly + co_argcount` when selecting positional names.
+Positional-only parameters are now included in the positional slice via
+`co_posonlyargcount + co_argcount` (see ISSUE-005). Remaining gap: structured
+encoding for `*args`/`**kwargs` per Definition of Done (currently accepted as
+backend-dependent; tests allow `Raw`).
 
 ## ISSUE-005
 ### Description
@@ -80,7 +81,11 @@ arguments (PEP 570). As a result, names before the `/` in a signature like
 - Tests add a function with positional-only parameters and assert their presence and correct encoding.
 
 ### Status
-Not started
+Done
+
+Implemented by selecting positional names from `co_varnames` with
+`co_posonlyargcount + co_argcount`. Tests in `test_all_argument_kinds_recorded_on_py_start`
+assert presence of the positional-only parameter `p` and pass.
 
 ## ISSUE-003
 ### Description