Summary

• fix sysmon arc tracking for single-line class bodies followed by more code
• keep per-thread frame state across line, resume, return, and yield events
• add a regression covering class Foo: ... followed by pass

Problem

With Python 3.14 and the sysmon core, coverage reports a missing branch for a single-line class followed by another statement:

class Foo: ...

pass

On main, this reports a missing 1->3 branch even though the class definition is fully covered. ctrace does not misreport it.

Solution

sys.monitoring line events were recording self-arcs and losing the previous traced line for active frames. This patch keeps per-thread frame state for traced frames and uses it to record arcs between successive lines and function exit. It also handles PY_RESUME and PY_YIELD so paused frames do not corrupt later arc reporting.