Rework error handling

[dmamelin]

This is a major change in Pyscript core. Please review it very carefully, especially ast_try, ast_raise, and EvalFunc.call.
Originally this was one large change, but I split it into smaller commits to make it easier to review. Each commit is consistent. Everything works and the tests pass.

Main idea:

• we shouldn't try to reimplement python’s exception system - we just need to avoid interfering with it
• exceptions should not be caught in the core and passed around; they should be handled at entry points
• exceptions should always be raised normally, and only wrapped in finally where needed to restore context
• formatting user messages should be separated from exception handling

Exception logging:

Initially, I planned to keep the old behavior and show only a single frame where the error occurred, but I ended up implementing a full traceback 🙂

#modules/mod_test.py
def problem():
    return 0 / 0

async def no_problem(callback):
    return 0 + callback()

#test.py
from mod_test import no_problem, problem

def func1(x):
    return x + func2(x)

@pyscript_compile
async def func2(x):
    return x + await no_problem(func3)

def func3():
    return 3 + problem()

@time_trigger
def start():
    try:
        func1(1)
    except ZeroDivisionError:
        del x

#console output: 
2026-02-13 02:38:36.622 ERROR (MainThread) [custom_components.pyscript.file.test.start]
  File "/config/pyscript/test.py", line 22, in file.test.start
    func1(1)
    ~~~~~^^^
  File "/config/pyscript/test.py", line 7, in func1
    return x + func2(x)
               ~~~~~^^^
  File "/config/pyscript/test.py", line 12, in func2
    return x + await no_problem(func3)
               ^^^^^^^^^^^^^^^^^^^^^^^
  File "/config/pyscript/modules/mod_test.py", line 9, in no_problem
    return 0 + callback()
               ~~~~~~~~^^
  File "/config/pyscript/test.py", line 16, in func3
    return 3 + problem()
               ~~~~~~~^^
  File "/config/pyscript/modules/mod_test.py", line 5, in problem
    return 0 / 0
           ~~^~~
ZeroDivisionError: division by zero

During handling of the above exception, another exception occurred:

  File "/config/custom_components/pyscript/trigger.py", line 1394, in do_func_call
    await ast_ctx.call_func(func, None, **kwargs)
  File "/config/pyscript/test.py", line 24, in start
    del x
NameError: name 'x' is not defined

EvalExceptionFormatter

• standard traceback mechanisms are used, with adjustments for user code
• iterates over the traceback and extracts all necessary data from local variables. lineno and col_offset are taken from ast.expr / ast.stmt, which results in more precise error locations
• it isn't perfect, but it's not core functionality and doesn't affect code execution. It can be refined over time
• there are some quirks in the core regarding context names, file names, and their source text. These are handled in formatter, but I plan to clean this up properly in the future

Tests:

There are many changes because the new mechanism closely matches native python behavior and is more precise.
Please pay attention to the last commit with exception chaining - it tests pyscript using pyscript itself.

[ALERTua]

you are the best!