`@app.function` does not pass `TypeIs` guards

[Antyos]

Describe the bug

TypeIs and TypeGuard functions wrapped in @app.function do not respect type hints when called, when other functions decorated with functools.wraps do. See:

Will you submit a PR?

• Yes

Environment

Details

{
  "marimo": "0.19.11",
  "editable": false,
  "location": "C:/Users/Andrew/Code/project/code/.venv/Lib/site-packages/marimo",
  "OS": "Windows",
  "OS Version": "11",
  "Processor": "Intel64 Family 6 Model 141 Stepping 1, GenuineIntel",
  "Python Version": "3.13.9",
  "Locale": "--",
  "Binaries": {
    "Browser": "--",
    "Node": "v22.15.1",
    "uv": "0.9.26 (ee4f00362 2026-01-15)"
  },
  "Dependencies": {
    "click": "8.2.1",
    "docutils": "0.22",
    "itsdangerous": "2.2.0",
    "jedi": "0.19.2",
    "markdown": "3.8.2",
    "narwhals": "2.2.0",
    "packaging": "25.0",
    "psutil": "7.0.0",
    "pygments": "2.19.2",
    "pymdown-extensions": "10.16.1",
    "pyyaml": "6.0.2",
    "starlette": "0.47.3",
    "tomlkit": "0.13.3",
    "typing-extensions": "4.15.0",
    "uvicorn": "0.35.0",
    "websockets": "15.0.1"
  },
  "Optional Dependencies": {
    "altair": "6.0.0",
    "duckdb": "1.3.2",
    "loro": "1.10.3",
    "mcp": "1.18.0",
    "nbformat": "5.10.4",
    "openai": "2.15.0",
    "pandas": "2.3.2",
    "polars": "1.32.3",
    "pyarrow": "21.0.0",
    "pytest": "8.4.1",
    "python-lsp-ruff": "2.2.2",
    "python-lsp-server": "1.13.1",
    "ruff": "0.12.11",
    "sqlglot": "27.9.0",
    "vegafusion": "2.0.3",
    "watchdog": "6.0.0"
  },
  "Experimental Flags": {}
}

Code to reproduce

from functools import wraps
from typing import Any, TypeIs

import marimo

app = marimo.App()


def wraps_decorator(func):
    @wraps(func)
    def wrapper(*args, **kwargs):
        return func(*args, **kwargs)

    return wrapper


@wraps_decorator
def type_is_int(x: Any) -> TypeIs[int]:
    return isinstance(x, int)


@app.function
def mo_type_is_int(x: Any) -> TypeIs[int]:
    return isinstance(x, int)


var: dict | int = {}

if type_is_int(var):
    var += 1
else:
    var |= {"key": "value"}

if mo_type_is_int(var):
    var += 1
else:
    var |= {"key": "value"}

[dmadisetti]

Which type checker are you using? We are just passing through wraps. There's a good chance it's us, but there's a possibility that it's not

[Antyos]

I'm using Pylance language server 2025.12.104 (pyright version 1.1.408, commit 138238b4).