`dmypy recheck --update [file]` failed to detect very recent changes in [file]

Bug Report

Hi, I'm trying to implement an interactive type checking environment where a (deep learning-based) type inference agent needs to repeatedly make small changes to a given source file and query mypy to figure out if the changes introduce any type error. I'm using the dmypy recheck --update command to reduce the type checking time since I need these queries to be as fast as possible. However, it seems that this command would fail to detect very recent file changes and report outdated results. Is there a way to explicitly tell dmypy that it should recheck a given file?

To Reproduce

Run the following script

from pathlib import Path
import subprocess
import time

# no type error
code_1 = '''
from typing import Any
def fib(n: int) -> int:
    if n == 0:
        return 0
    elif n == 1:
        return 1
    else:
        return fib(n-1) + fib(n-2)
'''

# incorrect return type
code_2 = '''
from typing import Any
def fib(n: int) -> str:
    if n == 0:
        return 0
    elif n == 1:
        return 1
    else:
        return fib(n-1) + fib(n-2)
'''

# changed return type to Any, should not error
code_3 = '''
from typing import Any
def fib(n: int) -> Any:
    if n == 0:
        return 0
    elif n == 1:
        return 1
    else:
        return fib(n-1) + fib(n-2)
'''

# this should be the dmypy path in the current virtual env
dmypy_path = '/home/jiayi/Projects/SPOT/.venv/bin/dmypy'

check_dir = Path("temp/type_check")
check_dir.mkdir(exist_ok=True, parents=True)
with open(check_dir / "code.py", "w") as f:
    f.write(code_1)
subprocess.run(['python', dmypy_path, 'restart', '--', '--follow-imports=skip'],cwd=check_dir)

print('---checking code_1---')
subprocess.run(['python', dmypy_path, 'check', '.'],cwd=check_dir)

with open(check_dir / "code.py", "w") as f:
    f.write(code_2)
print('---checking code_2---')
subprocess.run(['python', dmypy_path, 'recheck', "--update", "code.py"],cwd=check_dir)

with open(check_dir / "code.py", "w") as f:
    f.write(code_3)
print('---checking code_3---')
subprocess.run(['python', dmypy_path, 'recheck', "--update", "code.py"],cwd=check_dir)
print("test finished.")

print('---wait and check code_3 again---')
time.sleep(1.0)  # will not work if waiting time is shorter
with open(check_dir / "code.py", "w") as f:  # need this rewriting
    f.write(code_3)
subprocess.run(['python', dmypy_path, 'recheck', "--update", "code.py"],cwd=check_dir)
print("test finished.")

This produced the following result on my machine

Daemon stopped
Daemon started
---checking code_1---
Success: no issues found in 1 source file
---checking code_2---
code.py:5: error: Incompatible return value type (got "int", expected "str")
code.py:7: error: Incompatible return value type (got "int", expected "str")
Found 2 errors in 1 file (checked 2 source files)
---checking code_3---
code.py:5: error: Incompatible return value type (got "int", expected "str")
code.py:7: error: Incompatible return value type (got "int", expected "str")
Found 2 errors in 1 file (checked 2 source files)
test finished.
---wait and check code_3 again---
Success: no issues found in 2 source files
test finished.

Expected Behavior

The result for code_3 should contain no type error.

Actual Behavior

The result for code_3 without first waiting is incorrect and looks outdated (is the same as code_2).

(Write what happened.)

Your Environment

• Mypy version used: 0.950
• Mypy command-line flags:
• Mypy configuration options from mypy.ini (and other config files): empty
• Python version used: Python 3.10.4
• Operating system and version: Ubuntu 18.04.6 LTS

Start by running the supplied Python reproduction with dmypy restart, check, and repeated recheck --update code.py commands. Trace how dmypy recheck --update [file] handles rapid successive writes; done means the immediate code_3 update reports no errors without requiring a delay or rewrite.