`attr-defined` on modules depends on imports in other files

Bug Report

I'm not sure how to put together a good description of this, but here goes: mypy emits attr-defined errors (correctly) when importing concurrent (but not concurrent.futures), and then using concurrent.futures. However, if checking another file in the same pass which does import concurrent.futures, it doesn't emit an error for the first file.

To Reproduce

Create file a.py:

import concurrent

concurrent.futures

Create file b.py:

import concurrent.futures

concurrent.futures

Expected Behavior

Should emit an error for a.py, regardless of which other files are also being checked:

$ python -m mypy --no-incremental --cache-dir=/dev/null a.py
a.py:3: error: Module has no attribute "futures"  [attr-defined]
Found 1 error in 1 file (checked 1 source file)
$ python3 -m mypy --no-incremental --cache-dir=/dev/null a.py b.py
a.py:3: error: Module has no attribute "futures"  [attr-defined]
Found 1 error in 1 file (checked 2 source files)

Actual Behavior

$ python -m mypy --no-incremental --cache-dir=/dev/null a.py
a.py:3: error: Module has no attribute "futures"  [attr-defined]
Found 1 error in 1 file (checked 1 source file)
$ python -m mypy --no-incremental --cache-dir=/dev/null a.py b.py
Success: no issues found in 2 source files

Your Environment

• Mypy version used: tried both 1.11.2 and mypy-1.12.0+dev.0412590ba13395a04f122a5dd83764db9d001fe6
• Mypy command-line flags: --no-incremental --cache-dir=/dev/null, just because it's less confusing that way. I was also seeing this with caching
• Mypy configuration options from mypy.ini (and other config files): None
• Python version used: 3.8

Reproduce the issue with the provided a.py and b.py files, using python -m mypy --no-incremental --cache-dir=/dev/null on each file and together. Start by tracing module attribute handling during multi-file checking; done means a.py consistently reports the missing futures attribute regardless of whether b.py is checked.