--follow-imports=silent is not silent if imported file is in cache. #20508

Bug Report

When a file has been previously analyzed, and errors were found, and that result was cached,
(A clear and concise description of what the bug is.)

To Reproduce

Similar to

Create two files:

# a.py
import b

b.foo(1, 2)

and

# b.py
def foo(a: int, b: int) -> str:
    return a + b

Then, run the following three commands (in this order):

1. mypy --follow-imports=silent a.py
2. mypy --follow-imports=silent b.py
3. mypy --follow-imports=silent a.py (same as first command)

(A more 'minimal' example would be to not run mypy --follow-imports=silent a.py first, which still exhibits the bug, but I think running 'a', 'b', 'a' more clearly shows the bug).

Expected Behavior*

Only run 2 (the one directly analyzing b.py) produces output.

# mypy --follow-imports=silent a.py
Success: no issues found in 1 source file
# mypy --follow-imports=silent b.py
b.py:2: error: Incompatible return value type (got "int", expected "str")  [return-value]
Found 1 error in 1 file (checked 1 source file)
# mypy --follow-imports=silent a.py
Success: no issues found in 1 source file

Actual Behavior

# mypy --follow-imports=silent a.py
Success: no issues found in 1 source file
# mypy --follow-imports=silent b.py
b.py:2: error: Incompatible return value type (got "int", expected "str")  [return-value]
Found 1 error in 1 file (checked 1 source file)
# mypy --follow-imports=silent a.py
b.py:2: error: Incompatible return value type (got "int", expected "str")  [return-value]
Found 1 error in 1 file (checked 1 source file)

Note how the third run (which uses --follow-imports=silent) is not silent about errors in not explicitly listed files, while the first was.

Your Environment

• Mypy version used: 1.19.1 (but reproducible on master)
• Mypy command-line flags: --follow-imports=silent
• Mypy configuration options from mypy.ini (and other config files): None.
• Python version used: 3.13.11