Verify runpath does not contain a file

[tbwiik]

Issue
Resolves #14265

Approach
If the user provide a runpath, where parts of the runpath contain an existing file,
this is not a valid directory and a config error is thrown.

• PR title captures the intent of the changes, and is fitting for release notes.
• Added appropriate release note label
• Commit history is consistent and clean, in line with the contribution guidelines.
• Make sure unit tests pass locally after every commit (git rebase -i main --exec 'just rapid-tests')

When applicable

• When screenshots are changed: Review screenshot-PR in ert-testdata,
  merge screenshot-PR in ert-testdata before merging this PR.
• When there are user facing changes: Updated documentation
• New behavior or changes to existing untested code: Ensured that unit tests are added (See Ground Rules).
• Large PR: Prepare changes in small commits for more convenient review
• Bug fix: Add regression test for the bug
• Bug fix: Add backport label to latest release (format: 'backport release-branch-name')

[tbwiik]

Should this be backported?

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.96%. Comparing base (03e5ba6) to head (95733a6).
⚠️ Report is 28 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #14370      +/-   ##
==========================================
+ Coverage   90.81%   90.96%   +0.15%     
==========================================
  Files         497      495       -2     
  Lines       36063    36112      +49     
==========================================
+ Hits        32751    32851     +100     
+ Misses       3312     3261      -51     

Flag	Coverage Δ
cli-tests	?
fuzz	43.76% <88.23%> (-0.10%)	⬇️
gui-tests	58.52% <88.23%> (+0.38%)	⬆️
performance-and-unit-tests	80.95% <100.00%> (-0.10%)	⬇️
test	45.45% <88.23%> (+0.18%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/ert/config/model_config.py	100.00% <100.00%> (ø)

... and 50 files with indirect coverage changes

[Copilot]

🟡 Changes recommended

The validation mishandles legacy placeholders and can both miss invalid prefixes and reject unrelated paths.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

Adds early RUNPATH validation to prevent files from being used as directory prefixes.

Changes:

• Validates static RUNPATH components.
• Adds tests for file and directory prefixes.

File summaries

File	Description
src/ert/config/model_config.py	Adds RUNPATH prefix validation.
tests/ert/unit_tests/config/test_model_config.py	Tests static prefix validation.

Review details

Suppressed comments (1)

src/ert/config/model_config.py:142

• This comprehension does not stop at the first dynamic component and only the combined path is checked. Thus base/<IENS>/later checks the unrelated base/later, while base/file/child/<IENS> misses that file is an existing regular file because the combined path does not exist. Walk each prefix until the first token and reject any existing non-directory prefix.

        # stops when entering first dynamic part
        static_parts = [part for part in parts if not _TOKEN_REGEX.search(part)]

• Files reviewed: 2/2 changed files
• Comments generated: 2
• Review effort level: Balanced

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[codspeed-hq]

Merging this PR will not alter performance

✅ 36 untouched benchmarks

---

_{Comparing tbwiik:faulty-runpath-error-msg (95733a6) with main (074eb57)}

[Copilot]

🟡 Changes recommended

The validation can reject valid dynamic paths and miss files in earlier static components.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 2
• Review effort level: Balanced

[berland]

(maybe already fixed, but ensure the string "PosixPath" is not part the user experience)

[Copilot]

🟡 Changes recommended

The first-token stopping behavior needs targeted regression coverage.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 1
• Review effort level: Balanced

[xjules]

👍