There's a lot of possibility for off-by-one types of errors and other kinds of bugs in this kind of logic; could I trouble you to writing some tests covering this?

Thanks, I really appreciate your in-depth review. I will add more tests in the next days. Have a great sunday!

Update: I fixed all copilot comments in the MR. It found a bug, which is nice!

Also I added lot's of test cases. Tested: works like a charm:

$ curl -X 'POST' \
      'http://127.0.0.1:27123/search/simple/?query=Master%20Plan' \
      -H 'accept: application/json' \
      -H 'Authorization: Bearer 320fac56a929e907fd1f724b12eb55327b38a363e8c8a8cbc290c9c5f1c30631'
      
[
  [...],
  {
    "filename": "5 - Finanzen/1 - Master Plan.md",
    "score": -1.2066,
    "matches": [
      {
        "match": {
          "start": 4,
          "end": 10,
          "source": "filename"
        },
        "context": "1 - Master Plan"
      },
      {
        "match": {
          "start": 11,
          "end": 15,
          "source": "filename"
        },
        "context": "1 - Master Plan"
      }
    ]
  }
]

The condition match[0] < positionOffset doesn't handle matches that span across the filename boundary into the newlines or content. If a match starts in the filename but extends beyond it (e.g., searching for "filename\n"), the match end position could exceed the length of file.basename (the context), which may confuse API consumers. Consider checking match[1] <= positionOffset to ensure the entire match is within the filename, or clamp the end position to the basename length.

The context slicing has incorrect position calculations. Since match[0] and match[1] are positions in the combined text (filename + content), but we're slicing from cachedContents, the positions need to be adjusted. The slice should be:

cachedContents.slice(
  Math.max(match[0] - positionOffset - contextLength, 0),
  match[1] - positionOffset + contextLength
)

Currently, the code uses unadjusted positions match[0] and match[1] which will extract the wrong portion of the content.

[nitpick] The comment mentions "2 line breaks" but technically uses 2 newline characters (\n\n). While this is a minor point, consider updating to "2 newline characters" or "a double newline" for technical accuracy.

[nitpick] The comment refers to "headline" but the code is actually adding the filename/basename. Consider using "filename" instead of "headline" for clarity and consistency with the rest of the code.

Missing semicolon at the end of the statement. For consistency with the rest of the codebase, add a semicolon after content].

Just a quick note about this file, @phortx: since it lives under mocks/, it’s meant purely as a mock—basically something lightweight so the type checker and tests have a stand-in. We shouldn’t put any real implementation logic here.

Instead, the idea is that your tests can control what this mock returns in different scenarios. If you take a peek at some of the other mock functions in mocks/obsidian.ts, you’ll see how they’re set up to let tests override behavior as needed.

So to make this consistent: this function shouldn’t implement any real behavior. It should either do nothing or return whatever value your test explicitly configures, so that you can verify how requestHandler.ts responds to those different return values.