fix(formatters/markdown): stop leaking <error:> placeholder into output

[tmchow]

Summary

When lychee encounters a link whose URL can't be parsed, the markdown stats formatter was leaking <error:> into the report because the placeholder Uri constructed by lychee_lib::types::request_error has scheme "error" and the formatter always wraps the Uri in <…>. Addresses #2143.

Why

RequestError::into_response (in lychee-lib/src/types/request_error.rs) constructs a synthetic Response for reporting purposes whenever a raw link can't be turned into a valid URL. It uses a single static ERROR_URI: LazyLock<Uri> = LazyLock::new(|| Uri::try_from("error:").unwrap()); as the placeholder, backed by the error: scheme.

The existing markdown formatter treated every response identically:

let mut formatted = format!(
    "* [{}] <{}>",
    response.status.code_as_string(),
    response.uri,
);

For the placeholder, response.uri renders as error:, so the output became:

* [ERROR] <error:> (at 6:14) | Cannot parse 'https://example]org/malformed_two' into a URL: invalid international domain name

That's bad for two reasons: <error:> looks like a clickable anchor pointing at an unresolvable custom scheme, and it visually overshadows the actual failing URL which now only lives in the | details tail.

Changes

• lychee-bin/src/formatters/stats/markdown.rs:
  • New private constant UNPARSEABLE_URI_SCHEME = "error", kept in lockstep with lychee-lib's placeholder (the comment points back at request_error.rs so it doesn't drift silently).
  • markdown_response now branches: when response.uri.scheme() == UNPARSEABLE_URI_SCHEME, it omits the <uri> segment and emits just * [STATUS]; the subsequent (at span) and | details tail continue to render normally.
  • No behavioural change for any non-placeholder URI -- the old code path remains default.

Testing

• New test_markdown_response_unparseable_url_omits_uri_segment directly exercises the placeholder path:
  • Constructs a ResponseBody with Uri::try_from("error:") (the same value RequestError::into_response emits).
  • Asserts <error:> is not present in the output.
  • Asserts the prefix stays * [ERROR] so downstream consumers still see the status code.
  • Asserts the span (at 1:1) and the underlying malformed URL text survive in the details tail.
• cargo test --package lychee --bin lychee -> 78 passed, 0 failed.

Fixes #2143

This contribution was developed with AI assistance (Claude Code).