Preserve unparsed stack trace lines in the transformed output

[rmuratov]

Closes #28

Problem

The transformed output was fully re-generated from parsed frames, so:

• lines the parser does not recognize (async markers, Caused by: chains, etc.) were silently dropped,
• multi-line error messages were truncated to the first line,
• frames without a matching source map were re-formatted instead of being left alone.

Fix

The transformation is now line-based:

• StackTrace parses the input line by line and keeps { raw, frame } pairs (lines) instead of a detached message + frames split.
• transform only replaces lines whose frames were successfully mapped through a source map; every other line — messages, unparsed lines, unmapped frames — passes through verbatim in its original position.

A nice consequence: with no matching source maps the output now equals the input exactly, so the reconstructed fixture (a lossy re-rendering of the stack trace) is gone. The result and afterDeleteIndex fixtures did not change.

Tests

Two new tests (unparsed lines suite): a multi-line error message survives the transformation, and an async marker plus a Caused by: chain pass through in place between mapped frames. Both fail on main without the fix (verified via git stash). Existing expectations for unmapped frames were updated to the new pass-through behavior.

Coverage stays at 100%.

[cloudflare-workers-and-pages]

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View logs

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (48c176b) to head (a2d3894).

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #39   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            9         9           
  Lines          213       209    -4     
  Branches        53        55    +2     
=========================================
- Hits           213       209    -4     

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