[neSpecc]

Summary

• When originalPositionFor does not find a generated position, source-map-js returns nulls. Those nulls were written onto the frame and sourceCode became [], so the catcher location was lost.
• If originalLocation.source is missing, consumeBacktraceFrame now returns the original frame.
• Covers the miss with a test that a mapped file and an unmapped line/column keep the catcher coordinates.

Fixes #600

Test plan

• yarn jest workers/javascript/tests/index.test.ts -t "should keep the original frame|should parse source maps correctly"
• Confirm a real event whose frame matches a release map but misses originalPositionFor still shows the original file, line, and column

[Copilot]

🟢 Approved

There are no active review issues for the change preserving original backtrace frames when source-map lookups find no mapping.

No open issues 🎉

What changed in this PR

Preserves catcher-provided backtrace frames when source-map lookup finds no mapping, addressing #600 without overwriting the original location.

Changes:

• Returns the original frame when originalLocation.source is missing.
• Adds a regression test verifying that an unmapped position retains the original frame.

File	Description
workers/​javascript/​tests/​index.test.ts	Tests preservation of the original frame after a source-map lookup miss.
workers/​javascript/​src/​index.ts	Adds an early return to prevent missing mappings from overwriting frame data.

_{Review effort: Balanced}