fix(aws-lambda): omit headers whose value is an empty array

[dinwwwh]

The aws-lambda adapter no longer sends a header whose value is [] as an empty header (x-foo: ""). toLambdaHeaders joined array values with ', ', and [].join(', ') is ''. Now an empty array means the header is left out, as the fetch adapter already does.

Fixes

• A response header set to [] is now omitted from the Lambda response metadata. It used to be sent with an empty value.
• A header set explicitly to '' is still sent as an empty header.

Testing

• The toLambdaHeaders test now covers [] and '' values. The [] case fails against main.
• vitest run packages/aws-lambda (100 passed), eslint and tsc are clean.

🤖 Generated with Claude Code

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commit: c7d62c5

[pullfrog]

✅ No new issues found.

Reviewed changes

• Omit empty-array headers in the Lambda adapter — toLambdaHeaders now skips a header whose value is [] instead of serializing it as x-foo: ""; an explicitly empty string is still sent.
• Test coverage — the toLambdaHeaders case adds 'x-empty': [] (asserted omitted) and 'x-empty-string': '' (asserted kept), so the new branch is pinned and the [] assertion fails against main.

The guard matches the fetch adapter's behavior (toFetchHeaders appends nothing for an empty array), and the set-cookie branch is unaffected since [] already contributed no cookies. The change is minimal and well-covered.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[codspeed]

Merging this PR will not alter performance

✅ 26 untouched benchmarks
⏩ 108 skipped benchmarks¹

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_{Comparing claude/lambda-empty-header-fix-bde98b (c7d62c5) with main (7d2294c)}

Footnotes

1. 108 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩