fix(aws-lambda): always send the metadata prelude

[dinwwwh]

On AWS Lambda, sendStandardResponse could send a response without its metadata prelude, so the status, headers, and cookies were lost. HttpResponseStream.from() only sets the prelude up, and the runtime sends it just before the first write() call. end(chunk) skips that, and empty bodies never call write(). The fix makes one empty write right after from() so every response sends its prelude.

Fixes

• JSON, URLSearchParams, undefined, empty-Blob, and empty-stream responses now send their status, headers, and cookies. Before, they reached the wire as just the body, or as zero bytes.
• Non-empty streamed responses are unaffected, apart from sending their status and headers right away instead of waiting for the first chunk.

Testing

• Checked against the stream code in aws-lambda-ric 4.0.2 (3.3.0 uses the same prelude logic). The bytes were captured by a local HTTP server standing in for the Lambda API. Every body type now carries the prelude and delimiter exactly once. Not tested on a real Lambda deployment.
• The unit-test mock used to write the prelude itself, which hid the bug. It now waits for the first write() like the runtime. Without the fix, 3 tests fail: buffered (empty), buffered (json), and the new chunked (empty).

[pkg-pr-new]

• @standard-server/hono-node-playground
• @standard-server/node-http-playground

@standard-server/aws-lambda

npm i https://pkg.pr.new/@standard-server/aws-lambda@101

@standard-server/core

npm i https://pkg.pr.new/@standard-server/core@101

@standard-server/fastify

npm i https://pkg.pr.new/@standard-server/fastify@101

@standard-server/fetch

npm i https://pkg.pr.new/@standard-server/fetch@101

@standard-server/node

npm i https://pkg.pr.new/@standard-server/node@101

@standard-server/peer

npm i https://pkg.pr.new/@standard-server/peer@101

@standard-server/shared

npm i https://pkg.pr.new/@standard-server/shared@101

commit: e4a8cb1

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[codspeed]

Merging this PR will not alter performance

✅ 26 untouched benchmarks
⏩ 108 skipped benchmarks¹

---

_{Comparing claude/lambda-response-prelude-fix-a6b15e (e4a8cb1) with main (a6c90ca)}

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. ↩

[pullfrog]

✅ No new issues found.

Reviewed changes

• res.write('') forces the prelude — sendStandardResponse now writes an empty chunk right after HttpResponseStream.from(), so status/headers/cookies are flushed even when the body is undefined, an empty Blob/stream, or a string sent via end(chunk).
• Test mock now matches the runtime — fromSpy arms the prelude on the first write only (restoring the original write first) instead of emitting the prelude itself, which is what hid the bug.
• New chunked (empty) test — covers an empty Blob body, the case where pipe() never calls write.
• JSDoc wording — from() now documented as arming the prelude, sent only ahead of the first write.

I verified the fix against the aws-lambda-ric source and with a local reproduction: HttpResponseStream.from() only sets _onBeforeFirstWrite, the patched request.write emits the prelude when status is still ready, and Node's Writable.end(chunk) bypasses the overridden public write (so end(chunk) indeed skipped the prelude). Replicating the RIC logic against a raw TCP server shows the prelude + 8-byte delimiter emitted exactly once for empty, JSON, and streamed bodies, with no spurious empty HTTP chunk. Reverting res.write('') makes exactly the three named tests fail, so the new coverage is real. Tests, type:check, and eslint on the changed files all pass.

  ^{｜ View workflow run ｜ Using DeepSeek Flash (default — pick a model for stronger reviews) ｜ 𝕏}