Andrew B. d8499dacd3 fix(stream): emit terminal SSE frames on mid-stream upstream failure (#7699) (#7816) ...

* fix(stream): emit terminal SSE frames on mid-stream upstream failure (#7699)

On /v1/messages (Anthropic format), when the upstream SSE stream fails
mid-flight after bytes have been forwarded to the client, OmniRoute used
to silently close the connection with no terminal event. Anthropic SDK and
Claude Code report "Connection closed mid-response. The response above may
be incomplete."

Two fixes in open-sse/utils/streamHandler.ts:

1. buildStreamErrorChunks (Claude format) now emits event:message_stop
   after event:error — the Anthropic stream terminator that clients expect.
   Previously only event:error was sent, leaving the client hanging.

2. createDisconnectAwareStream pull() now detects upstream "done" without
   a client-visible terminal marker ([DONE] / response.completed /
   message_stop) and emits a synthetic terminal error frame instead of
   silently closing. This covers the case where the upstream drops the
   connection mid-stream without sending an error chunk.

Adds tests/unit/silent-sse-close-7699.test.ts covering both code paths
across Claude, OpenAI Chat, and OpenAI Responses formats.

Refs: diegosouzapw/OmniRoute#7699

* fix(stream): scope terminal-marker missing detection to known formats with forwarded bytes

Gate the done-path synthetic 502 error on bytesWereForwarded AND a known
clientResponseFormat. Without this gate, any stream that closes cleanly
without a terminal marker (including raw passthrough streams and non-API
transforms) is incorrectly treated as a mid-stream drop.

- Add bytesWereForwarded flag set on first Uint8Array chunk
- Require clientResponseFormat to be set before injecting 502
- Fixes 3 broken stream-handler tests (pipes transformed bytes,
  slow upstream stall watchdog, normal completion watchdog)
- Preserves #7699 fix: Claude-format streams that forwarded content
  but missed message_stop still get the synthetic terminal frame

* fix(stream): scope terminal-marker heuristic to Claude only, add non-SSE regression

#7699 is scoped to /v1/messages (Anthropic): Claude clients treat a stream
that ends without message_stop as an error, and Anthropic's SSE spec
explicitly permits a mid-stream event: error. The issue's own suggested fix
says the current OpenAI silent-close "remains reasonable" — so the
done-without-terminal-marker synthetic-502 heuristic must not fire for any
other clientResponseFormat (gemini/codex/kiro/cursor/openai/openai-responses
etc.), where a done stream with no [DONE]/response.completed/message_stop
equivalent is not necessarily a silent drop.

Narrows the gate from "any truthy clientResponseFormat" to
"clientResponseFormat === FORMATS.CLAUDE" specifically.

Adds a regression test asserting a plain non-SSE OpenAI-format completion
(bytes forwarded, no terminal marker) is NOT mutated with a synthetic
error frame.

Co-authored-by: diegosouzapw <8016841+diegosouzapw@users.noreply.github.com>

* test(stream): trim new regression test to clear the 800-line test-file cap

tests/unit/stream-handler.test.ts was 772 lines pre-#7816 (not in the
frozen file-size baseline, so it's evaluated as new-file-cap 800). The
added regression test pushed it to 807; trim boilerplate to land at 796.

Co-authored-by: diegosouzapw <8016841+diegosouzapw@users.noreply.github.com>

---------

Co-authored-by: diegosouzapw <8016841+diegosouzapw@users.noreply.github.com>
Co-authored-by: Diego Rodrigues de Sa e Souza <diegosouza.pw@gmail.com>

2026-07-20 10:08:43 -03:00

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