deepseek messages transport failed vs stream cut-off

Failing in 20 milliseconds and dying after 20 seconds are two different diseases; calling both transport failed means taking the wrong medicine. In DeepSeek Harness, DeepSeek Messages transport failed (code: TRANSPORT) is a transport-layer catch-all: any failure not classified as an idle timeout, a deliberate cancel or an existing LlmError gets wrapped in it (source). The real question is therefore not "why TRANSPORT" but "how far did this request get". This article follows a triage path rather than re-explaining the catch-all itself.

Reading the code first: what TRANSPORT, timeout and 401/400 mean in DeepSeek Harness

The error code sets the direction: TRANSPORT is unclassified, TIMEOUT means no new chunk for too long, and 401/400 is a business or credential rejection. Match the code before deciding whether to retry.

1. Find the turn/end record for this round in the log and confirm the outer code.
2. If the outer code is TRANSPORT, expand cause and read the original code inside.
3. If the outer code is TIMEOUT or ABORTED, stop debugging it as transport.
4. If the outer code is 401 or 400, inspect credentials and request parameters instead of the network.
5. Record both the code and its cause; do not copy only the message text.

The code is the entrance to triage, not the conclusion. TRANSPORT only says "could not classify"; the cause below it carries identity. A 401 or 400 should not look like transport failed in the first place, and if it does, the request was stopped before reaching the application layer.

Three signs of stream cut-off: DSH plugin changes count as variables

A cut-off stream looks like "some content arrived, then it froze", not "nothing happened at all". When the three signs appear together, the direction is almost certainly connection or proxy.

1. Content streams for a while, stops midway, and never ends cleanly.
2. The request status is 200, but the stream never finishes and the client waits for a final frame that never comes.
3. Logs show streaming events first, followed by a connection error or retry record.

Environment changes count too: a new proxy, a packet capture tool, a plugin upgrade or a network change can all start a cut-off. The plugin itself is not necessarily wrong, but it changed the request path, so do not look only at the model side. For an adjacent TLS re-signing issue, see antivirus TLS certificate chain errors.

Five-minute triage: DeepSeek Harness separates "never sent" from "died halfway"

Five minutes is enough for one triage pass: minutes 0–1 read the code, 1–2 check the request count, 2–3 the endpoint response, and 3–5 the cause before deciding. The order is fixed so you do not swap networks first.

# 1) Is a local proxy intercepting?
env | grep -i -E 'https?_proxy|no_proxy'
# 2) Hit the model endpoint directly for connection and status (replace with your provider base URL)
curl -sS -o /dev/null \
  -w 'HTTP %{http_code}  connect %{time_connect}s  total %{time_total}s\n' \
  https://api.deepseek.com/v1/models

1. 0–1 minute: confirm the outer code is TRANSPORT, TIMEOUT or 401/400.
2. 1–2 minutes: check whether this request was sent at all; a count of zero means local preparation.
3. 2–3 minutes: read the endpoint response code; 200 means reachable, 401/403 means rejected.
4. 3–4 minutes: read cause and the last streaming event to locate the break point.
5. 4–5 minutes: decide retry, resume or fix the environment; decide once instead of experimenting repeatedly.

"Was the request sent" is the highest-information test. A request count of zero with failure in tens of milliseconds usually means local preparation failed; a request that was sent and broke halfway means the connection layer. The fixes are completely different.

Ask one question before retrying

Is this failure deterministic or intermittent?

1. It fails at the same point every time: deterministic, fix it before retrying.
2. It works at another time: intermittent, record the timestamp and watch.
3. It fails only on a specific network or proxy: environment-specific, verify on another path first.

Evidence checklist: five things to copy from DeepSeek Harness logs

Collect five items: time, code and cause, request count, endpoint response code and the last streaming event; add one environment change. With all five, the problem usually lands on a layer.

1. The timestamp to the minute, for aligning with other logs.
2. The outer code and the original code inside cause; record both.
3. Whether the request was sent and the order of magnitude of the failure latency.
4. The most recent endpoint response code.
5. The last streaming event and whether retry records followed it.

The sixth item is the environment change: proxy, capture tool, plugin additions or removals, version updates. It does not explain the error directly but explains why today. After collecting evidence, decide whether to rerun, resume or file an issue; the session itself does not disappear because one round failed.

Telling it apart from neighbors: when it is not a DeepSeek Harness transport problem

Three cases should not be debugged as transport: credentials or parameters rejected, the front end unable to reach the host, and a missing attachment object. Their codes and scene signatures differ from a cut-off stream.

1. 401 / 400 class: these are LlmError with their own codes; check the key, model name and request parameters.
2. Front end cannot reach the host: this is the channel between browser and DeepSeek Harness, not a model request.
3. Missing attachment: request count is zero, failure takes tens of milliseconds, and every request in that session fails; this is a local preparation problem.
4. Plugin-induced environment change: roll back the most recent plugin change and reproduce before looking for model-side causes.
5. Same string, different cause: a missing attachment and TLS re-signing can both land on the same message; separate them with "was the request sent".

The point of distinguishing is not tidy categories but a justified next action. For the full mechanics of the transport catch-all, see transport failed troubleshooting; for the attachment-specific scene, see transport failed caused by a missing attachment.