this turn failed: deepseek messages transport failed

"This turn failed" and "deepseek messages transport failed" are two layers of one event: the turn did not finish, and the transport layer failed. It is not session corruption and not a reason to reinstall; read the cause first.

What the two prefixes mean

"This turn failed" is a turn-level message, not a session-level verdict. It only says the current turn did not finish; history and session files are usually intact (source).

"Transport failed" is a failure category, not a root cause. The maintainers explain it as DeepSeek Harness's own umbrella for transport-layer exceptions; the real cause is in logs (source).

Together they mean the request failed in transport. Whether that is TLS, an attachment, an upstream error, or a proxy depends on the next layer of information.

Do not infer "network problem" from the word transport. It is a fallback category; TLS, missing attachments, and unclassified errors can all land there.

Four causes, common to rare

One message, at least four root causes, each with a different fix.

TLS and certificate chains are the most common. A scanner or proxy replaces certificates, validation fails, and the connection error is categorized as TRANSPORT; logs show certificate-chain causes (source).

A missing attachment is the "one session only" signature. The session still references a deleted object, request assembly fails, and the error is wrapped as TRANSPORT; a new session or removing the reference recovers (source).

An unclassified error is more like a version issue. Upstream returns new wording, the classifier misses it, and the fallback code is not in the retry set; the same network works for other requests but this one never retries (source).

Network timeouts are the easiest to recognize. Behavior differs across networks, times, or models; usually transient, so retrying makes sense.

Evidence first: cause, then reproduction

Three minutes of evidence beats repeated retries.

1. Open logs and find the cause. Do not stop at transport failed; look for the certificate, attachment, timeout, or upstream error code.
2. Confirm the scope. Does it fail in one session or all sessions? One session points to data or attachments; all sessions points to network, certificates, or version.
3. Run a single-variable comparison. Change only the network, only the model, or only the session.
4. Record the time. Failure time, network, proxy, and antivirus state; these determine reproducibility.
5. Keep the log fragment with the cause, not just the generic line.

"One session only" is the most valuable clue. It almost rules out global network and certificate issues.

"All sessions fail" is the opposite. Check certificates, proxy, and upstream first, then version.

Three common misreactions

Three responses look reasonable and waste time.

1. Reinstall. It does not change a certificate chain or an attachment reference, and it destroys the scene.
2. Change the API key. Authentication errors usually carry 401-class information, not a bare transport failure; changing the key rarely helps.
3. Delete the session. It bypasses the attachment issue but loses context; try removing the reference or opening a new session first.

All three skip the cause. Seeing "transport" and thinking network or key ignores the more specific layer in the log.

Collect evidence before acting. Evidence makes reinstall or key rotation meaningful; without it, actions are guesses.

Recovery order: light to heavy

Sort recovery by cost.

1. Retry once. Only meaningful for transient network issues; twice with the same result means stop.
2. Change network or disable proxy. Rules out proxy and certificate scanning; try a mobile hotspot on corporate networks.
3. Open a new session. If it works, the original session data or attachment is the problem.
4. Remove the attachment reference. Restore the object or delete the reference, then retry the original session.
5. Roll back recent changes. Plugins, proxy settings, or upgrades; return to the previous version and verify.
6. Upgrade or wait for a fix. When the cause is a known unclassified error and the version is fixed.

The order preserves data and the scene. Deleting the session restores use but loses evidence; the first four steps keep more information.

Verify after recovery. Send a normal message in the same session and model; a successful reply is the real signal, not a disappeared toast.

When to stop

Three situations mean retrying is pointless.

1. The cause is identical every time. Not transient; retries will not change it.
2. It reproduces across networks and sessions. Global; check certificates, version, or upstream status.
3. Other features are affected. If all requests fail or plugins cannot load, restore the environment first.

Stopping is switching layers. Move from "why did this turn fail" to "which layer of the environment is broken."

Next steps

Read the cause, then recover by cost. For general TRANSPORT troubleshooting, read DeepSeek Harness messages transport failed. To separate streaming cut-offs, read Transport failed vs stream cut-off. For certificate chains, read Antivirus HTTPS scanning and certificate errors.

Sources: DeepSeek Harness Discussions #6987, #7834, #9262, DeepSeek Harness docs