Coding agent CLI: "API Error: Connection closed mid-response"

Mid-turn, the agent appears to be working, then the reply stops with a connection error and little or nothing usable. More common in long sessions with many tool calls, after compaction, or when one tool call writes a very large payload.

Difficulty

Moderate

Time

~15 min

Steps

Fixed in

—

Last checked

2026-10-15

Not fixed upstream yet: the issue is open. Source: issue open. Last checked 2026-10-15.

Symptom

Evidence what you'll see

Error: API Error: Connection closed mid-response. The response above may be incomplete.
Related: API Error: Stream idle timeout - no chunks received
Debug line tied to one lead: Stale connection — disabling keep-alive for retry

Cause

Several separate leads, none confirmed by a maintainer: issue #100353 reports that since 2.1.213 one connection error turns off keep-alive for the rest of the process; others link it to oversized single tool writes, network idle drops, or gateway timeouts.

Fix steps

0 of 4 done

Step 1If the debug log shows the keep-alive line, restart the process after it appears (per #100353, builds before 2.1.213 do not have that switch).
Step 2Ask the agent to write large plans or files in several smaller edits.
Step 3Check router or WAN logs for disconnects on a fixed interval.
Step 4Behind a proxy or gateway, raise its idle and timeout limits.

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Verify the fix worked

Rerun a multi-step task that failed before; replies complete without the error.
With --debug-file <path>, check whether the keep-alive line appears after a connection blip.

Did this fix it?

Sources and credit

Summarized in our own words from these public reports. Credit goes to their authors.

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