Debug a Coding Agent That Stops Streaming Halfway

§1 Start by Finding Where the Stream Stops

A coding agent begins explaining a change, writes half a function, and then goes silent. The process remains open, but no more tokens arrive. That symptom can mean a stalled connection, a buffered response, an unfinished tool call, or an application that ignored the final event. Debug it by locating the last successful boundary rather than immediately switching models.

§2 Step 1: Capture One Reproducible Failure

Reduce the task to a small repository and a predictable prompt, such as adding a validation helper and its tests. Keep the model, output limit, and tool permissions fixed. Disable automatic retries temporarily so one failed request does not become several overlapping attempts.

• – Record your request identifier, model identifier, SDK version, and timestamps.
• – Log when the request starts, headers arrive, the first event arrives, and the last event arrives.
• – Capture exceptions, cancellation signals, HTTP status, and completion metadata.
• – Redact credentials, private code, and tool arguments containing secrets.

The key question: Did the server stop sending data, or did your application stop displaying it?

§3 Step 2: Bypass the Agent Interface

Send the same request through a minimal streaming client, without the terminal renderer, editor extension, or orchestration framework. If the minimal client completes, investigate your agent’s event handling and display layer. If it also stalls, examine the transport, relay, and upstream response.

Fluxio fits this test when you want a streaming-first, pay-per-token relay with an OpenAI-style interface. For OpenAI-style clients, configure the base URL as https://api.fluxioapi.com/v1 and use your configured model identifier, such as Claude Haiku 4.5 if available to your account. Keep credentials in environment variables. A shared relay endpoint simplifies controlled comparisons, but does not eliminate client-side streaming bugs.

§4 Step 3: Inspect Events, Not Just Visible Text

For an SSE-based response, inspect the content type and raw event boundaries. Network chunks are not complete events: one event can span multiple reads, and one read can contain several events. Use an incremental parser rather than splitting each received chunk independently.

Log event types and byte counts alongside text deltas. An agent may be receiving tool-call arguments or other metadata while showing no visible text. Handle the terminal signal defined by your endpoint and SDK; do not assume that a usage record, an empty delta, or a closed socket always means successful completion.

§5 Step 4: Check Buffering and Timeout Layers

Repeat the test without your reverse proxy, gateway, or application server when possible. If direct streaming works, inspect intermediary response buffering, compression behavior, and idle timeout settings. Also check whether your renderer waits for a newline before displaying partial output.

Separate connection timeout, stream idle timeout, and total task deadline. A long tool execution can exceed an idle limit even when the overall task is healthy. Set limits deliberately, log which one fires, and verify whether heartbeat events are supported and forwarded. Do not solve every interruption by disabling deadlines.

§6 Step 5: Follow the Tool-Call State Machine

Tool calls often explain a stream that appears to stop halfway. The model finishes requesting a tool, but the agent never executes it, never returns its result, or waits forever for a subprocess. Accumulate streamed arguments until the tool call is complete before parsing or executing them.

• – Match tool results to the correct call identifiers.
• – Give subprocesses explicit deadlines and capture their exit status.
• – Verify that the agent sends tool results back and starts the next model turn.

§7 Step 6: Recover Without Repeating Side Effects

Check completion metadata for output-limit exhaustion before treating truncated code as a network failure. For interrupted connections, preserve partial output separately and mark the turn incomplete. Do not blindly replay a task that may already have edited files or run commands. Inspect repository changes, checkpoint completed tools, and use idempotency controls where supported.

§8 Step 7: Prove the Fix

Repeat the reproduction, then test delayed tools, forced disconnects, and cancellation. Success means every turn reaches a documented terminal state, failures surface clearly, and recovery does not duplicate actions. Once those checks pass, restore normal retries and monitor stream idle duration and incomplete-turn rates.

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