Avoid bun memory leak bug from TransformStream

[TheodoreSpeaks]

Summary

Bun has a bug in TransformStream: oven-sh/bun#28035 causing high memory consumption due to no backpressure signal. We use this in

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation
• Other: ___________

Testing

• Validated that streaming responses still work fine with an agent block in a workflow locally.

Checklist

• Code follows project style guidelines
• Self-reviewed my changes
• Tests added/updated and passing
• No new warnings introduced
• I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)

Screenshots/Videos

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@BugBot review

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PR Summary

Medium Risk
Changes the executor’s streaming consumption/persistence path and adds new callback semantics; mistakes could truncate streamed outputs or skip memory persistence for agent runs. Scope is limited to streaming execution handling but affects a core runtime path.

Overview
Redesigns streaming handling to avoid Bun’s TransformStream memory/backpressure bug. BlockExecutor.handleStreamingExecution no longer tee()s and separately drains an executor stream; it now reads from a single ReadableStreamDefaultReader, forwards bytes to the client via a new ReadableStream, and accumulates decoded text only when the source fully drains.

Adds a new StreamingExecution.onFullContent hook and moves agent memory persistence to it. Agent streaming no longer wraps the source stream with a persistence TransformStream; instead it registers an onFullContent callback to append the final assistant message to memory after the stream completes. Streaming output assembly also now guards against persisting/trusting truncated content and logs when the client consumer exits early.

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[greptile-apps]

Greptile Summary

This PR fixes a Bun runtime memory leak (oven-sh/bun#28035) caused by TransformStream lacking backpressure signals. The fix removes wrapStreamForPersistence (which piped through a TransformStream) and replaces it with a pull-based ReadableStream that accumulates chunks inline, then delivers the assembled content via a new onFullContent callback on StreamingExecution after the stream fully drains.

Confidence Score: 5/5

Safe to merge; the fix correctly avoids the Bun TransformStream memory leak and all remaining findings are P2 style suggestions.

The core logic is sound: the pull-based approach eliminates the TransformStream, backpressure is correctly propagated, and edge cases (stream error, early consumer exit, empty content) are all guarded. The only finding is a minor inconsistency where onFullContent is called even when fullContent is empty, which is handled defensively by the agent handler today.

apps/sim/executor/execution/block-executor.ts — minor onFullContent guard inconsistency at line 718.

Important Files Changed

Filename	Overview
apps/sim/executor/execution/block-executor.ts	Replaces tee()-based dual-stream approach with a pull-based ReadableStream that accumulates chunks inline; small inconsistency in onFullContent guard logic.
apps/sim/executor/handlers/agent/memory.ts	Removes wrapStreamForPersistence (the TransformStream that triggered the Bun memory leak); appendToMemory is now called directly via onFullContent.
apps/sim/executor/handlers/agent/agent-handler.ts	Wires onFullContent callback on the StreamingExecution object instead of wrapping the stream in a TransformStream.
apps/sim/executor/types.ts	Adds optional onFullContent callback to StreamingExecution interface with a clear JSDoc explaining the Bun bug motivation.

Sequence Diagram

sequenceDiagram
    participant AH as AgentHandler
    participant BE as BlockExecutor
    participant CS as clientSource (ReadableStream)
    participant PC as processedClientStream
    participant OS as onStream consumer

    AH->>BE: StreamingExecution { stream, execution, onFullContent }
    BE->>CS: Create pull-based ReadableStream (reads from sourceReader, accumulates chunks)
    BE->>PC: streamingResponseFormatProcessor.processStream(clientSource)
    BE->>OS: ctx.onStream({ stream: processedClientStream, execution })
    loop For each chunk
        OS->>PC: read chunk
        PC->>CS: pull
        CS->>CS: sourceReader.read() → decode → accumulated.push()
        CS-->>PC: enqueue(value)
        PC-->>OS: chunk
    end
    OS-->>BE: stream fully drained (sourceFullyDrained = true)
    BE->>BE: executionOutput.content = accumulated.join('')
    BE->>AH: onFullContent(fullContent)
    AH->>AH: memoryService.appendToMemory(ctx, inputs, { role: 'assistant', content })

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[greptile-apps]

onFullContent called unconditionally with empty string

onFullContent is invoked regardless of whether fullContent is empty, while the preceding block that sets executionOutput.content is guarded by if (fullContent). The current agent handler defensively checks !content.trim(), but any future onFullContent implementor might not, leading to spurious empty-content persistence calls.

Suggested change

	if (streamingExec.onFullContent) {
	try {
	await streamingExec.onFullContent(fullContent)
	} catch (error) {
	this.execLogger.error('onFullContent callback failed', { blockId, error })
	}
	}
	if (streamingExec.onFullContent && fullContent) {
	try {
	await streamingExec.onFullContent(fullContent)
	} catch (error) {
	this.execLogger.error('onFullContent callback failed', { blockId, error })
	}
	}