fix(streaming): project structured output live

[TheodoreSpeaks]

Summary

• project selected structured string outputs into the live agent event sink as JSON arrives
• forward projected text through nested workflows, deployed chat/API protocol streams, and Slack without duplicating byte-stream output

Type of Change

• Bug fix

Testing

• 203 focused streaming tests pass across executor, nested workflows, deployed streaming, and Slack
• lint and focused repository audits pass

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)

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1 Skipped Deployment

Project	Deployment	Actions	Updated
docs	Skipped		Sep 1, 2026 11:26am UTC

[greptile-apps]

Greptile Summary

The PR projects selected structured string fields into live agent-event sinks while keeping sink and byte-stream forwarding coordinated.

• Adds incremental JSON string-field projection with per-turn state reset.
• Marks transformed event sinks so nested workflows, deployed streams, and Slack can forward projected text live without duplicating byte-stream output.
• Adds focused coverage for projection, encoded selectors, JSON escapes, nested forwarding, deployed streaming, and Slack.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

Important Files Changed

Filename	Overview
apps/sim/executor/utils.ts	Adds incremental top-level JSON string projection, selector handling, escape decoding, and per-turn reset behavior.
apps/sim/executor/execution/block-executor.ts	Connects projected subscriptions to streaming executions and explicitly records when sink events match the transformed client stream.
apps/sim/lib/workflows/streaming/forward-agent-stream-events.ts	Allows answer text to come from a transformed sink only when its projection matches the transformed byte stream.
apps/sim/lib/workflows/streaming/streaming.ts	Reuses the sink-selection contract for negotiated deployed agent-event streams.
apps/sim/lib/webhooks/slack-execution-stream.ts	Streams matching projected sink text through Slack while preserving its acknowledged append-only turn behavior.
apps/sim/lib/workflows/streaming/streaming.test.ts	The previously reported contract bypass is fixed; the new fixture is contextually checked against production streaming types.

Sequence Diagram

sequenceDiagram
  participant P as Provider stream
  participant X as Block executor
  participant J as JSON field projector
  participant S as Event sink
  participant C as Client or Slack
  P->>X: Structured text_delta events
  X->>J: Raw JSON chunks
  J->>S: Selected string-field deltas
  S->>C: Live projected answer text
  P->>X: turn_end
  X->>J: Reset projection state
  X-->>C: Drain transformed byte stream without duplicate forwarding

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[cubic-dev-ai]

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[TheodoreSpeaks]

@greptile

[TheodoreSpeaks]

@greptile

[TheodoreSpeaks]

Closing in favor of a simpler streaming contract: unstructured agent text may stream, while structured outputs remain terminal values after complete validation. Tool and thinking events can continue streaming independently.