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compactEvents utility for reducing verbose streaming sequences

compactEvents#

compactEvents reduces verbose streaming sequences in an event array while preserving semantics. Use it to shrink logs before persistence or to simplify post‑processing of Server‑Sent Events (SSE) streams.

const compacted: BaseEvent[] = compactEvents(events)

API#

function compactEvents(events: BaseEvent[]): BaseEvent[]

What it does#

• Text messages: Groups TEXT_MESSAGE_START → TEXT_MESSAGE_CONTENT* → TEXT_MESSAGE_END for the same messageId, concatenating all delta chunks into a single TEXT_MESSAGE_CONTENT event.
• Tool calls: Groups TOOL_CALL_START → TOOL_CALL_ARGS* → TOOL_CALL_END for the same toolCallId, concatenating all delta chunks into a single TOOL_CALL_ARGS event.
• Interleaved events: Any events that occur between a start/end pair are moved after that sequence so the streaming block remains contiguous.
• Pass‑through: All other events (state, custom, etc.) are preserved unchanged.

Example#

Before:

[
  { type: EventType.TEXT_MESSAGE_START, messageId: "m1", role: "assistant" },
  { type: EventType.TEXT_MESSAGE_CONTENT, messageId: "m1", delta: "Hello" },
  { type: EventType.TEXT_MESSAGE_CONTENT, messageId: "m1", delta: " " },
  { type: EventType.CUSTOM, name: "thinking" },
  { type: EventType.TEXT_MESSAGE_CONTENT, messageId: "m1", delta: "world" },
  { type: EventType.TEXT_MESSAGE_END, messageId: "m1" },
]

After:

[
  { type: EventType.TEXT_MESSAGE_START, messageId: "m1", role: "assistant" },
  { type: EventType.TEXT_MESSAGE_CONTENT, messageId: "m1", delta: "Hello world" },
  { type: EventType.TEXT_MESSAGE_END, messageId: "m1" },
  { type: EventType.CUSTOM, name: "thinking" },
]

Tool call compaction works analogously for TOOL_CALL_ARGS chunks.

When to use#

• Persisting event history (store fewer frames with the same meaning)
• Preparing snapshots for analytics or export
• Reducing noise in tests or debugging output

Notes & limitations#

• This utility focuses on message and tool‑call streams. It does not modify state events (STATE_SNAPSHOT/STATE_DELTA) or generate message snapshots.
• For background and broader patterns (branching, normalization), see Serialization.