openhuman/docs/tinyagents-full-migration-plan/02-models/03-streaming-reasoning.md

02.3 — Native reasoning + tool-arg streaming

tinyagents 1.3.0 MessageDelta has a reasoning field and StreamAccumulator::reasoning(); ModelStreamItem::ToolCallDelta streams tool-arg fragments. The out-of-band ThinkingForwarder is not one-shot deletable: streaming reasoning can ride the crate stream, but OpenHuman still uses the forwarder for non-streaming post-hoc reasoning and tool-argument progress that preserves the UI's tool_name/start-event contract.

Current status (2026-07-02): streaming provider ThinkingDelta values are mapped to MessageDelta::reasoning(...), and OpenhumanEventBridge projects delta.reasoning into the same parent/sub-agent thinking progress events as the old forwarder path. Tool-call argument fragments now ride the crate stream too: forward_delta maps each ProviderDelta::ToolCallArgsDelta onto a ModelStreamItem::ToolCallDelta(ToolDelta { call_id, content }), the crate agent-loop surfaces it as MessageDelta.tool_call, and OpenhumanEventBridge projects it into AgentProgress::ToolCallArgsDelta. Because the crate ToolDelta has only call_id/content (no tool_name), the tool-call start event — the empty-delta ToolCallArgsDelta that carries the tool name and opens the UI timeline row — still rides ThinkingForwarder.note_tool_call, which records the name into a call_id → tool_name map (ToolNameMap) shared with the bridge so the streamed fragments stay labelled. The forwarder remains live for that start marker and for non-streaming post-hoc reasoning; its emit_tool_args argument-fragment path has been removed. The StreamAccumulator treats the terminal Completed response as authoritative, so streaming the fragments never disturbs the final native tool calls.

Steps

1. Done for streaming providers: src/openhuman/tinyagents/model.rs maps provider thinking deltas to MessageDelta::reasoning(...) on the crate stream, and OpenhumanEventBridge (observability.rs) projects delta.reasoning into OpenHuman progress events.
2. Done: provider tool-call argument fragments map onto ModelStreamItem::ToolCallDelta (crate ToolDelta { call_id, content }) and are projected by OpenhumanEventBridge. ToolDelta carries no tool_name, so the tool_name/start-event half of the UI timeline contract stays on ThinkingForwarder.note_tool_call, which shares a call_id → tool_name map (ToolNameMap) with the bridge so the streamed fragments keep their label. Only ThinkingForwarder.emit_tool_args was removed.
3. Verify sub-agent child thinking deltas still reach the scope-aware bridge (parity with the current forwarder behavior).

Deletions

• Reasoning side of ThinkingForwarder: moved for streaming providers; keep the non-streaming fallback until the non-streaming path has an equivalent event.
• Argument-fragment side of ThinkingForwarder (emit_tool_args, in tinyagents/model.rs): removed — fragments ride ToolCallDelta and are projected by the bridge. The tool-call start marker (note_tool_call, empty-delta ToolCallArgsDelta with tool_name) stays, since the crate ToolDelta cannot carry a tool name; it will only move if a future crate revision adds tool_name/start semantics to ToolDelta.

Acceptance

• UI receives visible-text, reasoning, and tool-arg deltas from crate stream items alone, including tool_name/start-event semantics; streaming e2e (chat
  • sub-agent) green.
• Non-streaming providers emit post-hoc reasoning once.