feat: enable tool-input-delta streaming in processor

[markokraemer]

Summary

Enable real-time streaming of tool call arguments to clients by wiring up the previously no-op tool-input-delta handler in the session processor.

Problem

The tool-input-delta events from the AI SDK (backed by Anthropic's fine-grained-tool-streaming beta header, which is already set in provider.ts) were being silently discarded:

case"tool-input-delta":
break;// All streaming data thrown away

This forced clients to wait for the complete tool-call event before showing any tool arguments — creating a noticeable lag for tools with large inputs (file writes, long commands, etc.).

Solution

• tool-input-start: Resolve toolCallId via value.toolCallId ?? value.id to handle both fullStream field naming conventions from the AI SDK
• tool-input-delta: Accumulate streaming argument text into state.raw and publish PartDelta events using the existing updatePartDelta infrastructure (same pattern as text-delta streaming)

The raw field on ToolStatePending already exists in the schema (message-v2.ts:265) — it was always initialized to "" but never populated.

How it works

Anthropic API (fine-grained-tool-streaming beta)
→ @ai-sdk/anthropic emits tool-input-start / tool-input-delta / tool-input-end
→ AI SDK passes through to fullStream
→ processor.ts accumulates raw text, publishes PartDelta
→ Bus → SSE endpoint → Frontend
→ Frontend parses partial JSON from raw field → shows tool args in real-time

Frontend impact

Frontends can now use part.state.raw (during status: "pending") to parse and display partial tool arguments as they stream in. The delta field on PartDelta events allows efficient incremental updates.

Changes

• packages/opencode/src/session/processor.ts — Wire up tool-input-start (toolCallId resolution) and tool-input-delta (accumulate raw + publish PartDelta)

No schema changes needed — the raw field and PartDelta event infrastructure already exist.

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[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Based on my search, I found two potentially related PRs:

1. PR feat(plugin): add stream.delta and stream.aborted hooks #14741: "feat(plugin): add stream.delta and stream.aborted hooks"

   • feat(plugin): add stream.delta and stream.aborted hooks #14741
   • Related because it deals with stream.delta hooks, which may be relevant to the PartDelta event publishing mentioned in PR feat: enable tool-input-delta streaming in processor #14945

2. PR feat: stream partial tool arguments #10925: "feat: stream partial tool arguments"

   • feat: stream partial tool arguments #10925
   • Directly related as it addresses streaming partial tool arguments, which is the core goal of PR feat: enable tool-input-delta streaming in processor #14945 for enabling real-time tool argument streaming

These should be reviewed to ensure there's no duplicate work or conflicting implementations around tool argument streaming.