Bug type

Behavior bug (incorrect output/state without crash)

Beta release blocker

No

Summary

Ollama returns tool_call arguments as a JSON string, but OpenClaw's buildAssistantMessage passes it directly to downstream handlers without JSON.parse, causing arguments to be lost or treated as [object Object].

Steps to reproduce

1. Configure ollama/gemma4:26b (or any Ollama model) as primary or fallback model
2. Ask the model to perform a local file operation (e.g. "list my workspace")
3. Observe that exec tool is called but arguments are empty/undefined

Expected behavior

Tool calls should receive correctly parsed arguments as an object (e.g. {command: "ls ~/Desktop"}), not a JSON string.

Actual behavior

Tool invocation fails or parameters are undefined. Ollama API returns arguments as a string: "{"command": "ls", "path": "/Users/..."}" Without deserialization, downstream handlers receive the raw string instead of a parsed object.

OpenClaw version

2026.4.8

Operating system

macOS 26.4.1

Install method

npm global

Model

ollama/gemma4:26b

Provider / routing chain

openclaw -> ollama (localhost:11434)

Additional provider/model setup details

No response

Logs, screenshots, and evidence

Root cause confirmed in stream-DqNCFbiN.js line 369:

Fix applied (backup saved as stream-DqNCFbiN.js.bak):

- arguments: toolCall.function.arguments,
+ arguments: typeof toolCall.function.arguments === "string" 
+   ? JSON.parse(toolCall.function.arguments) 
+   : toolCall.function.arguments,

Impact and severity

Affected: All Ollama model users who rely on tool_calls (exec, read, write, etc.) Severity: High — tool calls silently fail or receive undefined parameters Frequency: 100% of Ollama tool invocations Consequence: Models cannot perform local file operations despite having the tools available

Additional information

This is a provider-contract mismatch: Ollama's API spec defines arguments as string (per Ollama API format), while OpenClaw's downstream handlers expect a native JSON object. The fix is a one-line type guard + parse. Fix is backward-compatible: if arguments is already an object, it passes through unchanged.