Bug Report: Malformed tool call error leaked verbatim to user instead of being handled gracefully

Summary

When a tool call is malformed (invalid JSON in partialArgs), the JSON parsing error is surfaced directly to the user as a raw error message instead of being caught and handled gracefully by the framework.

Error Message Shown to User

Unexpected non-whitespace character after JSON at position 2 (line 1 column 3)

Steps to Reproduce

1. Setup: Configure OpenClaw with Venice.ai Kimi K2.5 as primary model:

   {
     "agents": {
       "defaults": {
         "model": {
           "primary": "venice/kimi-k2-5",
           "fallbacks": ["anthropic/claude-opus-4-5"]
         }
       }
     },
     "models": {
       "providers": {
         "venice": {
           "baseUrl": "https://api.venice.ai/api/v1",
           "api": "openai-completions"
         }
       }
     }
   }

2. Trigger: During a conversation, the model generated a malformed tool call with corrupted partialArgs:

   {
     "toolCall": {
       "id": "read:20",
       "name": "read",
       "arguments": {},
       "partialArgs": "{}{\"path\":\"~/clawd/AGENTS.md\",\"offset\":260,\"limit\":100}"
     }
   }

3. Observe: The JSON parsing error was sent directly to the user via Telegram instead of being caught and reformatted.

Technical Details

Session Data (from sessions_history):

{
  "role": "assistant",
  "content": [{
    "type": "toolCall",
    "id": "read:20",
    "name": "read",
    "arguments": {},
    "partialArgs": "{}{\"path\":\"~/clawd/AGENTS.md\",\"offset\":260,\"limit\":100}"
  }],
  "errorMessage": "Unexpected non-whitespace character after JSON at position 2 (line 1 column 3)",
  "stopReason": "error"
}

Root Cause Analysis:

1. The partialArgs field contains concatenated JSON: {} immediately followed by {"path":...}
2. When parsed, this fails at position 2 (the { of the second object) because the parser expects the JSON to end after the first }
3. The parsing error propagates uncaught to the user-facing output

Expected Behavior

The framework should:

1. Catch JSON parsing errors in tool call arguments
2. Log the error internally for debugging
3. Surface a user-friendly message like: "Tool call failed: invalid arguments format"
4. Optionally retry or request clarification from the model

Actual Behavior

The raw JSON parsing error message is sent directly to the user:

"Unexpected non-whitespace character after JSON at position 2 (line 1 column 3)"

Environment

• OpenClaw Version: 2026.2.1 (ed4529e)
• Primary Model: venice/kimi-k2-5 (Kimi K2.5 via Venice.ai)
• API: openai-completions
• Channel: Telegram
• OS: macOS 24.6.0 (Darwin)
• Node: v22.22.0

Additional Context

This occurred during model transition testing (Claude Opus → Kimi K2.5). The partialArgs corruption suggests either:

• Streaming/concatenation issue in tool call construction
• Model-generated malformed JSON that wasn't validated
• Race condition in argument assembly

Possible Fixes

1. Validation Layer: Add JSON schema validation before parsing tool arguments
2. Error Handler: Wrap tool call parsing in try-catch with user-friendly error messages
3. Sanitization: Clean/merge partialArgs with arguments more robustly
4. Logging: Ensure raw errors go to logs, not user output

Impact

• Severity: Medium (functionality works, but UX is poor)
• User Experience: Confusing raw error messages that reveal implementation details
• Security: Low (no sensitive data leaked, but exposes internal error format)

Related: This may be specific to the openai-completions API mode with certain providers that use partialArgs for streaming tool calls.