Tools with array/object parameters fail when LLM sends stringified JSON #7512

Bug Description

Tools with typed parameters (array, object, number, boolean) fail with Zod validation error when the LLM sends the parameter as a string instead of the proper type.

Error Examples

Case 1: Array as string (Todowrite)

⚙ Todowrite [todos=[{"id": "1", "content": "Database: Migration", "status": "completed", "priority": "high"}, ...]]

Error: The Todowrite tool was called with invalid arguments: [
  {
    "expected": "array",
    "code": "invalid_type",
    "path": ["todos"],
    "message": "Invalid input: expected array, received string"
  }
]

Case 2: Number as string (Bash timeout)

⚙ Bash [command=pnpm build 2>&1 | head -100, description=Build project to verify i18n fixes, timeout=180000]

Error: The Bash tool was called with invalid arguments: [
  {
    "expected": "number",
    "code": "invalid_type",
    "path": ["timeout"],
    "message": "Invalid input: expected number, received string"
  }
]

Root Cause

LLMs sometimes serialize typed parameters as strings:

• { "todos": "[{...}]" } instead of { "todos": [{...}] }
• { "timeout": "180000" } instead of { "timeout": 180000 }
• { "enabled": "true" } instead of { "enabled": true }

Affected Tools

Proposed Fix

Add automatic coercion in Tool.define():

1. If validation fails with type mismatch, attempt to coerce string values
2. For strings starting with [ or {: try JSON.parse()
3. For numeric strings: convert with Number()
4. For "true"/"false": convert to boolean
5. Retry validation with coerced values
6. Backward compatible: if coercion fails, throw original error

Environment

• OpenCode version: 1.1.8
• All providers affected (Anthropic, OpenAI, Google, etc.)