Dan Lynn 9ff21437a0 fix(mcp): coerce stringified arrays/objects in tool args ...

When a tool schema declares `type: array` or `type: object` and the model
emits the value as a JSON string (common with complex oneOf discriminated
unions), the MCP server rejects it with -32602 "expected array, received
string".  Extend `_coerce_value` to attempt `json.loads` for these types
and replace the string with the parsed value before dispatch.

Root cause confirmed via live testing: `add_reminders.reminders` uses a
oneOf discriminated union (relative/absolute/location) that triggers model
output drift.  Sending a real array passes validation; sending a string
reproduces the exact error.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

2026-04-23 16:38:38 -07:00

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