feat: coerce tool call arguments to match JSON Schema types (#5265)

LLMs frequently return numbers as strings ("42" instead of 42) and
booleans as strings ("true" instead of true). This causes silent
failures with MCP tools and any tool with strictly-typed parameters.

Added coerce_tool_args() in model_tools.py that runs before every tool
dispatch. For each argument, it checks the tool registry schema and
attempts safe coercion:
  - "42" → 42 when schema says "type": "integer"
  - "3.14" → 3.14 when schema says "type": "number"
  - "true"/"false" → True/False when schema says "type": "boolean"
  - Union types tried in order
  - Original values preserved when coercion fails or is not applicable

Inspired by Block/goose tool argument coercion system.

model_tools.py

@@ -365,6 +365,97 @@ _AGENT_LOOP_TOOLS = {"todo", "memory", "session_search", "delegate_task"}
 _READ_SEARCH_TOOLS = {"read_file", "search_files"}
 
 
+# =========================================================================
+# Tool argument type coercion
+# =========================================================================
+
+def coerce_tool_args(tool_name: str, args: Dict[str, Any]) -> Dict[str, Any]:
+    """Coerce tool call arguments to match their JSON Schema types.
+
+    LLMs frequently return numbers as strings (``"42"`` instead of ``42``)
+    and booleans as strings (``"true"`` instead of ``true``).  This compares
+    each argument value against the tool's registered JSON Schema and attempts
+    safe coercion when the value is a string but the schema expects a different
+    type.  Original values are preserved when coercion fails.
+
+    Handles ``"type": "integer"``, ``"type": "number"``, ``"type": "boolean"``,
+    and union types (``"type": ["integer", "string"]``).
+    """
+    if not args or not isinstance(args, dict):
+        return args
+
+    schema = registry.get_schema(tool_name)
+    if not schema:
+        return args
+
+    properties = (schema.get("parameters") or {}).get("properties")
+    if not properties:
+        return args
+
+    for key, value in args.items():
+        if not isinstance(value, str):
+            continue
+        prop_schema = properties.get(key)
+        if not prop_schema:
+            continue
+        expected = prop_schema.get("type")
+        if not expected:
+            continue
+        coerced = _coerce_value(value, expected)
+        if coerced is not value:
+            args[key] = coerced
+
+    return args
+
+
+def _coerce_value(value: str, expected_type):
+    """Attempt to coerce a string *value* to *expected_type*.
+
+    Returns the original string when coercion is not applicable or fails.
+    """
+    if isinstance(expected_type, list):
+        # Union type — try each in order, return first successful coercion
+        for t in expected_type:
+            result = _coerce_value(value, t)
+            if result is not value:
+                return result
+        return value
+
+    if expected_type in ("integer", "number"):
+        return _coerce_number(value, integer_only=(expected_type == "integer"))
+    if expected_type == "boolean":
+        return _coerce_boolean(value)
+    return value
+
+
+def _coerce_number(value: str, integer_only: bool = False):
+    """Try to parse *value* as a number.  Returns original string on failure."""
+    try:
+        f = float(value)
+    except (ValueError, OverflowError):
+        return value
+    # Guard against inf/nan before int() conversion
+    if f != f or f == float("inf") or f == float("-inf"):
+        return f
+    # If it looks like an integer (no fractional part), return int
+    if f == int(f):
+        return int(f)
+    if integer_only:
+        # Schema wants an integer but value has decimals — keep as string
+        return value
+    return f
+
+
+def _coerce_boolean(value: str):
+    """Try to parse *value* as a boolean.  Returns original string on failure."""
+    low = value.strip().lower()
+    if low == "true":
+        return True
+    if low == "false":
+        return False
+    return value
+
+
 def handle_function_call(
     function_name: str,
     function_args: Dict[str, Any],
@@ -388,6 +479,9 @@ def handle_function_call(
     Returns:
         Function result as a JSON string.
     """
+    # Coerce string arguments to their schema-declared types (e.g. "42"→42)
+    function_args = coerce_tool_args(function_name, function_args)
+
     # Notify the read-loop tracker when a non-read/search tool runs,
     # so the *consecutive* counter resets (reads after other work are fine).
     if function_name not in _READ_SEARCH_TOOLS: