fix(kimi,mcp): Moonshot schema sanitizer + MCP schema robustness (#14805)

Fixes a broader class of 'tools.function.parameters is not a valid
moonshot flavored json schema' errors on Nous / OpenRouter aggregators
routing to moonshotai/kimi-k2.6 with MCP tools loaded.

## Moonshot sanitizer (agent/moonshot_schema.py, new)

Model-name-routed (not base-URL-routed) so Nous / OpenRouter users are
covered alongside api.moonshot.ai.  Applied in
ChatCompletionsTransport.build_kwargs when is_moonshot_model(model).

Two repairs:
1. Fill missing 'type' on every property / items / anyOf-child schema
   node (structural walk — only schema-position dicts are touched, not
   container maps like properties/$defs).
2. Strip 'type' at anyOf parents; Moonshot rejects it.

## MCP normalizer hardened (tools/mcp_tool.py)

Draft-07 $ref rewrite from PR #14802 now also does:
- coerce missing / null 'type' on object-shaped nodes (salvages #4897)
- prune 'required' arrays to names that exist in 'properties'
  (salvages #4651; Gemini 400s on dangling required)
- apply recursively, not just top-level

These repairs are provider-agnostic so the same MCP schema is valid on
OpenAI, Anthropic, Gemini, and Moonshot in one pass.

## Crash fix: safe getattr for Tool.inputSchema

_convert_mcp_schema now uses getattr(t, 'inputSchema', None) so MCP
servers whose Tool objects omit the attribute entirely no longer abort
registration (salvages #3882).

## Validation

- tests/agent/test_moonshot_schema.py: 27 new tests (model detection,
  missing-type fill, anyOf-parent strip, non-mutation, real-world MCP
  shape)
- tests/tools/test_mcp_tool.py: 7 new tests (missing / null type,
  required pruning, nested repair, safe getattr)
- tests/agent/transports/test_chat_completions.py: 2 new integration
  tests (Moonshot route sanitizes, non-Moonshot route doesn't)
- Targeted suite: 49 passed
- E2E via execute_code with a realistic MCP tool carrying all three
  Moonshot rejection modes + dangling required + draft-07 refs:
  sanitizer produces a schema valid on Moonshot and Gemini

tests/agent/transports/test_chat_completions.py

@@ -238,6 +238,56 @@ class TestChatCompletionsKimi:
         )
         assert kw["extra_body"]["thinking"] == {"type": "disabled"}
 
+    def test_moonshot_tool_schemas_are_sanitized_by_model_name(self, transport):
+        """Aggregator routes (Nous, OpenRouter) hit Moonshot by model name, not base URL."""
+        tools = [
+            {
+                "type": "function",
+                "function": {
+                    "name": "search",
+                    "description": "Search",
+                    "parameters": {
+                        "type": "object",
+                        "properties": {
+                            "q": {"description": "query"},  # missing type
+                        },
+                    },
+                },
+            },
+        ]
+        kw = transport.build_kwargs(
+            model="moonshotai/kimi-k2.6",
+            messages=[{"role": "user", "content": "Hi"}],
+            tools=tools,
+            max_tokens_param_fn=lambda n: {"max_tokens": n},
+        )
+        assert kw["tools"][0]["function"]["parameters"]["properties"]["q"]["type"] == "string"
+
+    def test_non_moonshot_tools_are_not_mutated(self, transport):
+        """Other models don't go through the Moonshot sanitizer."""
+        original_params = {
+            "type": "object",
+            "properties": {"q": {"description": "query"}},  # missing type
+        }
+        tools = [
+            {
+                "type": "function",
+                "function": {
+                    "name": "search",
+                    "description": "Search",
+                    "parameters": original_params,
+                },
+            },
+        ]
+        kw = transport.build_kwargs(
+            model="anthropic/claude-sonnet-4.6",
+            messages=[{"role": "user", "content": "Hi"}],
+            tools=tools,
+            max_tokens_param_fn=lambda n: {"max_tokens": n},
+        )
+        # The parameters dict is passed through untouched (no synthetic type)
+        assert "type" not in kw["tools"][0]["function"]["parameters"]["properties"]["q"]
+
 
 class TestChatCompletionsValidate: