mcp/ppl: mcp_tool criterion should ignore non-tool call requests (#5695)

## Summary

## Related issues

Fix
https://linear.app/pomerium/issue/ENG-2543/mcp-tool-ignore-non-jsonrpc-calls

## User Explanation

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change doesn't create any user-facing changes, you can leave
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## Checklist

- [x] reference any related issues
- [x] updated unit tests
- [x] add appropriate label (`enhancement`, `bug`, `breaking`,
`dependencies`, `ci`)
- [x] ready for review

pkg/policy/criteria/mcp_tool_test.go

@@ -68,4 +68,15 @@ allow:
 		require.Equal(t, A{true, A{ReasonMCPNotAToolCall}, M{}}, res["allow"])
 		require.Equal(t, A{false, A{}}, res["deny"])
 	})
+	t.Run("no method name should pass", func(t *testing.T) {
+		res, err := evaluate(t, `
+allow:
+  and:
+    - mcp_tool:
+        is: list_tables
+`, []*databroker.Record{}, Input{})
+		require.NoError(t, err)
+		require.Equal(t, A{true, A{ReasonMCPNotAToolCall}, M{}}, res["allow"])
+		require.Equal(t, A{false, A{}}, res["deny"])
+	})
 }