feat(genai): support optional seed parameter

libs/genai/langchain_google_genai/_common.py

@@ -210,6 +210,15 @@ class _BaseGoogleGenerativeAI(BaseModel):
             ```
     """  # noqa: E501
 
+    seed: int | None = Field(
+        default=None,
+    )
+    """
+    Seed used in decoding.
+
+    If not set, the request uses a randomly generated seed.
+    """
+
     @property
     def lc_secrets(self) -> dict[str, str]:
         # Either could contain the API key

libs/genai/langchain_google_genai/chat_models.py

@@ -2032,6 +2032,7 @@ def _prepare_params(
                     or self.include_thoughts is not None
                     else None
                 ),
+                "seed": self.seed,
             }.items()
             if v is not None
         }

libs/genai/langchain_google_genai/llms.py

@@ -83,6 +83,7 @@ def validate_environment(self) -> Self:
             transport=self.transport,
             additional_headers=self.additional_headers,
             safety_settings=self.safety_settings,
+            seed=self.seed,
         )
 
         return self