Update ADK doc according to issue #1048 - 1 - Interactions API support

docs/agents/interactions-api.md

@@ -0,0 +1,24 @@
+# Using the Gemini Interactions API
+
+The Gemini Interactions API provides stateful conversation capabilities, allowing you to chain interactions using a `previous_interaction_id` instead of sending the full conversation history with each request. This can be more efficient for long conversations.
+
+To enable the Interactions API, set the `use_interactions_api=True` parameter in the `Gemini` model configuration.
+
+## Example
+
+```python
+from google.adk.agents.llm_agent import Agent
+from google.adk.models.google_llm import Gemini
+
+root_agent = Agent(
+    model=Gemini(
+        model="gemini-2.5-flash",
+        use_interactions_api=True,
+    ),
+    name="interactions_test_agent",
+    description="An agent for testing the Interactions API integration",
+    instruction="You are a helpful assistant.",
+)
+```
+
+For a more detailed example, see the [Interactions API sample](https://github.com/google/adk-python/tree/main/contributing/samples/interactions_api).

mkdocs.yml

@@ -202,6 +202,7 @@ nav:
       - Multi-agent systems: agents/multi-agents.md
       - Agent Config: agents/config.md
       - Models & Authentication: agents/models.md
+      - Interactions API: agents/interactions-api.md
     - Tools for Agents:
       - tools/index.md
       - Built-in tools: tools/built-in-tools.md