Link Environment Simulation from evaluation overview and plugin list (#1256)

docs/evaluate/index.md

@@ -476,6 +476,18 @@ generated by an AI model.
 For details on how to set up an eval with user simulation, see
 [User Simulation](./user-sim.md).
 
+### Environment simulation
+
+When evaluating agents that rely on external tools, it is often useful to
+simulate tool responses rather than calling real APIs. This allows for:
+
+-   Deterministic testing
+-   Fault injection, such as errors and latency
+-   Cost savings
+
+The [Environment Simulation](./environment_simulation.md) feature provides a
+flexible way to mock tools and inject faults during evaluation.
+
 ## How to run evaluation with ADK
 
 As a developer, you can evaluate your agents using the ADK in the following ways:

docs/plugins/index.md

@@ -70,7 +70,9 @@ immediately:
     Saves files included in user messages as Artifacts.
 *   [**Logging**](https://github.com/google/adk-python/blame/main/src/google/adk/plugins/logging_plugin.py):
     Log important information at each agent workflow callback point.
-
+*   [**Environment Simulation**](/evaluate/environment_simulation/):
+    Simulates tool responses and injects faults to test agent behavior.
+
 ## Define and register Plugins
 
 This section explains how to define Plugin classes and register them as part of