diff --git a/dotnet/src/Microsoft.Agents.AI.Harness/ChatClientHarnessExtensions.cs b/dotnet/src/Microsoft.Agents.AI.Harness/ChatClientHarnessExtensions.cs
index 1a55624f3d..be66e9e635 100644
--- a/dotnet/src/Microsoft.Agents.AI.Harness/ChatClientHarnessExtensions.cs
+++ b/dotnet/src/Microsoft.Agents.AI.Harness/ChatClientHarnessExtensions.cs
@@ -1,7 +1,9 @@
 // Copyright (c) Microsoft. All rights reserved.
 
+using System;
 using System.Diagnostics.CodeAnalysis;
 using Microsoft.Agents.AI;
+using Microsoft.Extensions.Logging;
 using Microsoft.Shared.DiagnosticIds;
 
 namespace Microsoft.Extensions.AI;
@@ -32,11 +34,19 @@ public static class ChatClientHarnessExtensions
     /// additional context providers, and chat history provider.
     /// When <see langword="null"/>, the agent uses built-in default settings.
     /// </param>
+    /// <param name="loggerFactory">
+    /// Optional logger factory for creating loggers used by the agent and its components.
+    /// </param>
+    /// <param name="services">
+    /// Optional service provider for resolving dependencies required by AI functions and other agent components.
+    /// </param>
     /// <returns>A new <see cref="HarnessAgent"/> instance.</returns>
     public static HarnessAgent AsHarnessAgent(
         this IChatClient chatClient,
         int maxContextWindowTokens,
         int maxOutputTokens,
-        HarnessAgentOptions? options = null) =>
-        new(chatClient, maxContextWindowTokens, maxOutputTokens, options);
+        HarnessAgentOptions? options = null,
+        ILoggerFactory? loggerFactory = null,
+        IServiceProvider? services = null) =>
+        new(chatClient, maxContextWindowTokens, maxOutputTokens, options, loggerFactory, services);
 }
diff --git a/dotnet/src/Microsoft.Agents.AI.Harness/HarnessAgent.cs b/dotnet/src/Microsoft.Agents.AI.Harness/HarnessAgent.cs
index ef1af05513..139f47db3c 100644
--- a/dotnet/src/Microsoft.Agents.AI.Harness/HarnessAgent.cs
+++ b/dotnet/src/Microsoft.Agents.AI.Harness/HarnessAgent.cs
@@ -10,6 +10,7 @@ using Microsoft.Agents.AI.Compaction;
 using Microsoft.Agents.AI.Tools.Shell;
 #endif
 using Microsoft.Extensions.AI;
+using Microsoft.Extensions.Logging;
 using Microsoft.Shared.DiagnosticIds;
 using Microsoft.Shared.Diagnostics;
 
@@ -105,6 +106,12 @@ public sealed class HarnessAgent : DelegatingAIAgent
     /// additional context providers, and chat history provider.
     /// When <see langword="null"/>, the agent uses built-in default settings.
     /// </param>
+    /// <param name="loggerFactory">
+    /// Optional logger factory for creating loggers used by the agent and its components.
+    /// </param>
+    /// <param name="services">
+    /// Optional service provider for resolving dependencies required by AI functions and other agent components.
+    /// </param>
     /// <exception cref="ArgumentNullException">
     /// <paramref name="chatClient"/> is <see langword="null"/>.
     /// </exception>
@@ -112,18 +119,20 @@ public sealed class HarnessAgent : DelegatingAIAgent
     /// <paramref name="maxContextWindowTokens"/> is not positive, or
     /// <paramref name="maxOutputTokens"/> is negative or greater than or equal to <paramref name="maxContextWindowTokens"/>.
     /// </exception>
-    public HarnessAgent(IChatClient chatClient, int maxContextWindowTokens, int maxOutputTokens, HarnessAgentOptions? options = null)
+    public HarnessAgent(IChatClient chatClient, int maxContextWindowTokens, int maxOutputTokens, HarnessAgentOptions? options = null, ILoggerFactory? loggerFactory = null, IServiceProvider? services = null)
         : base(BuildAgent(
             Throw.IfNull(chatClient),
             maxContextWindowTokens,
             maxOutputTokens,
-            options))
+            options,
+            loggerFactory,
+            services))
     {
     }
 
-    private static AIAgent BuildAgent(IChatClient chatClient, int maxContextWindowTokens, int maxOutputTokens, HarnessAgentOptions? options)
+    private static AIAgent BuildAgent(IChatClient chatClient, int maxContextWindowTokens, int maxOutputTokens, HarnessAgentOptions? options, ILoggerFactory? loggerFactory, IServiceProvider? services)
     {
-        ChatClientAgent innerAgent = BuildInnerAgent(chatClient, maxContextWindowTokens, maxOutputTokens, options);
+        ChatClientAgent innerAgent = BuildInnerAgent(chatClient, maxContextWindowTokens, maxOutputTokens, options, loggerFactory, services);
 
         AIAgentBuilder builder = innerAgent.AsBuilder();
 
@@ -137,10 +146,10 @@ public sealed class HarnessAgent : DelegatingAIAgent
             builder.UseOpenTelemetry(sourceName: options?.OpenTelemetrySourceName);
         }
 
-        return builder.Build();
+        return builder.Build(services);
     }
 
-    private static ChatClientAgent BuildInnerAgent(IChatClient chatClient, int maxContextWindowTokens, int maxOutputTokens, HarnessAgentOptions? options)
+    private static ChatClientAgent BuildInnerAgent(IChatClient chatClient, int maxContextWindowTokens, int maxOutputTokens, HarnessAgentOptions? options, ILoggerFactory? loggerFactory, IServiceProvider? services)
     {
         var compactionStrategy = new ContextWindowCompactionStrategy(
             maxContextWindowTokens: maxContextWindowTokens,
@@ -165,13 +174,13 @@ public sealed class HarnessAgent : DelegatingAIAgent
 
         ChatOptions chatOptions = BuildChatOptions(options, instructions, maxOutputTokens);
 
-        var compactionProvider = new CompactionProvider(compactionStrategy);
+        var compactionProvider = new CompactionProvider(compactionStrategy, loggerFactory: loggerFactory);
 
-        IEnumerable<AIContextProvider> contextProviders = BuildContextProviders(options);
+        IEnumerable<AIContextProvider> contextProviders = BuildContextProviders(options, loggerFactory);
 
         return chatClient
             .AsBuilder()
-            .UseFunctionInvocation(configure: options?.MaximumIterationsPerRequest is int maxIterations
+            .UseFunctionInvocation(loggerFactory, configure: options?.MaximumIterationsPerRequest is int maxIterations
                 ? ficc => ficc.MaximumIterationsPerRequest = maxIterations
                 : null)
             .UseMessageInjection()
@@ -189,7 +198,9 @@ public sealed class HarnessAgent : DelegatingAIAgent
                 RequirePerServiceCallChatHistoryPersistence = true,
                 WarnOnChatHistoryProviderConflict = false,
                 ThrowOnChatHistoryProviderConflict = false,
-            });
+            },
+            loggerFactory,
+            services);
     }
 
     private static ChatOptions BuildChatOptions(HarnessAgentOptions? options, string instructions, int maxOutputTokens)
@@ -215,7 +226,7 @@ public sealed class HarnessAgent : DelegatingAIAgent
         return result;
     }
 
-    private static List<AIContextProvider> BuildContextProviders(HarnessAgentOptions? options)
+    private static List<AIContextProvider> BuildContextProviders(HarnessAgentOptions? options, ILoggerFactory? loggerFactory)
     {
         var providers = new List<AIContextProvider>();
 
@@ -255,8 +266,8 @@ public sealed class HarnessAgent : DelegatingAIAgent
         if (options?.DisableAgentSkillsProvider is not true)
         {
             AgentSkillsProvider skillsProvider = options?.AgentSkillsSource is AgentSkillsSource source
-                ? new AgentSkillsProvider(source)
-                : new AgentSkillsProvider(Directory.GetCurrentDirectory());
+                ? new AgentSkillsProvider(source, loggerFactory: loggerFactory)
+                : new AgentSkillsProvider(Directory.GetCurrentDirectory(), loggerFactory: loggerFactory);
 
             providers.Add(skillsProvider);
         }
diff --git a/dotnet/tests/Microsoft.Agents.AI.Harness.UnitTests/HarnessAgentTests.cs b/dotnet/tests/Microsoft.Agents.AI.Harness.UnitTests/HarnessAgentTests.cs
index 4f08209bd8..2711fa1458 100644
--- a/dotnet/tests/Microsoft.Agents.AI.Harness.UnitTests/HarnessAgentTests.cs
+++ b/dotnet/tests/Microsoft.Agents.AI.Harness.UnitTests/HarnessAgentTests.cs
@@ -9,6 +9,7 @@ using System.Threading.Tasks;
 using Microsoft.Agents.AI.Tools.Shell;
 #endif
 using Microsoft.Extensions.AI;
+using Microsoft.Extensions.Logging;
 using Moq;
 
 namespace Microsoft.Agents.AI.UnitTests;
@@ -1460,4 +1461,131 @@ public class HarnessAgentTests
 
     #endregion
 #endif
+
+    #region LoggerFactory and ServiceProvider
+
+    /// <summary>
+    /// Verify that the constructor succeeds when loggerFactory is provided.
+    /// </summary>
+    [Fact]
+    public void Constructor_SucceedsWithLoggerFactory()
+    {
+        // Arrange
+        var chatClient = new Mock<IChatClient>().Object;
+        var loggerFactory = new Mock<ILoggerFactory>().Object;
+
+        // Act
+        var agent = new HarnessAgent(chatClient, TestMaxContextWindowTokens, TestMaxOutputTokens, CreateAllDisabledOptions(), loggerFactory);
+
+        // Assert
+        Assert.NotNull(agent);
+    }
+
+    /// <summary>
+    /// Verify that the constructor succeeds when serviceProvider is provided.
+    /// </summary>
+    [Fact]
+    public void Constructor_SucceedsWithServiceProvider()
+    {
+        // Arrange
+        var chatClient = new Mock<IChatClient>().Object;
+        var services = new Mock<IServiceProvider>().Object;
+
+        // Act
+        var agent = new HarnessAgent(chatClient, TestMaxContextWindowTokens, TestMaxOutputTokens, CreateAllDisabledOptions(), services: services);
+
+        // Assert
+        Assert.NotNull(agent);
+    }
+
+    /// <summary>
+    /// Verify that the constructor succeeds when both loggerFactory and serviceProvider are provided.
+    /// </summary>
+    [Fact]
+    public void Constructor_SucceedsWithLoggerFactoryAndServiceProvider()
+    {
+        // Arrange
+        var chatClient = new Mock<IChatClient>().Object;
+        var loggerFactory = new Mock<ILoggerFactory>().Object;
+        var services = new Mock<IServiceProvider>().Object;
+
+        // Act
+        var agent = new HarnessAgent(chatClient, TestMaxContextWindowTokens, TestMaxOutputTokens, CreateAllDisabledOptions(), loggerFactory, services);
+
+        // Assert
+        Assert.NotNull(agent);
+    }
+
+    /// <summary>
+    /// Verify that AsHarnessAgent extension method accepts loggerFactory and serviceProvider.
+    /// </summary>
+    [Fact]
+    public void AsHarnessAgent_SucceedsWithLoggerFactoryAndServiceProvider()
+    {
+        // Arrange
+        var chatClient = new Mock<IChatClient>().Object;
+        var loggerFactory = new Mock<ILoggerFactory>().Object;
+        var services = new Mock<IServiceProvider>().Object;
+
+        // Act
+        var agent = chatClient.AsHarnessAgent(TestMaxContextWindowTokens, TestMaxOutputTokens, CreateAllDisabledOptions(), loggerFactory, services);
+
+        // Assert
+        Assert.NotNull(agent);
+    }
+
+    /// <summary>
+    /// Verify that ILoggerFactory is threaded to downstream components by confirming CreateLogger is called.
+    /// </summary>
+    [Fact]
+    public void Constructor_LoggerFactoryIsUsedByDownstreamComponents()
+    {
+        // Arrange
+        var chatClient = new Mock<IChatClient>().Object;
+        var mockLoggerFactory = new Mock<ILoggerFactory>();
+        mockLoggerFactory
+            .Setup(lf => lf.CreateLogger(It.IsAny<string>()))
+            .Returns(new Mock<ILogger>().Object);
+
+        // Act — use options that leave CompactionProvider and AgentSkillsProvider enabled
+        var options = new HarnessAgentOptions
+        {
+            DisableToolApproval = true,
+            DisableOpenTelemetry = true,
+            DisableFileMemory = true,
+            DisableFileAccess = true,
+            DisableWebSearch = true,
+            DisableTodoProvider = true,
+            DisableAgentModeProvider = true,
+        };
+        var agent = new HarnessAgent(chatClient, TestMaxContextWindowTokens, TestMaxOutputTokens, options, mockLoggerFactory.Object);
+
+        // Assert — CreateLogger should have been called by one or more downstream components
+        Assert.NotNull(agent);
+        mockLoggerFactory.Verify(lf => lf.CreateLogger(It.IsAny<string>()), Times.AtLeastOnce());
+    }
+
+    /// <summary>
+    /// Verify that IServiceProvider is propagated through the agent pipeline by confirming
+    /// it is queried during agent construction.
+    /// </summary>
+    [Fact]
+    public void Constructor_ServiceProviderIsQueriedDuringBuild()
+    {
+        // Arrange
+        var chatClient = new Mock<IChatClient>().Object;
+        var mockServices = new Mock<IServiceProvider>();
+        mockServices
+            .Setup(sp => sp.GetService(It.IsAny<Type>()))
+            .Returns(null!);
+
+        // Act
+        var agent = new HarnessAgent(chatClient, TestMaxContextWindowTokens, TestMaxOutputTokens, CreateAllDisabledOptions(), services: mockServices.Object);
+
+        // Assert — the service provider should have been queried during pipeline construction
+        Assert.NotNull(agent);
+        mockServices.Verify(sp => sp.GetService(It.IsAny<Type>()), Times.AtLeastOnce());
+    }
+
+    #endregion
 }
diff --git a/python/packages/core/AGENTS.md b/python/packages/core/AGENTS.md
index ffb6b3e2c5..a0f4c81b56 100644
--- a/python/packages/core/AGENTS.md
+++ b/python/packages/core/AGENTS.md
@@ -56,7 +56,7 @@ agent_framework/
 - **`AgentMiddleware`** - Intercepts agent `run()` calls
 - **`ChatMiddleware`** - Intercepts chat client `get_response()` calls
 - **`FunctionMiddleware`** - Intercepts function/tool invocations
-- **`AgentContext`** / **`ChatContext`** / **`FunctionInvocationContext`** - Context objects passed through middleware
+- **`AgentContext`** / **`ChatContext`** / **`FunctionInvocationContext`** - Context objects passed through middleware. A tool can declare a `FunctionInvocationContext` parameter to receive it; `context.tools` is the live, mutable tools list for the run, and `context.add_tools(...)` / `context.remove_tools(...)` enable progressive tool exposure (changes apply on the next function-calling iteration).
 
 ### Sessions (`_sessions.py`)
 
diff --git a/python/packages/core/agent_framework/_feature_stage.py b/python/packages/core/agent_framework/_feature_stage.py
index dfa9cb6343..455c61bb7e 100644
--- a/python/packages/core/agent_framework/_feature_stage.py
+++ b/python/packages/core/agent_framework/_feature_stage.py
@@ -58,6 +58,7 @@ class ExperimentalFeature(str, Enum):
     FOUNDRY_PREVIEW_TOOLS = "FOUNDRY_PREVIEW_TOOLS"
     FUNCTIONAL_WORKFLOWS = "FUNCTIONAL_WORKFLOWS"
     HARNESS = "HARNESS"
+    PROGRESSIVE_TOOLS = "PROGRESSIVE_TOOLS"
     SKILLS = "SKILLS"
     TO_PROMPT_AGENT = "TO_PROMPT_AGENT"
 
diff --git a/python/packages/core/agent_framework/_middleware.py b/python/packages/core/agent_framework/_middleware.py
index 4f90030368..2eddb08a07 100644
--- a/python/packages/core/agent_framework/_middleware.py
+++ b/python/packages/core/agent_framework/_middleware.py
@@ -11,6 +11,7 @@ from enum import Enum
 from typing import TYPE_CHECKING, Any, Generic, Literal, TypeAlias, cast, overload
 
 from ._clients import SupportsChatGetResponse
+from ._feature_stage import ExperimentalFeature, experimental
 from ._types import (
     AgentResponse,
     AgentResponseUpdate,
@@ -214,6 +215,12 @@ class FunctionInvocationContext:
         result: Function execution result. Can be observed after calling ``call_next()``
                 to see the actual execution result or can be set to override the execution result.
         kwargs: Additional runtime keyword arguments forwarded to the function invocation.
+        tools: The live, mutable list of tools available to the model for the current
+                agent run, or ``None`` when the function is invoked outside of a
+                function-calling loop (for example via ``FunctionTool.invoke`` directly).
+                Tools can add or remove tools during execution using :meth:`add_tools`
+                and :meth:`remove_tools` (progressive tool exposure). Mutations take
+                effect on the **next** model iteration, not the in-flight batch.
 
     Examples:
         .. code-block:: python
@@ -232,6 +239,18 @@ class FunctionInvocationContext:
 
                     # Continue execution
                     await call_next()
+
+        Progressive tool exposure from inside a tool:
+
+        .. code-block:: python
+
+            from agent_framework import FunctionInvocationContext, tool
+
+
+            @tool(approval_mode="never_require")
+            def load_math_tools(ctx: FunctionInvocationContext) -> str:
+                ctx.add_tools([factorial, fibonacci])
+                return "Math tools are now available."
     """
 
     def __init__(
@@ -242,6 +261,7 @@ class FunctionInvocationContext:
         metadata: Mapping[str, Any] | None = None,
         result: Any = None,
         kwargs: Mapping[str, Any] | None = None,
+        tools: list[ToolTypes] | None = None,
     ) -> None:
         """Initialize the FunctionInvocationContext.
 
@@ -252,6 +272,9 @@ class FunctionInvocationContext:
             metadata: Metadata dictionary for sharing data between function middleware.
             result: Function execution result.
             kwargs: Additional runtime keyword arguments forwarded to the function invocation.
+            tools: The live, mutable list of tools for the current agent run. When provided,
+                this is the same list object the model sees on the next iteration, so
+                appending or removing tools changes the model's available tools.
         """
         self.function = function
         self.arguments = arguments
@@ -259,6 +282,96 @@ class FunctionInvocationContext:
         self.metadata: dict[str, Any] = dict(metadata) if metadata is not None else {}
         self.result = result
         self.kwargs: dict[str, Any] = dict(kwargs) if kwargs is not None else {}
+        self.tools = tools
+
+    @experimental(feature_id=ExperimentalFeature.PROGRESSIVE_TOOLS)
+    def add_tools(
+        self,
+        tools: ToolTypes | Callable[..., Any] | Sequence[ToolTypes | Callable[..., Any]],
+    ) -> None:
+        """Add one or more tools to the current agent run (progressive tool exposure).
+
+        Callable inputs are converted to :class:`FunctionTool`, and tool collections are
+        flattened, using the same normalization as the rest of the framework. Added tools
+        become available to the model on the **next** iteration of the function-calling
+        loop; they do not affect tool calls already requested in the in-flight batch.
+
+        Adding a tool whose name already exists is a no-op when it is the same object, and
+        raises ``ValueError`` when it is a different object with a duplicate name.
+
+        Args:
+            tools: A single tool/callable or a sequence of tools/callables to add.
+
+        Raises:
+            RuntimeError: If the context has no live tools list (for example when the
+                function is invoked outside of a function-calling loop).
+            ValueError: If a different tool with a duplicate name is added.
+        """
+        from ._tools import _append_unique_tools, normalize_tools  # type: ignore[reportPrivateUsage]
+
+        if self.tools is None:
+            raise RuntimeError(
+                "Cannot add tools: this FunctionInvocationContext is not bound to a live "
+                "agent run. add_tools is only available for functions invoked within an "
+                "agent's function-calling loop."
+            )
+        # Validate the whole batch against a throwaway copy first, so a duplicate-name
+        # clash partway through the batch raises before the live tool list is mutated
+        # (all-or-nothing semantics).
+        merged = _append_unique_tools(list(self.tools), normalize_tools(tools))
+        self.tools[:] = merged
+
+    @experimental(feature_id=ExperimentalFeature.PROGRESSIVE_TOOLS)
+    def remove_tools(
+        self,
+        tools: ToolTypes | Callable[..., Any] | Sequence[ToolTypes | Callable[..., Any]] | str | Sequence[str],
+    ) -> None:
+        """Remove one or more tools from the current agent run (progressive tool exposure).
+
+        Tools may be specified by name, by tool object, or by the original callable. Names
+        that are not currently present are ignored. Removals take effect on the **next**
+        iteration of the function-calling loop; tool calls already requested in the
+        in-flight batch still execute.
+
+        Args:
+            tools: A tool name, tool/callable, or a sequence of any of these to remove.
+
+        Raises:
+            RuntimeError: If the context has no live tools list (for example when the
+                function is invoked outside of a function-calling loop).
+        """
+        from ._tools import _get_tool_name, normalize_tools  # type: ignore[reportPrivateUsage]
+
+        if self.tools is None:
+            raise RuntimeError(
+                "Cannot remove tools: this FunctionInvocationContext is not bound to a live "
+                "agent run. remove_tools is only available for functions invoked within an "
+                "agent's function-calling loop."
+            )
+
+        names_to_remove: set[str] = set()
+        raw_items: list[Any]
+        if isinstance(tools, str):
+            raw_items = [tools]
+        elif isinstance(tools, Sequence) and not isinstance(tools, (bytes, bytearray)):
+            raw_items = list(cast("Sequence[Any]", tools))
+        else:
+            raw_items = [tools]
+        for item in raw_items:
+            if isinstance(item, str):
+                names_to_remove.add(item)
+                continue
+            for normalized in normalize_tools(item):
+                if name := _get_tool_name(normalized):  # type: ignore[reportPrivateUsage]
+                    names_to_remove.add(name)
+
+        if not names_to_remove:
+            return
+        self.tools[:] = [
+            tool
+            for tool in self.tools
+            if _get_tool_name(tool) not in names_to_remove  # type: ignore[reportPrivateUsage]
+        ]
 
 
 class ChatContext:
diff --git a/python/packages/core/agent_framework/_tools.py b/python/packages/core/agent_framework/_tools.py
index 93722a8987..5237cf62ba 100644
--- a/python/packages/core/agent_framework/_tools.py
+++ b/python/packages/core/agent_framework/_tools.py
@@ -1418,6 +1418,7 @@ async def _auto_invoke_function(
     sequence_index: int | None = None,
     request_index: int | None = None,
     middleware_pipeline: FunctionMiddlewarePipeline | None = None,
+    live_tools: list[ToolTypes] | None = None,
 ) -> Content:
     """Invoke a function call requested by the agent, applying middleware that is defined.
 
@@ -1432,6 +1433,8 @@ async def _auto_invoke_function(
         sequence_index: The index of the function call in the sequence.
         request_index: The index of the request iteration.
         middleware_pipeline: Optional middleware pipeline to apply during execution.
+        live_tools: The live, mutable tools list for the current agent run, exposed on
+            the FunctionInvocationContext so tools can add/remove tools at runtime.
 
     Returns:
         The function result content.
@@ -1523,6 +1526,7 @@ async def _auto_invoke_function(
                     arguments=args,
                     session=invocation_session,
                     kwargs=runtime_kwargs.copy(),
+                    tools=live_tools,
                 )
             function_result = await tool.invoke(
                 arguments=args,
@@ -1537,6 +1541,10 @@ async def _auto_invoke_function(
         except UserInputRequiredException:
             raise
         except Exception as exc:
+            logger.warning(
+                f"Function '{tool.name}' raised an exception; returning an error result to the "
+                f"model. Set include_detailed_errors=True for the full detail. Exception: {exc!r}"
+            )
             message = "Error: Function failed."
             if config.get("include_detailed_errors", False):
                 message = f"{message} Exception: {exc}"
@@ -1552,6 +1560,7 @@ async def _auto_invoke_function(
         arguments=args,
         session=invocation_session,
         kwargs=runtime_kwargs.copy(),
+        tools=live_tools,
     )
 
     call_id = function_call_content.call_id
@@ -1608,6 +1617,10 @@ async def _auto_invoke_function(
     except UserInputRequiredException:
         raise
     except Exception as exc:
+        logger.warning(
+            f"Function '{tool.name}' raised an exception; returning an error result to the "
+            f"model. Set include_detailed_errors=True for the full detail. Exception: {exc!r}"
+        )
         message = "Error: Function failed."
         if config.get("include_detailed_errors", False):
             message = f"{message} Exception: {exc}"
@@ -1659,6 +1672,9 @@ async def _try_execute_function_calls(
     from ._types import Content
 
     tool_map = _get_tool_map(tools)
+    # The live tools list (when tools is the run-local list) is exposed on the
+    # FunctionInvocationContext so tools can add/remove tools during the run.
+    live_tools: list[ToolTypes] | None = cast("list[ToolTypes]", tools) if isinstance(tools, list) else None
     approval_tools = [tool_name for tool_name, tool in tool_map.items() if tool.approval_mode == "always_require"]
     logger.debug(
         "_try_execute_function_calls: tool_map keys=%s, approval_tools=%s",
@@ -1733,6 +1749,7 @@ async def _try_execute_function_calls(
                 request_index=attempt_idx,
                 middleware_pipeline=middleware_pipeline,
                 config=config,
+                live_tools=live_tools,
             )
             return (result, False)
         except MiddlewareTermination as exc:
@@ -2371,6 +2388,13 @@ class FunctionInvocationLayer(Generic[OptionsCoT]):
                 function_invocation_kwargs=function_invocation_kwargs,
                 client_kwargs=filtered_kwargs,
             )
+        # Establish a single, run-local mutable tools list so that tools can add or remove
+        # tools during the run (progressive tool exposure). A fresh list is created via
+        # normalize_tools so the caller's original tools container is never mutated, while
+        # the same list object is shared with the model (options["tools"]) and the tool map
+        # rebuilt on every loop iteration.
+        if mutable_options.get("tools"):
+            mutable_options["tools"] = normalize_tools(mutable_options["tools"])
         if not stream:
 
             async def _get_response() -> ChatResponse[Any]:
diff --git a/python/packages/core/tests/core/test_function_invocation_logic.py b/python/packages/core/tests/core/test_function_invocation_logic.py
index 3d20a26080..f96ca99ad5 100644
--- a/python/packages/core/tests/core/test_function_invocation_logic.py
+++ b/python/packages/core/tests/core/test_function_invocation_logic.py
@@ -3975,3 +3975,425 @@ async def test_user_input_request_empty_contents_returns_fallback(chat_client_ba
     ]
     assert len(function_results) >= 1
     assert any("user input" in (fr.result or "").lower() for fr in function_results)
+
+
+# region Progressive tool exposure (FunctionInvocationContext.add_tools / remove_tools)
+
+
+def _pte_function_call_response(call_id: str, name: str, arguments: str = "{}") -> ChatResponse:
+    return ChatResponse(
+        messages=Message(
+            role="assistant",
+            contents=[Content.from_function_call(call_id=call_id, name=name, arguments=arguments)],
+        )
+    )
+
+
+def _pte_text_response(text: str = "done") -> ChatResponse:
+    return ChatResponse(messages=Message(role="assistant", contents=[text]))
+
+
+@tool(name="factorial", approval_mode="never_require")
+def _pte_factorial(n: int) -> int:
+    """Compute the factorial of n."""
+    result = 1
+    for value in range(2, n + 1):
+        result *= value
+    return result
+
+
+async def test_context_exposes_live_tools(chat_client_base: SupportsChatGetResponse):
+    from agent_framework import FunctionTool
+
+    seen_names: list[str] = []
+
+    @tool(name="inspect_tools", approval_mode="never_require")
+    def inspect_tools(ctx: FunctionInvocationContext) -> str:
+        assert ctx.tools is not None
+        seen_names.extend(t.name for t in ctx.tools if isinstance(t, FunctionTool))
+        return "inspected"
+
+    chat_client_base.run_responses = [
+        _pte_function_call_response("1", "inspect_tools"),
+        _pte_text_response(),
+    ]
+    await chat_client_base.get_response(
+        [Message(role="user", contents=["hi"])],
+        options={"tool_choice": "auto", "tools": [inspect_tools]},
+    )
+    assert "inspect_tools" in seen_names
+
+
+async def test_add_tools_available_next_iteration(chat_client_base: SupportsChatGetResponse):
+    exec_counter = 0
+
+    @tool(name="factorial", approval_mode="never_require")
+    def factorial(n: int) -> int:
+        nonlocal exec_counter
+        exec_counter += 1
+        return 120
+
+    @tool(name="load_math", approval_mode="never_require")
+    def load_math(ctx: FunctionInvocationContext) -> str:
+        ctx.add_tools(factorial)
+        return "math tools loaded"
+
+    chat_client_base.function_invocation_configuration["max_iterations"] = 3  # type: ignore[attr-defined]
+    chat_client_base.run_responses = [
+        _pte_function_call_response("1", "load_math"),
+        _pte_function_call_response("2", "factorial", '{"n": 5}'),
+        _pte_text_response(),
+    ]
+    response = await chat_client_base.get_response(
+        [Message(role="user", contents=["compute 5!"])],
+        options={"tool_choice": "auto", "tools": [load_math]},
+    )
+    assert exec_counter == 1
+    assert response.messages[-1].text == "done"
+
+
+async def test_add_tools_model_sees_added_tools_in_options(chat_client_base: SupportsChatGetResponse):
+    from agent_framework import FunctionTool
+
+    recorded: list[list[str]] = []
+    client_cls = type(chat_client_base)
+    original = client_cls._get_non_streaming_response
+
+    async def recording(self: Any, *, messages: Any, options: dict[str, Any], **kwargs: Any) -> ChatResponse:
+        tools = options.get("tools") or []
+        recorded.append([t.name for t in tools if isinstance(t, FunctionTool)])
+        return await original(self, messages=messages, options=options, **kwargs)
+
+    @tool(name="load_math", approval_mode="never_require")
+    def load_math(ctx: FunctionInvocationContext) -> str:
+        ctx.add_tools(_pte_factorial)
+        return "loaded"
+
+    chat_client_base.function_invocation_configuration["max_iterations"] = 3  # type: ignore[attr-defined]
+    chat_client_base.run_responses = [
+        _pte_function_call_response("1", "load_math"),
+        _pte_function_call_response("2", "factorial", '{"n": 5}'),
+        _pte_text_response(),
+    ]
+    monkey = pytest.MonkeyPatch()
+    monkey.setattr(client_cls, "_get_non_streaming_response", recording)
+    try:
+        await chat_client_base.get_response(
+            [Message(role="user", contents=["compute 5!"])],
+            options={"tool_choice": "auto", "tools": [load_math]},
+        )
+    finally:
+        monkey.undo()
+
+    assert recorded[0] == ["load_math"]
+    assert "factorial" in recorded[1]
+
+
+async def test_remove_tools_next_iteration(chat_client_base: SupportsChatGetResponse):
+    from agent_framework import FunctionTool
+
+    recorded: list[list[str]] = []
+    client_cls = type(chat_client_base)
+    original = client_cls._get_non_streaming_response
+
+    async def recording(self: Any, *, messages: Any, options: dict[str, Any], **kwargs: Any) -> ChatResponse:
+        tools = options.get("tools") or []
+        recorded.append([t.name for t in tools if isinstance(t, FunctionTool)])
+        return await original(self, messages=messages, options=options, **kwargs)
+
+    @tool(name="get_weather", approval_mode="never_require")
+    def get_weather(location: str) -> str:
+        return "sunny"
+
+    @tool(name="drop_weather", approval_mode="never_require")
+    def drop_weather(ctx: FunctionInvocationContext) -> str:
+        ctx.remove_tools("get_weather")
+        return "removed"
+
+    chat_client_base.function_invocation_configuration["max_iterations"] = 3  # type: ignore[attr-defined]
+    chat_client_base.run_responses = [
+        _pte_function_call_response("1", "drop_weather"),
+        _pte_text_response(),
+    ]
+    monkey = pytest.MonkeyPatch()
+    monkey.setattr(client_cls, "_get_non_streaming_response", recording)
+    try:
+        await chat_client_base.get_response(
+            [Message(role="user", contents=["hi"])],
+            options={"tool_choice": "auto", "tools": [get_weather, drop_weather]},
+        )
+    finally:
+        monkey.undo()
+
+    assert set(recorded[0]) == {"get_weather", "drop_weather"}
+    assert "get_weather" not in recorded[1]
+
+
+async def test_add_tools_does_not_mutate_caller_tools_list(chat_client_base: SupportsChatGetResponse):
+    @tool(name="load_math", approval_mode="never_require")
+    def load_math(ctx: FunctionInvocationContext) -> str:
+        ctx.add_tools(_pte_factorial)
+        return "loaded"
+
+    original_tools: list[Any] = [load_math]
+    chat_client_base.function_invocation_configuration["max_iterations"] = 3  # type: ignore[attr-defined]
+    chat_client_base.run_responses = [
+        _pte_function_call_response("1", "load_math"),
+        _pte_text_response(),
+    ]
+    await chat_client_base.get_response(
+        [Message(role="user", contents=["hi"])],
+        options={"tool_choice": "auto", "tools": original_tools},
+    )
+    assert original_tools == [load_math]
+
+
+async def test_add_tools_persists_across_iterations(chat_client_base: SupportsChatGetResponse):
+    from agent_framework import FunctionTool
+
+    recorded: list[list[str]] = []
+    client_cls = type(chat_client_base)
+    original = client_cls._get_non_streaming_response
+
+    async def recording(self: Any, *, messages: Any, options: dict[str, Any], **kwargs: Any) -> ChatResponse:
+        tools = options.get("tools") or []
+        recorded.append([t.name for t in tools if isinstance(t, FunctionTool)])
+        return await original(self, messages=messages, options=options, **kwargs)
+
+    @tool(name="load_math", approval_mode="never_require")
+    def load_math(ctx: FunctionInvocationContext) -> str:
+        ctx.add_tools(_pte_factorial)
+        return "loaded"
+
+    chat_client_base.function_invocation_configuration["max_iterations"] = 4  # type: ignore[attr-defined]
+    chat_client_base.run_responses = [
+        _pte_function_call_response("1", "load_math"),
+        _pte_function_call_response("2", "factorial", '{"n": 5}'),
+        _pte_function_call_response("3", "factorial", '{"n": 3}'),
+        _pte_text_response(),
+    ]
+    monkey = pytest.MonkeyPatch()
+    monkey.setattr(client_cls, "_get_non_streaming_response", recording)
+    try:
+        await chat_client_base.get_response(
+            [Message(role="user", contents=["hi"])],
+            options={"tool_choice": "auto", "tools": [load_math]},
+        )
+    finally:
+        monkey.undo()
+
+    assert "factorial" in recorded[1]
+    assert "factorial" in recorded[2]
+
+
+async def test_add_tools_through_function_middleware(chat_client_base: SupportsChatGetResponse):
+    exec_counter = 0
+
+    class PassthroughMiddleware(FunctionMiddleware):
+        async def process(self, context: FunctionInvocationContext, call_next: Any) -> None:
+            await call_next()
+
+    @tool(name="factorial", approval_mode="never_require")
+    def factorial(n: int) -> int:
+        nonlocal exec_counter
+        exec_counter += 1
+        return 120
+
+    @tool(name="load_math", approval_mode="never_require")
+    def load_math(ctx: FunctionInvocationContext) -> str:
+        ctx.add_tools(factorial)
+        return "loaded"
+
+    chat_client_base.function_invocation_configuration["max_iterations"] = 3  # type: ignore[attr-defined]
+    chat_client_base.run_responses = [
+        _pte_function_call_response("1", "load_math"),
+        _pte_function_call_response("2", "factorial", '{"n": 5}'),
+        _pte_text_response(),
+    ]
+    await chat_client_base.get_response(
+        [Message(role="user", contents=["hi"])],
+        options={"tool_choice": "auto", "tools": [load_math]},
+        middleware=[PassthroughMiddleware()],
+    )
+    assert exec_counter == 1
+
+
+async def test_add_tools_with_approval_required_tool(chat_client_base: SupportsChatGetResponse):
+    @tool(name="secure_tool", approval_mode="always_require")
+    def secure_tool(value: str) -> str:
+        return f"secure: {value}"
+
+    @tool(name="load_secure", approval_mode="never_require")
+    def load_secure(ctx: FunctionInvocationContext) -> str:
+        ctx.add_tools(secure_tool)
+        return "loaded"
+
+    chat_client_base.function_invocation_configuration["max_iterations"] = 3  # type: ignore[attr-defined]
+    chat_client_base.run_responses = [
+        _pte_function_call_response("1", "load_secure"),
+        _pte_function_call_response("2", "secure_tool", '{"value": "x"}'),
+        _pte_text_response(),
+    ]
+    response = await chat_client_base.get_response(
+        [Message(role="user", contents=["hi"])],
+        options={"tool_choice": "auto", "tools": [load_secure]},
+    )
+    assert any(item.type == "function_approval_request" for msg in response.messages for item in msg.contents)
+
+
+async def test_add_tools_accepts_plain_callable(chat_client_base: SupportsChatGetResponse):
+    exec_counter = 0
+
+    def plain_factorial(n: int) -> int:
+        """Compute factorial."""
+        nonlocal exec_counter
+        exec_counter += 1
+        return 120
+
+    @tool(name="load_math", approval_mode="never_require")
+    def load_math(ctx: FunctionInvocationContext) -> str:
+        ctx.add_tools(plain_factorial)
+        return "loaded"
+
+    chat_client_base.function_invocation_configuration["max_iterations"] = 3  # type: ignore[attr-defined]
+    chat_client_base.run_responses = [
+        _pte_function_call_response("1", "load_math"),
+        _pte_function_call_response("2", "plain_factorial", '{"n": 5}'),
+        _pte_text_response(),
+    ]
+    await chat_client_base.get_response(
+        [Message(role="user", contents=["hi"])],
+        options={"tool_choice": "auto", "tools": [load_math]},
+    )
+    assert exec_counter == 1
+
+
+async def test_add_tools_streaming(chat_client_base: SupportsChatGetResponse):
+    exec_counter = 0
+
+    @tool(name="factorial", approval_mode="never_require")
+    def factorial(n: int) -> int:
+        nonlocal exec_counter
+        exec_counter += 1
+        return 120
+
+    @tool(name="load_math", approval_mode="never_require")
+    def load_math(ctx: FunctionInvocationContext) -> str:
+        ctx.add_tools(factorial)
+        return "loaded"
+
+    chat_client_base.function_invocation_configuration["max_iterations"] = 3  # type: ignore[attr-defined]
+    chat_client_base.streaming_responses = [
+        [
+            ChatResponseUpdate(
+                contents=[Content.from_function_call(call_id="1", name="load_math", arguments="{}")],
+                role="assistant",
+            )
+        ],
+        [
+            ChatResponseUpdate(
+                contents=[Content.from_function_call(call_id="2", name="factorial", arguments='{"n": 5}')],
+                role="assistant",
+            )
+        ],
+        [ChatResponseUpdate(contents=[Content.from_text("done")], role="assistant", finish_reason="stop")],
+    ]
+    async for _ in chat_client_base.get_response(
+        [Message(role="user", contents=["hi"])],
+        stream=True,
+        options={"tool_choice": "auto", "tools": [load_math]},
+    ):
+        pass
+    assert exec_counter == 1
+
+
+def test_add_tools_duplicate_same_object_is_noop():
+    @tool(name="dup", approval_mode="never_require")
+    def dup(x: int) -> int:
+        return x
+
+    ctx = FunctionInvocationContext(function=dup, arguments={}, tools=[dup])
+    ctx.add_tools(dup)
+    assert ctx.tools is not None
+    assert len(ctx.tools) == 1
+
+
+def test_add_tools_duplicate_name_different_object_raises():
+    @tool(name="dup", approval_mode="never_require")
+    def dup_a(x: int) -> int:
+        return x
+
+    @tool(name="dup", approval_mode="never_require")
+    def dup_b(x: int) -> int:
+        return x
+
+    ctx = FunctionInvocationContext(function=dup_a, arguments={}, tools=[dup_a])
+    with pytest.raises(ValueError):
+        ctx.add_tools(dup_b)
+
+
+def test_add_tools_batch_with_duplicate_is_atomic():
+    """A duplicate-name clash partway through a batch must leave the live list unchanged."""
+
+    @tool(name="existing", approval_mode="never_require")
+    def existing(x: int) -> int:
+        return x
+
+    @tool(name="fresh", approval_mode="never_require")
+    def fresh(x: int) -> int:
+        return x
+
+    @tool(name="existing", approval_mode="never_require")
+    def clashing(x: int) -> int:
+        return x
+
+    ctx = FunctionInvocationContext(function=existing, arguments={}, tools=[existing])
+    with pytest.raises(ValueError):
+        ctx.add_tools([fresh, clashing])
+    assert ctx.tools is not None
+    # The valid "fresh" tool must not have been committed before the clash raised.
+    assert ctx.tools == [existing]
+
+
+def test_remove_tools_by_name_and_object():
+    @tool(name="a", approval_mode="never_require")
+    def a(x: int) -> int:
+        return x
+
+    @tool(name="b", approval_mode="never_require")
+    def b(x: int) -> int:
+        return x
+
+    ctx = FunctionInvocationContext(function=a, arguments={}, tools=[a, b])
+    ctx.remove_tools("a")
+    assert ctx.tools is not None
+    assert [t.name for t in ctx.tools] == ["b"]
+    ctx.remove_tools(b)
+    assert ctx.tools == []
+
+
+def test_remove_tools_unknown_name_is_noop():
+    @tool(name="a", approval_mode="never_require")
+    def a(x: int) -> int:
+        return x
+
+    ctx = FunctionInvocationContext(function=a, arguments={}, tools=[a])
+    ctx.remove_tools("nonexistent")
+    assert ctx.tools is not None
+    assert [t.name for t in ctx.tools] == ["a"]
+
+
+def test_progressive_tools_helpers_raise_without_live_tools():
+    @tool(name="a", approval_mode="never_require")
+    def a(x: int) -> int:
+        return x
+
+    ctx = FunctionInvocationContext(function=a, arguments={})
+    assert ctx.tools is None
+    with pytest.raises(RuntimeError):
+        ctx.add_tools(a)
+    with pytest.raises(RuntimeError):
+        ctx.remove_tools("a")
+
+
+# endregion
diff --git a/python/samples/02-agents/tools/README.md b/python/samples/02-agents/tools/README.md
new file mode 100644
index 0000000000..ad07d86ecd
--- /dev/null
+++ b/python/samples/02-agents/tools/README.md
@@ -0,0 +1,75 @@
+# Tools
+
+Samples that show how to define, configure, and control function tools for an
+agent — from basic declarations to approvals, invocation limits, session
+injection, and dynamic (progressive) tool exposure.
+
+## Function tools
+
+| File | Demonstrates |
+|------|--------------|
+| [`function_tool_with_explicit_schema.py`](function_tool_with_explicit_schema.py) | Defining a tool with an explicit JSON schema. |
+| [`function_tool_declaration_only.py`](function_tool_declaration_only.py) | A declaration-only tool (schema without a local implementation). |
+| [`function_tool_with_kwargs.py`](function_tool_with_kwargs.py) | Passing extra keyword arguments into a tool. |
+| [`function_tool_from_dict_with_dependency_injection.py`](function_tool_from_dict_with_dependency_injection.py) | Dependency injection into a tool defined from a dict. |
+| [`function_tool_with_session_injection.py`](function_tool_with_session_injection.py) | Injecting the session into a tool. |
+| [`tool_in_class.py`](tool_in_class.py) | Using a method on a class as a tool. |
+| [`agent_as_tool_with_session_propagation.py`](agent_as_tool_with_session_propagation.py) | Exposing an agent as a tool with session propagation. |
+
+## Approvals & invocation control
+
+| File | Demonstrates |
+|------|--------------|
+| [`function_tool_with_approval.py`](function_tool_with_approval.py) | Requiring human approval before a tool runs. |
+| [`function_tool_with_approval_and_sessions.py`](function_tool_with_approval_and_sessions.py) | Tool approvals combined with sessions. |
+| [`function_invocation_configuration.py`](function_invocation_configuration.py) | Configuring function-invocation settings (e.g. max iterations). |
+| [`control_total_tool_executions.py`](control_total_tool_executions.py) | All the ways to cap how many times tools run. |
+| [`function_tool_with_max_invocations.py`](function_tool_with_max_invocations.py) | Limiting the number of invocations per tool. |
+| [`function_tool_with_max_exceptions.py`](function_tool_with_max_exceptions.py) | Limiting the number of exceptions a tool may raise. |
+| [`function_tool_recover_from_failures.py`](function_tool_recover_from_failures.py) | Returning errors so the agent can recover from tool failures. |
+
+## Progressive tool exposure (dynamic loading)
+
+| File | Demonstrates |
+|------|--------------|
+| [`dynamic_tool_exposure.py`](dynamic_tool_exposure.py) | A "loader" tool that adds more tools at runtime via `FunctionInvocationContext`. |
+
+Frontloading a model with hundreds of tools hurts tool-selection accuracy,
+bloats context, and raises cost. Instead, start with a small set of loader
+tools and let the model pull in more on demand. Inside a tool, the injected
+`ctx: FunctionInvocationContext` exposes a live `ctx.tools` list plus
+`ctx.add_tools(...)` / `ctx.remove_tools(...)` helpers. Tools added or removed
+take effect on the **next iteration** of the function-calling loop.
+
+> [!NOTE]
+> Progressive tool exposure applies to the standard function-calling loop. It
+> does **not** apply to CodeAct providers (`agent-framework-monty`,
+> `agent-framework-hyperlight`). In CodeAct the model only sees a single
+> `execute_code` tool, and host tools are exposed *inside the sandbox* as typed
+> Python functions rather than as model tool-schemas. Host tools there are
+> invoked without a `FunctionInvocationContext`, so `ctx.add_tools()` is not
+> available; the helpers fail fast with a clear `RuntimeError` instead of
+> silently doing nothing. To change a CodeAct agent's tool set, use the
+> provider's own `add_tools` / `remove_tool` / `clear_tools` methods (applied
+> between runs). The recommended provider-driven path for Monty and Hyperlight
+> is shown in [`../context_providers/code_act/`](../context_providers/code_act/)
+> ([`code_act.py`](../context_providers/code_act/code_act.py) for Hyperlight,
+> [`monty_code_act.py`](../context_providers/code_act/monty_code_act.py) for
+> Monty).
+
+## Local shell & code interpreters
+
+| Path | Demonstrates |
+|------|--------------|
+| [`local_shell_with_allowlist.py`](local_shell_with_allowlist.py) | `LocalShellTool` restricted by a strict command allow-list. |
+| [`local_shell_with_environment_provider.py`](local_shell_with_environment_provider.py) | `LocalShellTool` wired with a `ShellEnvironmentProvider`. |
+| [`local_code_interpreter/`](local_code_interpreter/) | Hyperlight-backed sandboxed code interpreter (standalone tool — *extra* pattern). |
+| [`monty_code_interpreter/`](monty_code_interpreter/) | Monty-backed sandboxed code interpreter (standalone tool — *extra* pattern). |
+
+> [!TIP]
+> The `local_code_interpreter/` and `monty_code_interpreter/` samples show the
+> standalone-tool wiring and are provided as *extra* reference. For most
+> Monty/Hyperlight use cases the **recommended** path is the provider-driven
+> CodeAct setup in
+> [`../context_providers/code_act/`](../context_providers/code_act/), which adds
+> dynamic tool / capability management.
diff --git a/python/samples/02-agents/tools/dynamic_tool_exposure.py b/python/samples/02-agents/tools/dynamic_tool_exposure.py
new file mode 100644
index 0000000000..2886399486
--- /dev/null
+++ b/python/samples/02-agents/tools/dynamic_tool_exposure.py
@@ -0,0 +1,79 @@
+# Copyright (c) Microsoft. All rights reserved.
+
+import asyncio
+from typing import Annotated
+
+from agent_framework import Agent, FunctionInvocationContext, tool
+from agent_framework.openai import OpenAIChatClient
+from dotenv import load_dotenv
+from pydantic import Field
+
+# Load environment variables from .env file
+load_dotenv()
+
+"""
+Dynamic Tool Exposure (Progressive Tool Loading) Example
+
+This example demonstrates "progressive tool exposure": a tool that adds more tools to
+the agent at runtime, in the same run, via ``FunctionInvocationContext``.
+
+Frontloading a model with hundreds of tools hurts tool-selection accuracy, bloats
+context, and raises cost. Instead, you can start with a small set of "loader" tools and
+let the model pull in additional tools on demand. Tools added with ``ctx.add_tools(...)``
+(or removed with ``ctx.remove_tools(...)``) become available to the model on the next
+iteration of the function-calling loop.
+"""
+
+
+# These math tools are not registered on the agent up front. They are added on demand by
+# the ``load_math_tools`` tool below, and only then become callable by the model.
+@tool(approval_mode="never_require")
+def factorial(n: Annotated[int, Field(description="A non-negative integer.")]) -> str:
+    """Compute the factorial of n."""
+    if n < 0:
+        return "Error: n must be a non-negative integer."
+    result = 1
+    for value in range(2, n + 1):
+        result *= value
+    return f"{n}! = {result}"
+
+
+@tool(approval_mode="never_require")
+def fibonacci(n: Annotated[int, Field(description="The 0-based index in the Fibonacci sequence.")]) -> str:
+    """Compute the n-th Fibonacci number."""
+    if n < 0:
+        return "Error: n must be a non-negative integer."
+    a, b = 0, 1
+    for _ in range(n):
+        a, b = b, a + b
+    return f"fib({n}) = {a}"
+
+
+# The only tool the agent starts with. When called, it exposes the math tools above so the
+# model can use them on the next turn. Note the ``ctx`` parameter is injected by the
+# framework and is not visible to the model.
+@tool(approval_mode="never_require")
+def load_math_tools(ctx: FunctionInvocationContext) -> str:
+    """Load additional math tools (factorial, fibonacci) so they can be used."""
+    ctx.add_tools([factorial, fibonacci])
+    return "Loaded math tools: factorial, fibonacci. You can now call them."
+
+
+async def main() -> None:
+    agent = Agent(
+        client=OpenAIChatClient(),
+        name="MathAgent",
+        instructions=(
+            "You are a math assistant. If you need math capabilities that are not yet "
+            "available, call load_math_tools first, then use the newly available tools."
+        ),
+        tools=[load_math_tools],
+    )
+
+    # The agent starts with only ``load_math_tools``. To answer the question it must first
+    # load the math tools, then call ``factorial`` on the next iteration.
+    print(f"Agent: {await agent.run('What is 5 factorial?')}")
+
+
+if __name__ == "__main__":
+    asyncio.run(main())
diff --git a/python/uv.lock b/python/uv.lock
index 1f816411e3..676413c1cc 100644
--- a/python/uv.lock
+++ b/python/uv.lock
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