Add changelog for v0.1.30 (#642)

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: github-actions[bot]

CHANGELOG.md

@@ -4,3 +4,53 @@ All notable changes to the Copilot SDK are documented in this file.
 
 This changelog is automatically generated by an AI agent when stable releases are published.
 See [GitHub Releases](https://github.com/github/copilot-sdk/releases) for the full list.
+
+## [v0.1.30](https://github.com/github/copilot-sdk/releases/tag/v0.1.30) (2026-03-03)
+
+### Feature: support overriding built-in tools
+
+Applications can now override built-in tools such as `grep`, `edit_file`, or `read_file`. To do this, register a custom tool with the same name and set the override flag. Without the flag, the runtime will return an error if the name clashes with a built-in. ([#636](https://github.com/github/copilot-sdk/pull/636))
+
+```ts
+import { defineTool } from "@github/copilot-sdk";
+
+const session = await client.createSession({
+  tools: [defineTool("grep", {
+    overridesBuiltInTool: true,
+    handler: async (params) => `CUSTOM_GREP_RESULT: ${params.query}`,
+  })],
+  onPermissionRequest: approveAll,
+});
+```
+
+```cs
+var grep = AIFunctionFactory.Create(
+    ([Description("Search query")] string query) => $"CUSTOM_GREP_RESULT: {query}",
+    "grep",
+    "Custom grep implementation",
+    new AIFunctionFactoryOptions
+    {
+        AdditionalProperties = new ReadOnlyDictionary<string, object?>(
+            new Dictionary<string, object?> { ["is_override"] = true })
+    });
+```
+
+### Feature: simpler API for changing model mid-session
+
+While `session.rpc.model.switchTo()` already worked, there is now a convenience method directly on the session object. ([#621](https://github.com/github/copilot-sdk/pull/621))
+
+- TypeScript: `await session.setModel("gpt-4.1")`
+- C#: `await session.SetModelAsync("gpt-4.1")`
+- Python: `await session.set_model("gpt-4.1")`
+- Go: `err := session.SetModel(ctx, "gpt-4.1")`
+
+### Other changes
+
+- improvement: **[C#]** use event delegate for thread-safe, insertion-ordered event handler dispatch ([#624](https://github.com/github/copilot-sdk/pull/624))
+- improvement: **[C#]** deduplicate `OnDisposeCall` and improve implementation ([#626](https://github.com/github/copilot-sdk/pull/626))
+- improvement: **[C#]** remove unnecessary `SemaphoreSlim` locks for handler fields ([#625](https://github.com/github/copilot-sdk/pull/625))
+- bugfix: **[Python]** correct `PermissionHandler.approve_all` type annotations ([#618](https://github.com/github/copilot-sdk/pull/618))
+
+### New contributors
+
+- @giulio-leone made their first contribution in [#618](https://github.com/github/copilot-sdk/pull/618)