feat: add configuration for model, mode, and thought level

docs/agent-sessions.mdx

@@ -82,6 +82,49 @@ if (sessions.items.length > 0) {
 }
 ```
 
+## Configure model, mode, and thought level
+
+Set the model, mode, or thought level on a session at creation time or after:
+
+```ts
+// At creation time
+const session = await sdk.createSession({
+  agent: "codex",
+  model: "gpt-5.3-codex",
+  mode: "plan",
+  thoughtLevel: "high",
+});
+```
+
+```ts
+// After creation
+await session.setModel("gpt-5.2-codex");
+await session.setMode("build");
+await session.setThoughtLevel("medium");
+```
+
+Query available modes:
+
+```ts
+const modes = await session.getModes();
+console.log(modes?.currentModeId, modes?.availableModes);
+```
+
+### Advanced config options
+
+For config options beyond model, mode, and thought level, use `getConfigOptions` to discover what the agent supports and `setConfigOption` to set any option by ID:
+
+```ts
+const options = await session.getConfigOptions();
+for (const opt of options) {
+  console.log(opt.id, opt.category, opt.type);
+}
+```
+
+```ts
+await session.setConfigOption("some-agent-option", "value");
+```
+
 ## Destroy a session
 
 ```ts