Docs: Add documentation for model steering (experimental). (#21154)

docs/cli/model-steering.md

@@ -0,0 +1,79 @@
+# Model steering (experimental)
+
+Model steering lets you provide real-time guidance and feedback to Gemini CLI
+while it is actively executing a task. This lets you correct course, add missing
+context, or skip unnecessary steps without having to stop and restart the agent.
+
+> **Note:** This is a preview feature under active development. Preview features
+> may only be available in the **Preview** channel or may need to be enabled
+> under `/settings`.
+
+Model steering is particularly useful during complex [Plan Mode](./plan-mode.md)
+workflows or long-running subagent executions where you want to ensure the agent
+stays on the right track.
+
+## Enabling model steering
+
+Model steering is an experimental feature and is disabled by default. You can
+enable it using the `/settings` command or by updating your `settings.json`
+file.
+
+1.  Type `/settings` in the Gemini CLI.
+2.  Search for **Model Steering**.
+3.  Set the value to **true**.
+
+Alternatively, add the following to your `settings.json`:
+
+```json
+{
+  "experimental": {
+    "modelSteering": true
+  }
+}
+```
+
+## Using model steering
+
+When model steering is enabled, Gemini CLI treats any text you type while the
+agent is working as a steering hint.
+
+1.  Start a task (for example, "Refactor the database service").
+2.  While the agent is working (the spinner is visible), type your feedback in
+    the input box.
+3.  Press **Enter**.
+
+Gemini CLI acknowledges your hint with a brief message and injects it directly
+into the model's context for the very next turn. The model then re-evaluates its
+current plan and adjusts its actions accordingly.
+
+### Common use cases
+
+You can use steering hints to guide the model in several ways:
+
+- **Correcting a path:** "Actually, the utilities are in `src/common/utils`."
+- **Skipping a step:** "Skip the unit tests for now and just focus on the
+  implementation."
+- **Adding context:** "The `User` type is defined in `packages/core/types.ts`."
+- **Redirecting the effort:** "Stop searching the codebase and start drafting
+  the plan now."
+- **Handling ambiguity:** "Use the existing `Logger` class instead of creating a
+  new one."
+
+## How it works
+
+When you submit a steering hint, Gemini CLI performs the following actions:
+
+1.  **Immediate acknowledgment:** It uses a small, fast model to generate a
+    one-sentence acknowledgment so you know your hint was received.
+2.  **Context injection:** It prepends an internal instruction to your hint that
+    tells the main agent to:
+    - Re-evaluate the active plan.
+    - Classify the update (for example, as a new task or extra context).
+    - Apply minimal-diff changes to affected tasks.
+3.  **Real-time update:** The hint is delivered to the agent at the beginning of
+    its next turn, ensuring the most immediate course correction possible.
+
+## Next steps
+
+- Tackle complex tasks with [Plan Mode](./plan-mode.md).
+- Build custom [Agent Skills](./skills.md).

docs/cli/tutorials/plan-mode-steering.md

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+# Use Plan Mode with model steering for complex tasks
+
+Architecting a complex solution requires precision. By combining Plan Mode's
+structured environment with model steering's real-time feedback, you can guide
+Gemini CLI through the research and design phases to ensure the final
+implementation plan is exactly what you need.
+
+> **Note:** This is a preview feature under active development. Preview features
+> may only be available in the **Preview** channel or may need to be enabled
+> under `/settings`.
+
+## Prerequisites
+
+- Gemini CLI installed and authenticated.
+- [Plan Mode](../plan-mode.md) enabled in your settings.
+- [Model steering](../model-steering.md) enabled in your settings.
+
+## Why combine Plan Mode and model steering?
+
+[Plan Mode](../plan-mode.md) typically follows a linear path: research, propose,
+and draft. Adding model steering lets you:
+
+1.  **Direct the research:** Correct the agent if it's looking in the wrong
+    directory or missing a key dependency.
+2.  **Iterate mid-draft:** Suggest a different architectural pattern while the
+    agent is still writing the plan.
+3.  **Speed up the loop:** Avoid waiting for a full research turn to finish
+    before providing critical context.
+
+## Step 1: Start a complex task
+
+Enter Plan Mode and start a task that requires research.
+
+**Prompt:** `/plan I want to implement a new notification service using Redis.`
+
+Gemini CLI enters Plan Mode and starts researching your existing codebase to
+identify where the new service should live.
+
+## Step 2: Steer the research phase
+
+As you see the agent calling tools like `list_directory` or `grep_search`, you
+might realize it's missing the relevant context.
+
+**Action:** While the spinner is active, type your hint:
+`"Don't forget to check packages/common/queues for the existing Redis config."`
+
+**Result:** Gemini CLI acknowledges your hint and immediately incorporates it
+into its research. You'll see it start exploring the directory you suggested in
+its very next turn.
+
+## Step 3: Refine the design mid-turn
+
+After research, the agent starts drafting the implementation plan. If you notice
+it's proposing a design that doesn't align with your goals, steer it.
+
+**Action:** Type:
+`"Actually, let's use a Publisher/Subscriber pattern instead of a simple queue for this service."`
+
+**Result:** The agent stops drafting the current version of the plan,
+re-evaluates the design based on your feedback, and starts a new draft that uses
+the Pub/Sub pattern.
+
+## Step 4: Approve and implement
+
+Once the agent has used your hints to craft the perfect plan, review the final
+`.md` file.
+
+**Action:** Type: `"Looks perfect. Let's start the implementation."`
+
+Gemini CLI exits Plan Mode and transitions to the implementation phase. Because
+the plan was refined in real-time with your feedback, the agent can now execute
+each step with higher confidence and fewer errors.
+
+## Tips for effective steering
+
+- **Be specific:** Instead of "do it differently," try "use the existing
+  `Logger` class in `src/utils`."
+- **Steer early:** Providing feedback during the research phase is more
+  efficient than waiting for the final plan to be drafted.
+- **Use for context:** Steering is a great way to provide knowledge that might
+  not be obvious from reading the code (e.g., "We are planning to deprecate this
+  module next month").
+
+## Next steps
+
+- Explore [Agent Skills](../skills.md) to add specialized expertise to your
+  planning turns.
+- See the [Model steering reference](../model-steering.md) for technical
+  details.

docs/sidebar.json

@@ -47,6 +47,11 @@
             "label": "Plan tasks with todos",
             "slug": "docs/cli/tutorials/task-planning"
           },
+          {
+            "label": "Use Plan Mode with model steering",
+            "badge": "🔬",
+            "slug": "docs/cli/tutorials/plan-mode-steering"
+          },
           {
             "label": "Web search and fetch",
             "slug": "docs/cli/tutorials/web-tools"
@@ -106,6 +111,11 @@
           { "label": "MCP servers", "slug": "docs/tools/mcp-server" },
           { "label": "Model routing", "slug": "docs/cli/model-routing" },
           { "label": "Model selection", "slug": "docs/cli/model" },
+          {
+            "label": "Model steering",
+            "badge": "🔬",
+            "slug": "docs/cli/model-steering"
+          },
           {
             "label": "Notifications",
             "badge": "🔬",