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content/labs/lab-5-api-and-harnesses.md

@@ -0,0 +1,360 @@
+---
+order: 5
+title: Lab 5 - API & Harnesses
+description: Generate an Open WebUI API key, connect one of three coding harnesses, and build a small Zork-style game.
+---
+
+<!-- breakout-style: instruction-rails -->
+<!-- step-style: underline -->
+<!-- objective-style: divider -->
+
+# Lab 5 - API & Harnesses
+
+In this lab, we will:
+
+- Generate a personal API key inside Open WebUI
+- Install one of three coding harnesses
+- Configure that harness to talk to Open WebUI as the backend
+- Use the harness to build a small Zork-style game
+
+<div class="lab-callout lab-callout--info">
+  <strong>Lab Flow Guide</strong><br />
+  This lab stays on a single high-level track, but Objectives 2 and 3 branch into three harness paths.<br />
+  Pick one harness, complete its branch, then rejoin the common Zork objective at the end.
+</div>
+
+To start this lab, one web service has been preconfigured:
+
+- Open WebUI - http://<IP>:8080
+
+## Objective 1 Execute: Generate an Open WebUI API Key
+
+Before we install any harness, we need a key that lets the harness call the same model backend exposed through Open WebUI.
+
+### Execute: Sign in to Open WebUI
+
+1. Navigate to `http://<YOUR STUDENT IP>:8080`.
+2. Sign in with the same account you used in Lab 4, or the credentials supplied by your instructor.
+3. Confirm that you can reach the normal chat screen before continuing.
+
+### Execute: Create a personal access token
+
+According to the Open WebUI reference docs, API keys are created from **Settings -> Account** and authenticate with the same permissions as the user who created them.
+
+1. Click your avatar in the lower-left corner.
+
+<figure style="text-align: center;">
+  <a href="https://i.imgur.com/oZuZwWQ.png" target="_blank">
+    <img 
+      src="https://i.imgur.com/oZuZwWQ.png" 
+      style="width: 50%; display: block; margin-left: auto; margin-right: auto; border: 5px solid black;">
+  </a>
+  <figcaption style="margin-top: 8px; font-size: 1.1em;">
+    User Settings
+  </figcaption>
+</figure>
+<br>
+
+2. Open **Settings**.
+3. Open **Account**.
+4. Locate the **API Keys** section.
+
+<figure style="text-align: center;">
+  <a href="https://i.imgur.com/oDe6cpE.png" target="_blank">
+    <img 
+      src="https://i.imgur.com/oDe6cpE.png" 
+      style="width: 50%; display: block; margin-left: auto; margin-right: auto; border: 5px solid black;">
+  </a>
+  <figcaption style="margin-top: 8px; font-size: 1.1em;">
+    API Key
+  </figcaption>
+</figure>
+<br>
+
+6. Copy the key immediately and store it somewhere safe for the duration of the lab.
+
+<div class="lab-callout lab-callout--warning">
+  <strong>If you do not see API Keys:</strong> Open WebUI requires the feature to be enabled globally, and your user account needs permission to generate keys. Ask your instructor for help before continuing.
+</div>
+
+### Execute: Sanity-check the key from the terminal
+
+Run a quick authenticated request against the Open WebUI model list endpoint. You should receive JSON back instead of an authentication error.
+
+```bash
+curl http://<YOUR STUDENT IP>:8080/api/models \
+  -H "Authorization: Bearer YOUR_OPENWEBUI_API_KEY"
+```
+
+If this request works, your harness will use the same key for later steps.
+
+---
+
+## Objective 2 Execute: Choose and Install a Harness
+
+All three branches ultimately talk to the same Open WebUI backend. The difference is the user interface and configuration style for each harness.
+
+<div class="lab-harness-chooser" role="group" aria-label="Harness installation paths">
+  <button type="button" class="lab-harness-card" data-harness-choice="opencode" aria-pressed="false">
+    <span class="lab-harness-card__tag">Path A</span>
+    <strong>OpenCode</strong>
+    <span>Terminal-first coding agent</span>
+  </button>
+  <button type="button" class="lab-harness-card" data-harness-choice="kilocode" aria-pressed="false">
+    <span class="lab-harness-card__tag">Path B</span>
+    <strong>Kilo Code VS Code</strong>
+    <span>Editor-driven coding assistant</span>
+  </button>
+  <button type="button" class="lab-harness-card" data-harness-choice="droid" aria-pressed="false">
+    <span class="lab-harness-card__tag">Path C</span>
+    <strong>Factory Droid</strong>
+    <span>Advanced CLI harness with powerful Spec Driven Development (Missions)</span>
+  </button>
+</div>
+
+<p>Select a path to reveal that harness's instructions throughout the rest of the lab. Select the same card again if you want to hide the harness-specific instructions and return to the shared overview.</p>
+
+### Execute: Install the harness you want to use
+
+<section class="lab-harness-branch" id="opencode-install" data-harness-branch="opencode">
+  <p class="lab-harness-branch__eyebrow">Path A</p>
+  <h3>Install OpenCode</h3>
+  <p>OpenCode is a terminal-native coding agent. Its official docs recommend either the install script or the npm package.</p>
+  <pre><code class="language-bash">curl -fsSL https://opencode.ai/install | bash
+opencode --version</code></pre>
+  <p>If you prefer npm and already have Node.js installed:</p>
+  <pre><code class="language-bash">npm install -g opencode-ai
+opencode --version</code></pre>
+  <p>Once installed, stay in the terminal. We will configure OpenCode in Objective 3.</p>
+</section>
+
+<section class="lab-harness-branch" id="kilocode-install" data-harness-branch="kilocode">
+  <p class="lab-harness-branch__eyebrow">Path B</p>
+  <h3>Install Kilo Code for VS Code</h3>
+  <p>Kilo Code is primarily used through the editor UI. For this Linux-first lab flow, use VS Code on the student workstation and install the extension from the marketplace.</p>
+  <ol>
+    <li>Open <strong>VS Code</strong>.</li>
+    <li>Open the <strong>Extensions</strong> view.</li>
+    <li>Search for <strong>Kilo Code</strong>.</li>
+    <li>Click <strong>Install</strong>.</li>
+    <li>Reload VS Code if prompted.</li>
+    <li>Open the project folder you want to work in before moving to Objective 3.</li>
+  </ol>
+  <div class="lab-callout lab-callout--info">
+    <strong>Tip:</strong> Kilo Code supports several providers and local-model options. In this lab, we will use its <strong>OpenAI Compatible</strong> provider flow so it can target Open WebUI.
+  </div>
+</section>
+
+<section class="lab-harness-branch" id="droid-install" data-harness-branch="droid">
+  <p class="lab-harness-branch__eyebrow">Path C</p>
+  <h3>Install Factory Droid</h3>
+  <p>Factory's Droid harness runs in the terminal and supports BYOK custom models through Factory configuration files.</p>
+  <pre><code class="language-bash">curl -fsSL https://app.factory.ai/cli | sh
+droid --version</code></pre>
+  <p>If the shell needs to be reloaded after install, open a fresh terminal and rerun <code>droid --version</code>.</p>
+</section>
+
+---
+
+## Objective 3 Execute: Configure Your Harness for Open WebUI
+
+For all three harnesses, the common backend values are:
+
+- `Base URL` - `http://<YOUR STUDENT IP>:8080/api`
+- `API Key` - `YOUR_OPENWEBUI_API_KEY`
+- `Model ID` - Any model ID returned by Open WebUI, such as `qwen3.5:4b`
+
+The shared idea is simple: your harness sends requests to Open WebUI's authenticated API endpoints instead of directly to a cloud provider.
+
+### Execute: Apply the configuration for your chosen harness
+
+<section class="lab-harness-branch" id="opencode-config" data-harness-branch="opencode">
+  <p class="lab-harness-branch__eyebrow">Path A</p>
+  <h3>Configure OpenCode</h3>
+  <p>OpenCode supports OpenAI-compatible providers through its JSON config. Create either a project-local <code>opencode.json</code> file or a global config under <code>~/.config/opencode/opencode.json</code>.</p>
+  
+  <p>It can also be easier to start opencode once, and exit with /exit.  Use the following example to help structure your opencode.json file.  
+  <pre><code class="language-json">{
+  "$schema": "https://opencode.ai/config.json",
+  "provider": {
+    "openwebui": {
+      "name": "Open WebUI",
+      "options": {
+        "baseURL": "http://&lt;YOUR STUDENT IP&gt;:8080/api",
+      },
+      "models": {
+        "qwen3.5:4b": {
+          "name": "Qwen 3.5 4B"
+        }
+      }
+    }
+  },
+  "model": "openwebui/qwen3.5:4b"
+}</code></pre>
+  <p>After saving the config, you can login with <code>opencode auth login: </code></p>
+<figure style="text-align: center;">
+  <a href="https://i.imgur.com/wLPJOpz.png" target="_blank">
+    <img 
+      src="https://i.imgur.com/wLPJOpz.png" 
+      style="width: 50%; display: block; margin-left: auto; margin-right: auto; border: 5px solid black;">
+  </a>
+  <figcaption style="margin-top: 8px; font-size: 1.1em;">
+    opencode auth login
+  </figcaption>
+</figure>
+  <p>After logging in, start OpenCode from your project directory:</p>
+  <pre><code class="language-bash">cd /path/to/your/project
+opencode</code></pre>
+</section>
+
+<section class="lab-harness-branch" id="kilocode-config" data-harness-branch="kilocode">
+  <p class="lab-harness-branch__eyebrow">Path B</p>
+  <h3>Configure Kilo Code in VS Code</h3>
+  <p>Kilo Code's documented workflow is provider-driven through the extension settings UI. Use the following values when creating or editing your provider profile.</p>
+  <ul>
+    <li><code>API Provider</code> - <code>OpenAI Compatible</code></li>
+    <li><code>OpenAI Base URL</code> - <code>http://&lt;YOUR STUDENT IP&gt;:8080/api</code></li>
+    <li><code>API Key</code> - <code>YOUR_OPENWEBUI_API_KEY</code></li>
+    <li><code>Model ID</code> - <code>qwen3.5:4b</code> or another model exposed by Open WebUI</li>
+    <li><code>Approval Mode</code> - Leave the safer default enabled for your first run</li>
+  </ul>
+  <br>
+  <ol>
+    <li>Open the Kilo Code panel in VS Code.</li>
+    <li>Open its provider or API settings.</li>
+    <li>Select <strong>OpenAI Compatible</strong> as the provider.</li>
+    <li>Paste in the base URL and API key values above.</li>
+    <li>Pick a model ID that exists in Open WebUI.</li>
+    <li>Start a new task to verify Kilo Code can connect successfully.</li>
+  </ol>
+
+  <figure style="text-align: center;">
+  <a href="https://i.imgur.com/Q61IK03.png" target="_blank">
+    <img 
+      src="https://i.imgur.com/Q61IK03.png" 
+      style="width: 50%; display: block; margin-left: auto; margin-right: auto; border: 5px solid black;">
+  </a>
+  <figcaption style="margin-top: 8px; font-size: 1.1em;">
+    Kilo Code Settings
+  </figcaption>
+</figure>
+<br>
+
+<figure style="text-align: center;">
+  <a href="https://i.imgur.com/vZV9qWW.png" target="_blank">
+    <img 
+      src="https://i.imgur.com/vZV9qWW.png" 
+      style="width: 50%; display: block; margin-left: auto; margin-right: auto; border: 5px solid black;">
+  </a>
+  <figcaption style="margin-top: 8px; font-size: 1.1em;">
+    Provider Settings
+  </figcaption>
+</figure>
+<br>
+
+  <div class="lab-callout lab-callout--info">
+    <strong>Tip:</strong> If model discovery fails, go back to your terminal and rerun the <code>curl /api/models</code> check from Objective 1. The harness and the curl command use the same authentication path.
+  </div>
+</section>
+
+<section class="lab-harness-branch" id="droid-config" data-harness-branch="droid">
+  <p class="lab-harness-branch__eyebrow">Path C</p>
+  <h3>Configure Factory Droid</h3>
+  <p>Factory's BYOK documentation supports custom model entries in <code>~/.factory/config.json</code>. Because Open WebUI exposes a chat-completions-compatible API, use the <code>generic-chat-completion-api</code> provider type.</p>
+  <pre><code class="language-json">{
+  "custom_models": [
+    {
+      "model_display_name": "Open WebUI - Qwen 3.5 4B",
+      "model": "qwen3.5:4b",
+      "base_url": "http://&lt;YOUR STUDENT IP&gt;:8080/api",
+      "api_key": "YOUR_OPENWEBUI_API_KEY",
+      "provider": "generic-chat-completion-api",
+      "max_tokens": 4096
+    }
+  ]
+}</code></pre>
+  <p>After saving the config:</p>
+  <ol>
+    <li>Launch <code>droid</code>.</li>
+    <li>Open the model selector with <code>/model</code>.</li>
+    <li>Choose your new custom Open WebUI model entry.</li>
+    <li>Start a new session in the target project directory.</li>
+  </ol>
+</section>
+
+---
+
+## Objective 4 Execute: Build a Tiny Zork Clone
+
+At this point, all three branches reconnect. The rest of the lab is the same no matter which harness you chose.
+
+### Execute: Start your harness session
+
+<div class="lab-harness-chooser" aria-label="Harness launch reminders">
+  <div class="lab-harness-card" data-harness-branch="opencode">
+    <span class="lab-harness-card__tag">OpenCode</span>
+    <strong>Terminal Session</strong>
+    <span>Run <code>opencode</code> inside the project directory.</span>
+  </div>
+  <div class="lab-harness-card" data-harness-branch="kilocode">
+    <span class="lab-harness-card__tag">Kilo Code</span>
+    <strong>VS Code Task</strong>
+    <span>Open the repo folder and start a new Kilo Code task from the side panel.</span>
+  </div>
+  <div class="lab-harness-card" data-harness-branch="droid">
+    <span class="lab-harness-card__tag">Factory Droid</span>
+    <strong>CLI Session</strong>
+    <span>Run <code>droid</code>, type "/mission", and ensure you've selected your custom model for each phase.</span>
+  </div>
+</div>
+
+### Execute: Give the harness a shared prompt
+
+Use the following prompt as your starting task.  Ensure you are in **Plan** mode (or a Droid Mission):
+
+```text
+You are helping me build a tiny terminal adventure game in Python.
+
+Create a Zork-style prototype with:
+- at least 5 connected rooms
+- movement commands like north, south, east, and west
+- a simple inventory system
+- one collectible key
+- one locked room or door
+- a short win condition
+
+Use clean, readable Python and keep everything runnable from the terminal.
+After writing the code, explain how to launch the game and what commands the player can use.
+```
+
+### Explore: Execute the result
+
+Once your harness produces the first version, keep pushing it with follow-up prompts:
+
+1. Ask it to add a help command.
+2. Ask it to improve room descriptions.
+3. Ask it to prevent impossible movement.
+4. Ask it to add one extra puzzle or hidden interaction.
+
+Alternatively, reflect if you'd instead focused on using a Spec Driven development flow.  How might the AI model perform more accurately as the requirements become more complicated?
+
+### Checkpoint: What success can look like
+
+Before finishing the lab, confirm that your game can:
+
+1. Start from the terminal without errors.
+2. Accept basic movement commands.
+3. Let the player pick up at least one item.
+4. Use that item to unlock progress.
+5. Reach a clear win state.
+
+## Conclusion
+
+In this lab, we:
+
+1. Generated an Open WebUI API key.
+2. Installed a harness of our choice.
+3. Connected that harness back to Open WebUI.
+4. Used the harness to build a small but complete coding exercise.
+
+You should now have a repeatable pattern for testing other harnesses against the same Open WebUI deployment. We've also shown how a full local stack can work, from model selection, inference, harness installation, to real coding work.

content/labs/lab-6-embedding-and-chunking.md

@@ -1,6 +1,6 @@
 ---
-order: 5
+order: 6
-title: Lab 5 - Embedding and Chunking
+title: Lab 6 - Embedding and Chunking
 description: Explore chunking strategies and embeddings, then connect them to retrieval workflows.
 ---
 
@@ -8,7 +8,7 @@ description: Explore chunking strategies and embeddings, then connect them to re
 <!-- step-style: underline -->
 <!-- objective-style: divider -->
 
-# Lab 5 - Embedding and Chunking
+# Lab 6 - Embedding and Chunking
 
 In this lab, we will:
 

content/labs/lab-7-dataset-generation-and-fine-tuning.md

@@ -1,6 +1,6 @@
 ---
-order: 6
+order: 7
-title: Lab 6 - Dataset Generation and Fine Tuning
+title: Lab 7 - Dataset Generation and Fine Tuning
 description: Review dataset options, generate examples with Kiln.ai, and fine-tune a model in Unsloth.
 ---
 
@@ -8,7 +8,7 @@ description: Review dataset options, generate examples with Kiln.ai, and fine-tu
 <!-- step-style: underline -->
 <!-- objective-style: divider -->
 
-# Lab 6 - Dataset Generation and Fine Tuning
+# Lab 7 - Dataset Generation and Fine Tuning
 
 In this lab, we will:
 

content/labs/lab-8-evaluation-and-red-teaming.md

@@ -1,6 +1,6 @@
 ---
-order: 7
+order: 8
-title: Lab 7 - Evaluation and Red Teaming
+title: Lab 8 - Evaluation and Red Teaming
 description: Probe model defenses manually and with Promptfoo to evaluate security controls.
 ---
 
@@ -8,7 +8,7 @@ description: Probe model defenses manually and with Promptfoo to evaluate securi
 <!-- step-style: underline -->
 <!-- objective-style: divider -->
 
-# Lab 7 - Evaluation and Red Teaming
+# Lab 8 - Evaluation and Red Teaming
 
 In this lab, we will:
 
@@ -97,7 +97,7 @@ Promptfoo is available on our lab machine at http://<YOUR STUDENT IP>:15500. We
 Promptfoo is designed to be approachable for both beginners and practitioners. Its wizard guides you through configuring the target, selecting datasets and mutation strategies, and tracking execution.
 
 <div class="lab-callout lab-callout--info">
-  <strong>Tip:</strong> Although the Promptfoo WebUI is convenient, it hides a critical configuration option for this lab inside the YAML file. Please use the provided configuration file: [lab-7-evaluation-and-red-teaming/promptfoo.yaml](content/labs/lab-7-evaluation-and-red-teaming/promptfoo.yaml). Upload it with the <strong>Load Config</strong> button in the lower-left corner, then proceed with the following screenshot steps.
+  <strong>Tip:</strong> Although the Promptfoo WebUI is convenient, it hides a critical configuration option for this lab inside the YAML file. Please use the provided configuration file: [lab-8-evaluation-and-red-teaming/promptfoo.yaml](/labs/lab-8-evaluation-and-red-teaming/promptfoo.yaml). Upload it with the <strong>Load Config</strong> button in the lower-left corner, then proceed with the following screenshot steps.
 </div>
 
 <figure style="text-align: center;">
@@ -167,7 +167,7 @@ Promptfoo is highly flexible. Anything that involves mass evaluation of prompts
 ### Explore: Promptfoo evaluation workflow
 
 <div class="lab-callout lab-callout--info">
-  <strong>Tip:</strong> Please use the provided evaluation configuration file: [lab-7-evaluation-and-red-teaming/mmlu-promptfoo-config.yaml](content/labs/lab-7-evaluation-and-red-teaming/mmlu-promptfoo-config.yaml). Upload it with the <strong>Load Config</strong> button in the lower-left corner, then proceed with the following screenshot steps.
+  <strong>Tip:</strong> Please use the provided evaluation configuration file: [lab-8-evaluation-and-red-teaming/mmlu-promptfoo-config.yaml](/labs/lab-8-evaluation-and-red-teaming/mmlu-promptfoo-config.yaml). Upload it with the <strong>Load Config</strong> button in the lower-left corner, then proceed with the following screenshot steps.
 </div>
 
 <figure style="text-align: center;">

src/components/labs/LabContent.test.tsx

@@ -1,4 +1,4 @@
-import { render, screen, waitFor } from "@testing-library/react";
+import { fireEvent, render, screen, waitFor } from "@testing-library/react";
 import { afterEach, describe, expect, it, vi } from "vitest";
 
 import { LabContent } from "~/components/labs/LabContent";
@@ -36,4 +36,55 @@ describe("LabContent", () => {
     expect(screen.getByText("Tokenizer Playground")).toBeInTheDocument();
     expect(screen.getByText("Visualize token confidence locally")).toBeInTheDocument();
   });
+
+  it("filters harness branches from a single Objective 2 selector", () => {
+    render(
+      <LabContent
+        className="lab-content"
+        html={[
+          '<div class="lab-harness-chooser">',
+          '<button type="button" class="lab-harness-card" data-harness-choice="opencode">OpenCode</button>',
+          '<button type="button" class="lab-harness-card" data-harness-choice="kilocode">Kilo Code</button>',
+          '<button type="button" class="lab-harness-card" data-harness-choice="droid">Factory Droid</button>',
+          "</div>",
+          '<section data-harness-branch="opencode"><h3>OpenCode Install</h3></section>',
+          '<section data-harness-branch="kilocode"><h3>Kilo Code Install</h3></section>',
+          '<section data-harness-branch="droid"><h3>Factory Droid Install</h3></section>',
+          '<section data-harness-branch="opencode"><h3>OpenCode Config</h3></section>',
+          '<section data-harness-branch="kilocode"><h3>Kilo Code Config</h3></section>',
+        ].join("")}
+      />,
+    );
+
+    const openCodeInstall = screen.getByText("OpenCode Install").closest("section");
+    const kiloCodeInstall = screen.getByText("Kilo Code Install").closest("section");
+    const droidInstall = screen.getByText("Factory Droid Install").closest("section");
+    const kiloCodeConfig = screen.getByText("Kilo Code Config").closest("section");
+
+    expect(openCodeInstall?.hidden).toBe(true);
+    expect(kiloCodeInstall?.hidden).toBe(true);
+    expect(droidInstall?.hidden).toBe(true);
+    expect(kiloCodeConfig?.hidden).toBe(true);
+
+    fireEvent.click(screen.getByRole("button", { name: "Kilo Code" }));
+
+    expect(screen.getByRole("button", { name: "Kilo Code" })).toHaveAttribute(
+      "aria-pressed",
+      "true",
+    );
+    expect(openCodeInstall?.hidden).toBe(true);
+    expect(kiloCodeInstall?.hidden).toBe(false);
+    expect(droidInstall?.hidden).toBe(true);
+    expect(kiloCodeConfig?.hidden).toBe(false);
+
+    fireEvent.click(screen.getByRole("button", { name: "Kilo Code" }));
+
+    expect(screen.getByRole("button", { name: "Kilo Code" })).toHaveAttribute(
+      "aria-pressed",
+      "false",
+    );
+    expect(openCodeInstall?.hidden).toBe(true);
+    expect(kiloCodeInstall?.hidden).toBe(true);
+    expect(droidInstall?.hidden).toBe(true);
+  });
 });

src/components/labs/LabContent.tsx

@@ -198,6 +198,64 @@ async function copyTextToClipboard(text: string) {
   }
 }
 
+function enhanceHarnessSelectors(root: HTMLElement) {
+  const harnessButtons = Array.from(
+    root.querySelectorAll<HTMLButtonElement>("button[data-harness-choice]"),
+  );
+  const harnessBranches = Array.from(
+    root.querySelectorAll<HTMLElement>("[data-harness-branch]"),
+  );
+
+  if (harnessButtons.length === 0 || harnessBranches.length === 0) {
+    return () => {};
+  }
+
+  const supportedHarnesses = new Set(
+    harnessButtons
+      .map((button) => button.dataset.harnessChoice?.trim())
+      .filter((value): value is string => Boolean(value)),
+  );
+
+  let selectedHarness: string | null = null;
+
+  const syncHarnessSelection = () => {
+    for (const button of harnessButtons) {
+      const harnessId = button.dataset.harnessChoice?.trim() ?? "";
+      const isSelected = selectedHarness !== null && harnessId === selectedHarness;
+      button.setAttribute("aria-pressed", isSelected ? "true" : "false");
+      button.dataset.selected = isSelected ? "true" : "false";
+    }
+
+    for (const branch of harnessBranches) {
+      const harnessId = branch.dataset.harnessBranch?.trim() ?? "";
+      const shouldHide =
+        selectedHarness === null || harnessId !== selectedHarness;
+      branch.hidden = shouldHide;
+      branch.setAttribute("aria-hidden", shouldHide ? "true" : "false");
+    }
+  };
+
+  syncHarnessSelection();
+
+  const handleHarnessClick = (event: Event) => {
+    const target = event.target as HTMLElement;
+    const button = target.closest<HTMLButtonElement>("button[data-harness-choice]");
+    if (!button || !root.contains(button)) return;
+
+    const harnessId = button.dataset.harnessChoice?.trim() ?? "";
+    if (!supportedHarnesses.has(harnessId)) return;
+
+    event.preventDefault();
+    selectedHarness = selectedHarness === harnessId ? null : harnessId;
+    syncHarnessSelection();
+  };
+
+  root.addEventListener("click", handleHarnessClick);
+  return () => {
+    root.removeEventListener("click", handleHarnessClick);
+  };
+}
+
 export function LabContent({ className, html }: LabContentProps) {
   const containerRef = useRef<HTMLElement>(null);
   const [zoomedImage, setZoomedImage] = useState<ZoomedImageState | null>(null);
@@ -273,6 +331,7 @@ export function LabContent({ className, html }: LabContentProps) {
     }
 
     enhanceSettingsLists(root);
+    const cleanupHarnessSelectors = enhanceHarnessSelectors(root);
 
     const handleRootClick = (event: Event) => {
       const target = event.target as HTMLElement;
@@ -320,6 +379,7 @@ export function LabContent({ className, html }: LabContentProps) {
 
     root.addEventListener("click", handleRootClick);
     return () => {
+      cleanupHarnessSelectors();
       root.removeEventListener("click", handleRootClick);
     };
   }, [html]);

src/lib/labs.test.ts

@@ -0,0 +1,28 @@
+import { describe, expect, it } from "vitest";
+
+import { getLabDocument, getLabSummaries } from "~/lib/labs";
+
+describe("labs discovery", () => {
+  it("returns the renumbered labs in order including the new Lab 5", () => {
+    const labs = getLabSummaries();
+
+    expect(labs.map((lab) => lab.slug)).toEqual([
+      "lab-1-visualization-in-transformerlab",
+      "lab-2-quantization-tradeoffs",
+      "lab-3-llama-cpp-and-ollama",
+      "lab-4-oi-prompting",
+      "lab-5-api-and-harnesses",
+      "lab-6-embedding-and-chunking",
+      "lab-7-dataset-generation-and-fine-tuning",
+      "lab-8-evaluation-and-red-teaming",
+    ]);
+  });
+
+  it("resolves the new Lab 5 document", () => {
+    const lab = getLabDocument("lab-5-api-and-harnesses");
+
+    expect(lab).not.toBeNull();
+    expect(lab?.title).toBe("Lab 5 - API & Harnesses");
+    expect(lab?.fileName).toBe("lab-5-api-and-harnesses.md");
+  });
+});

src/styles/globals.css

@@ -417,6 +417,105 @@ ol {
   white-space: nowrap;
 }
 
+.lab-content .lab-harness-chooser {
+  display: grid;
+  grid-template-columns: repeat(3, minmax(0, 1fr));
+  gap: 0.9rem;
+  margin: 1rem 0 1.35rem;
+}
+
+.lab-content .lab-harness-card {
+  display: flex;
+  flex-direction: column;
+  gap: 0.38rem;
+  min-height: 100%;
+  padding: 0.95rem 1rem;
+  border: 1px solid #d9e4ed;
+  border-radius: 16px;
+  background:
+    linear-gradient(180deg, rgba(255, 255, 255, 0.98), rgba(244, 249, 253, 0.96)),
+    radial-gradient(circle at top right, rgba(248, 156, 39, 0.12), transparent 32%);
+  box-shadow: 0 12px 28px -28px rgba(15, 23, 42, 0.35);
+  color: #18384f;
+  text-decoration: none;
+}
+
+.lab-content button.lab-harness-card {
+  width: 100%;
+  cursor: pointer;
+  text-align: left;
+  font: inherit;
+}
+
+.lab-content a.lab-harness-card:hover,
+.lab-content button.lab-harness-card:hover {
+  transform: translateY(-1px);
+  border-color: #f1bd70;
+  box-shadow: 0 20px 36px -30px rgba(15, 23, 42, 0.45);
+}
+
+.lab-content .lab-harness-card[aria-pressed="true"] {
+  border-color: #cf7a08;
+  background:
+    linear-gradient(180deg, rgba(255, 251, 243, 0.98), rgba(255, 244, 227, 0.96)),
+    radial-gradient(circle at top right, rgba(248, 156, 39, 0.18), transparent 32%);
+  box-shadow: 0 20px 36px -30px rgba(114, 63, 8, 0.5);
+}
+
+.lab-content .lab-harness-card strong {
+  color: #0f3d58;
+  font-size: 1rem;
+  line-height: 1.35;
+}
+
+.lab-content .lab-harness-card span {
+  color: #486073;
+  font-size: 0.92rem;
+}
+
+.lab-content .lab-harness-card__tag {
+  display: inline-flex;
+  align-items: center;
+  width: fit-content;
+  border-radius: 999px;
+  padding: 0.22rem 0.58rem;
+  background: #e7f2fb;
+  color: #0f5c8b;
+  font-size: 0.72rem;
+  font-weight: 800;
+  letter-spacing: 0.06em;
+  text-transform: uppercase;
+}
+
+.lab-content .lab-harness-branch {
+  margin: 1rem 0 1.4rem;
+  padding: 1rem 1.1rem 1.1rem;
+  border: 1px solid #dce7f0;
+  border-left: 6px solid #0f5c8b;
+  border-radius: 16px;
+  background:
+    linear-gradient(180deg, rgba(250, 252, 254, 0.98), rgba(244, 249, 252, 0.95)),
+    radial-gradient(circle at top right, rgba(248, 156, 39, 0.08), transparent 26%);
+  scroll-margin-top: 1.5rem;
+}
+
+.lab-content .lab-harness-branch__eyebrow {
+  margin: 0 0 0.4rem;
+  color: #9a5f00;
+  font-size: 0.74rem;
+  font-weight: 800;
+  letter-spacing: 0.08em;
+  text-transform: uppercase;
+}
+
+.lab-content .lab-harness-branch > h3 {
+  margin: 0 0 0.45rem;
+}
+
+.lab-content .lab-harness-branch > p:last-child {
+  margin-bottom: 0;
+}
+
 .lab-content hr {
   margin: 2rem 0 1.4rem;
   border-color: #d7dee6;
@@ -1686,6 +1785,15 @@ ol {
     padding: 0.52rem 0.75rem;
   }
 
+  .lab-content .lab-harness-chooser {
+    grid-template-columns: 1fr;
+  }
+
+  .lab-content .lab-harness-card,
+  .lab-content .lab-harness-branch {
+    padding: 0.85rem 0.9rem;
+  }
+
   .lab-content ul.lab-settings-list .lab-setting-value {
     justify-self: start;
   }