Document Poolside external agent setup (#62225)

# Objective

Document how to use Poolside in Zed through the ACP Registry, Poolside
Agent CLI, manual Custom Agent configuration, and Terminal Threads.

## Solution

- Add Poolside paths to the AI by Company guide.
- Document ACP Registry installation and in-thread login.
- Document CLI-assisted and manual Custom Agent configuration.
- Explain the settings-path and PATH requirements.
- Link to the public Poolside Agent CLI repository and Poolside’s Zed
documentation.

## Testing

- Ran `./script/prettier`.
- Ran `git diff --check`.
- Verified Poolside’s live ACP Registry entry.
- Verified the commands, configuration, and authentication behavior
against the Poolside and Zed implementations.

## Self-Review Checklist:

- [x] I've reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks are not applicable
- [x] The content follows Zed’s documentation and UI conventions
- [x] Code tests are not applicable to this documentation-only change
- [x] Performance impact is not applicable

---

Release Notes:

- N/A

docs/src/ai/by-company.md

@@ -1,6 +1,6 @@
 ---
 title: AI by Company - Zed
-description: Find the right Zed setup path for OpenAI, ChatGPT, Codex, Claude, Gemini, Copilot, Cursor, OpenCode, Pi, OpenRouter, Bedrock, local models, and other AI tools.
+description: Find the right Zed setup path for OpenAI, ChatGPT, Codex, Claude, Gemini, Copilot, Cursor, OpenCode, Pi, Poolside, OpenRouter, Bedrock, local models, and other AI tools.
 ---
 
 # AI by Company
@@ -77,6 +77,15 @@ Cursor subscriptions do not configure Zed's LLM provider settings. If you want t
 
 Pi is an agent harness, not a Zed LLM subscription. Pi may support provider auth such as ChatGPT, Claude, or Copilot through its own setup flow.
 
+## Poolside {#poolside}
+
+| Path                    | Support level   | What you get                         | Account / billing               | Setup                                            |
+| ----------------------- | --------------- | ------------------------------------ | ------------------------------- | ------------------------------------------------ |
+| Poolside External Agent | Hosted in Zed   | Poolside in an External Agent thread | Poolside or configured provider | [External Agents](./external-agents.md#poolside) |
+| `pool` CLI              | Run in terminal | Native Poolside Agent CLI experience | Poolside or configured provider | [Terminal Threads](./terminal-threads.md)        |
+
+Install Poolside from the ACP Registry, configure Zed with the Poolside Agent CLI, or add Poolside as a Custom Agent. See [External Agents](./external-agents.md#poolside) for setup steps and platform-specific details.
+
 ## DeepSeek {#deepseek}
 
 | Path         | Support level     | What you get                        | Account / billing                               | Setup                                          |

docs/src/ai/external-agents.md

@@ -34,7 +34,7 @@ Common External Agents include:
 
 This list is curated, not exhaustive. Open the ACP Registry in Zed for the current list of available agents.
 
-For company-specific setup paths, including Claude, Codex, Gemini, OpenCode, Copilot, Cursor, and Pi, see [AI by Company](./by-company.md).
+For company-specific setup paths, including Claude, Codex, Gemini, OpenCode, Copilot, Cursor, Pi, and Poolside, see [AI by Company](./by-company.md).
 
 ## Claude Agent {#claude-agent}
 
@@ -84,6 +84,36 @@ Use Pi Coding Agent when you want Pi running as an ACP-integrated External Agent
 
 Pi is an agent harness, not a Zed LLM subscription. Configure any provider auth, subscriptions, tools, or model choices in Pi.
 
+## Poolside {#poolside}
+
+Use Poolside when you want Poolside running as an ACP-integrated External Agent in Zed.
+
+Install Poolside from the [ACP Registry](#registry), then start a Poolside thread from the Agent Panel or Threads Sidebar. If you haven't authenticated yet, the thread offers `Log in to Poolside`, which runs `pool login` in a terminal. Authentication and model selection are configured through Poolside, not Zed.
+
+To configure Poolside from the terminal instead, install the [Poolside Agent CLI](https://github.com/poolsideai/pool), then run:
+
+```sh
+pool acp setup --editor zed
+```
+
+This command always writes to `~/.config/zed/settings.json`, which is Zed's settings file on macOS and on Linux without a custom `XDG_CONFIG_HOME`. On Windows, or with a custom config directory, install from the registry or use the manual configuration below instead. You do not need to restart Zed. It detects the settings change automatically. Select `Poolside` from the new-thread menu.
+
+To configure it manually, install the [Poolside Agent CLI](https://github.com/poolsideai/pool), make sure `pool` is on your `PATH`, then add it as a [Custom Agent](#custom-agents):
+
+```json [settings]
+{
+  "agent_servers": {
+    "Poolside": {
+      "command": "pool",
+      "args": ["acp"],
+      "type": "custom"
+    }
+  }
+}
+```
+
+See [Poolside's Zed documentation](https://docs.poolside.ai/tools/zed) for more setup details.
+
 ## Start an External Agent Thread {#start-thread}
 
 Open the [Agent Panel](./agent-panel.md), then use the agent selector or the new-thread menu to start a thread with an installed External Agent.