docs: Updated the MCP docs to mention the redirectHost escape hatch

MCP-Servers.md

@@ -100,6 +100,7 @@ For remote MCP servers that support the Streamable HTTP transport:
 | `headers`            | no       | Custom HTTP headers to include with every request                                                             |
 | `oauth.clientId`     | no       | OAuth client ID. Omit to use Dynamic Client Registration (auto-registers on first `.mcp auth`)                |
 | `oauth.callbackPort` | no       | Callback port for the OAuth redirect listener. Required when the server enforces a specific redirect URI port |
+| `oauth.redirectHost` | no       | Hostname used in the OAuth redirect URI. Defaults to `127.0.0.1`. Set to `localhost` if the server's registered redirect URI uses that form instead (e.g. some Slack OAuth apps) |
 
 ## SSE Servers
 
@@ -127,6 +128,7 @@ prefer `http` where the server supports it):
 | `headers`            | no       | Custom HTTP headers to include with every request                                                             |
 | `oauth.clientId`     | no       | OAuth client ID. Omit to use Dynamic Client Registration (auto-registers on first `.mcp auth`)                |
 | `oauth.callbackPort` | no       | Callback port for the OAuth redirect listener. Required when the server enforces a specific redirect URI port |
+| `oauth.redirectHost` | no       | Hostname used in the OAuth redirect URI. Defaults to `127.0.0.1`. Set to `localhost` if the server's registered redirect URI uses that form instead (e.g. some Slack OAuth apps) |
 
 **Note:** Both `http` and `sse` types use the same underlying transport, which auto-negotiates the
 protocol with the server. The `type` field primarily serves as documentation of which protocol the
@@ -227,6 +229,27 @@ fixed port. Use `oauth.callbackPort` in that case:
 }
 ```
 
+Coyote's redirect URI uses `127.0.0.1` by default (e.g. `http://127.0.0.1:3118/callback`). If the OAuth app
+you registered uses `localhost` instead, set `oauth.redirectHost` to match:
+
+```json
+{
+  "mcpServers": {
+    "notion": {
+      "type": "http",
+      "url": "https://mcp.slack.com/mcp",
+      "oauth": {
+        "clientId": "your-slack-client-id",
+        "redirectHost": "localhost"
+      }
+    }
+  }
+}
+```
+
+> **Note:** This only applies when using a pre-registered `clientId`. When DCR is used (no `clientId`
+> configured), Coyote registers its own redirect URI so the host format never mismatches.
+
 ### Using a static token instead of OAuth
 
 If the server issues long-lived tokens (e.g. Notion internal integrations), you can skip the OAuth flow