docs(sandboxes): add T3 Code SSH integration page

T3 Code connects to sandboxes over the same SSH integration as VS
Code and Cursor, with no dedicated Docker Sandboxes support on its
side. Adds a Connect page plus a disk-space troubleshooting note for
the "server never became ready" timeout.

Signed-off-by: Manuel de la Peña <manuel.delapena@docker.com>

Author: mdelapenya

content/manuals/ai/sandboxes/integrations/_index.md

@@ -77,6 +77,7 @@ For example, if you mount `/Users/bob/src/my-project`, select
 - [Cursor](cursor.md)
 - [Claude Desktop](claude-desktop.md)
 - [ChatGPT](chatgpt.md)
+- [T3 Code](t3-code.md)
 
 ## How SSH connections work
 

content/manuals/ai/sandboxes/integrations/t3-code.md

@@ -0,0 +1,91 @@
+---
+title: Connect T3 Code to a sandbox
+linkTitle: T3 Code
+weight: 50
+description: Run T3 Code against a Docker Sandbox over SSH.
+keywords: docker sandboxes, t3 code, remote ssh, remote development, sbx
+---
+
+{{< summary-bar feature_name="Docker Sandboxes SSH" >}}
+
+T3 Code's SSH integration lets the desktop app drive coding agents inside a
+sandbox. T3 Code has no dedicated Docker Sandboxes integration — it treats the
+sandbox as an ordinary SSH host, connects to it, and starts a T3 server inside
+that tunnels back to the app.
+
+## Prerequisites
+
+- SSH access set up. See [Editor and app integrations](_index.md#enable-ssh-access).
+- T3 Code installed.
+
+## Connect
+
+Confirm that you can connect to the sandbox from a terminal:
+
+```console
+$ ssh demo.sbx
+```
+
+In T3 Code, add an SSH environment and enter the sandbox hostname, such as
+`demo.sbx`, as the host. The first connection installs the T3 server inside
+the sandbox, so it can take a moment. Later connections are faster.
+
+Then add a new project, select the SSH environment from the list, and
+[choose the mounted workspace](_index.md#select-the-workspace-folder) as the
+project directory inside the sandbox.
+
+## Troubleshoot a server that never becomes ready
+
+T3 Code can fail to connect with an error like the following, wrapped here
+for readability. It concatenates the connection failure with npm's install
+output from inside the sandbox into a single error dialog:
+
+```text
+Could not prepare the SSH environment: ... SshCommandError: Connecting to
+sandbox "sandboxes"… Remote T3 server did not become ready on
+127.0.0.1:3773. npm WARN EBADENGINE Unsupported engine { package:
+'ini@7.0.0', required: { node: '^22.22.2 || ^24.15.0 || >=26.0.0' },
+current: { node: 'v22.22.1', npm: '9.2.0' } }
+```
+
+The `npm WARN EBADENGINE` lines warn about the transitive `ini` dependency.
+They aren't the cause of the failure — npm doesn't enforce engine
+requirements by default, so this warning alone doesn't stop the install.
+Check free disk space in the sandbox. A full disk can fail the T3 server
+install partway through, and T3 Code reports this the same way as a
+connection timeout:
+
+```console
+$ sbx exec <sandbox> -- df -h /
+```
+
+Free up space and reconnect if the sandbox is close to full.
+
+## Troubleshoot `turn/setPermissionMode failed`
+
+If your organization manages Claude Code with a policy file, a local T3 Code
+thread can fail to start with `turn/setPermissionMode failed`. T3 Code's
+default runtime mode is Full access, which maps to the Claude Agent SDK's
+`bypassPermissions` mode. A managed policy that disables that mode rejects
+the request.
+
+On macOS, check whether this applies to you:
+
+```console
+$ cat "/Library/Application Support/ClaudeCode/managed-settings.json"
+```
+
+If `permissions.disableBypassPermissionsMode` is set to `disable`, switch T3
+Code to a different runtime mode, such as Supervised, Auto-accept edits, or
+Auto, then start a new thread. The permission mode is captured once when a
+thread starts, so switching modes in an already-failing thread doesn't
+recover it.
+
+This restriction applies to the host running Claude Code, not to a sandbox.
+A thread connected to a sandbox isn't subject to the host's managed policy,
+so Full access works normally there.
+
+## Related
+
+- [Editor and app integrations](_index.md) — how SSH access works and how to
+  set it up