feat(tui): --sidebar-section shows a command's output in the sidebar

[ALLiDoizCode]

What

A new run flag, --sidebar-section "Title=command", adds a section to the TUI's sidebar, below Tools, whose body is the output of a shell command.

• The command runs when the TUI starts and again every 5 seconds, with a 5 second timeout.
• Its output is shown as plain text: color sequences are stripped, long lines are cut to the sidebar's width, and at most 12 lines are kept.
• A section with no output is hidden. A failing command still shows what it printed.
• The flag is repeatable. With no flag, nothing changes.

$ docker agent run agent.yaml --sidebar-section "Services=docker compose ps --format '{{.Name}} {{.State}}'"

Why

The sidebar's sections are fixed: Session, Token Usage, Agent, Tools, Todos, Plans. A project that runs an agent beside services of its own has no place in the TUI to show their state, so the person at the keyboard asks the agent, or leaves the TUI, to learn whether they are up.

We hit this in spaceturtle, where the agent runs a node with apps behind it and the person wants to see which are running and which wait for approval. We carry this as a patch on v1.150.0, next to #4578, and would rather not.

How

• pkg/tui/components/sidebar/command_sections.go: the section's state, its run and its rendering. It follows the git-branch watcher's shape: a sidebar-private message that the chat page already forwards to the sidebar. Init runs on every tab switch, so the refresh chain starts once per sidebar.
• sidebar.go: the section is appended after Tools, and the cache is invalidated only when the output changes.
• chat, tui, cmd/root: WithSidebarSections and the flag. A value that is not Title=command is an error before the TUI starts.
• Docs: the CLI flag table and a "Custom Sidebar Sections" entry on the TUI page.

Testing

• Unit tests: parsing the flag, showing and hiding the section, cutting long lines, bounding the output, running a real command once and not starting a second chain.
• go test on pkg/tui/... and cmd/root, golangci-lint run on the changed packages and go run ./lint . pass locally. I did not run the whole of task test.
• By hand: a section that prints a clock ticks every 5 seconds in the full TUI.

Open questions

• The interval and the limits are constants. Happy to make them configurable, or to move this to user settings or the agent config if you prefer that shape.
• The command runs with the TUI's own environment and working directory, like a hook. It is given by whoever starts docker-agent, never by the agent.
• With several tabs, a refresh lands on the active tab's sidebar, as the git-branch watcher's does. Every tab has the same sections, so the active one is always current; a background tab catches up when it is shown.
• The lean TUI has no sidebar and ignores the flag.

🤖 Generated with Claude Code

[aheritier]

👋 Some commits in this PR are not signed and verified by GitHub. Please sign your commits with a GPG or SSH key registered in your GitHub account, then force-push.

Commits that are not verified: 0198f65

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[aheritier]

In addition of signing your commits please remove claude code as co-author. You should give a try to Docker Agent it's pretty nice :)

[aheritier]

👋 Some commits in this PR are not signed and verified by GitHub. Please sign your commits with a GPG or SSH key registered in your GitHub account, then force-push.\n\nCommits that are not verified: 0198f65\n\nSee GitHub's guide on signing commits for setup instructions. I've added status/needs-signed-commits; it will be removed automatically once every commit in this PR carries a valid GitHub-verified signature.