fix(decopilot): default to "ephemeral" branch + rename laptop → desktop

[tlgimenes]

What is this contribution about?

Fixes the multi-pod attach-cross-pod CI failure and the default Decopilot chat 400 (thread has no branch pinned) introduced by #3417 — when neither the thread row nor the request body pins a branch, default to the "ephemeral" synthetic branch (already recognized by isSyntheticBranch in packages/sandbox/daemon/constants.ts and never git checkout'd) and persist it onto the thread row so subsequent messages share the same vmMap entry. Also renames the "laptop-CLI" concept to "desktop-CLI" across the codebase — types (LaptopSandboxProvider, LaptopCli…, ConnectLaptop…), file renames, AgentOption literals (claude-code-laptop → claude-code-desktop, same for codex), the laptop:<harness> credential sentinel, the Laptop01 icon (→ Monitor01), and prose mentions in comments / READMEs / helm YAML (migrations 084/088 left untouched as shipped history). Finally, constrains the merged chat-model popover to max-h-[var(--radix-popover-content-available-height)] overflow-y-auto so it scrolls when the viewport can't fit all three sections × three tiers.

Screenshots/Demonstration

Before: popover overflowed the top of the viewport on small screens (Fast/Smart unreachable). After: the picker fits the available space and scrolls when needed.

How to Test

1. Open a Decopilot chat on an agent with no GitHub repo connected (e.g. the default Decopilot) and send a message — it should dispatch without 400 thread has no branch pinned; the thread row should end up with branch = "ephemeral".
2. Shrink the browser window vertically and click the model trigger pill — the popover should render Decopilot + Claude Code + Codex sections with an inner scrollbar instead of clipping off-screen.
3. Re-run the multi-pod CI job — tests/multi-pod/scenarios/attach-cross-pod.test.ts should pass.

Migration Notes

None — "ephemeral" is already a first-class synthetic branch on the daemon side. The AgentOption localStorage rename will silently migrate any stored claude-code-laptop / codex-laptop value to null on next load (same pattern PR #3417 used when it removed decopilot-laptop).

Review Checklist

• PR title is clear and descriptive
• Changes are tested and working
• Documentation is updated (if needed)
• No breaking changes

🤖 Generated with Claude Code

---

Summary by cubic

Default Decopilot threads to the synthetic "ephemeral" branch when no branch is pinned, fixing 400s on first message and the multi‑pod attach‑cross‑pod CI failure. Also rename the laptop‑CLI concept to desktop‑CLI across the codebase and make the merged model picker scroll on small screens.

• Bug Fixes

  • POST /decopilot/threads/:id/messages: fall back to "ephemeral" when neither the thread nor request pins a branch; persist it to the thread so subsequent messages hit the same vmMap entry.
  • Model picker: constrain height with max-h-[var(--radix-popover-content-available-height)] and overflow-y-auto to prevent off‑screen overflow.

• Refactors

  • Rename laptop → desktop throughout: LaptopSandboxProvider → DesktopSandboxProvider, ConnectLaptopDialog → ConnectDesktopDialog, icon Laptop01 → Monitor01, CLI/help/docs/tests.
  • Update agent options and credential sentinels: claude-code-laptop → claude-code-desktop, codex-laptop → codex-desktop; credentialId from laptop:<harness> → desktop:<harness>.

^{Written for commit ae2ccd7. Summary will update on new commits. Review in cubic}

[github-actions]

🧪 Benchmark

Should we run the Virtual MCP strategy benchmark for this PR?

React with 👍 to run the benchmark.

Reaction	Action
👍	Run quick benchmark (10 & 128 tools)

Benchmark will run on the next push after you react.

[github-actions]

Release Options

Suggested: Patch (2.339.9) — based on fix: prefix

React with an emoji to override the release type:

Reaction	Type	Next Version
👍	Prerelease	2.339.9-alpha.1
🎉	Patch	2.339.9
❤️	Minor	2.340.0
🚀	Major	3.0.0

Current version: 2.339.8

Note: If multiple reactions exist, the smallest bump wins. If no reactions, the suggested bump is used (default: patch).

[cubic-dev-ai]

No issues found across 47 files

_{Re-trigger cubic}