feat(app): connect to fleet device from the sidebar #1409

Acceptance Criteria

• Clicking a remote device row in the fleet sidebar shows a Quick Pick with
  "Thin Client (Poor Connection)" and "Remote SSH (Strong Connection)"
• "Thin Client" calls POST /amicode/fleet/attach with the target machine_id,
  base_url, and token, then reloads the window on success
• After reload, the extension reads the attachment pointer at boot, spins up
  the per-attachment transport, and registers the HubProxy — remote sessions are
  visible (boot-time pointer recovery, ADR 0030 §D3)
• "Remote SSH" opens a new VS Code window connected to the device via
  vscode-remote://ssh-remote+<sshAlias>/
• Clicking the local device ("This Machine") shows a Quick Pick with
  "Go Standalone"
• On the hub, "Go Standalone" warns about disconnecting N other devices
• Thin Client disabled for devices without serving capability
  (inline note: "Not running a server")
• Thin Client disabled for devices with health === "down"
  (inline note: "Device unreachable")
• Thin Client disabled when no credentials can be resolved
  (inline note: "No credentials available — use the Fleet Manager to connect")
• Remote SSH disabled for devices with no sshAlias
  (inline note: "No SSH alias configured")
• Remote SSH disabled when ms-vscode-remote.remote-ssh is not installed
  (inline note: "Requires Remote-SSH extension")
• Device rows show cursor: pointer and a hover highlight
• One-shot click guard prevents rapid double-clicks from stacking Quick Picks
• Confirmation dialog before window reload for Thin Client
• Two-branch device resolution: roster lookup by machine_id, then topology
  fallback for the canonical-server row (ADR 0030 §D4)
• Attach API amended to accept canonical server as valid target when not in roster
• Write seam is separate from the read-only FleetSectionDeps (ADR 0030 §D6)

Testing Decisions

Extend the existing fleet sidebar tests (sidebar_fleet_section.test.ts) for:

• Click handler emits the correct bridge message with machineId/isLocal
• renderDeviceRow includes cursor pointer styling
• One-shot click guard prevents duplicate messages

New unit tests for fleet_connect_device.ts:

• Quick Pick selection dispatches to the correct path (attach vs Remote SSH vs standalone)
• Thin Client calls attach API with correct machine_id + credentials
• Remote SSH resolves the correct URI from sshAlias
• Two-branch resolution: roster hit, roster miss + topology fallback
• Precondition gating: no serving capability, down health, no sshAlias, no Remote-SSH ext, no credentials
• Hub-specific Go Standalone warning includes device count

New unit tests for boot-time pointer recovery:

• Valid pointer at boot → transport spun up, proxy registered
• Empty/absent pointer → no proxy, local sessions shown
• Malformed pointer → honest degradation, no proxy

Extend fleet_connect_remote_ssh.test.ts for the generalised resolver:

• resolveDeviceRemoteSshTarget with a valid alias
• resolveDeviceRemoteSshTarget with an empty alias

Extend attach_action.test.ts for the canonical-server amendment:

• machine_id not in roster but matches canonical → attach succeeds
• machine_id not in roster AND not canonical → refused

Key Decisions

• Left-click + Quick Pick (not context menu) — consistent with VS Code patterns
• Re-attach for Thin Client (not full per-device proxy) — reuses existing infra
• Boot-time pointer recovery scoped here, live re-target stays with Peer fleet studios (ADR 0027, Horizon 1) — #1341–#1346 #1353
• capabilities.includes("serving") as the Thin Client gate (ADR 0029 model)
• Separate write seam (FleetConnectDeps), not the read-only FleetSectionDeps
• Two-branch resolution (roster + topology) for synthesized canonical-server row
• Generalise the existing Remote SSH resolver (not fork)
• Roster-sole-candidate invariant amended for topology canonical (security preserved)

Constraints & Invariants

• ADR 0026: sidebar emits no roster-write message (connect-to-device is navigation)
• ADR 0027 §D3: single-writer attachment pointer; Thin Client uses existing attach API
• ADR 0027 §D3: roster-as-sole-candidate amended — topology canonical is a second
  trusted source; security property preserved (coordinates from fleet.json, not request)
• ADR 0025: Remote-SSH uses the same vscode-remote://ssh-remote+ URI scheme
• ADR 0029: serving capability is the attachability predicate, not server_mode
• FleetSectionDeps remains read-only; write path uses a separate seam

Prior Art

• fleet_connect_remote_ssh.ts — the hub-only Remote-SSH command (generalise it)
• attach_action.ts — POST /amicode/fleet/attach (amend for canonical server)
• attachment_transport.ts — per-attachment transport bring-up (reuse at boot)
• amicode_service_wiring.ts — where boot-time fleet options are constructed (wire pointer recovery)
• sidebar_fleet_section.ts — device row rendering (add click handler)
• sidebar_bridge.ts — typed message bridge (add new message kind)

Source

ADR 0030 — connect to fleet device from the sidebar.
Adversarial review: round 2, approved-mechanical (3 manual critics, no tooling).

Sub-issues

• feat(app): boot-time attachment pointer recovery (ADR 0030 §D3) #1410 — Boot-time attachment pointer recovery (§D3)
• feat(app): attach API accepts canonical server as valid target (ADR 0030 §D4) #1411 — Attach API accepts canonical server (§D4)
• feat(app): generalise Remote SSH resolver for any fleet device (ADR 0030 §D8) #1412 — Generalise Remote SSH resolver (§D8)
• feat(app): sidebar device click → Quick Pick with Thin Client / Remote SSH (ADR 0030 §D1/D2) #1413 — Sidebar click → Quick Pick integration (§D1/D2/D5/D6/D7) — blocked by feat(app): boot-time attachment pointer recovery (ADR 0030 §D3) #1410, feat(app): attach API accepts canonical server as valid target (ADR 0030 §D4) #1411, feat(app): generalise Remote SSH resolver for any fleet device (ADR 0030 §D8) #1412

Dependency graph

#1410 (boot-time recovery)    ──┐
#1411 (attach API amendment)  ──┼──► #1413 (sidebar click → Quick Pick)
#1412 (Remote SSH generalise) ─┘

Slices 1–3 are independent (parallelizable). Slice 4 integrates them.