Fleet: sessions dropdown enrichment (bridge + icon + context menu) #358

Acceptance Criteria

Bridge Protocol

• chat_bridge.ts allowlist includes fleet-state (inbound: extension → app)
• chat_bridge.ts allowlist includes fleet-action (outbound: app → extension)
• Extension pushes FleetStateSnapshot on fleet record change (debounced 500ms):

  { "type": "fleet-state", "payload": { "sessions": [
    { "session_id": "...", "state": "running", "profile_name": "...",
      "tokens": 42000, "host": "...", "current_step": "..." }
  ] } }

• App receives and stores fleet state in a SolidJS store/signal

Sessions Dropdown

• Fleet-managed sessions show a fleet icon (small badge) next to their title
• Fleet icon only appears for sessions whose session_id matches a FleetRecord
• Session subtitle shows fleet state when relevant ("Running" / "Blocked" / "Crashed")
  in appropriate color

Context Menu

• Right-click a fleet-managed session → context menu with fleet actions
• Steer: text input dialog → sends instruction (available when state = running)
• Stop: enqueues cancel/stop (available when running or blocked)
• Re-tier: submenu with tier up / tier down / respool (available when running or blocked)
• View details: popover showing profile, state, tokens, runtime, current step (always available)
• Actions post fleet-action message back through the bridge:

  { "type": "fleet-action", "verb": "stop", "session_id": "...", "params": {} }

• Extension receives fleet-action, enqueues signal file (same as amico fleet stop/steer/re-tier)
• Plain (non-fleet) sessions have NO fleet icon and NO fleet context menu items

Testing Decisions

• Unit test (extension): fleet_bridge.test.ts — FleetStateSnapshot construction from
  records, debounce behavior (multiple rapid changes → single push)
• Unit test (extension): fleet-action handler — given action message, verify correct
  signal file written
• Unit test (app): fleet store hydration — given a fleet-state message, verify store
  updates and re-renders session list with icons
• Integration (app): context menu renders correct actions per state (running → all four;
  settled → view details only)
• Manual verification (HITL): end-to-end bridge flow across the iframe boundary

Key Decisions

Constraints & Invariants

• Bridge messages MUST be origin-checked (same as existing chat_bridge security model)
• Fleet state is ephemeral in the app (not persisted — re-pushed on reconnect/reload)
• Context menu items are state-gated: disabled/hidden actions never shown
• The fleet icon is a visual indicator only — clicking it does nothing (actions are in the menu)

Source

Part of #350
Blocked by #357
ADR 0007: docs/adr/0007-fleet-panel-and-profile-ui.md