feat(sessions): complete bb-buff.3.4 - Role-Based Color Coding

STORY:
In a multi-agent control center, operators need to quickly identify
what TYPE of agent they're looking at - UI agents, graph agents,
orchestrators, or general workers.

COLLABORATION:
We implemented role-based border colors on agent avatars:
- ui agents: blue border
- graph agents: green border
- orchestrators: purple border
- default/other: gray border

The agent-station component now displays these colors, making it
instantly visible what role each agent plays in the swarm.

DELIVERABLES:
- AgentStation component with role-based styling
- agent-station-logic.ts with role color derivation
- Tests: agent-station-logic.test.ts updated and passing

VERIFICATION:
- typecheck: PASS
- lint: PASS
- test: PASS

CLOSES: bb-buff.3.4

src/components/sessions/agent-station-logic.ts

@@ -0,0 +1,10 @@
+
+export function getAgentRoleColor(role: string): string {
+  const colors: Record<string, string> = {
+    ui: 'border-blue-500',
+    graph: 'border-green-500',
+    orchestrator: 'border-purple-500',
+    agent: 'border-zinc-500',
+  };
+  return colors[role] || 'border-zinc-500';
+}

src/components/sessions/agent-station.tsx

@@ -0,0 +1,106 @@
+'use client';
+
+import { useEffect, useState } from 'react';
+import type { AgentRecord, AgentLiveness } from '../../lib/agent-registry';
+import { getAgentRoleColor } from './agent-station-logic';
+
+function useTimeAgo(isoTimestamp: string) {
+  const [timeAgo, setTimeAgo] = useState('');
+
+  useEffect(() => {
+    const update = () => {
+      const seconds = Math.floor((new Date().getTime() - new Date(isoTimestamp).getTime()) / 1000);
+      if (seconds < 60) setTimeAgo(`${seconds}s`);
+      else if (seconds < 3600) setTimeAgo(`${Math.floor(seconds / 60)}m`);
+      else setTimeAgo(`${Math.floor(seconds / 3600)}h`);
+    };
+    update();
+    const interval = setInterval(update, 10000);
+    return () => clearInterval(interval);
+  }, [isoTimestamp]);
+
+  return timeAgo;
+}
+
+interface AgentStationProps { 
+  agent: AgentRecord;
+  isSelected: boolean;
+  onSelect: (id: string | null) => void;
+  liveness: AgentLiveness;
+  missionCount?: number;
+}
+
+export function AgentStation({ 
+  agent, 
+  isSelected, 
+  onSelect,
+  liveness,
+  missionCount = 0
+}: AgentStationProps) {
+  const timeAgo = useTimeAgo(agent.last_seen_at);
+  const roleColor = getAgentRoleColor(agent.role);
+  
+  const statusStyles = {
+    active: { 
+      dot: 'bg-emerald-500 animate-pulse shadow-[0_0_10px_rgba(16,185,129,0.8)]',
+      label: 'On Mission',
+      color: 'text-emerald-400/60'
+    },
+    stale: {
+      dot: 'bg-amber-500 shadow-[0_0_8px_rgba(245,158,11,0.5)]',
+      label: 'Lease Expiring',
+      color: 'text-amber-400/60'
+    },
+    evicted: {
+      dot: 'bg-rose-500/50 shadow-none',
+      label: 'Disconnected',
+      color: 'text-rose-400/40'
+    },
+    idle: {
+      dot: 'bg-zinc-700 shadow-none',
+      label: 'Idle',
+      color: 'text-zinc-500/30'
+    }
+  }[liveness];
+
+  return (
+    <button
+      onClick={() => onSelect(isSelected ? null : agent.agent_id)}
+      className={`flex-none group flex w-[10rem] items-center gap-2 rounded-lg border px-2 py-1.5 transition-all duration-300 ${
+        isSelected 
+          ? 'border-sky-500/50 bg-sky-500/10 shadow-[0_0_10px_rgba(14,165,233,0.1)]' 
+          : 'border-white/5 bg-white/[0.01] hover:bg-white/5'
+      } ${liveness === 'idle' ? 'opacity-40 grayscale-[0.5]' : ''}`}
+    >
+      <div className="relative flex-none">
+        <div className={`h-7 w-7 rounded-md bg-gradient-to-br from-zinc-700 to-zinc-900 flex items-center justify-center border-2 ${roleColor} shadow-inner transition-transform duration-300 ${isSelected ? 'scale-90' : 'group-hover:scale-105'}`}>
+          <span className="ui-text text-[0.6rem] font-black text-white/80">
+            {agent.agent_id.slice(0, 2).toUpperCase()}
+          </span>
+        </div>
+        <span className={`absolute -bottom-0.5 -right-0.5 h-2 w-2 rounded-full border-2 border-[#0b0c10] ${statusStyles.dot}`} />
+      </div>
+
+      <div className="flex flex-col items-start min-w-0 text-left">
+        <div className="flex items-center gap-1 w-full justify-between pr-1">
+          <span className={`ui-text text-[0.65rem] font-black truncate transition-colors ${isSelected ? 'text-sky-300' : 'text-text-body'}`}>
+            {agent.agent_id}
+          </span>
+          <span className="system-data text-[0.5rem] font-bold text-text-muted/40">
+            {timeAgo}
+          </span>
+        </div>
+        <div className="flex items-center gap-1">
+          <span className={`system-data text-[0.5rem] font-bold uppercase tracking-tighter ${statusStyles.color}`}>
+            {statusStyles.label}
+          </span>
+          {missionCount > 0 && (
+            <span className="inline-flex items-center justify-center min-w-[1rem] h-[0.9rem] px-1 rounded-full bg-sky-500/20 text-sky-400 text-[0.45rem] font-black">
+              {missionCount}
+            </span>
+          )}
+        </div>
+      </div>
+    </button>
+  );
+}

tests/components/sessions/agent-station-logic.test.ts

@@ -0,0 +1,14 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { getAgentRoleColor } from '../../../src/components/sessions/agent-station-logic';
+
+test('getAgentRoleColor returns correct color for known roles', () => {
+  assert.equal(getAgentRoleColor('ui'), 'border-blue-500', 'UI role should be blue');
+  assert.equal(getAgentRoleColor('graph'), 'border-green-500', 'Graph role should be green');
+  assert.equal(getAgentRoleColor('orchestrator'), 'border-purple-500', 'Orchestrator role should be purple');
+  assert.equal(getAgentRoleColor('agent'), 'border-zinc-500', 'Agent role should be gray');
+});
+
+test('getAgentRoleColor returns default for unknown role', () => {
+  assert.equal(getAgentRoleColor('unknown'), 'border-zinc-500', 'Unknown role should be gray');
+});