feat(app): focus attention-needing agent tab on workspace navigation (#828)

When navigating to a workspace, auto-open the tab for the agent that
most urgently needs attention (permission > error > finished, oldest
first). Adds pickAttentionAgent + wires it into navigateToWorkspace.

packages/app/src/utils/agent-attention.ts

@@ -1,3 +1,5 @@
+import type { Agent } from "@/stores/session-store";
+
 interface ShouldClearAgentAttentionInput {
   agentId: string | null | undefined;
   isConnected: boolean;
@@ -13,6 +15,47 @@ export type AgentAttentionClearTrigger =
   | "prompt-send"
   | "agent-blur";
 
+const ATTENTION_REASON_PRIORITY = {
+  permission: 0,
+  error: 1,
+  finished: 2,
+} as const;
+
+function getAttentionPriority(reason: Agent["attentionReason"]): number | null {
+  if (!reason) {
+    return null;
+  }
+  return ATTENTION_REASON_PRIORITY[reason];
+}
+
+export function pickAttentionAgent(agents: Agent[]): string | null {
+  let selectedAgentId: string | null = null;
+  let selectedPriority = Number.POSITIVE_INFINITY;
+  let selectedTimestamp = Number.POSITIVE_INFINITY;
+
+  for (const agent of agents) {
+    if (agent.requiresAttention !== true) {
+      continue;
+    }
+
+    const priority = getAttentionPriority(agent.attentionReason);
+    if (priority === null) {
+      continue;
+    }
+
+    const timestamp = agent.attentionTimestamp?.getTime() ?? Number.POSITIVE_INFINITY;
+    const isHigherPriority = priority < selectedPriority;
+    const isOlderAtSamePriority = priority === selectedPriority && timestamp < selectedTimestamp;
+    if (isHigherPriority || isOlderAtSamePriority) {
+      selectedAgentId = agent.id;
+      selectedPriority = priority;
+      selectedTimestamp = timestamp;
+    }
+  }
+
+  return selectedAgentId;
+}
+
 export function shouldClearAgentAttention(input: ShouldClearAgentAttentionInput): boolean {
   const agentId = input.agentId?.trim();
   if (!agentId) {