fix(ui): align primary agent selection with OpenCode (#409)

## Summary

This PR keeps only the UI-side fix for primary agent selection in
CodeNomad.

It aligns the primary agent selector with OpenCode's behavior by:
- filtering primary-session agents through a shared selectable-primary
rule
- avoiding re-inserting an invalid current agent back into the primary
selector
- using the same primary-agent rule when choosing the default agent for
a newly created session

## Why

The earlier investigation showed that the config-loading problem was
actually rooted in OMO's handling of `OPENCODE_CONFIG_DIR`, not in
CodeNomad itself.

However, there was still an independent UI issue in CodeNomad:
- the primary selector could keep showing an agent that should no longer
be selectable
- new sessions could derive their default agent from a looser filter
than the one used by the selector

This PR keeps only that UI-side fix.

## Changes

- `packages/ui/src/components/agent-selector.tsx`
- use a shared `isSelectablePrimaryAgent` helper for primary-session
filtering
- stop force-inserting the current invalid agent back into the primary
selector list

- `packages/ui/src/stores/session-api.ts`
- use the same `isSelectablePrimaryAgent` helper when selecting the
default agent for a new session

- `packages/ui/src/types/session.ts`
  - add `isSelectablePrimaryAgent(agent)` helper

## Scope

This PR intentionally does **not** include any config merge / config
copy workaround related to `OPENCODE_CONFIG_DIR`.

That part was removed so this PR stays narrowly focused on the
primary-agent selection behavior only.

## Validation

- verified changed files are clean in editor diagnostics
- confirmed this is a minimal UI-only diff

---------

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

packages/ui/src/components/agent-selector.tsx

@@ -1,8 +1,8 @@
 import { Select } from "@kobalte/core/select"
-import { For, Show, createEffect, createMemo } from "solid-js"
+import { Show, createEffect, createMemo } from "solid-js"
 import { agents, fetchAgents, sessions } from "../stores/sessions"
 import { ChevronDown } from "lucide-solid"
-import type { Agent } from "../types/session"
+import { isSelectablePrimaryAgent, type Agent } from "../types/session"
 import { useI18n } from "../lib/i18n"
 import { getLogger } from "../lib/logger"
 const log = getLogger("session")
@@ -34,14 +34,7 @@ export default function AgentSelector(props: AgentSelectorProps) {
       return allAgents.filter((agent) => !agent.hidden)
     }
 
-    const filtered = allAgents.filter((agent) => !agent.hidden && agent.mode !== "subagent")
-
-    const currentAgent = allAgents.find((a) => a.name === props.currentAgent)
-    if (currentAgent && !filtered.find((a) => a.name === props.currentAgent)) {
-      return [currentAgent, ...filtered]
-    }
-
-    return filtered
+    return allAgents.filter(isSelectablePrimaryAgent)
   })
 
   createEffect(() => {
@@ -58,7 +51,6 @@ export default function AgentSelector(props: AgentSelectorProps) {
     }
   })
 
-
   const handleChange = async (value: Agent | null) => {
     if (value && value.name !== props.currentAgent) {
       await props.onAgentChange(value.name)

packages/ui/src/components/session-picker.tsx

@@ -1,6 +1,6 @@
 import { Component, createSignal, Show, For, createEffect } from "solid-js"
 import { Dialog } from "@kobalte/core/dialog"
-import type { Session, Agent } from "../types/session"
+import { isSelectablePrimaryAgent, type Session, type Agent } from "../types/session"
 import { getParentSessions, createSession, setActiveParentSession } from "../stores/sessions"
 import { instances, stopInstance } from "../stores/instances"
 import { agents } from "../stores/sessions"
@@ -22,7 +22,7 @@ const SessionPicker: Component<SessionPickerProps> = (props) => {
 
   const instance = () => instances().get(props.instanceId)
   const parentSessions = () => getParentSessions(props.instanceId)
-  const agentList = () => agents().get(props.instanceId) || []
+  const agentList = () => (agents().get(props.instanceId) || []).filter(isSelectablePrimaryAgent)
 
   createEffect(() => {
     const list = agentList()

packages/ui/src/stores/session-api.ts

@@ -1,4 +1,11 @@
-import { getIdleSinceForStatusTransition, mapSdkSessionRetry, mapSdkSessionStatus, type Session, type SessionStatus } from "../types/session"
+import {
+  getIdleSinceForStatusTransition,
+  isSelectablePrimaryAgent,
+  mapSdkSessionRetry,
+  mapSdkSessionStatus,
+  type Session,
+  type SessionStatus,
+} from "../types/session"
 import type { Message } from "../types/message"
 import type { FileDiff } from "@opencode-ai/sdk/v2/client"
 
@@ -341,8 +348,8 @@ async function createSession(instanceId: string, agent?: string): Promise<Sessio
   const client = getOrCreateWorktreeClient(instanceId, worktreeSlug)
 
   const instanceAgents = agents().get(instanceId) || []
-  const nonSubagents = instanceAgents.filter((a) => a.mode !== "subagent")
-  const selectedAgent = agent || (nonSubagents.length > 0 ? nonSubagents[0].name : "")
+  const primaryAgents = instanceAgents.filter(isSelectablePrimaryAgent)
+  const selectedAgent = agent || (primaryAgents.length > 0 ? primaryAgents[0].name : "")
 
   const defaultModel = await getDefaultModel(instanceId, selectedAgent)
 

packages/ui/src/types/session.ts

@@ -112,6 +112,13 @@ export interface Agent {
   }
 }
 
+/**
+ * Matches OpenCode TUI's primary-agent visibility rule: visible iff not a subagent and not hidden.
+ */
+export function isSelectablePrimaryAgent(agent: Agent): boolean {
+  return !agent.hidden && agent.mode !== "subagent"
+}
+
 // Our client-specific Provider interface (simplified version of SDK Provider)
 export interface Provider {
   id: string