Add requireTuiAgentConfig to validate agent ids

Agent ids persist in automations and settings, so they outlive the
build that wrote them. Direct config lookups fail with unclear
"Cannot read properties of undefined" when an id becomes unknown.
This function validates the agent and throws a clear error message
naming the unknown id.

src/renderer/src/lib/launch-agent-background-session.ts

@@ -11,7 +11,7 @@ import {
   resolveTuiAgentLaunchArgs,
   resolveTuiAgentLaunchEnv
 } from '../../../shared/tui-agent-launch-defaults'
-import { TUI_AGENT_CONFIG } from '../../../shared/tui-agent-config'
+import { requireTuiAgentConfig } from '../../../shared/require-tui-agent-config'
 import { resolveAgentBackgroundLaunchHost } from '@/lib/agent-background-session-launch-host'
 import { makePaneKey } from '../../../shared/stable-pane-id'
 import {
@@ -62,7 +62,7 @@ export async function launchAgentBackgroundSession(
     worktreePath: worktree.path,
     repo
   })
-  const preflight = TUI_AGENT_CONFIG[agent].preflightTrust
+  const preflight = requireTuiAgentConfig(agent).preflightTrust
   if (preflight && worktree.path && window.api.agentTrust?.markTrusted) {
     try {
       await window.api.agentTrust.markTrusted({
@@ -82,7 +82,7 @@ export async function launchAgentBackgroundSession(
   })
   const trimmedPrompt = prompt?.trim() ?? ''
   const hasPrompt = trimmedPrompt.length > 0
-  const isFollowupPath = TUI_AGENT_CONFIG[agent].promptInjectionMode === 'stdin-after-start'
+  const isFollowupPath = requireTuiAgentConfig(agent).promptInjectionMode === 'stdin-after-start'
 
   const pasteDraftAfterLaunch = hasPrompt && isFollowupPath ? trimmedPrompt : null
   const startupPlan = buildAgentStartupPlan({

src/shared/require-tui-agent-config.test.ts

@@ -0,0 +1,21 @@
+import { describe, expect, it } from 'vitest'
+import type { TuiAgent } from './tui-agent'
+import { requireTuiAgentConfig } from './require-tui-agent-config'
+
+describe('requireTuiAgentConfig', () => {
+  it('returns the config for a known agent', () => {
+    expect(requireTuiAgentConfig('codex').preflightTrust).toBe('codex')
+  })
+
+  it('names the unknown id instead of throwing a property-of-undefined error', () => {
+    // A custom-agent id persisted by a branch build, read back by one without the feature.
+    const stale = 'custom-agent:codex:b2e1ff6f-8932-413a-9133-edffa44e0ee9' as TuiAgent
+    expect(() => requireTuiAgentConfig(stale)).toThrow(
+      `Unknown agent "${stale}". This version of Orca has no such agent — pick a different agent and try again.`
+    )
+  })
+
+  it('rejects a prototype key that Object.hasOwn keeps off the config', () => {
+    expect(() => requireTuiAgentConfig('toString' as TuiAgent)).toThrow(/Unknown agent "toString"/)
+  })
+})

src/shared/require-tui-agent-config.ts

@@ -0,0 +1,15 @@
+import type { TuiAgent } from './tui-agent'
+import { isTuiAgent, TUI_AGENT_CONFIG, type TuiAgentConfig } from './tui-agent-config'
+
+/** Why: agent ids persist in automations and settings, so they outlive the build that
+ * wrote them — an id a branch build understood reads back as unknown here. Name the id
+ * instead of letting a bare `TUI_AGENT_CONFIG[agent].x` lookup fail with the unreadable
+ * "Cannot read properties of undefined (reading 'preflightTrust')". */
+export function requireTuiAgentConfig(agent: TuiAgent): TuiAgentConfig {
+  if (!isTuiAgent(agent)) {
+    throw new Error(
+      `Unknown agent "${String(agent)}". This version of Orca has no such agent — pick a different agent and try again.`
+    )
+  }
+  return TUI_AGENT_CONFIG[agent]
+}