Add Codex multi-agent timeline support (#588)

* checkpoint codex multiagent UI state

* fix codex multiagent event scoping

* fix: stabilize codex subagent timeline

* chore: remove codex subagent nesting prompt

* test(web): stabilize tool result rendering tests

* fix: collapse codex agent trace rows by default

* fix(web): keep chat scrolled to bottom

* fix(web): backfill agent-run-heavy message loads

* fix(codex): fail stuck subagent spawns

* fix(codex): preserve wrapped child event scope

* fix(codex): surface agent tool completions

cli/src/codex/utils/appServerConfig.ts

@@ -11,6 +11,12 @@ import type {
 } from '../appServerTypes';
 import { resolveCodexPermissionModeConfig } from './permissionModeConfig';
 
+export const codexCollaborationSpawnAgentInstructions = [
+    'Codex sub-agent spawning rules:',
+    '- If you call spawn_agent with fork_context: true, do not set agent_type, model, or reasoning_effort; full-history forked agents inherit these values from the parent.',
+    '- If you need a specific agent_type, model, or reasoning_effort, omit fork_context or set fork_context: false, and include only the necessary context in the message.'
+].join('\n');
+
 function resolveApprovalPolicy(mode: EnhancedMode): ApprovalPolicy {
     return resolveCodexPermissionModeConfig(mode.permissionMode).approvalPolicy;
 }
@@ -63,6 +69,10 @@ function resolveInstructions(args: {
     };
 }
 
+function appendCollaborationInstructions(developerInstructions: string): string {
+    return `${developerInstructions}\n\n${codexCollaborationSpawnAgentInstructions}`;
+}
+
 export function buildThreadStartParams(args: {
     cwd: string;
     mode: EnhancedMode;
@@ -158,7 +168,7 @@ export function buildTurnStartParams(args: {
             settings: {
                 model,
                 ...(args.mode?.modelReasoningEffort ? { reasoning_effort: args.mode.modelReasoningEffort } : {}),
-                developer_instructions: developerInstructions
+                developer_instructions: appendCollaborationInstructions(developerInstructions)
             }
         };
     } else if (model) {