feat(config): add runtime_fallback and fallback_models schema

Add configuration schemas for runtime model fallback feature:
- RuntimeFallbackConfigSchema with enabled, retry_on_errors,
  max_fallback_attempts, cooldown_seconds, notify_on_fallback
- FallbackModelsSchema for init-time fallback model selection
- Add fallback_models to AgentOverrideConfigSchema and CategoryConfigSchema
- Export types and schemas from config/index.ts

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)
Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/plugin/chat-message.ts

@@ -54,6 +54,7 @@ export function createChatMessageHandler(args: {
     }
 
     await hooks.stopContinuationGuard?.["chat.message"]?.(input)
+    await hooks.runtimeFallback?.["chat.message"]?.(input, output)
     await hooks.keywordDetector?.["chat.message"]?.(input, output)
     await hooks.claudeCodeHooks?.["chat.message"]?.(input, output)
     await hooks.autoSlashCommand?.["chat.message"]?.(input, output)

src/plugin/event.ts

@@ -42,6 +42,7 @@ export function createEventHandler(args: {
     await Promise.resolve(hooks.rulesInjector?.event?.(input))
     await Promise.resolve(hooks.thinkMode?.event?.(input))
     await Promise.resolve(hooks.anthropicContextWindowLimitRecovery?.event?.(input))
+    await Promise.resolve(hooks.runtimeFallback?.event?.(input))
     await Promise.resolve(hooks.agentUsageReminder?.event?.(input))
     await Promise.resolve(hooks.categorySkillReminder?.event?.(input))
     await Promise.resolve(hooks.interactiveBashSession?.event?.(input))

src/plugin/hooks/create-session-hooks.ts

@@ -24,6 +24,7 @@ import {
   createNoHephaestusNonGptHook,
   createQuestionLabelTruncatorHook,
   createPreemptiveCompactionHook,
+  createRuntimeFallbackHook,
 } from "../../hooks"
 import { createAnthropicEffortHook } from "../../hooks/anthropic-effort"
 import {
@@ -57,6 +58,7 @@ export type SessionHooks = {
   questionLabelTruncator: ReturnType<typeof createQuestionLabelTruncatorHook>
   taskResumeInfo: ReturnType<typeof createTaskResumeInfoHook>
   anthropicEffort: ReturnType<typeof createAnthropicEffortHook> | null
+  runtimeFallback: ReturnType<typeof createRuntimeFallbackHook> | null
 }
 
 export function createSessionHooks(args: {
@@ -175,6 +177,11 @@ export function createSessionHooks(args: {
     ? safeHook("anthropic-effort", () => createAnthropicEffortHook())
     : null
 
+  const runtimeFallback = isHookEnabled("runtime-fallback")
+    ? safeHook("runtime-fallback", () =>
+        createRuntimeFallbackHook(ctx, { config: pluginConfig.runtime_fallback }))
+    : null
+
   return {
     contextWindowMonitor,
     preemptiveCompaction,
@@ -198,5 +205,6 @@ export function createSessionHooks(args: {
     questionLabelTruncator,
     taskResumeInfo,
     anthropicEffort,
+    runtimeFallback,
   }
 }