fix(#2852): forward model overrides from categories/agent config to subagents

- fix(switcher): use lastIndexOf for multi-slash model IDs (e.g. aws/anthropic/claude-sonnet-4)
- fix(model-resolution): same lastIndexOf fix in doctor parseProviderModel
- fix(call-omo-agent): resolve model from agent config and forward to both
  background and sync executors via DelegatedModelConfig
- fix(subagent-resolver): inherit category model/variant when agent uses
  category reference without explicit model override
- test: add model override forwarding tests for call-omo-agent
- test: add multi-slash model ID test for switcher

src/tools/call-omo-agent/background-executor.ts

@@ -2,6 +2,7 @@ import type { CallOmoAgentArgs } from "./types"
 import type { BackgroundManager } from "../../features/background-agent"
 import type { PluginInput } from "@opencode-ai/plugin"
 import { log } from "../../shared"
+import type { DelegatedModelConfig } from "../../shared/model-resolution-types"
 import type { FallbackEntry } from "../../shared/model-requirements"
 import { resolveMessageContext } from "../../features/hook-message-injector"
 import { getSessionAgent } from "../../features/claude-code-session-state"
@@ -20,6 +21,7 @@ export async function executeBackground(
   manager: BackgroundManager,
   client: PluginInput["client"],
   fallbackChain?: FallbackEntry[],
+  model?: DelegatedModelConfig,
 ): Promise<string> {
   try {
     const messageDir = getMessageDir(toolContext.sessionID)
@@ -50,6 +52,7 @@ export async function executeBackground(
       parentMessageID: toolContext.messageID,
       parentAgent,
       parentTools: getSessionTools(toolContext.sessionID),
+      model,
       fallbackChain,
     })