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/delegate-task/subagent-resolver.ts

@@ -101,12 +101,15 @@ Create the work plan directly - that's your job as the planning agent.`,
     const agentOverride = agentOverrides?.[agentConfigKey as keyof typeof agentOverrides]
       ?? (agentOverrides ? Object.entries(agentOverrides).find(([key]) => key.toLowerCase() === agentConfigKey)?.[1] : undefined)
     const agentRequirement = AGENT_MODEL_REQUIREMENTS[agentConfigKey]
+    const agentCategoryModel = agentOverride?.category
+      ? userCategories?.[agentOverride.category]?.model
+      : undefined
     const normalizedAgentFallbackModels = normalizeFallbackModels(
       agentOverride?.fallback_models
       ?? (agentOverride?.category ? userCategories?.[agentOverride.category]?.fallback_models : undefined)
     )
 
-    if (agentOverride?.model || agentRequirement || matchedAgent.model) {
+    if (agentOverride?.model || agentCategoryModel || agentRequirement || matchedAgent.model) {
       const availableModels = await getAvailableModelsForDelegateTask(client)
 
       const normalizedMatchedModel = matchedAgent.model
@@ -117,7 +120,7 @@ Create the work plan directly - that's your job as the planning agent.`,
         : undefined
 
       const resolution = resolveModelForDelegateTask({
-        userModel: agentOverride?.model,
+        userModel: agentOverride?.model ?? agentCategoryModel,
         userFallbackModels: flattenToFallbackModelStrings(normalizedAgentFallbackModels),
         categoryDefaultModel: matchedAgentModelStr,
         fallbackChain: agentRequirement?.fallbackChain,
@@ -133,16 +136,19 @@ Create the work plan directly - that's your job as the planning agent.`,
           const variantToUse = agentOverride?.variant ?? resolution.variant
           categoryModel = variantToUse ? { ...normalized, variant: variantToUse } : normalized
         }
-      } else if (resolutionSkipped && agentOverride?.model) {
+      } else if (resolutionSkipped && (agentOverride?.model ?? agentCategoryModel)) {
         // Cold cache: resolution was skipped but user explicitly configured a model.
         // Honor the user override directly — don't fall through to hardcoded fallback chain.
-        const normalized = normalizeModelFormat(agentOverride.model)
+        const normalized = normalizeModelFormat((agentOverride?.model ?? agentCategoryModel)!)
         if (normalized) {
-          const variantToUse = agentOverride?.variant
+          const agentCategoryVariant = agentOverride?.category
+            ? userCategories?.[agentOverride.category]?.variant
+            : undefined
+          const variantToUse = agentOverride?.variant ?? agentCategoryVariant
           categoryModel = variantToUse ? { ...normalized, variant: variantToUse } : normalized
           log("[delegate-task] Cold cache: using explicit user override for subagent", {
             agent: agentToUse,
-            model: agentOverride.model,
+            model: agentOverride?.model ?? agentCategoryModel,
           })
         }
       }