diff --git a/src/agents/sisyphus-junior.ts b/src/agents/sisyphus-junior.ts
index 671983a1..690b3eeb 100644
--- a/src/agents/sisyphus-junior.ts
+++ b/src/agents/sisyphus-junior.ts
@@ -84,13 +84,14 @@ export const SISYPHUS_JUNIOR_DEFAULTS = {
 } as const
 
 export function createSisyphusJuniorAgentWithOverrides(
-  override: AgentOverrideConfig | undefined
+  override: AgentOverrideConfig | undefined,
+  systemDefaultModel?: string
 ): AgentConfig {
   if (override?.disable) {
     override = undefined
   }
 
-  const model = override?.model ?? SISYPHUS_JUNIOR_DEFAULTS.model
+  const model = override?.model ?? systemDefaultModel ?? SISYPHUS_JUNIOR_DEFAULTS.model
   const temperature = override?.temperature ?? SISYPHUS_JUNIOR_DEFAULTS.temperature
 
   const promptAppend = override?.prompt_append
diff --git a/src/agents/utils.ts b/src/agents/utils.ts
index 808a6ef3..d831caa8 100644
--- a/src/agents/utils.ts
+++ b/src/agents/utils.ts
@@ -192,7 +192,7 @@ export function createBuiltinAgents(
 
   if (!disabledAgents.includes("orchestrator-sisyphus")) {
     const orchestratorOverride = agentOverrides["orchestrator-sisyphus"]
-    const orchestratorModel = orchestratorOverride?.model
+    const orchestratorModel = orchestratorOverride?.model ?? systemDefaultModel
     let orchestratorConfig = createOrchestratorSisyphusAgent({
       model: orchestratorModel,
       availableAgents,
diff --git a/src/features/task-toast-manager/index.ts b/src/features/task-toast-manager/index.ts
index f779eee8..26d91af0 100644
--- a/src/features/task-toast-manager/index.ts
+++ b/src/features/task-toast-manager/index.ts
@@ -1,2 +1,2 @@
 export { TaskToastManager, getTaskToastManager, initTaskToastManager } from "./manager"
-export type { TrackedTask, TaskStatus, TaskToastOptions } from "./types"
+export type { TrackedTask, TaskStatus, TaskToastOptions, ModelFallbackInfo } from "./types"
diff --git a/src/features/task-toast-manager/manager.test.ts b/src/features/task-toast-manager/manager.test.ts
index 1e813ba8..069f1851 100644
--- a/src/features/task-toast-manager/manager.test.ts
+++ b/src/features/task-toast-manager/manager.test.ts
@@ -142,4 +142,109 @@ describe("TaskToastManager", () => {
       expect(call.body.message).toContain("Running (1):")
     })
   })
+
+  describe("model fallback info in toast message", () => {
+    test("should display warning when model falls back to category-default", () => {
+      // #given - a task with model fallback to category-default
+      const task = {
+        id: "task_1",
+        description: "Task with category default model",
+        agent: "Sisyphus-Junior",
+        isBackground: false,
+        modelInfo: { model: "google/gemini-3-pro-preview", type: "category-default" as const },
+      }
+
+      // #when - addTask is called
+      toastManager.addTask(task)
+
+      // #then - toast should show warning with model info
+      expect(mockClient.tui.showToast).toHaveBeenCalled()
+      const call = mockClient.tui.showToast.mock.calls[0][0]
+      expect(call.body.message).toContain("⚠️")
+      expect(call.body.message).toContain("google/gemini-3-pro-preview")
+      expect(call.body.message).toContain("(category default)")
+    })
+
+    test("should display warning when model falls back to system-default", () => {
+      // #given - a task with model fallback to system-default
+      const task = {
+        id: "task_1b",
+        description: "Task with system default model",
+        agent: "Sisyphus-Junior",
+        isBackground: false,
+        modelInfo: { model: "anthropic/claude-sonnet-4-5", type: "system-default" as const },
+      }
+
+      // #when - addTask is called
+      toastManager.addTask(task)
+
+      // #then - toast should show warning with model info
+      expect(mockClient.tui.showToast).toHaveBeenCalled()
+      const call = mockClient.tui.showToast.mock.calls[0][0]
+      expect(call.body.message).toContain("⚠️")
+      expect(call.body.message).toContain("anthropic/claude-sonnet-4-5")
+      expect(call.body.message).toContain("(system default)")
+    })
+
+    test("should display warning when model is inherited from parent", () => {
+      // #given - a task with inherited model
+      const task = {
+        id: "task_2",
+        description: "Task with inherited model",
+        agent: "Sisyphus-Junior",
+        isBackground: false,
+        modelInfo: { model: "cliproxy/claude-opus-4-5", type: "inherited" as const },
+      }
+
+      // #when - addTask is called
+      toastManager.addTask(task)
+
+      // #then - toast should show warning with inherited model
+      expect(mockClient.tui.showToast).toHaveBeenCalled()
+      const call = mockClient.tui.showToast.mock.calls[0][0]
+      expect(call.body.message).toContain("⚠️")
+      expect(call.body.message).toContain("cliproxy/claude-opus-4-5")
+      expect(call.body.message).toContain("(inherited)")
+    })
+
+    test("should not display model info when user-defined", () => {
+      // #given - a task with user-defined model
+      const task = {
+        id: "task_3",
+        description: "Task with user model",
+        agent: "Sisyphus-Junior",
+        isBackground: false,
+        modelInfo: { model: "my-provider/my-model", type: "user-defined" as const },
+      }
+
+      // #when - addTask is called
+      toastManager.addTask(task)
+
+      // #then - toast should NOT show model warning
+      expect(mockClient.tui.showToast).toHaveBeenCalled()
+      const call = mockClient.tui.showToast.mock.calls[0][0]
+      expect(call.body.message).not.toContain("⚠️ Model:")
+      expect(call.body.message).not.toContain("(inherited)")
+      expect(call.body.message).not.toContain("(category default)")
+      expect(call.body.message).not.toContain("(system default)")
+    })
+
+    test("should not display model info when not provided", () => {
+      // #given - a task without model info
+      const task = {
+        id: "task_4",
+        description: "Task without model info",
+        agent: "explore",
+        isBackground: true,
+      }
+
+      // #when - addTask is called
+      toastManager.addTask(task)
+
+      // #then - toast should NOT show model warning
+      expect(mockClient.tui.showToast).toHaveBeenCalled()
+      const call = mockClient.tui.showToast.mock.calls[0][0]
+      expect(call.body.message).not.toContain("⚠️ Model:")
+    })
+  })
 })
diff --git a/src/features/task-toast-manager/manager.ts b/src/features/task-toast-manager/manager.ts
index 66a03b2a..5cb5a7b1 100644
--- a/src/features/task-toast-manager/manager.ts
+++ b/src/features/task-toast-manager/manager.ts
@@ -1,5 +1,5 @@
 import type { PluginInput } from "@opencode-ai/plugin"
-import type { TrackedTask, TaskStatus } from "./types"
+import type { TrackedTask, TaskStatus, ModelFallbackInfo } from "./types"
 import type { ConcurrencyManager } from "../background-agent/concurrency"
 
 type OpencodeClient = PluginInput["client"]
@@ -25,6 +25,7 @@ export class TaskToastManager {
     isBackground: boolean
     status?: TaskStatus
     skills?: string[]
+    modelInfo?: ModelFallbackInfo
   }): void {
     const trackedTask: TrackedTask = {
       id: task.id,
@@ -34,6 +35,7 @@ export class TaskToastManager {
       startedAt: new Date(),
       isBackground: task.isBackground,
       skills: task.skills,
+      modelInfo: task.modelInfo,
     }
 
     this.tasks.set(task.id, trackedTask)
@@ -105,6 +107,19 @@ export class TaskToastManager {
 
     const lines: string[] = []
 
+    // Show model fallback warning for the new task if applicable
+    if (newTask.modelInfo && newTask.modelInfo.type !== "user-defined") {
+      const icon = "⚠️"
+      const suffixMap: Partial<Record<ModelFallbackInfo["type"], string>> = {
+        inherited: " (inherited)",
+        "category-default": " (category default)",
+        "system-default": " (system default)",
+      }
+      const suffix = suffixMap[newTask.modelInfo.type] ?? ""
+      lines.push(`${icon} Model: ${newTask.modelInfo.model}${suffix}`)
+      lines.push("")
+    }
+
     if (running.length > 0) {
       lines.push(`Running (${running.length}):${concurrencyInfo}`)
       for (const task of running) {
diff --git a/src/features/task-toast-manager/types.ts b/src/features/task-toast-manager/types.ts
index de4aca0a..33d6f451 100644
--- a/src/features/task-toast-manager/types.ts
+++ b/src/features/task-toast-manager/types.ts
@@ -1,5 +1,10 @@
 export type TaskStatus = "running" | "queued" | "completed" | "error"
 
+export interface ModelFallbackInfo {
+  model: string
+  type: "user-defined" | "inherited" | "category-default" | "system-default"
+}
+
 export interface TrackedTask {
   id: string
   description: string
@@ -8,6 +13,7 @@ export interface TrackedTask {
   startedAt: Date
   isBackground: boolean
   skills?: string[]
+  modelInfo?: ModelFallbackInfo
 }
 
 export interface TaskToastOptions {
diff --git a/src/plugin-handlers/config-handler.ts b/src/plugin-handlers/config-handler.ts
index 96ff156f..55c4f24e 100644
--- a/src/plugin-handlers/config-handler.ts
+++ b/src/plugin-handlers/config-handler.ts
@@ -154,7 +154,8 @@ export function createConfigHandler(deps: ConfigHandlerDeps) {
       };
 
       agentConfig["Sisyphus-Junior"] = createSisyphusJuniorAgentWithOverrides(
-        pluginConfig.agents?.["Sisyphus-Junior"]
+        pluginConfig.agents?.["Sisyphus-Junior"],
+        config.model as string | undefined
       );
 
       if (builderEnabled) {
diff --git a/src/tools/sisyphus-task/tools.test.ts b/src/tools/sisyphus-task/tools.test.ts
index 58dfe66d..7b3cae68 100644
--- a/src/tools/sisyphus-task/tools.test.ts
+++ b/src/tools/sisyphus-task/tools.test.ts
@@ -4,8 +4,13 @@ import type { CategoryConfig } from "../../config/schema"
 
 function resolveCategoryConfig(
   categoryName: string,
-  userCategories?: Record<string, CategoryConfig>
-): { config: CategoryConfig; promptAppend: string } | null {
+  options: {
+    userCategories?: Record<string, CategoryConfig>
+    parentModelString?: string
+    systemDefaultModel?: string
+  }
+): { config: CategoryConfig; promptAppend: string; model: string | undefined } | null {
+  const { userCategories, parentModelString, systemDefaultModel } = options
   const defaultConfig = DEFAULT_CATEGORIES[categoryName]
   const userConfig = userCategories?.[categoryName]
   const defaultPromptAppend = CATEGORY_PROMPT_APPENDS[categoryName] ?? ""
@@ -14,10 +19,11 @@ function resolveCategoryConfig(
     return null
   }
 
+  const model = userConfig?.model ?? parentModelString ?? defaultConfig?.model ?? systemDefaultModel
   const config: CategoryConfig = {
     ...defaultConfig,
     ...userConfig,
-    model: userConfig?.model ?? defaultConfig?.model ?? "anthropic/claude-sonnet-4-5",
+    model,
   }
 
   let promptAppend = defaultPromptAppend
@@ -27,7 +33,7 @@ function resolveCategoryConfig(
       : userConfig.prompt_append
   }
 
-  return { config, promptAppend }
+  return { config, promptAppend, model }
 }
 
 describe("sisyphus-task", () => {
@@ -114,7 +120,7 @@ describe("sisyphus-task", () => {
       const categoryName = "unknown-category"
 
       // #when
-      const result = resolveCategoryConfig(categoryName)
+      const result = resolveCategoryConfig(categoryName, {})
 
       // #then
       expect(result).toBeNull()
@@ -125,7 +131,7 @@ describe("sisyphus-task", () => {
       const categoryName = "visual-engineering"
 
       // #when
-      const result = resolveCategoryConfig(categoryName)
+      const result = resolveCategoryConfig(categoryName, {})
 
       // #then
       expect(result).not.toBeNull()
@@ -141,7 +147,7 @@ describe("sisyphus-task", () => {
       }
 
       // #when
-      const result = resolveCategoryConfig(categoryName, userCategories)
+      const result = resolveCategoryConfig(categoryName, { userCategories })
 
       // #then
       expect(result).not.toBeNull()
@@ -159,7 +165,7 @@ describe("sisyphus-task", () => {
       }
 
       // #when
-      const result = resolveCategoryConfig(categoryName, userCategories)
+      const result = resolveCategoryConfig(categoryName, { userCategories })
 
       // #then
       expect(result).not.toBeNull()
@@ -179,7 +185,7 @@ describe("sisyphus-task", () => {
       }
 
       // #when
-      const result = resolveCategoryConfig(categoryName, userCategories)
+      const result = resolveCategoryConfig(categoryName, { userCategories })
 
       // #then
       expect(result).not.toBeNull()
@@ -199,12 +205,53 @@ describe("sisyphus-task", () => {
       }
 
       // #when
-      const result = resolveCategoryConfig(categoryName, userCategories)
+      const result = resolveCategoryConfig(categoryName, { userCategories })
 
       // #then
       expect(result).not.toBeNull()
       expect(result!.config.temperature).toBe(0.3)
     })
+
+    test("parentModelString is used when no user model and takes precedence over default", () => {
+      // #given
+      const categoryName = "visual-engineering"
+      const parentModelString = "cliproxy/claude-opus-4-5"
+
+      // #when
+      const result = resolveCategoryConfig(categoryName, { parentModelString })
+
+      // #then
+      expect(result).not.toBeNull()
+      expect(result!.config.model).toBe("cliproxy/claude-opus-4-5")
+    })
+
+    test("user model takes precedence over parentModelString", () => {
+      // #given
+      const categoryName = "visual-engineering"
+      const userCategories = {
+        "visual-engineering": { model: "my-provider/my-model" },
+      }
+      const parentModelString = "cliproxy/claude-opus-4-5"
+
+      // #when
+      const result = resolveCategoryConfig(categoryName, { userCategories, parentModelString })
+
+      // #then
+      expect(result).not.toBeNull()
+      expect(result!.config.model).toBe("my-provider/my-model")
+    })
+
+    test("default model is used when no user model and no parentModelString", () => {
+      // #given
+      const categoryName = "visual-engineering"
+
+      // #when
+      const result = resolveCategoryConfig(categoryName, {})
+
+      // #then
+      expect(result).not.toBeNull()
+      expect(result!.config.model).toBe("google/gemini-3-pro-preview")
+    })
   })
 
   describe("category variant", () => {
@@ -228,6 +275,7 @@ describe("sisyphus-task", () => {
 
       const mockClient = {
         app: { agents: async () => ({ data: [] }) },
+        config: { get: async () => ({}) },
         session: {
           create: async () => ({ data: { id: "test-session" } }),
           prompt: async () => ({ data: {} }),
@@ -285,6 +333,7 @@ describe("sisyphus-task", () => {
       const mockManager = { launch: async () => ({}) }
       const mockClient = {
         app: { agents: async () => ({ data: [] }) },
+        config: { get: async () => ({}) },
         session: {
           create: async () => ({ data: { id: "test-session" } }),
           prompt: async () => ({ data: {} }),
@@ -352,6 +401,7 @@ describe("sisyphus-task", () => {
           ],
         }),
       },
+      config: { get: async () => ({}) },
       app: {
         agents: async () => ({ data: [] }),
       },
@@ -409,6 +459,7 @@ describe("sisyphus-task", () => {
           data: [],
         }),
       },
+      config: { get: async () => ({}) },
     }
     
     const tool = createSisyphusTask({
@@ -460,6 +511,7 @@ describe("sisyphus-task", () => {
           messages: async () => ({ data: [] }),
           status: async () => ({ data: {} }),
         },
+        config: { get: async () => ({}) },
         app: {
           agents: async () => ({ data: [{ name: "ultrabrain", mode: "subagent" }] }),
         },
@@ -518,6 +570,7 @@ describe("sisyphus-task", () => {
           }),
           status: async () => ({ data: { "ses_sync_success": { type: "idle" } } }),
         },
+        config: { get: async () => ({}) },
         app: {
           agents: async () => ({ data: [{ name: "ultrabrain", mode: "subagent" }] }),
         },
@@ -570,6 +623,7 @@ describe("sisyphus-task", () => {
           messages: async () => ({ data: [] }),
           status: async () => ({ data: {} }),
         },
+        config: { get: async () => ({}) },
         app: {
           agents: async () => ({ data: [{ name: "ultrabrain", mode: "subagent" }] }),
         },
@@ -624,6 +678,7 @@ describe("sisyphus-task", () => {
           }),
           status: async () => ({ data: {} }),
         },
+        config: { get: async () => ({}) },
         app: { agents: async () => ({ data: [] }) },
       }
 
@@ -665,7 +720,7 @@ describe("sisyphus-task", () => {
       const { buildSystemContent } = require("./tools")
 
       // #when
-      const result = buildSystemContent({ skills: undefined, categoryPromptAppend: undefined })
+      const result = buildSystemContent({ skillContent: undefined, categoryPromptAppend: undefined })
 
       // #then
       expect(result).toBeUndefined()
@@ -710,4 +765,111 @@ describe("sisyphus-task", () => {
       expect(result).toContain("\n\n")
     })
   })
+
+  describe("modelInfo detection via resolveCategoryConfig", () => {
+    test("when parentModelString exists but default model wins - modelInfo should report category-default", () => {
+      // #given - Bug scenario: parentModelString is passed but userModel is undefined,
+      // and the resolution order is: userModel ?? parentModelString ?? defaultModel
+      // If parentModelString matches the resolved model, it's "inherited"
+      // If defaultModel matches, it's "category-default"
+      const categoryName = "ultrabrain"
+      const parentModelString = undefined
+      
+      // #when
+      const resolved = resolveCategoryConfig(categoryName, { parentModelString })
+      
+      // #then - actualModel should be defaultModel, type should be "category-default"
+      expect(resolved).not.toBeNull()
+      const actualModel = resolved!.config.model
+      const defaultModel = DEFAULT_CATEGORIES[categoryName]?.model
+      expect(actualModel).toBe(defaultModel)
+      expect(actualModel).toBe("openai/gpt-5.2")
+    })
+
+    test("when parentModelString is used - modelInfo should report inherited", () => {
+      // #given
+      const categoryName = "ultrabrain"
+      const parentModelString = "cliproxy/claude-opus-4-5"
+      
+      // #when
+      const resolved = resolveCategoryConfig(categoryName, { parentModelString })
+      
+      // #then - actualModel should be parentModelString, type should be "inherited"
+      expect(resolved).not.toBeNull()
+      const actualModel = resolved!.config.model
+      expect(actualModel).toBe(parentModelString)
+    })
+
+    test("when user defines model - modelInfo should report user-defined regardless of parentModelString", () => {
+      // #given
+      const categoryName = "ultrabrain"
+      const userCategories = { "ultrabrain": { model: "my-provider/custom-model" } }
+      const parentModelString = "cliproxy/claude-opus-4-5"
+      
+      // #when
+      const resolved = resolveCategoryConfig(categoryName, { userCategories, parentModelString })
+      
+      // #then - actualModel should be userModel, type should be "user-defined"
+      expect(resolved).not.toBeNull()
+      const actualModel = resolved!.config.model
+      const userDefinedModel = userCategories[categoryName]?.model
+      expect(actualModel).toBe(userDefinedModel)
+      expect(actualModel).toBe("my-provider/custom-model")
+    })
+
+    test("detection logic: actualModel comparison correctly identifies source", () => {
+      // #given - This test verifies the fix for PR #770 bug
+      // The bug was: checking `if (parentModelString)` instead of `if (actualModel === parentModelString)`
+      const categoryName = "ultrabrain"
+      const parentModelString = "cliproxy/claude-opus-4-5"
+      const userCategories = { "ultrabrain": { model: "user/model" } }
+      
+      // #when - user model wins
+      const resolved = resolveCategoryConfig(categoryName, { userCategories, parentModelString })
+      const actualModel = resolved!.config.model
+      const userDefinedModel = userCategories[categoryName]?.model
+      const defaultModel = DEFAULT_CATEGORIES[categoryName]?.model
+      
+      // #then - detection should compare against actual resolved model
+      const detectedType = actualModel === userDefinedModel 
+        ? "user-defined" 
+        : actualModel === parentModelString 
+        ? "inherited" 
+        : actualModel === defaultModel 
+        ? "category-default" 
+        : undefined
+      
+      expect(detectedType).toBe("user-defined")
+      expect(actualModel).not.toBe(parentModelString)
+    })
+
+    test("systemDefaultModel is used when no other model is available", () => {
+      // #given - custom category with no model, but systemDefaultModel is set
+      const categoryName = "my-custom"
+      // Using type assertion since we're testing fallback behavior for categories without model
+      const userCategories = { "my-custom": { temperature: 0.5 } } as unknown as Record<string, CategoryConfig>
+      const systemDefaultModel = "anthropic/claude-sonnet-4-5"
+      
+      // #when
+      const resolved = resolveCategoryConfig(categoryName, { userCategories, systemDefaultModel })
+      
+      // #then - actualModel should be systemDefaultModel
+      expect(resolved).not.toBeNull()
+      expect(resolved!.model).toBe(systemDefaultModel)
+    })
+
+    test("model is undefined when no model available anywhere", () => {
+      // #given - custom category with no model, no systemDefaultModel
+      const categoryName = "my-custom"
+      // Using type assertion since we're testing fallback behavior for categories without model
+      const userCategories = { "my-custom": { temperature: 0.5 } } as unknown as Record<string, CategoryConfig>
+      
+      // #when
+      const resolved = resolveCategoryConfig(categoryName, { userCategories })
+      
+      // #then - model should be undefined
+      expect(resolved).not.toBeNull()
+      expect(resolved!.model).toBeUndefined()
+    })
+  })
 })
diff --git a/src/tools/sisyphus-task/tools.ts b/src/tools/sisyphus-task/tools.ts
index d4b72079..b8a519ef 100644
--- a/src/tools/sisyphus-task/tools.ts
+++ b/src/tools/sisyphus-task/tools.ts
@@ -9,6 +9,7 @@ import { findNearestMessageWithFields, findFirstMessageWithAgent, MESSAGE_STORAG
 import { resolveMultipleSkills } from "../../features/opencode-skill-loader/skill-content"
 import { createBuiltinSkills } from "../../features/builtin-skills/skills"
 import { getTaskToastManager } from "../../features/task-toast-manager"
+import type { ModelFallbackInfo } from "../../features/task-toast-manager/types"
 import { subagentSessions, getSessionAgent } from "../../features/claude-code-session-state"
 import { log } from "../../shared/logger"
 
@@ -60,8 +61,13 @@ type ToolContextWithMetadata = {
 
 function resolveCategoryConfig(
   categoryName: string,
-  userCategories?: CategoriesConfig
-): { config: CategoryConfig; promptAppend: string } | null {
+  options: {
+    userCategories?: CategoriesConfig
+    parentModelString?: string
+    systemDefaultModel?: string
+  }
+): { config: CategoryConfig; promptAppend: string; model: string | undefined } | null {
+  const { userCategories, parentModelString, systemDefaultModel } = options
   const defaultConfig = DEFAULT_CATEGORIES[categoryName]
   const userConfig = userCategories?.[categoryName]
   const defaultPromptAppend = CATEGORY_PROMPT_APPENDS[categoryName] ?? ""
@@ -70,10 +76,13 @@ function resolveCategoryConfig(
     return null
   }
 
+  // Model priority: user override > parent model (inherit) > category default > system default
+  // Parent model takes precedence over category default so custom providers work out-of-box
+  const model = userConfig?.model ?? parentModelString ?? defaultConfig?.model ?? systemDefaultModel
   const config: CategoryConfig = {
     ...defaultConfig,
     ...userConfig,
-    model: userConfig?.model ?? defaultConfig?.model ?? "anthropic/claude-sonnet-4-5",
+    model,
   }
 
   let promptAppend = defaultPromptAppend
@@ -83,7 +92,7 @@ function resolveCategoryConfig(
       : userConfig.prompt_append
   }
 
-  return { config, promptAppend }
+  return { config, promptAppend, model }
 }
 
 export interface SisyphusTaskToolOptions {
@@ -325,18 +334,66 @@ ${textContent || "(No text output)"}`
         return `❌ Invalid arguments: Must provide either category or subagent_type.`
       }
 
+      // Fetch OpenCode config at boundary to get system default model
+      let systemDefaultModel: string | undefined
+      try {
+        const openCodeConfig = await client.config.get()
+        systemDefaultModel = (openCodeConfig as { model?: string })?.model
+      } catch {
+        // Config fetch failed, proceed without system default
+        systemDefaultModel = undefined
+      }
+
       let agentToUse: string
       let categoryModel: { providerID: string; modelID: string; variant?: string } | undefined
       let categoryPromptAppend: string | undefined
 
+      const parentModelString = parentModel
+        ? `${parentModel.providerID}/${parentModel.modelID}`
+        : undefined
+
+      let modelInfo: ModelFallbackInfo | undefined
+
       if (args.category) {
-        const resolved = resolveCategoryConfig(args.category, userCategories)
+        const resolved = resolveCategoryConfig(args.category, {
+          userCategories,
+          parentModelString,
+          systemDefaultModel,
+        })
         if (!resolved) {
           return `❌ Unknown category: "${args.category}". Available: ${Object.keys({ ...DEFAULT_CATEGORIES, ...userCategories }).join(", ")}`
         }
 
+        // Determine model source by comparing against the actual resolved model
+        const actualModel = resolved.model
+        const userDefinedModel = userCategories?.[args.category]?.model
+        const categoryDefaultModel = DEFAULT_CATEGORIES[args.category]?.model
+
+        if (!actualModel) {
+          return `❌ No model configured. Set a model in your OpenCode config, plugin config, or use a category with a default model.`
+        }
+
+        if (!parseModelString(actualModel)) {
+          return `❌ Invalid model format "${actualModel}". Expected "provider/model" format (e.g., "anthropic/claude-sonnet-4-5").`
+        }
+
+        switch (actualModel) {
+          case userDefinedModel:
+            modelInfo = { model: actualModel, type: "user-defined" }
+            break
+          case parentModelString:
+            modelInfo = { model: actualModel, type: "inherited" }
+            break
+          case categoryDefaultModel:
+            modelInfo = { model: actualModel, type: "category-default" }
+            break
+          case systemDefaultModel:
+            modelInfo = { model: actualModel, type: "system-default" }
+            break
+        }
+
         agentToUse = SISYPHUS_JUNIOR_AGENT
-        const parsedModel = parseModelString(resolved.config.model)
+        const parsedModel = parseModelString(actualModel)
         categoryModel = parsedModel
           ? (resolved.config.variant
             ? { ...parsedModel, variant: resolved.config.variant }
@@ -344,10 +401,11 @@ ${textContent || "(No text output)"}`
           : undefined
         categoryPromptAppend = resolved.promptAppend || undefined
       } else {
-        agentToUse = args.subagent_type!.trim()
-        if (!agentToUse) {
+        if (!args.subagent_type?.trim()) {
           return `❌ Agent name cannot be empty.`
         }
+        const agentName = args.subagent_type.trim()
+        agentToUse = agentName
 
         // Validate agent exists and is callable (not a primary agent)
         try {
@@ -448,6 +506,7 @@ System notifies on completion. Use \`background_output\` with task_id="${task.id
             agent: agentToUse,
             isBackground: false,
             skills: args.skills,
+            modelInfo,
           })
         }