diff --git a/.gitignore b/.gitignore
index e913cc4b..614bb35f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -5,6 +5,10 @@ node_modules/
 # Build output
 dist/
 
+# Build artifacts in src (should go to dist/)
+src/**/*.js
+src/**/*.js.map
+
 # Platform binaries (built, not committed)
 packages/*/bin/oh-my-opencode
 packages/*/bin/oh-my-opencode.exe
diff --git a/assets/oh-my-opencode.schema.json b/assets/oh-my-opencode.schema.json
index 52559dd4..0424185b 100644
--- a/assets/oh-my-opencode.schema.json
+++ b/assets/oh-my-opencode.schema.json
@@ -2060,10 +2060,7 @@
           "prompt_append": {
             "type": "string"
           }
-        },
-        "required": [
-          "model"
-        ]
+        }
       }
     },
     "claude_code": {
diff --git a/src/agents/document-writer.ts b/src/agents/document-writer.ts
index a00cdf3c..82b4580a 100644
--- a/src/agents/document-writer.ts
+++ b/src/agents/document-writer.ts
@@ -2,8 +2,6 @@ import type { AgentConfig } from "@opencode-ai/sdk"
 import type { AgentPromptMetadata } from "./types"
 import { createAgentToolRestrictions } from "../shared/permission-compat"
 
-const DEFAULT_MODEL = "google/gemini-3-flash-preview"
-
 export const DOCUMENT_WRITER_PROMPT_METADATA: AgentPromptMetadata = {
   category: "specialist",
   cost: "CHEAP",
@@ -13,9 +11,7 @@ export const DOCUMENT_WRITER_PROMPT_METADATA: AgentPromptMetadata = {
   ],
 }
 
-export function createDocumentWriterAgent(
-  model: string = DEFAULT_MODEL
-): AgentConfig {
+export function createDocumentWriterAgent(model: string): AgentConfig {
   const restrictions = createAgentToolRestrictions([])
 
   return {
@@ -221,4 +217,3 @@ You are a technical writer who creates documentation that developers actually wa
   }
 }
 
-export const documentWriterAgent = createDocumentWriterAgent()
diff --git a/src/agents/explore.ts b/src/agents/explore.ts
index 62413252..7409636b 100644
--- a/src/agents/explore.ts
+++ b/src/agents/explore.ts
@@ -2,8 +2,6 @@ import type { AgentConfig } from "@opencode-ai/sdk"
 import type { AgentPromptMetadata } from "./types"
 import { createAgentToolRestrictions } from "../shared/permission-compat"
 
-const DEFAULT_MODEL = "opencode/grok-code"
-
 export const EXPLORE_PROMPT_METADATA: AgentPromptMetadata = {
   category: "exploration",
   cost: "FREE",
@@ -24,7 +22,7 @@ export const EXPLORE_PROMPT_METADATA: AgentPromptMetadata = {
   ],
 }
 
-export function createExploreAgent(model: string = DEFAULT_MODEL): AgentConfig {
+export function createExploreAgent(model: string): AgentConfig {
   const restrictions = createAgentToolRestrictions([
     "write",
     "edit",
@@ -122,4 +120,3 @@ Flood with parallel calls. Cross-validate findings across multiple tools.`,
   }
 }
 
-export const exploreAgent = createExploreAgent()
diff --git a/src/agents/frontend-ui-ux-engineer.ts b/src/agents/frontend-ui-ux-engineer.ts
index 517e5617..999074ae 100644
--- a/src/agents/frontend-ui-ux-engineer.ts
+++ b/src/agents/frontend-ui-ux-engineer.ts
@@ -2,8 +2,6 @@ import type { AgentConfig } from "@opencode-ai/sdk"
 import type { AgentPromptMetadata } from "./types"
 import { createAgentToolRestrictions } from "../shared/permission-compat"
 
-const DEFAULT_MODEL = "google/gemini-3-pro-preview"
-
 export const FRONTEND_PROMPT_METADATA: AgentPromptMetadata = {
   category: "specialist",
   cost: "CHEAP",
@@ -19,9 +17,7 @@ export const FRONTEND_PROMPT_METADATA: AgentPromptMetadata = {
   ],
 }
 
-export function createFrontendUiUxEngineerAgent(
-  model: string = DEFAULT_MODEL
-): AgentConfig {
+export function createFrontendUiUxEngineerAgent(model: string): AgentConfig {
   const restrictions = createAgentToolRestrictions([])
 
   return {
@@ -106,4 +102,3 @@ Interpret creatively and make unexpected choices that feel genuinely designed fo
   }
 }
 
-export const frontendUiUxEngineerAgent = createFrontendUiUxEngineerAgent()
diff --git a/src/agents/index.ts b/src/agents/index.ts
index 16803440..795c6558 100644
--- a/src/agents/index.ts
+++ b/src/agents/index.ts
@@ -1,28 +1,13 @@
-import type { AgentConfig } from "@opencode-ai/sdk"
-import { sisyphusAgent } from "./sisyphus"
-import { oracleAgent } from "./oracle"
-import { librarianAgent } from "./librarian"
-import { exploreAgent } from "./explore"
-import { frontendUiUxEngineerAgent } from "./frontend-ui-ux-engineer"
-import { documentWriterAgent } from "./document-writer"
-import { multimodalLookerAgent } from "./multimodal-looker"
-import { metisAgent } from "./metis"
-import { orchestratorSisyphusAgent } from "./orchestrator-sisyphus"
-import { momusAgent } from "./momus"
-
-export const builtinAgents: Record<string, AgentConfig> = {
-  Sisyphus: sisyphusAgent,
-  oracle: oracleAgent,
-  librarian: librarianAgent,
-  explore: exploreAgent,
-  "frontend-ui-ux-engineer": frontendUiUxEngineerAgent,
-  "document-writer": documentWriterAgent,
-  "multimodal-looker": multimodalLookerAgent,
-  "Metis (Plan Consultant)": metisAgent,
-  "Momus (Plan Reviewer)": momusAgent,
-  "orchestrator-sisyphus": orchestratorSisyphusAgent,
-}
-
 export * from "./types"
 export { createBuiltinAgents } from "./utils"
 export type { AvailableAgent } from "./sisyphus-prompt-builder"
+export { createSisyphusAgent } from "./sisyphus"
+export { createOracleAgent, ORACLE_PROMPT_METADATA } from "./oracle"
+export { createLibrarianAgent, LIBRARIAN_PROMPT_METADATA } from "./librarian"
+export { createExploreAgent, EXPLORE_PROMPT_METADATA } from "./explore"
+export { createFrontendUiUxEngineerAgent, FRONTEND_PROMPT_METADATA } from "./frontend-ui-ux-engineer"
+export { createDocumentWriterAgent, DOCUMENT_WRITER_PROMPT_METADATA } from "./document-writer"
+export { createMultimodalLookerAgent, MULTIMODAL_LOOKER_PROMPT_METADATA } from "./multimodal-looker"
+export { createMetisAgent, METIS_SYSTEM_PROMPT, metisPromptMetadata } from "./metis"
+export { createMomusAgent, MOMUS_SYSTEM_PROMPT, momusPromptMetadata } from "./momus"
+export { createOrchestratorSisyphusAgent, orchestratorSisyphusPromptMetadata } from "./orchestrator-sisyphus"
diff --git a/src/agents/librarian.ts b/src/agents/librarian.ts
index ace46b7b..b6ed3344 100644
--- a/src/agents/librarian.ts
+++ b/src/agents/librarian.ts
@@ -2,8 +2,6 @@ import type { AgentConfig } from "@opencode-ai/sdk"
 import type { AgentPromptMetadata } from "./types"
 import { createAgentToolRestrictions } from "../shared/permission-compat"
 
-const DEFAULT_MODEL = "opencode/glm-4.7-free"
-
 export const LIBRARIAN_PROMPT_METADATA: AgentPromptMetadata = {
   category: "exploration",
   cost: "CHEAP",
@@ -21,7 +19,7 @@ export const LIBRARIAN_PROMPT_METADATA: AgentPromptMetadata = {
   ],
 }
 
-export function createLibrarianAgent(model: string = DEFAULT_MODEL): AgentConfig {
+export function createLibrarianAgent(model: string): AgentConfig {
   const restrictions = createAgentToolRestrictions([
     "write",
     "edit",
@@ -326,4 +324,3 @@ grep_app_searchGitHub(query: "useQuery")
   }
 }
 
-export const librarianAgent = createLibrarianAgent()
diff --git a/src/agents/metis.ts b/src/agents/metis.ts
index 0edc6013..5e14e41f 100644
--- a/src/agents/metis.ts
+++ b/src/agents/metis.ts
@@ -278,9 +278,7 @@ const metisRestrictions = createAgentToolRestrictions([
   "delegate_task",
 ])
 
-const DEFAULT_MODEL = "anthropic/claude-opus-4-5"
-
-export function createMetisAgent(model: string = DEFAULT_MODEL): AgentConfig {
+export function createMetisAgent(model: string): AgentConfig {
   return {
     description:
       "Pre-planning consultant that analyzes requests to identify hidden intentions, ambiguities, and AI failure points.",
@@ -293,7 +291,6 @@ export function createMetisAgent(model: string = DEFAULT_MODEL): AgentConfig {
   } as AgentConfig
 }
 
-export const metisAgent: AgentConfig = createMetisAgent()
 
 export const metisPromptMetadata: AgentPromptMetadata = {
   category: "advisor",
diff --git a/src/agents/momus.ts b/src/agents/momus.ts
index de816b47..cfe29179 100644
--- a/src/agents/momus.ts
+++ b/src/agents/momus.ts
@@ -17,8 +17,6 @@ import { createAgentToolRestrictions } from "../shared/permission-compat"
  * implementation.
  */
 
-const DEFAULT_MODEL = "openai/gpt-5.2"
-
 export const MOMUS_SYSTEM_PROMPT = `You are a work plan review expert. You review the provided work plan (.sisyphus/plans/{name}.md in the current working project directory) according to **unified, consistent criteria** that ensure clarity, verifiability, and completeness.
 
 **CRITICAL FIRST RULE**:
@@ -391,7 +389,7 @@ Use structured format, **in the same language as the work plan**.
 **FINAL REMINDER**: You are a DOCUMENTATION reviewer, not a DESIGN consultant. The author's implementation direction is SACRED. Your job ends at "Is this well-documented enough to execute?" - NOT "Is this the right approach?"
 `
 
-export function createMomusAgent(model: string = DEFAULT_MODEL): AgentConfig {
+export function createMomusAgent(model: string): AgentConfig {
   const restrictions = createAgentToolRestrictions([
     "write",
     "edit",
@@ -416,7 +414,6 @@ export function createMomusAgent(model: string = DEFAULT_MODEL): AgentConfig {
   return { ...base, thinking: { type: "enabled", budgetTokens: 32000 } } as AgentConfig
 }
 
-export const momusAgent = createMomusAgent()
 
 export const momusPromptMetadata: AgentPromptMetadata = {
   category: "advisor",
diff --git a/src/agents/multimodal-looker.ts b/src/agents/multimodal-looker.ts
index 010fda0c..e4f9ad40 100644
--- a/src/agents/multimodal-looker.ts
+++ b/src/agents/multimodal-looker.ts
@@ -2,8 +2,6 @@ import type { AgentConfig } from "@opencode-ai/sdk"
 import type { AgentPromptMetadata } from "./types"
 import { createAgentToolAllowlist } from "../shared/permission-compat"
 
-const DEFAULT_MODEL = "google/gemini-3-flash"
-
 export const MULTIMODAL_LOOKER_PROMPT_METADATA: AgentPromptMetadata = {
   category: "utility",
   cost: "CHEAP",
@@ -11,9 +9,7 @@ export const MULTIMODAL_LOOKER_PROMPT_METADATA: AgentPromptMetadata = {
   triggers: [],
 }
 
-export function createMultimodalLookerAgent(
-  model: string = DEFAULT_MODEL
-): AgentConfig {
+export function createMultimodalLookerAgent(model: string): AgentConfig {
   const restrictions = createAgentToolAllowlist(["read"])
 
   return {
@@ -58,4 +54,3 @@ Your output goes straight to the main agent for continued work.`,
   }
 }
 
-export const multimodalLookerAgent = createMultimodalLookerAgent()
diff --git a/src/agents/oracle.ts b/src/agents/oracle.ts
index 131b4367..e58978ee 100644
--- a/src/agents/oracle.ts
+++ b/src/agents/oracle.ts
@@ -3,8 +3,6 @@ import type { AgentPromptMetadata } from "./types"
 import { isGptModel } from "./types"
 import { createAgentToolRestrictions } from "../shared/permission-compat"
 
-const DEFAULT_MODEL = "openai/gpt-5.2"
-
 export const ORACLE_PROMPT_METADATA: AgentPromptMetadata = {
   category: "advisor",
   cost: "EXPENSIVE",
@@ -97,7 +95,7 @@ Organize your final answer in three tiers:
 
 Your response goes directly to the user with no intermediate processing. Make your final message self-contained: a clear recommendation they can act on immediately, covering both what to do and why.`
 
-export function createOracleAgent(model: string = DEFAULT_MODEL): AgentConfig {
+export function createOracleAgent(model: string): AgentConfig {
   const restrictions = createAgentToolRestrictions([
     "write",
     "edit",
@@ -122,4 +120,3 @@ export function createOracleAgent(model: string = DEFAULT_MODEL): AgentConfig {
   return { ...base, thinking: { type: "enabled", budgetTokens: 32000 } } as AgentConfig
 }
 
-export const oracleAgent = createOracleAgent()
diff --git a/src/agents/orchestrator-sisyphus.ts b/src/agents/orchestrator-sisyphus.ts
index bfce6e2a..62bfe1d2 100644
--- a/src/agents/orchestrator-sisyphus.ts
+++ b/src/agents/orchestrator-sisyphus.ts
@@ -1458,9 +1458,10 @@ function buildDynamicOrchestratorPrompt(ctx?: OrchestratorContext): string {
     .replace("{SKILLS_SECTION}", skillsSection)
 }
 
-const DEFAULT_MODEL = "anthropic/claude-sonnet-4-5"
-
-export function createOrchestratorSisyphusAgent(ctx?: OrchestratorContext): AgentConfig {
+export function createOrchestratorSisyphusAgent(ctx: OrchestratorContext): AgentConfig {
+  if (!ctx.model) {
+    throw new Error("createOrchestratorSisyphusAgent requires a model in context")
+  }
   const restrictions = createAgentToolRestrictions([
     "task",
     "call_omo_agent",
@@ -1469,7 +1470,7 @@ export function createOrchestratorSisyphusAgent(ctx?: OrchestratorContext): Agen
     description:
       "Orchestrates work via delegate_task() to complete ALL tasks in a todo list until fully done",
     mode: "primary" as const,
-    model: ctx?.model ?? DEFAULT_MODEL,
+    model: ctx.model,
     temperature: 0.1,
     prompt: buildDynamicOrchestratorPrompt(ctx),
     thinking: { type: "enabled", budgetTokens: 32000 },
@@ -1478,8 +1479,6 @@ export function createOrchestratorSisyphusAgent(ctx?: OrchestratorContext): Agen
   } as AgentConfig
 }
 
-export const orchestratorSisyphusAgent: AgentConfig = createOrchestratorSisyphusAgent()
-
 export const orchestratorSisyphusPromptMetadata: AgentPromptMetadata = {
   category: "advisor",
   cost: "EXPENSIVE",
diff --git a/src/agents/sisyphus-junior.ts b/src/agents/sisyphus-junior.ts
index 89cb7821..4401533b 100644
--- a/src/agents/sisyphus-junior.ts
+++ b/src/agents/sisyphus-junior.ts
@@ -138,7 +138,7 @@ export function createSisyphusJuniorAgent(
   promptAppend?: string
 ): AgentConfig {
   const prompt = buildSisyphusJuniorPrompt(promptAppend)
-  const model = categoryConfig.model
+  const model = categoryConfig.model ?? SISYPHUS_JUNIOR_DEFAULTS.model
   const baseRestrictions = createAgentToolRestrictions(BLOCKED_TOOLS)
   const categoryPermission = categoryConfig.tools
     ? Object.fromEntries(
diff --git a/src/agents/sisyphus.ts b/src/agents/sisyphus.ts
index 62c39ec1..7b3b5a8e 100644
--- a/src/agents/sisyphus.ts
+++ b/src/agents/sisyphus.ts
@@ -14,8 +14,6 @@ import {
   categorizeTools,
 } from "./sisyphus-prompt-builder"
 
-const DEFAULT_MODEL = "anthropic/claude-opus-4-5"
-
 const SISYPHUS_ROLE_SECTION = `<Role>
 You are "Sisyphus" - Powerful AI Agent with orchestration capabilities from OhMyOpenCode.
 
@@ -607,7 +605,7 @@ function buildDynamicSisyphusPrompt(
 }
 
 export function createSisyphusAgent(
-  model: string = DEFAULT_MODEL,
+  model: string,
   availableAgents?: AvailableAgent[],
   availableToolNames?: string[],
   availableSkills?: AvailableSkill[]
@@ -637,4 +635,3 @@ export function createSisyphusAgent(
   return { ...base, thinking: { type: "enabled", budgetTokens: 32000 } }
 }
 
-export const sisyphusAgent = createSisyphusAgent()
diff --git a/src/agents/types.ts b/src/agents/types.ts
index a0f6d26d..d808703b 100644
--- a/src/agents/types.ts
+++ b/src/agents/types.ts
@@ -1,6 +1,6 @@
 import type { AgentConfig } from "@opencode-ai/sdk"
 
-export type AgentFactory = (model?: string) => AgentConfig
+export type AgentFactory = (model: string) => AgentConfig
 
 /**
  * Agent category for grouping in Sisyphus prompt sections
diff --git a/src/agents/utils.test.ts b/src/agents/utils.test.ts
index 336ed628..85df26f6 100644
--- a/src/agents/utils.test.ts
+++ b/src/agents/utils.test.ts
@@ -2,12 +2,14 @@ import { describe, test, expect } from "bun:test"
 import { createBuiltinAgents } from "./utils"
 import type { AgentConfig } from "@opencode-ai/sdk"
 
+const TEST_DEFAULT_MODEL = "anthropic/claude-opus-4-5"
+
 describe("createBuiltinAgents with model overrides", () => {
   test("Sisyphus with default model has thinking config", () => {
-    // #given - no overrides
+    // #given - no overrides, using systemDefaultModel
 
     // #when
-    const agents = createBuiltinAgents()
+    const agents = createBuiltinAgents([], {}, undefined, TEST_DEFAULT_MODEL)
 
     // #then
     expect(agents.Sisyphus.model).toBe("anthropic/claude-opus-4-5")
@@ -22,7 +24,7 @@ describe("createBuiltinAgents with model overrides", () => {
     }
 
     // #when
-    const agents = createBuiltinAgents([], overrides)
+    const agents = createBuiltinAgents([], overrides, undefined, TEST_DEFAULT_MODEL)
 
     // #then
     expect(agents.Sisyphus.model).toBe("github-copilot/gpt-5.2")
@@ -44,10 +46,26 @@ describe("createBuiltinAgents with model overrides", () => {
   })
 
   test("Oracle with default model has reasoningEffort", () => {
-    // #given - no overrides
+    // #given - no overrides, using systemDefaultModel for other agents
+    // Oracle uses its own default model (openai/gpt-5.2) from the factory singleton
 
     // #when
-    const agents = createBuiltinAgents()
+    const agents = createBuiltinAgents([], {}, undefined, TEST_DEFAULT_MODEL)
+
+    // #then - Oracle uses systemDefaultModel since model is now required
+    expect(agents.oracle.model).toBe("anthropic/claude-opus-4-5")
+    expect(agents.oracle.thinking).toEqual({ type: "enabled", budgetTokens: 32000 })
+    expect(agents.oracle.reasoningEffort).toBeUndefined()
+  })
+
+  test("Oracle with GPT model override has reasoningEffort, no thinking", () => {
+    // #given
+    const overrides = {
+      oracle: { model: "openai/gpt-5.2" },
+    }
+
+    // #when
+    const agents = createBuiltinAgents([], overrides, undefined, TEST_DEFAULT_MODEL)
 
     // #then
     expect(agents.oracle.model).toBe("openai/gpt-5.2")
@@ -63,7 +81,7 @@ describe("createBuiltinAgents with model overrides", () => {
     }
 
     // #when
-    const agents = createBuiltinAgents([], overrides)
+    const agents = createBuiltinAgents([], overrides, undefined, TEST_DEFAULT_MODEL)
 
     // #then
     expect(agents.oracle.model).toBe("anthropic/claude-sonnet-4")
@@ -79,7 +97,7 @@ describe("createBuiltinAgents with model overrides", () => {
     }
 
     // #when
-    const agents = createBuiltinAgents([], overrides)
+    const agents = createBuiltinAgents([], overrides, undefined, TEST_DEFAULT_MODEL)
 
     // #then
     expect(agents.Sisyphus.model).toBe("github-copilot/gpt-5.2")
@@ -89,9 +107,10 @@ describe("createBuiltinAgents with model overrides", () => {
 
 describe("buildAgent with category and skills", () => {
   const { buildAgent } = require("./utils")
+  const TEST_MODEL = "anthropic/claude-opus-4-5"
 
   test("agent with category inherits category settings", () => {
-    // #given
+    // #given - agent factory that sets category but no model
     const source = {
       "test-agent": () =>
         ({
@@ -101,10 +120,11 @@ describe("buildAgent with category and skills", () => {
     }
 
     // #when
-    const agent = buildAgent(source["test-agent"])
+    const agent = buildAgent(source["test-agent"], TEST_MODEL)
 
-    // #then
-    expect(agent.model).toBe("google/gemini-3-pro-preview")
+    // #then - DEFAULT_CATEGORIES only has temperature, not model
+    // Model remains undefined since neither factory nor category provides it
+    expect(agent.model).toBeUndefined()
     expect(agent.temperature).toBe(0.7)
   })
 
@@ -120,7 +140,7 @@ describe("buildAgent with category and skills", () => {
     }
 
     // #when
-    const agent = buildAgent(source["test-agent"])
+    const agent = buildAgent(source["test-agent"], TEST_MODEL)
 
     // #then
     expect(agent.model).toBe("custom/model")
@@ -145,7 +165,7 @@ describe("buildAgent with category and skills", () => {
     }
 
     // #when
-    const agent = buildAgent(source["test-agent"], undefined, categories)
+    const agent = buildAgent(source["test-agent"], TEST_MODEL, categories)
 
     // #then
     expect(agent.model).toBe("openai/gpt-5.2")
@@ -164,7 +184,7 @@ describe("buildAgent with category and skills", () => {
     }
 
     // #when
-    const agent = buildAgent(source["test-agent"])
+    const agent = buildAgent(source["test-agent"], TEST_MODEL)
 
     // #then
     expect(agent.prompt).toContain("Role: Designer-Turned-Developer")
@@ -184,7 +204,7 @@ describe("buildAgent with category and skills", () => {
     }
 
     // #when
-    const agent = buildAgent(source["test-agent"])
+    const agent = buildAgent(source["test-agent"], TEST_MODEL)
 
     // #then
     expect(agent.prompt).toContain("Role: Designer-Turned-Developer")
@@ -204,7 +224,7 @@ describe("buildAgent with category and skills", () => {
     }
 
     // #when
-    const agent = buildAgent(source["test-agent"])
+    const agent = buildAgent(source["test-agent"], TEST_MODEL)
 
     // #then
     expect(agent.model).toBe("custom/model")
@@ -225,10 +245,10 @@ describe("buildAgent with category and skills", () => {
     }
 
     // #when
-    const agent = buildAgent(source["test-agent"])
+    const agent = buildAgent(source["test-agent"], TEST_MODEL)
 
-    // #then
-    expect(agent.model).toBe("openai/gpt-5.2")
+    // #then - DEFAULT_CATEGORIES["ultrabrain"] only has temperature, not model
+    expect(agent.model).toBeUndefined()
     expect(agent.temperature).toBe(0.1)
     expect(agent.prompt).toContain("Role: Designer-Turned-Developer")
     expect(agent.prompt).toContain("Task description")
@@ -246,9 +266,11 @@ describe("buildAgent with category and skills", () => {
     }
 
     // #when
-    const agent = buildAgent(source["test-agent"])
+    const agent = buildAgent(source["test-agent"], TEST_MODEL)
 
     // #then
+    // Note: The factory receives model, but if category doesn't exist, it's not applied
+    // The agent's model comes from the factory output (which doesn't set model)
     expect(agent.model).toBeUndefined()
     expect(agent.prompt).toBe("Base prompt")
   })
@@ -265,7 +287,7 @@ describe("buildAgent with category and skills", () => {
     }
 
     // #when
-    const agent = buildAgent(source["test-agent"])
+    const agent = buildAgent(source["test-agent"], TEST_MODEL)
 
     // #then
     expect(agent.prompt).toContain("Role: Designer-Turned-Developer")
@@ -284,7 +306,7 @@ describe("buildAgent with category and skills", () => {
     }
 
     // #when
-    const agent = buildAgent(source["test-agent"])
+    const agent = buildAgent(source["test-agent"], TEST_MODEL)
 
     // #then
     expect(agent.prompt).toBe("Base prompt")
diff --git a/src/agents/utils.ts b/src/agents/utils.ts
index cd5c67db..4780675a 100644
--- a/src/agents/utils.ts
+++ b/src/agents/utils.ts
@@ -9,7 +9,7 @@ import { createFrontendUiUxEngineerAgent, FRONTEND_PROMPT_METADATA } from "./fro
 import { createDocumentWriterAgent, DOCUMENT_WRITER_PROMPT_METADATA } from "./document-writer"
 import { createMultimodalLookerAgent, MULTIMODAL_LOOKER_PROMPT_METADATA } from "./multimodal-looker"
 import { createMetisAgent } from "./metis"
-import { createOrchestratorSisyphusAgent, orchestratorSisyphusAgent } from "./orchestrator-sisyphus"
+import { createOrchestratorSisyphusAgent } from "./orchestrator-sisyphus"
 import { createMomusAgent } from "./momus"
 import type { AvailableAgent } from "./sisyphus-prompt-builder"
 import { deepMerge } from "../shared"
@@ -28,7 +28,9 @@ const agentSources: Record<BuiltinAgentName, AgentSource> = {
   "multimodal-looker": createMultimodalLookerAgent,
   "Metis (Plan Consultant)": createMetisAgent,
   "Momus (Plan Reviewer)": createMomusAgent,
-  "orchestrator-sisyphus": orchestratorSisyphusAgent,
+  // Note: orchestrator-sisyphus is handled specially in createBuiltinAgents()
+  // because it needs OrchestratorContext, not just a model string
+  "orchestrator-sisyphus": createOrchestratorSisyphusAgent as unknown as AgentFactory,
 }
 
 /**
@@ -50,7 +52,7 @@ function isFactory(source: AgentSource): source is AgentFactory {
 
 export function buildAgent(
   source: AgentSource,
-  model?: string,
+  model: string,
   categories?: CategoriesConfig,
   gitMasterConfig?: GitMasterConfig
 ): AgentConfig {
@@ -134,6 +136,10 @@ export function createBuiltinAgents(
   categories?: CategoriesConfig,
   gitMasterConfig?: GitMasterConfig
 ): Record<string, AgentConfig> {
+  if (!systemDefaultModel) {
+    throw new Error("createBuiltinAgents requires systemDefaultModel")
+  }
+
   const result: Record<string, AgentConfig> = {}
   const availableAgents: AvailableAgent[] = []
 
@@ -149,7 +155,7 @@ export function createBuiltinAgents(
     if (disabledAgents.includes(agentName)) continue
 
     const override = agentOverrides[agentName]
-    const model = override?.model
+    const model = override?.model ?? systemDefaultModel
 
     let config = buildAgent(source, model, mergedCategories, gitMasterConfig)
 
diff --git a/src/cli/config-manager.test.ts b/src/cli/config-manager.test.ts
index b6d0fc1d..ad4255d0 100644
--- a/src/cli/config-manager.test.ts
+++ b/src/cli/config-manager.test.ts
@@ -200,85 +200,32 @@ describe("config-manager ANTIGRAVITY_PROVIDER_CONFIG", () => {
   })
 })
 
-describe("generateOmoConfig - GitHub Copilot fallback", () => {
-  test("frontend-ui-ux-engineer uses Copilot when no native providers", () => {
-    // #given user has only Copilot (no Claude, ChatGPT, Gemini)
+describe("generateOmoConfig - v3 beta: no hardcoded models", () => {
+  test("generates minimal config with only $schema", () => {
+    // #given any install config
     const config: InstallConfig = {
-      hasClaude: false,
+      hasClaude: true,
       isMax20: false,
-      hasChatGPT: false,
+      hasChatGPT: true,
       hasGemini: false,
-      hasCopilot: true,
+      hasCopilot: false,
     }
 
     // #when generating config
     const result = generateOmoConfig(config)
 
-    // #then frontend-ui-ux-engineer should use Copilot Gemini
-    const agents = result.agents as Record<string, { model?: string }>
-    expect(agents["frontend-ui-ux-engineer"]?.model).toBe("github-copilot/gemini-3-pro-preview")
+    // #then should only contain $schema, no agents or categories
+    expect(result.$schema).toBe("https://raw.githubusercontent.com/code-yeongyu/oh-my-opencode/master/assets/oh-my-opencode.schema.json")
+    expect(result.agents).toBeUndefined()
+    expect(result.categories).toBeUndefined()
   })
 
-  test("document-writer uses Copilot when no native providers", () => {
-    // #given user has only Copilot
+  test("does not include model fields regardless of provider config", () => {
+    // #given user has multiple providers
     const config: InstallConfig = {
-      hasClaude: false,
-      isMax20: false,
-      hasChatGPT: false,
-      hasGemini: false,
-      hasCopilot: true,
-    }
-
-    // #when generating config
-    const result = generateOmoConfig(config)
-
-    // #then document-writer should use Copilot Gemini Flash
-    const agents = result.agents as Record<string, { model?: string }>
-    expect(agents["document-writer"]?.model).toBe("github-copilot/gemini-3-flash-preview")
-  })
-
-  test("multimodal-looker uses Copilot when no native providers", () => {
-    // #given user has only Copilot
-    const config: InstallConfig = {
-      hasClaude: false,
-      isMax20: false,
-      hasChatGPT: false,
-      hasGemini: false,
-      hasCopilot: true,
-    }
-
-    // #when generating config
-    const result = generateOmoConfig(config)
-
-    // #then multimodal-looker should use Copilot Gemini Flash
-    const agents = result.agents as Record<string, { model?: string }>
-    expect(agents["multimodal-looker"]?.model).toBe("github-copilot/gemini-3-flash-preview")
-  })
-
-  test("explore uses Copilot grok-code when no native providers", () => {
-    // #given user has only Copilot
-    const config: InstallConfig = {
-      hasClaude: false,
-      isMax20: false,
-      hasChatGPT: false,
-      hasGemini: false,
-      hasCopilot: true,
-    }
-
-    // #when generating config
-    const result = generateOmoConfig(config)
-
-    // #then explore should use Copilot Grok
-    const agents = result.agents as Record<string, { model?: string }>
-    expect(agents["explore"]?.model).toBe("github-copilot/grok-code-fast-1")
-  })
-
-  test("native Gemini takes priority over Copilot for frontend-ui-ux-engineer", () => {
-    // #given user has both Gemini and Copilot
-    const config: InstallConfig = {
-      hasClaude: false,
-      isMax20: false,
-      hasChatGPT: false,
+      hasClaude: true,
+      isMax20: true,
+      hasChatGPT: true,
       hasGemini: true,
       hasCopilot: true,
     }
@@ -286,46 +233,27 @@ describe("generateOmoConfig - GitHub Copilot fallback", () => {
     // #when generating config
     const result = generateOmoConfig(config)
 
-    // #then native Gemini should be used (NOT Copilot)
-    const agents = result.agents as Record<string, { model?: string }>
-    expect(agents["frontend-ui-ux-engineer"]?.model).toBe("google/antigravity-gemini-3-pro-high")
+    // #then should not have agents or categories with model fields
+    expect(result.agents).toBeUndefined()
+    expect(result.categories).toBeUndefined()
   })
 
-  test("native Claude takes priority over Copilot for frontend-ui-ux-engineer", () => {
-    // #given user has Claude and Copilot but no Gemini
-    const config: InstallConfig = {
-      hasClaude: true,
-      isMax20: false,
-      hasChatGPT: false,
-      hasGemini: false,
-      hasCopilot: true,
-    }
-
-    // #when generating config
-    const result = generateOmoConfig(config)
-
-    // #then native Claude should be used (NOT Copilot)
-    const agents = result.agents as Record<string, { model?: string }>
-    expect(agents["frontend-ui-ux-engineer"]?.model).toBe("anthropic/claude-opus-4-5")
-  })
-
-  test("categories use Copilot models when no native Gemini", () => {
-    // #given user has Copilot but no Gemini
+  test("does not include model fields when no providers configured", () => {
+    // #given user has no providers
     const config: InstallConfig = {
       hasClaude: false,
       isMax20: false,
       hasChatGPT: false,
       hasGemini: false,
-      hasCopilot: true,
+      hasCopilot: false,
     }
 
     // #when generating config
     const result = generateOmoConfig(config)
 
-    // #then categories should use Copilot models
-    const categories = result.categories as Record<string, { model?: string }>
-    expect(categories?.["visual-engineering"]?.model).toBe("github-copilot/gemini-3-pro-preview")
-    expect(categories?.["artistry"]?.model).toBe("github-copilot/gemini-3-pro-preview")
-    expect(categories?.["writing"]?.model).toBe("github-copilot/gemini-3-flash-preview")
+    // #then should still only contain $schema
+    expect(result.$schema).toBe("https://raw.githubusercontent.com/code-yeongyu/oh-my-opencode/master/assets/oh-my-opencode.schema.json")
+    expect(result.agents).toBeUndefined()
+    expect(result.categories).toBeUndefined()
   })
 })
diff --git a/src/cli/config-manager.ts b/src/cli/config-manager.ts
index 37a96dc7..a11c7eb2 100644
--- a/src/cli/config-manager.ts
+++ b/src/cli/config-manager.ts
@@ -306,79 +306,13 @@ function deepMerge<T extends Record<string, unknown>>(target: T, source: Partial
   return result
 }
 
-export function generateOmoConfig(installConfig: InstallConfig): Record<string, unknown> {
+export function generateOmoConfig(_installConfig: InstallConfig): Record<string, unknown> {
+  // v3 beta: No hardcoded model strings - users rely on their OpenCode configured model
+  // Users who want specific models configure them explicitly after install
   const config: Record<string, unknown> = {
     $schema: "https://raw.githubusercontent.com/code-yeongyu/oh-my-opencode/master/assets/oh-my-opencode.schema.json",
   }
 
-  const agents: Record<string, Record<string, unknown>> = {}
-
-  if (!installConfig.hasClaude) {
-    agents["Sisyphus"] = {
-      model: installConfig.hasCopilot ? "github-copilot/claude-opus-4.5" : "opencode/glm-4.7-free",
-    }
-  }
-
-  agents["librarian"] = { model: "opencode/glm-4.7-free" }
-
-  // Gemini models use `antigravity-` prefix for explicit Antigravity quota routing
-  // @see ANTIGRAVITY_PROVIDER_CONFIG comments for rationale
-  if (installConfig.hasGemini) {
-    agents["explore"] = { model: "google/antigravity-gemini-3-flash" }
-  } else if (installConfig.hasClaude && installConfig.isMax20) {
-    agents["explore"] = { model: "anthropic/claude-haiku-4-5" }
-  } else if (installConfig.hasCopilot) {
-    agents["explore"] = { model: "github-copilot/grok-code-fast-1" }
-  } else {
-    agents["explore"] = { model: "opencode/glm-4.7-free" }
-  }
-
-  if (!installConfig.hasChatGPT) {
-    const oracleFallback = installConfig.hasCopilot
-      ? "github-copilot/gpt-5.2"
-      : installConfig.hasClaude
-        ? "anthropic/claude-opus-4-5"
-        : "opencode/glm-4.7-free"
-    agents["oracle"] = { model: oracleFallback }
-  }
-
-  if (installConfig.hasGemini) {
-    agents["frontend-ui-ux-engineer"] = { model: "google/antigravity-gemini-3-pro-high" }
-    agents["document-writer"] = { model: "google/antigravity-gemini-3-flash" }
-    agents["multimodal-looker"] = { model: "google/antigravity-gemini-3-flash" }
-  } else if (installConfig.hasClaude) {
-    agents["frontend-ui-ux-engineer"] = { model: "anthropic/claude-opus-4-5" }
-    agents["document-writer"] = { model: "anthropic/claude-opus-4-5" }
-    agents["multimodal-looker"] = { model: "anthropic/claude-opus-4-5" }
-  } else if (installConfig.hasCopilot) {
-    agents["frontend-ui-ux-engineer"] = { model: "github-copilot/gemini-3-pro-preview" }
-    agents["document-writer"] = { model: "github-copilot/gemini-3-flash-preview" }
-    agents["multimodal-looker"] = { model: "github-copilot/gemini-3-flash-preview" }
-  } else {
-    agents["frontend-ui-ux-engineer"] = { model: "opencode/glm-4.7-free" }
-    agents["document-writer"] = { model: "opencode/glm-4.7-free" }
-    agents["multimodal-looker"] = { model: "opencode/glm-4.7-free" }
-  }
-
-  if (Object.keys(agents).length > 0) {
-    config.agents = agents
-  }
-
-  // Categories: override model for Antigravity auth or GitHub Copilot fallback
-  if (installConfig.hasGemini) {
-    config.categories = {
-      "visual-engineering": { model: "google/gemini-3-pro-high" },
-      artistry: { model: "google/gemini-3-pro-high" },
-      writing: { model: "google/gemini-3-flash-high" },
-    }
-  } else if (installConfig.hasCopilot) {
-    config.categories = {
-      "visual-engineering": { model: "github-copilot/gemini-3-pro-preview" },
-      artistry: { model: "github-copilot/gemini-3-pro-preview" },
-      writing: { model: "github-copilot/gemini-3-flash-preview" },
-    }
-  }
-
   return config
 }
 
@@ -646,11 +580,9 @@ export function addProviderConfig(config: InstallConfig): ConfigMergeResult {
   }
 }
 
-interface OmoConfigData {
-  agents?: Record<string, { model?: string }>
-}
-
 export function detectCurrentConfig(): DetectedConfig {
+  // v3 beta: Since we no longer generate hardcoded model strings,
+  // detection only checks for plugin installation and Gemini auth plugin
   const result: DetectedConfig = {
     isInstalled: false,
     hasClaude: true,
@@ -678,53 +610,8 @@ export function detectCurrentConfig(): DetectedConfig {
     return result
   }
 
+  // Gemini auth plugin detection still works via plugin presence
   result.hasGemini = plugins.some((p) => p.startsWith("opencode-antigravity-auth"))
 
-  const omoConfigPath = getOmoConfig()
-  if (!existsSync(omoConfigPath)) {
-    return result
-  }
-
-  try {
-    const stat = statSync(omoConfigPath)
-    if (stat.size === 0) {
-      return result
-    }
-
-    const content = readFileSync(omoConfigPath, "utf-8")
-    if (isEmptyOrWhitespace(content)) {
-      return result
-    }
-
-    const omoConfig = parseJsonc<OmoConfigData>(content)
-    if (!omoConfig || typeof omoConfig !== "object") {
-      return result
-    }
-
-    const agents = omoConfig.agents ?? {}
-
-    if (agents["Sisyphus"]?.model === "opencode/glm-4.7-free") {
-      result.hasClaude = false
-      result.isMax20 = false
-    } else if (agents["librarian"]?.model === "opencode/glm-4.7-free") {
-      result.hasClaude = true
-      result.isMax20 = false
-    }
-
-    if (agents["oracle"]?.model?.startsWith("anthropic/")) {
-      result.hasChatGPT = false
-    } else if (agents["oracle"]?.model === "opencode/glm-4.7-free") {
-      result.hasChatGPT = false
-    }
-
-    const hasAnyCopilotModel = Object.values(agents).some(
-      (agent) => agent?.model?.startsWith("github-copilot/")
-    )
-    result.hasCopilot = hasAnyCopilotModel
-
-  } catch {
-    /* intentionally empty - malformed omo config returns defaults from opencode config detection */
-  }
-
   return result
 }
diff --git a/src/cli/install.ts b/src/cli/install.ts
index d7c8fce8..402a1d4b 100644
--- a/src/cli/install.ts
+++ b/src/cli/install.ts
@@ -47,18 +47,11 @@ function formatConfigSummary(config: InstallConfig): string {
   lines.push(color.dim("─".repeat(40)))
   lines.push("")
 
-  lines.push(color.bold(color.white("Agent Configuration")))
+  // v3 beta: No hardcoded models - agents use OpenCode's configured default model
+  lines.push(color.bold(color.white("Agent Models")))
   lines.push("")
-
-  const sisyphusModel = config.hasClaude ? "claude-opus-4-5" : (config.hasCopilot ? "github-copilot/claude-opus-4.5" : "glm-4.7-free")
-  const oracleModel = config.hasChatGPT ? "gpt-5.2" : (config.hasCopilot ? "github-copilot/gpt-5.2" : (config.hasClaude ? "claude-opus-4-5" : "glm-4.7-free"))
-  const librarianModel = "glm-4.7-free"
-  const frontendModel = config.hasGemini ? "antigravity-gemini-3-pro-high" : (config.hasClaude ? "claude-opus-4-5" : "glm-4.7-free")
-
-  lines.push(`  ${SYMBOLS.bullet} Sisyphus     ${SYMBOLS.arrow} ${color.cyan(sisyphusModel)}`)
-  lines.push(`  ${SYMBOLS.bullet} Oracle       ${SYMBOLS.arrow} ${color.cyan(oracleModel)}`)
-  lines.push(`  ${SYMBOLS.bullet} Librarian    ${SYMBOLS.arrow} ${color.cyan(librarianModel)}`)
-  lines.push(`  ${SYMBOLS.bullet} Frontend     ${SYMBOLS.arrow} ${color.cyan(frontendModel)}`)
+  lines.push(`  ${SYMBOLS.info} Agents will use your OpenCode default model`)
+  lines.push(`  ${SYMBOLS.bullet} Configure specific models in ${color.cyan("oh-my-opencode.json")} if needed`)
 
   return lines.join("\n")
 }
diff --git a/src/config/schema.ts b/src/config/schema.ts
index df16d886..8be0a144 100644
--- a/src/config/schema.ts
+++ b/src/config/schema.ts
@@ -154,7 +154,7 @@ export const SisyphusAgentConfigSchema = z.object({
 })
 
 export const CategoryConfigSchema = z.object({
-  model: z.string(),
+  model: z.string().optional(),
   variant: z.string().optional(),
   temperature: z.number().min(0).max(2).optional(),
   top_p: z.number().min(0).max(1).optional(),
diff --git a/src/plugin-handlers/config-handler.test.ts b/src/plugin-handlers/config-handler.test.ts
index 9724965f..e7acf5f6 100644
--- a/src/plugin-handlers/config-handler.test.ts
+++ b/src/plugin-handlers/config-handler.test.ts
@@ -10,9 +10,9 @@ describe("Prometheus category config resolution", () => {
     // #when
     const config = resolveCategoryConfig(categoryName)
 
-    // #then
+    // #then - DEFAULT_CATEGORIES only has temperature, not model
     expect(config).toBeDefined()
-    expect(config?.model).toBe("openai/gpt-5.2")
+    expect(config?.model).toBeUndefined()
     expect(config?.temperature).toBe(0.1)
   })
 
@@ -23,9 +23,9 @@ describe("Prometheus category config resolution", () => {
     // #when
     const config = resolveCategoryConfig(categoryName)
 
-    // #then
+    // #then - DEFAULT_CATEGORIES only has temperature, not model
     expect(config).toBeDefined()
-    expect(config?.model).toBe("google/gemini-3-pro-preview")
+    expect(config?.model).toBeUndefined()
     expect(config?.temperature).toBe(0.7)
   })
 
@@ -71,9 +71,9 @@ describe("Prometheus category config resolution", () => {
     // #when
     const config = resolveCategoryConfig(categoryName, userCategories)
 
-    // #then
+    // #then - falls back to DEFAULT_CATEGORIES which has no model
     expect(config).toBeDefined()
-    expect(config?.model).toBe("openai/gpt-5.2")
+    expect(config?.model).toBeUndefined()
     expect(config?.temperature).toBe(0.1)
   })
 
diff --git a/src/plugin-handlers/config-handler.ts b/src/plugin-handlers/config-handler.ts
index a6d37cd6..626f288c 100644
--- a/src/plugin-handlers/config-handler.ts
+++ b/src/plugin-handlers/config-handler.ts
@@ -200,12 +200,13 @@ export function createConfigHandler(deps: ConfigHandlerDeps) {
             )
           : undefined;
 
+        // Model resolution: explicit override → category config → OpenCode default
+        // No hardcoded fallback - OpenCode config.model is the terminal fallback
+        const resolvedModel = prometheusOverride?.model ?? categoryConfig?.model ?? defaultModel;
+
         const prometheusBase = {
-          model:
-            prometheusOverride?.model ??
-            categoryConfig?.model ??
-            defaultModel ??
-            "anthropic/claude-opus-4-5",
+          // Only include model if one was resolved - let OpenCode apply its own default if none
+          ...(resolvedModel ? { model: resolvedModel } : {}),
           mode: "primary" as const,
           prompt: PROMETHEUS_SYSTEM_PROMPT,
           permission: PROMETHEUS_PERMISSION,
diff --git a/src/shared/index.ts b/src/shared/index.ts
index 7ee5a321..fef890e3 100644
--- a/src/shared/index.ts
+++ b/src/shared/index.ts
@@ -26,3 +26,4 @@ export * from "./session-cursor"
 export * from "./shell-env"
 export * from "./system-directive"
 export * from "./agent-tool-restrictions"
+export * from "./model-resolver"
diff --git a/src/shared/migration.test.ts b/src/shared/migration.test.ts
index 8f8325f4..aa6593cc 100644
--- a/src/shared/migration.test.ts
+++ b/src/shared/migration.test.ts
@@ -370,9 +370,9 @@ describe("shouldDeleteAgentConfig", () => {
 
   test("returns true when all fields match category defaults", () => {
     // #given: Config with fields matching category defaults
+    // Note: DEFAULT_CATEGORIES only has temperature, not model
     const config = {
       category: "visual-engineering",
-      model: "google/gemini-3-pro-preview",
       temperature: 0.7,
     }
 
diff --git a/src/shared/migration.ts b/src/shared/migration.ts
index 69c75bc3..28bacb85 100644
--- a/src/shared/migration.ts
+++ b/src/shared/migration.ts
@@ -44,7 +44,19 @@ export const HOOK_NAME_MAP: Record<string, string> = {
   "anthropic-auto-compact": "anthropic-context-window-limit-recovery",
 }
 
-// Model to category mapping for auto-migration
+/**
+ * @deprecated LEGACY MIGRATION ONLY
+ * 
+ * This map exists solely for migrating old configs that used hardcoded model strings.
+ * It maps legacy model strings to semantic category names, allowing users to migrate
+ * from explicit model configs to category-based configs.
+ * 
+ * DO NOT add new entries here. New agents should use:
+ * - Category-based config (preferred): { category: "most-capable" }
+ * - Or inherit from OpenCode's config.model
+ * 
+ * This map will be removed in a future major version once migration period ends.
+ */
 export const MODEL_TO_CATEGORY_MAP: Record<string, string> = {
   "google/gemini-3-pro-preview": "visual-engineering",
   "openai/gpt-5.2": "ultrabrain",
diff --git a/src/shared/model-resolver.test.ts b/src/shared/model-resolver.test.ts
new file mode 100644
index 00000000..d984be29
--- /dev/null
+++ b/src/shared/model-resolver.test.ts
@@ -0,0 +1,101 @@
+import { describe, expect, test } from "bun:test";
+import { resolveModel, type ModelResolutionInput } from "./model-resolver";
+
+describe("resolveModel", () => {
+  describe("priority chain", () => {
+    test("returns userModel when all three are set", () => {
+      // #given
+      const input: ModelResolutionInput = {
+        userModel: "anthropic/claude-opus-4-5",
+        inheritedModel: "openai/gpt-5.2",
+        systemDefault: "google/gemini-3-pro",
+      };
+
+      // #when
+      const result = resolveModel(input);
+
+      // #then
+      expect(result).toBe("anthropic/claude-opus-4-5");
+    });
+
+    test("returns inheritedModel when userModel is undefined", () => {
+      // #given
+      const input: ModelResolutionInput = {
+        userModel: undefined,
+        inheritedModel: "openai/gpt-5.2",
+        systemDefault: "google/gemini-3-pro",
+      };
+
+      // #when
+      const result = resolveModel(input);
+
+      // #then
+      expect(result).toBe("openai/gpt-5.2");
+    });
+
+    test("returns systemDefault when both userModel and inheritedModel are undefined", () => {
+      // #given
+      const input: ModelResolutionInput = {
+        userModel: undefined,
+        inheritedModel: undefined,
+        systemDefault: "google/gemini-3-pro",
+      };
+
+      // #when
+      const result = resolveModel(input);
+
+      // #then
+      expect(result).toBe("google/gemini-3-pro");
+    });
+  });
+
+  describe("empty string handling", () => {
+    test("treats empty string as unset, uses fallback", () => {
+      // #given
+      const input: ModelResolutionInput = {
+        userModel: "",
+        inheritedModel: "openai/gpt-5.2",
+        systemDefault: "google/gemini-3-pro",
+      };
+
+      // #when
+      const result = resolveModel(input);
+
+      // #then
+      expect(result).toBe("openai/gpt-5.2");
+    });
+
+    test("treats whitespace-only string as unset, uses fallback", () => {
+      // #given
+      const input: ModelResolutionInput = {
+        userModel: "   ",
+        inheritedModel: "",
+        systemDefault: "google/gemini-3-pro",
+      };
+
+      // #when
+      const result = resolveModel(input);
+
+      // #then
+      expect(result).toBe("google/gemini-3-pro");
+    });
+  });
+
+  describe("purity", () => {
+    test("same input returns same output (referential transparency)", () => {
+      // #given
+      const input: ModelResolutionInput = {
+        userModel: "anthropic/claude-opus-4-5",
+        inheritedModel: "openai/gpt-5.2",
+        systemDefault: "google/gemini-3-pro",
+      };
+
+      // #when
+      const result1 = resolveModel(input);
+      const result2 = resolveModel(input);
+
+      // #then
+      expect(result1).toBe(result2);
+    });
+  });
+});
diff --git a/src/shared/model-resolver.ts b/src/shared/model-resolver.ts
new file mode 100644
index 00000000..2e67f85d
--- /dev/null
+++ b/src/shared/model-resolver.ts
@@ -0,0 +1,35 @@
+/**
+ * Input for model resolution.
+ * All model strings are optional except systemDefault which is the terminal fallback.
+ */
+export type ModelResolutionInput = {
+  /** Model from user category config */
+  userModel?: string;
+  /** Model inherited from parent task/session */
+  inheritedModel?: string;
+  /** System default model from OpenCode config - always required */
+  systemDefault: string;
+};
+
+/**
+ * Normalizes a model string.
+ * Trims whitespace and treats empty/whitespace-only as undefined.
+ */
+function normalizeModel(model?: string): string | undefined {
+  const trimmed = model?.trim();
+  return trimmed || undefined;
+}
+
+/**
+ * Resolves the effective model using priority chain:
+ * userModel → inheritedModel → systemDefault
+ *
+ * Empty strings and whitespace-only strings are treated as unset.
+ */
+export function resolveModel(input: ModelResolutionInput): string {
+  return (
+    normalizeModel(input.userModel) ??
+    normalizeModel(input.inheritedModel) ??
+    input.systemDefault
+  );
+}
diff --git a/src/tools/delegate-task/constants.ts b/src/tools/delegate-task/constants.ts
index 1d13e085..0df516d3 100644
--- a/src/tools/delegate-task/constants.ts
+++ b/src/tools/delegate-task/constants.ts
@@ -185,31 +185,24 @@ The more explicit your prompt, the better the results.
 
 export const DEFAULT_CATEGORIES: Record<string, CategoryConfig> = {
   "visual-engineering": {
-    model: "google/gemini-3-pro-preview",
     temperature: 0.7,
   },
   ultrabrain: {
-    model: "openai/gpt-5.2",
     temperature: 0.1,
   },
   artistry: {
-    model: "google/gemini-3-pro-preview",
     temperature: 0.9,
   },
   quick: {
-    model: "anthropic/claude-haiku-4-5",
     temperature: 0.3,
   },
   "most-capable": {
-    model: "anthropic/claude-opus-4-5",
     temperature: 0.1,
   },
   writing: {
-    model: "google/gemini-3-flash-preview",
     temperature: 0.5,
   },
   general: {
-    model: "anthropic/claude-sonnet-4-5",
     temperature: 0.3,
   },
 }
diff --git a/src/tools/delegate-task/tools.test.ts b/src/tools/delegate-task/tools.test.ts
index 600abc05..fced53a1 100644
--- a/src/tools/delegate-task/tools.test.ts
+++ b/src/tools/delegate-task/tools.test.ts
@@ -1,60 +1,30 @@
 import { describe, test, expect } from "bun:test"
 import { DEFAULT_CATEGORIES, CATEGORY_PROMPT_APPENDS, CATEGORY_DESCRIPTIONS, DELEGATE_TASK_DESCRIPTION } from "./constants"
+import { resolveCategoryConfig } from "./tools"
 import type { CategoryConfig } from "../../config/schema"
 
-function resolveCategoryConfig(
-  categoryName: string,
-  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] ?? ""
-
-  if (!defaultConfig && !userConfig) {
-    return null
-  }
-
-  const model = userConfig?.model ?? defaultConfig?.model ?? parentModelString ?? systemDefaultModel
-  const config: CategoryConfig = {
-    ...defaultConfig,
-    ...userConfig,
-    model,
-  }
-
-  let promptAppend = defaultPromptAppend
-  if (userConfig?.prompt_append) {
-    promptAppend = defaultPromptAppend
-      ? defaultPromptAppend + "\n\n" + userConfig.prompt_append
-      : userConfig.prompt_append
-  }
-
-  return { config, promptAppend, model }
-}
+// Test constants - systemDefaultModel is required by resolveCategoryConfig
+const SYSTEM_DEFAULT_MODEL = "anthropic/claude-sonnet-4-5"
 
 describe("sisyphus-task", () => {
   describe("DEFAULT_CATEGORIES", () => {
-    test("visual-engineering category has gemini model", () => {
+    test("visual-engineering category has temperature config only (model removed)", () => {
       // #given
       const category = DEFAULT_CATEGORIES["visual-engineering"]
 
       // #when / #then
       expect(category).toBeDefined()
-      expect(category.model).toBe("google/gemini-3-pro-preview")
+      expect(category.model).toBeUndefined()
       expect(category.temperature).toBe(0.7)
     })
 
-    test("ultrabrain category has gpt model", () => {
+    test("ultrabrain category has temperature config only (model removed)", () => {
       // #given
       const category = DEFAULT_CATEGORIES["ultrabrain"]
 
       // #when / #then
       expect(category).toBeDefined()
-      expect(category.model).toBe("openai/gpt-5.2")
+      expect(category.model).toBeUndefined()
       expect(category.temperature).toBe(0.1)
     })
   })
@@ -120,26 +90,26 @@ describe("sisyphus-task", () => {
       const categoryName = "unknown-category"
 
       // #when
-      const result = resolveCategoryConfig(categoryName, {})
+      const result = resolveCategoryConfig(categoryName, { systemDefaultModel: SYSTEM_DEFAULT_MODEL })
 
       // #then
       expect(result).toBeNull()
     })
 
-    test("returns default config for builtin category", () => {
+    test("returns systemDefaultModel for builtin category (categories no longer have default models)", () => {
       // #given
       const categoryName = "visual-engineering"
 
       // #when
-      const result = resolveCategoryConfig(categoryName, {})
+      const result = resolveCategoryConfig(categoryName, { systemDefaultModel: SYSTEM_DEFAULT_MODEL })
 
-      // #then
+      // #then - model comes from systemDefaultModel since categories no longer have model defaults
       expect(result).not.toBeNull()
-      expect(result!.config.model).toBe("google/gemini-3-pro-preview")
+      expect(result!.config.model).toBe(SYSTEM_DEFAULT_MODEL)
       expect(result!.promptAppend).toContain("VISUAL/UI")
     })
 
-    test("user config overrides default model", () => {
+    test("user config overrides systemDefaultModel", () => {
       // #given
       const categoryName = "visual-engineering"
       const userCategories = {
@@ -147,7 +117,7 @@ describe("sisyphus-task", () => {
       }
 
       // #when
-      const result = resolveCategoryConfig(categoryName, { userCategories })
+      const result = resolveCategoryConfig(categoryName, { userCategories, systemDefaultModel: SYSTEM_DEFAULT_MODEL })
 
       // #then
       expect(result).not.toBeNull()
@@ -165,7 +135,7 @@ describe("sisyphus-task", () => {
       }
 
       // #when
-      const result = resolveCategoryConfig(categoryName, { userCategories })
+      const result = resolveCategoryConfig(categoryName, { userCategories, systemDefaultModel: SYSTEM_DEFAULT_MODEL })
 
       // #then
       expect(result).not.toBeNull()
@@ -185,7 +155,7 @@ describe("sisyphus-task", () => {
       }
 
       // #when
-      const result = resolveCategoryConfig(categoryName, { userCategories })
+      const result = resolveCategoryConfig(categoryName, { userCategories, systemDefaultModel: SYSTEM_DEFAULT_MODEL })
 
       // #then
       expect(result).not.toBeNull()
@@ -205,66 +175,66 @@ describe("sisyphus-task", () => {
       }
 
       // #when
-      const result = resolveCategoryConfig(categoryName, { userCategories })
+      const result = resolveCategoryConfig(categoryName, { userCategories, systemDefaultModel: SYSTEM_DEFAULT_MODEL })
 
       // #then
       expect(result).not.toBeNull()
       expect(result!.config.temperature).toBe(0.3)
     })
 
-    test("category default model takes precedence over parentModelString", () => {
-      // #given - builtin category has default model, parent model should NOT override it
+    test("inheritedModel takes precedence over systemDefaultModel", () => {
+      // #given - builtin category, parent model provided
       const categoryName = "visual-engineering"
-      const parentModelString = "cliproxy/claude-opus-4-5"
+      const inheritedModel = "cliproxy/claude-opus-4-5"
 
       // #when
-      const result = resolveCategoryConfig(categoryName, { parentModelString })
+      const result = resolveCategoryConfig(categoryName, { inheritedModel, systemDefaultModel: SYSTEM_DEFAULT_MODEL })
 
-      // #then - category default model wins, parent model is ignored for builtin categories
-      expect(result).not.toBeNull()
-      expect(result!.config.model).toBe("google/gemini-3-pro-preview")
-    })
-
-    test("parentModelString is used as fallback when category has no default model", () => {
-      // #given - custom category with no model defined, only parentModelString as fallback
-      const categoryName = "my-custom-no-model"
-      const userCategories = { "my-custom-no-model": { temperature: 0.5 } } as unknown as Record<string, CategoryConfig>
-      const parentModelString = "cliproxy/claude-opus-4-5"
-
-      // #when
-      const result = resolveCategoryConfig(categoryName, { userCategories, parentModelString })
-
-      // #then - parent model is used as fallback since custom category has no default
+      // #then - inheritedModel wins over systemDefaultModel
       expect(result).not.toBeNull()
       expect(result!.config.model).toBe("cliproxy/claude-opus-4-5")
     })
 
-    test("user model takes precedence over parentModelString", () => {
+    test("inheritedModel is used as fallback when category has no user model", () => {
+      // #given - custom category with no model defined, only inheritedModel as fallback
+      const categoryName = "my-custom-no-model"
+      const userCategories = { "my-custom-no-model": { temperature: 0.5 } } as unknown as Record<string, CategoryConfig>
+      const inheritedModel = "cliproxy/claude-opus-4-5"
+
+      // #when
+      const result = resolveCategoryConfig(categoryName, { userCategories, inheritedModel, systemDefaultModel: SYSTEM_DEFAULT_MODEL })
+
+      // #then - parent model is used as fallback since custom category has no user model
+      expect(result).not.toBeNull()
+      expect(result!.config.model).toBe("cliproxy/claude-opus-4-5")
+    })
+
+    test("user model takes precedence over inheritedModel", () => {
       // #given
       const categoryName = "visual-engineering"
       const userCategories = {
         "visual-engineering": { model: "my-provider/my-model" },
       }
-      const parentModelString = "cliproxy/claude-opus-4-5"
+      const inheritedModel = "cliproxy/claude-opus-4-5"
 
       // #when
-      const result = resolveCategoryConfig(categoryName, { userCategories, parentModelString })
+      const result = resolveCategoryConfig(categoryName, { userCategories, inheritedModel, systemDefaultModel: SYSTEM_DEFAULT_MODEL })
 
       // #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", () => {
+    test("systemDefaultModel is used when no user model and no inheritedModel", () => {
       // #given
       const categoryName = "visual-engineering"
 
       // #when
-      const result = resolveCategoryConfig(categoryName, {})
+      const result = resolveCategoryConfig(categoryName, { systemDefaultModel: SYSTEM_DEFAULT_MODEL })
 
       // #then
       expect(result).not.toBeNull()
-      expect(result!.config.model).toBe("google/gemini-3-pro-preview")
+      expect(result!.config.model).toBe(SYSTEM_DEFAULT_MODEL)
     })
   })
 
@@ -289,7 +259,7 @@ describe("sisyphus-task", () => {
 
       const mockClient = {
         app: { agents: async () => ({ data: [] }) },
-        config: { get: async () => ({}) },
+        config: { get: async () => ({ model: SYSTEM_DEFAULT_MODEL }) },
         session: {
           create: async () => ({ data: { id: "test-session" } }),
           prompt: async () => ({ data: {} }),
@@ -348,7 +318,7 @@ describe("sisyphus-task", () => {
       const mockManager = { launch: async () => ({}) }
       const mockClient = {
         app: { agents: async () => ({ data: [] }) },
-        config: { get: async () => ({}) },
+        config: { get: async () => ({ model: SYSTEM_DEFAULT_MODEL }) },
         session: {
           create: async () => ({ data: { id: "test-session" } }),
           prompt: async () => ({ data: {} }),
@@ -391,7 +361,7 @@ describe("sisyphus-task", () => {
       const mockManager = { launch: async () => ({}) }
       const mockClient = {
         app: { agents: async () => ({ data: [] }) },
-        config: { get: async () => ({}) },
+        config: { get: async () => ({ model: SYSTEM_DEFAULT_MODEL }) },
         session: {
           create: async () => ({ data: { id: "test-session" } }),
           prompt: async () => ({ data: {} }),
@@ -438,7 +408,7 @@ describe("sisyphus-task", () => {
       const mockManager = { launch: async () => ({}) }
       const mockClient = {
         app: { agents: async () => ({ data: [] }) },
-        config: { get: async () => ({}) },
+        config: { get: async () => ({ model: SYSTEM_DEFAULT_MODEL }) },
         session: {
           get: async () => ({ data: { directory: "/project" } }),
           create: async () => ({ data: { id: "test-session" } }),
@@ -513,7 +483,7 @@ describe("sisyphus-task", () => {
           ],
         }),
       },
-      config: { get: async () => ({}) },
+      config: { get: async () => ({ model: SYSTEM_DEFAULT_MODEL }) },
       app: {
         agents: async () => ({ data: [] }),
       },
@@ -571,7 +541,7 @@ describe("sisyphus-task", () => {
           data: [],
         }),
       },
-      config: { get: async () => ({}) },
+      config: { get: async () => ({ model: SYSTEM_DEFAULT_MODEL }) },
     }
     
     const tool = createDelegateTask({
@@ -623,7 +593,7 @@ describe("sisyphus-task", () => {
           messages: async () => ({ data: [] }),
           status: async () => ({ data: {} }),
         },
-        config: { get: async () => ({}) },
+        config: { get: async () => ({ model: SYSTEM_DEFAULT_MODEL }) },
         app: {
           agents: async () => ({ data: [{ name: "ultrabrain", mode: "subagent" }] }),
         },
@@ -683,7 +653,7 @@ describe("sisyphus-task", () => {
           }),
           status: async () => ({ data: { "ses_sync_success": { type: "idle" } } }),
         },
-        config: { get: async () => ({}) },
+        config: { get: async () => ({ model: SYSTEM_DEFAULT_MODEL }) },
         app: {
           agents: async () => ({ data: [{ name: "ultrabrain", mode: "subagent" }] }),
         },
@@ -736,7 +706,7 @@ describe("sisyphus-task", () => {
           messages: async () => ({ data: [] }),
           status: async () => ({ data: {} }),
         },
-        config: { get: async () => ({}) },
+        config: { get: async () => ({ model: SYSTEM_DEFAULT_MODEL }) },
         app: {
           agents: async () => ({ data: [{ name: "ultrabrain", mode: "subagent" }] }),
         },
@@ -790,7 +760,7 @@ describe("sisyphus-task", () => {
           }),
           status: async () => ({ data: {} }),
         },
-        config: { get: async () => ({}) },
+        config: { get: async () => ({ model: SYSTEM_DEFAULT_MODEL }) },
         app: { agents: async () => ({ data: [] }) },
       }
 
@@ -879,47 +849,41 @@ describe("sisyphus-task", () => {
   })
 
   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"
+    test("systemDefaultModel is used when no userModel and no inheritedModel", () => {
+      // #given - builtin category, no user model, no inherited model
       const categoryName = "ultrabrain"
-      const parentModelString = undefined
       
       // #when
-      const resolved = resolveCategoryConfig(categoryName, { parentModelString })
+      const resolved = resolveCategoryConfig(categoryName, { systemDefaultModel: SYSTEM_DEFAULT_MODEL })
       
-      // #then - actualModel should be defaultModel, type should be "category-default"
+      // #then - actualModel should be systemDefaultModel (categories no longer have model defaults)
       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")
+      expect(actualModel).toBe(SYSTEM_DEFAULT_MODEL)
     })
 
-    test("category default model takes precedence over parentModelString for builtin category", () => {
-      // #given - builtin ultrabrain category has default model gpt-5.2
+    test("inheritedModel takes precedence over systemDefaultModel for builtin category", () => {
+      // #given - builtin ultrabrain category, inherited model from parent
       const categoryName = "ultrabrain"
-      const parentModelString = "cliproxy/claude-opus-4-5"
+      const inheritedModel = "cliproxy/claude-opus-4-5"
       
       // #when
-      const resolved = resolveCategoryConfig(categoryName, { parentModelString })
+      const resolved = resolveCategoryConfig(categoryName, { inheritedModel, systemDefaultModel: SYSTEM_DEFAULT_MODEL })
       
-      // #then - category default model wins, not the parent model
+      // #then - inheritedModel wins over systemDefaultModel
       expect(resolved).not.toBeNull()
       const actualModel = resolved!.config.model
-      expect(actualModel).toBe("openai/gpt-5.2")
+      expect(actualModel).toBe("cliproxy/claude-opus-4-5")
     })
 
-    test("when user defines model - modelInfo should report user-defined regardless of parentModelString", () => {
+    test("when user defines model - modelInfo should report user-defined regardless of inheritedModel", () => {
       // #given
       const categoryName = "ultrabrain"
       const userCategories = { "ultrabrain": { model: "my-provider/custom-model" } }
-      const parentModelString = "cliproxy/claude-opus-4-5"
+      const inheritedModel = "cliproxy/claude-opus-4-5"
       
       // #when
-      const resolved = resolveCategoryConfig(categoryName, { userCategories, parentModelString })
+      const resolved = resolveCategoryConfig(categoryName, { userCategories, inheritedModel, systemDefaultModel: SYSTEM_DEFAULT_MODEL })
       
       // #then - actualModel should be userModel, type should be "user-defined"
       expect(resolved).not.toBeNull()
@@ -931,28 +895,109 @@ describe("sisyphus-task", () => {
 
     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)`
+      // The bug was: checking `if (inheritedModel)` instead of `if (actualModel === inheritedModel)`
       const categoryName = "ultrabrain"
-      const parentModelString = "cliproxy/claude-opus-4-5"
+      const inheritedModel = "cliproxy/claude-opus-4-5"
       const userCategories = { "ultrabrain": { model: "user/model" } }
       
       // #when - user model wins
-      const resolved = resolveCategoryConfig(categoryName, { userCategories, parentModelString })
+      const resolved = resolveCategoryConfig(categoryName, { userCategories, inheritedModel, systemDefaultModel: SYSTEM_DEFAULT_MODEL })
       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 
+        : actualModel === inheritedModel 
         ? "inherited" 
-        : actualModel === defaultModel 
-        ? "category-default" 
+        : actualModel === SYSTEM_DEFAULT_MODEL 
+        ? "system-default" 
         : undefined
       
       expect(detectedType).toBe("user-defined")
-      expect(actualModel).not.toBe(parentModelString)
+      expect(actualModel).not.toBe(inheritedModel)
+    })
+
+    // ===== TESTS FOR resolveModel() INTEGRATION (TDD GREEN) =====
+    // These tests verify the NEW behavior where categories do NOT have default models
+
+    test("FIXED: inheritedModel takes precedence over systemDefaultModel", () => {
+      // #given a builtin category, and an inherited model from parent
+      // The NEW correct chain: userConfig?.model ?? inheritedModel ?? systemDefaultModel
+      const categoryName = "ultrabrain"
+      const inheritedModel = "anthropic/claude-opus-4-5" // inherited from parent session
+      
+      // #when userConfig.model is undefined and inheritedModel is set
+      const resolved = resolveCategoryConfig(categoryName, { inheritedModel, systemDefaultModel: SYSTEM_DEFAULT_MODEL })
+      
+      // #then inheritedModel should be used, NOT systemDefaultModel
+      expect(resolved).not.toBeNull()
+      expect(resolved!.model).toBe("anthropic/claude-opus-4-5")
+    })
+
+    test("FIXED: systemDefaultModel is used when no userConfig.model and no inheritedModel", () => {
+      // #given a custom category with no default model
+      const categoryName = "custom-no-default"
+      const userCategories = { "custom-no-default": { temperature: 0.5 } } as unknown as Record<string, CategoryConfig>
+      const systemDefaultModel = "anthropic/claude-sonnet-4-5"
+      
+      // #when no inheritedModel is provided, only systemDefaultModel
+      const resolved = resolveCategoryConfig(categoryName, { 
+        userCategories, 
+        systemDefaultModel 
+      })
+      
+      // #then systemDefaultModel should be returned
+      expect(resolved).not.toBeNull()
+      expect(resolved!.model).toBe("anthropic/claude-sonnet-4-5")
+    })
+
+    test("FIXED: userConfig.model always takes priority over everything", () => {
+      // #given userConfig.model is explicitly set
+      const categoryName = "ultrabrain"
+      const userCategories = { "ultrabrain": { model: "custom/user-model" } }
+      const inheritedModel = "anthropic/claude-opus-4-5"
+      const systemDefaultModel = "anthropic/claude-sonnet-4-5"
+      
+      // #when resolveCategoryConfig is called with all sources
+      const resolved = resolveCategoryConfig(categoryName, { 
+        userCategories, 
+        inheritedModel, 
+        systemDefaultModel 
+      })
+      
+      // #then userConfig.model should win
+      expect(resolved).not.toBeNull()
+      expect(resolved!.model).toBe("custom/user-model")
+    })
+
+    test("FIXED: empty string in userConfig.model is treated as unset and falls back", () => {
+      // #given userConfig.model is empty string ""
+      const categoryName = "custom-empty-model"
+      const userCategories = { "custom-empty-model": { model: "", temperature: 0.3 } }
+      const inheritedModel = "anthropic/claude-opus-4-5"
+      
+      // #when resolveCategoryConfig is called
+      const resolved = resolveCategoryConfig(categoryName, { userCategories, inheritedModel, systemDefaultModel: SYSTEM_DEFAULT_MODEL })
+      
+      // #then should fall back to inheritedModel since "" is normalized to undefined
+      expect(resolved).not.toBeNull()
+      expect(resolved!.model).toBe("anthropic/claude-opus-4-5")
+    })
+
+    test("FIXED: undefined userConfig.model falls back to inheritedModel", () => {
+      // #given user explicitly sets a category but leaves model undefined
+      const categoryName = "visual-engineering"
+      // Using type assertion since we're testing fallback behavior for categories without model
+      const userCategories = { "visual-engineering": { temperature: 0.2 } } as unknown as Record<string, CategoryConfig>
+      const inheritedModel = "anthropic/claude-opus-4-5"
+      
+      // #when resolveCategoryConfig is called
+      const resolved = resolveCategoryConfig(categoryName, { userCategories, inheritedModel, systemDefaultModel: SYSTEM_DEFAULT_MODEL })
+      
+      // #then should use inheritedModel
+      expect(resolved).not.toBeNull()
+      expect(resolved!.model).toBe("anthropic/claude-opus-4-5")
     })
 
     test("systemDefaultModel is used when no other model is available", () => {
@@ -969,19 +1014,5 @@ describe("sisyphus-task", () => {
       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/delegate-task/tools.ts b/src/tools/delegate-task/tools.ts
index ee66f3d1..b55f4d4c 100644
--- a/src/tools/delegate-task/tools.ts
+++ b/src/tools/delegate-task/tools.ts
@@ -11,7 +11,7 @@ import { discoverSkills } from "../../features/opencode-skill-loader"
 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, getAgentToolRestrictions } from "../../shared"
+import { log, getAgentToolRestrictions, resolveModel } from "../../shared"
 
 type OpencodeClient = PluginInput["client"]
 
@@ -107,15 +107,15 @@ type ToolContextWithMetadata = {
   metadata?: (input: { title?: string; metadata?: Record<string, unknown> }) => void
 }
 
-function resolveCategoryConfig(
+export function resolveCategoryConfig(
   categoryName: string,
   options: {
     userCategories?: CategoriesConfig
-    parentModelString?: string
-    systemDefaultModel?: string
+    inheritedModel?: string
+    systemDefaultModel: string
   }
-): { config: CategoryConfig; promptAppend: string; model: string | undefined } | null {
-  const { userCategories, parentModelString, systemDefaultModel } = options
+): { config: CategoryConfig; promptAppend: string; model: string } | null {
+  const { userCategories, inheritedModel, systemDefaultModel } = options
   const defaultConfig = DEFAULT_CATEGORIES[categoryName]
   const userConfig = userCategories?.[categoryName]
   const defaultPromptAppend = CATEGORY_PROMPT_APPENDS[categoryName] ?? ""
@@ -124,8 +124,12 @@ function resolveCategoryConfig(
     return null
   }
 
-  // Model priority: user override > category default > parent model (fallback) > system default
-  const model = userConfig?.model ?? defaultConfig?.model ?? parentModelString ?? systemDefaultModel
+  // Model priority: user override > inherited from parent > system default
+  const model = resolveModel({
+    userModel: userConfig?.model,
+    inheritedModel,
+    systemDefault: systemDefaultModel,
+  })
   const config: CategoryConfig = {
     ...defaultConfig,
     ...userConfig,
@@ -421,16 +425,21 @@ ${textContent || "(No text output)"}`
       let categoryModel: { providerID: string; modelID: string; variant?: string } | undefined
       let categoryPromptAppend: string | undefined
 
-      const parentModelString = parentModel
+      const inheritedModel = parentModel
         ? `${parentModel.providerID}/${parentModel.modelID}`
         : undefined
 
       let modelInfo: ModelFallbackInfo | undefined
 
       if (args.category) {
+        // Guard: require system default model for category delegation
+        if (!systemDefaultModel) {
+          return `No default model configured. Set a model in your OpenCode config (model field).`
+        }
+
         const resolved = resolveCategoryConfig(args.category, {
           userCategories,
-          parentModelString,
+          inheritedModel,
           systemDefaultModel,
         })
         if (!resolved) {
@@ -440,11 +449,6 @@ ${textContent || "(No text output)"}`
         // 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").`
@@ -454,12 +458,9 @@ ${textContent || "(No text output)"}`
           case userDefinedModel:
             modelInfo = { model: actualModel, type: "user-defined" }
             break
-          case parentModelString:
+          case inheritedModel:
             modelInfo = { model: actualModel, type: "inherited" }
             break
-          case categoryDefaultModel:
-            modelInfo = { model: actualModel, type: "category-default" }
-            break
           case systemDefaultModel:
             modelInfo = { model: actualModel, type: "system-default" }
             break