diff --git a/src/shared/migration.test.ts b/src/shared/migration.test.ts
index f02d0f3c3..fcb01a4a8 100644
--- a/src/shared/migration.test.ts
+++ b/src/shared/migration.test.ts
@@ -1018,6 +1018,40 @@ describe("migrateConfigFile with backup", () => {
     expect(agents.oracle.category).toBe("ultrabrain")
   })
 
+  test("does not write or create backups for experimental.task_system", () => {
+    //#given: Config with experimental.task_system enabled
+    const testConfigPath = "/tmp/test-config-task-system.json"
+    const rawConfig: Record<string, unknown> = {
+      experimental: { task_system: true },
+    }
+
+    fs.writeFileSync(testConfigPath, globalThis.JSON.stringify(rawConfig, null, 2))
+    cleanupPaths.push(testConfigPath)
+
+    const dir = path.dirname(testConfigPath)
+    const basename = path.basename(testConfigPath)
+    const existingFiles = fs.readdirSync(dir)
+    const existingBackups = existingFiles.filter((f) => f.startsWith(`${basename}.bak.`))
+    existingBackups.forEach((f) => {
+      const backupPath = path.join(dir, f)
+      try {
+        fs.unlinkSync(backupPath)
+        cleanupPaths.splice(cleanupPaths.indexOf(backupPath), 1)
+      } catch {
+      }
+    })
+
+    //#when: Migrate config file
+    const needsWrite = migrateConfigFile(testConfigPath, rawConfig)
+
+    //#then: No write or backup should occur
+    expect(needsWrite).toBe(false)
+
+    const files = fs.readdirSync(dir)
+    const backupFiles = files.filter((f) => f.startsWith(`${basename}.bak.`))
+    expect(backupFiles.length).toBe(0)
+  })
+
   test("does not write when no migration needed", () => {
      // given: Config with no migrations needed
      const testConfigPath = "/tmp/test-config-no-migration.json"
diff --git a/src/shared/migration.ts b/src/shared/migration.ts
index ae57e24d4..969d21392 100644
--- a/src/shared/migration.ts
+++ b/src/shared/migration.ts
@@ -1,330 +1,5 @@
-import * as fs from "fs"
-import { log } from "./logger"
-
-// Migration map: old keys → new keys (for backward compatibility)
-export const AGENT_NAME_MAP: Record<string, string> = {
-  // Sisyphus variants → "sisyphus"
-  omo: "sisyphus",
-  OmO: "sisyphus",
-  Sisyphus: "sisyphus",
-  sisyphus: "sisyphus",
-
-  // Prometheus variants → "prometheus"
-  "OmO-Plan": "prometheus",
-  "omo-plan": "prometheus",
-  "Planner-Sisyphus": "prometheus",
-  "planner-sisyphus": "prometheus",
-  "Prometheus (Planner)": "prometheus",
-  prometheus: "prometheus",
-
-  // Atlas variants → "atlas"
-  "orchestrator-sisyphus": "atlas",
-  Atlas: "atlas",
-  atlas: "atlas",
-
-  // Metis variants → "metis"
-  "plan-consultant": "metis",
-  "Metis (Plan Consultant)": "metis",
-  metis: "metis",
-
-  // Momus variants → "momus"
-  "Momus (Plan Reviewer)": "momus",
-  momus: "momus",
-
-  // Sisyphus-Junior → "sisyphus-junior"
-  "Sisyphus-Junior": "sisyphus-junior",
-  "sisyphus-junior": "sisyphus-junior",
-
-  // Already lowercase - passthrough
-  build: "build",
-  oracle: "oracle",
-  librarian: "librarian",
-  explore: "explore",
-  "multimodal-looker": "multimodal-looker",
-}
-
-export const BUILTIN_AGENT_NAMES = new Set([
-  "sisyphus",           // was "Sisyphus"
-  "oracle",
-  "librarian",
-  "explore",
-  "multimodal-looker",
-  "metis",              // was "Metis (Plan Consultant)"
-  "momus",              // was "Momus (Plan Reviewer)"
-  "prometheus",         // was "Prometheus (Planner)"
-  "atlas",              // was "Atlas"
-  "build",
-])
-
-// Migration map: old hook names → new hook names (for backward compatibility)
-// null means the hook was removed and should be filtered out from disabled_hooks
-export const HOOK_NAME_MAP: Record<string, string | null> = {
-  // Legacy names (backward compatibility)
-  "anthropic-auto-compact": "anthropic-context-window-limit-recovery",
-  "sisyphus-orchestrator": "atlas",
-
-  // Removed hooks (v3.0.0) - will be filtered out and user warned
-  "empty-message-sanitizer": null,
-}
-
-/**
- * @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: "unspecified-high" }
- * - 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": "visual-engineering",
-  "google/gemini-3-flash": "writing",
-  "openai/gpt-5.2": "ultrabrain",
-  "anthropic/claude-haiku-4-5": "quick",
-  "anthropic/claude-opus-4-6": "unspecified-high",
-  "anthropic/claude-sonnet-4-5": "unspecified-low",
-}
-
-/**
- * Model version migration map: old full model strings → new full model strings.
- * Used to auto-upgrade hardcoded model versions in user configs when the plugin
- * bumps to newer model versions.
- *
- * Keys are full "provider/model" strings. Only openai and anthropic entries needed.
- */
-export const MODEL_VERSION_MAP: Record<string, string> = {
-  "openai/gpt-5.2-codex": "openai/gpt-5.3-codex",
-  "anthropic/claude-opus-4-5": "anthropic/claude-opus-4-6",
-}
-
-export function migrateAgentNames(agents: Record<string, unknown>): { migrated: Record<string, unknown>; changed: boolean } {
-  const migrated: Record<string, unknown> = {}
-  let changed = false
-
-  for (const [key, value] of Object.entries(agents)) {
-    const newKey = AGENT_NAME_MAP[key.toLowerCase()] ?? AGENT_NAME_MAP[key] ?? key
-    if (newKey !== key) {
-      changed = true
-    }
-    migrated[newKey] = value
-  }
-
-  return { migrated, changed }
-}
-
-/**
- * Generate a consistent migration key for tracking applied migrations.
- */
-function migrationKey(oldModel: string, newModel: string): string {
-  return `model-version:${oldModel}->${newModel}`
-}
-
-export function migrateModelVersions(
-  configs: Record<string, unknown>,
-  appliedMigrations?: Set<string>,
-): { migrated: Record<string, unknown>; changed: boolean; newMigrations: string[] } {
-  const migrated: Record<string, unknown> = {}
-  let changed = false
-  const newMigrations: string[] = []
-
-  for (const [key, value] of Object.entries(configs)) {
-    if (value && typeof value === "object" && !Array.isArray(value)) {
-      const config = value as Record<string, unknown>
-      if (typeof config.model === "string" && MODEL_VERSION_MAP[config.model]) {
-        const oldModel = config.model
-        const newModel = MODEL_VERSION_MAP[oldModel]
-        const mKey = migrationKey(oldModel, newModel)
-
-        // Skip if this migration was already applied (user may have reverted)
-        if (appliedMigrations?.has(mKey)) {
-          migrated[key] = value
-          continue
-        }
-
-        migrated[key] = { ...config, model: newModel }
-        changed = true
-        newMigrations.push(mKey)
-        continue
-      }
-    }
-    migrated[key] = value
-  }
-
-  return { migrated, changed, newMigrations }
-}
-
-export function migrateHookNames(hooks: string[]): { migrated: string[]; changed: boolean; removed: string[] } {
-  const migrated: string[] = []
-  const removed: string[] = []
-  let changed = false
-
-  for (const hook of hooks) {
-    const mapping = HOOK_NAME_MAP[hook]
-
-    if (mapping === null) {
-      removed.push(hook)
-      changed = true
-      continue
-    }
-
-    const newHook = mapping ?? hook
-    if (newHook !== hook) {
-      changed = true
-    }
-    migrated.push(newHook)
-  }
-
-  return { migrated, changed, removed }
-}
-
-export function migrateAgentConfigToCategory(config: Record<string, unknown>): {
-  migrated: Record<string, unknown>
-  changed: boolean
-} {
-  const { model, ...rest } = config
-  if (typeof model !== "string") {
-    return { migrated: config, changed: false }
-  }
-
-  const category = MODEL_TO_CATEGORY_MAP[model]
-  if (!category) {
-    return { migrated: config, changed: false }
-  }
-
-  return {
-    migrated: { category, ...rest },
-    changed: true,
-  }
-}
-
-export function shouldDeleteAgentConfig(
-  config: Record<string, unknown>,
-  category: string
-): boolean {
-  const { DEFAULT_CATEGORIES } = require("../tools/delegate-task/constants")
-  const defaults = DEFAULT_CATEGORIES[category]
-  if (!defaults) return false
-
-  const keys = Object.keys(config).filter((k) => k !== "category")
-  if (keys.length === 0) return true
-
-  for (const key of keys) {
-    if (config[key] !== (defaults as Record<string, unknown>)[key]) {
-      return false
-    }
-  }
-  return true
-}
-
-export function migrateConfigFile(configPath: string, rawConfig: Record<string, unknown>): boolean {
-  let needsWrite = false
-
-  // Load previously applied migrations
-  const existingMigrations = Array.isArray(rawConfig._migrations)
-    ? new Set(rawConfig._migrations as string[])
-    : new Set<string>()
-  const allNewMigrations: string[] = []
-
-  if (rawConfig.agents && typeof rawConfig.agents === "object") {
-    const { migrated, changed } = migrateAgentNames(rawConfig.agents as Record<string, unknown>)
-    if (changed) {
-      rawConfig.agents = migrated
-      needsWrite = true
-    }
-  }
-
-  // Migrate model versions in agents (skip already-applied migrations)
-  if (rawConfig.agents && typeof rawConfig.agents === "object") {
-    const { migrated, changed, newMigrations } = migrateModelVersions(
-      rawConfig.agents as Record<string, unknown>,
-      existingMigrations,
-    )
-    if (changed) {
-      rawConfig.agents = migrated
-      needsWrite = true
-      log(`Migrated model versions in agents config`)
-    }
-    allNewMigrations.push(...newMigrations)
-  }
-
-  // Migrate model versions in categories (skip already-applied migrations)
-  if (rawConfig.categories && typeof rawConfig.categories === "object") {
-    const { migrated, changed, newMigrations } = migrateModelVersions(
-      rawConfig.categories as Record<string, unknown>,
-      existingMigrations,
-    )
-    if (changed) {
-      rawConfig.categories = migrated
-      needsWrite = true
-      log(`Migrated model versions in categories config`)
-    }
-    allNewMigrations.push(...newMigrations)
-  }
-
-  // Record newly applied migrations
-  if (allNewMigrations.length > 0) {
-    const updatedMigrations = Array.from(existingMigrations)
-    updatedMigrations.push(...allNewMigrations)
-    rawConfig._migrations = updatedMigrations
-    needsWrite = true
-  }
-
-  if (rawConfig.omo_agent) {
-    rawConfig.sisyphus_agent = rawConfig.omo_agent
-    delete rawConfig.omo_agent
-    needsWrite = true
-  }
-
-  if (rawConfig.disabled_agents && Array.isArray(rawConfig.disabled_agents)) {
-    const migrated: string[] = []
-    let changed = false
-    for (const agent of rawConfig.disabled_agents as string[]) {
-      const newAgent = AGENT_NAME_MAP[agent.toLowerCase()] ?? AGENT_NAME_MAP[agent] ?? agent
-      if (newAgent !== agent) {
-        changed = true
-      }
-      migrated.push(newAgent)
-    }
-    if (changed) {
-      rawConfig.disabled_agents = migrated
-      needsWrite = true
-    }
-  }
-
-  if (rawConfig.disabled_hooks && Array.isArray(rawConfig.disabled_hooks)) {
-    const { migrated, changed, removed } = migrateHookNames(rawConfig.disabled_hooks as string[])
-    if (changed) {
-      rawConfig.disabled_hooks = migrated
-      needsWrite = true
-    }
-    if (removed.length > 0) {
-      log(`Removed obsolete hooks from disabled_hooks: ${removed.join(", ")} (these hooks no longer exist in v3.0.0)`)
-    }
-  }
-
-  if (rawConfig.experimental && typeof rawConfig.experimental === "object") {
-    const exp = rawConfig.experimental as Record<string, unknown>
-    if ("task_system" in exp && exp.task_system !== undefined) {
-      needsWrite = true
-    }
-  }
-
-  if (needsWrite) {
-    try {
-      const timestamp = new Date().toISOString().replace(/[:.]/g, "-")
-      const backupPath = `${configPath}.bak.${timestamp}`
-      fs.copyFileSync(configPath, backupPath)
-
-      fs.writeFileSync(configPath, JSON.stringify(rawConfig, null, 2) + "\n", "utf-8")
-      log(`Migrated config file: ${configPath} (backup: ${backupPath})`)
-    } catch (err) {
-      log(`Failed to write migrated config to ${configPath}:`, err)
-    }
-  }
-
-  return needsWrite
-}
+export { AGENT_NAME_MAP, BUILTIN_AGENT_NAMES, migrateAgentNames } from "./migration/agent-names"
+export { HOOK_NAME_MAP, migrateHookNames } from "./migration/hook-names"
+export { MODEL_VERSION_MAP, migrateModelVersions } from "./migration/model-versions"
+export { MODEL_TO_CATEGORY_MAP, migrateAgentConfigToCategory, shouldDeleteAgentConfig } from "./migration/agent-category"
+export { migrateConfigFile } from "./migration/config-migration"
diff --git a/src/shared/migration/config-migration.ts b/src/shared/migration/config-migration.ts
new file mode 100644
index 000000000..60cf708aa
--- /dev/null
+++ b/src/shared/migration/config-migration.ts
@@ -0,0 +1,112 @@
+import * as fs from "fs"
+import { log } from "../logger"
+import { AGENT_NAME_MAP, migrateAgentNames } from "./agent-names"
+import { migrateHookNames } from "./hook-names"
+import { migrateModelVersions } from "./model-versions"
+
+export function migrateConfigFile(
+  configPath: string,
+  rawConfig: Record<string, unknown>
+): boolean {
+  let needsWrite = false
+
+  // Load previously applied migrations
+  const existingMigrations = Array.isArray(rawConfig._migrations)
+    ? new Set(rawConfig._migrations as string[])
+    : new Set<string>()
+  const allNewMigrations: string[] = []
+
+  if (rawConfig.agents && typeof rawConfig.agents === "object") {
+    const { migrated, changed } = migrateAgentNames(rawConfig.agents as Record<string, unknown>)
+    if (changed) {
+      rawConfig.agents = migrated
+      needsWrite = true
+    }
+  }
+
+  // Migrate model versions in agents (skip already-applied migrations)
+  if (rawConfig.agents && typeof rawConfig.agents === "object") {
+    const { migrated, changed, newMigrations } = migrateModelVersions(
+      rawConfig.agents as Record<string, unknown>,
+      existingMigrations
+    )
+    if (changed) {
+      rawConfig.agents = migrated
+      needsWrite = true
+      log("Migrated model versions in agents config")
+    }
+    allNewMigrations.push(...newMigrations)
+  }
+
+  // Migrate model versions in categories (skip already-applied migrations)
+  if (rawConfig.categories && typeof rawConfig.categories === "object") {
+    const { migrated, changed, newMigrations } = migrateModelVersions(
+      rawConfig.categories as Record<string, unknown>,
+      existingMigrations
+    )
+    if (changed) {
+      rawConfig.categories = migrated
+      needsWrite = true
+      log("Migrated model versions in categories config")
+    }
+    allNewMigrations.push(...newMigrations)
+  }
+
+  // Record newly applied migrations
+  if (allNewMigrations.length > 0) {
+    const updatedMigrations = Array.from(existingMigrations)
+    updatedMigrations.push(...allNewMigrations)
+    rawConfig._migrations = updatedMigrations
+    needsWrite = true
+  }
+
+  if (rawConfig.omo_agent) {
+    rawConfig.sisyphus_agent = rawConfig.omo_agent
+    delete rawConfig.omo_agent
+    needsWrite = true
+  }
+
+  if (rawConfig.disabled_agents && Array.isArray(rawConfig.disabled_agents)) {
+    const migrated: string[] = []
+    let changed = false
+    for (const agent of rawConfig.disabled_agents as string[]) {
+      const newAgent = AGENT_NAME_MAP[agent.toLowerCase()] ?? AGENT_NAME_MAP[agent] ?? agent
+      if (newAgent !== agent) {
+        changed = true
+      }
+      migrated.push(newAgent)
+    }
+    if (changed) {
+      rawConfig.disabled_agents = migrated
+      needsWrite = true
+    }
+  }
+
+  if (rawConfig.disabled_hooks && Array.isArray(rawConfig.disabled_hooks)) {
+    const { migrated, changed, removed } = migrateHookNames(rawConfig.disabled_hooks as string[])
+    if (changed) {
+      rawConfig.disabled_hooks = migrated
+      needsWrite = true
+    }
+    if (removed.length > 0) {
+      log(
+        `Removed obsolete hooks from disabled_hooks: ${removed.join(", ")} (these hooks no longer exist in v3.0.0)`
+      )
+    }
+  }
+
+  if (needsWrite) {
+    try {
+      const timestamp = new Date().toISOString().replace(/[:.]/g, "-")
+      const backupPath = `${configPath}.bak.${timestamp}`
+      fs.copyFileSync(configPath, backupPath)
+
+      fs.writeFileSync(configPath, JSON.stringify(rawConfig, null, 2) + "\n", "utf-8")
+      log(`Migrated config file: ${configPath} (backup: ${backupPath})`)
+    } catch (err) {
+      log(`Failed to write migrated config to ${configPath}:`, err)
+    }
+  }
+
+  return needsWrite
+}