fix: migrate config on deep copy, apply to rawConfig only on successful file write (#1660)

Previously, migrateConfigFile() mutated rawConfig directly. If the file
write failed (e.g. read-only file, permissions), the in-memory config was
already changed to the migrated values, causing the plugin to use migrated
models even though the user's file was untouched. On the next run, the
migration would fire again since _migrations was never persisted.

Now all mutations happen on a structuredClone copy. The original rawConfig
is only updated after the file write succeeds. If the write fails,
rawConfig stays untouched and the function returns false.

src/shared/migration/config-migration.ts

@@ -8,30 +8,32 @@ export function migrateConfigFile(
   configPath: string,
   rawConfig: Record<string, unknown>
 ): boolean {
+  // Work on a deep copy — only apply changes to rawConfig if file write succeeds
+  const copy = structuredClone(rawConfig)
   let needsWrite = false
 
   // Load previously applied migrations
-  const existingMigrations = Array.isArray(rawConfig._migrations)
+  const existingMigrations = Array.isArray(copy._migrations)
-    ? new Set(rawConfig._migrations as string[])
+    ? new Set(copy._migrations as string[])
     : new Set<string>()
   const allNewMigrations: string[] = []
 
-  if (rawConfig.agents && typeof rawConfig.agents === "object") {
+  if (copy.agents && typeof copy.agents === "object") {
-    const { migrated, changed } = migrateAgentNames(rawConfig.agents as Record<string, unknown>)
+    const { migrated, changed } = migrateAgentNames(copy.agents as Record<string, unknown>)
     if (changed) {
-      rawConfig.agents = migrated
+      copy.agents = migrated
       needsWrite = true
     }
   }
 
   // Migrate model versions in agents (skip already-applied migrations)
-  if (rawConfig.agents && typeof rawConfig.agents === "object") {
+  if (copy.agents && typeof copy.agents === "object") {
     const { migrated, changed, newMigrations } = migrateModelVersions(
-      rawConfig.agents as Record<string, unknown>,
+      copy.agents as Record<string, unknown>,
       existingMigrations
     )
     if (changed) {
-      rawConfig.agents = migrated
+      copy.agents = migrated
       needsWrite = true
       log("Migrated model versions in agents config")
     }
@@ -39,13 +41,13 @@ export function migrateConfigFile(
   }
 
   // Migrate model versions in categories (skip already-applied migrations)
-  if (rawConfig.categories && typeof rawConfig.categories === "object") {
+  if (copy.categories && typeof copy.categories === "object") {
     const { migrated, changed, newMigrations } = migrateModelVersions(
-      rawConfig.categories as Record<string, unknown>,
+      copy.categories as Record<string, unknown>,
       existingMigrations
     )
     if (changed) {
-      rawConfig.categories = migrated
+      copy.categories = migrated
       needsWrite = true
       log("Migrated model versions in categories config")
     }
@@ -56,20 +58,20 @@ export function migrateConfigFile(
   if (allNewMigrations.length > 0) {
     const updatedMigrations = Array.from(existingMigrations)
     updatedMigrations.push(...allNewMigrations)
-    rawConfig._migrations = updatedMigrations
+    copy._migrations = updatedMigrations
     needsWrite = true
   }
 
-  if (rawConfig.omo_agent) {
+  if (copy.omo_agent) {
-    rawConfig.sisyphus_agent = rawConfig.omo_agent
+    copy.sisyphus_agent = copy.omo_agent
-    delete rawConfig.omo_agent
+    delete copy.omo_agent
     needsWrite = true
   }
 
-  if (rawConfig.disabled_agents && Array.isArray(rawConfig.disabled_agents)) {
+  if (copy.disabled_agents && Array.isArray(copy.disabled_agents)) {
     const migrated: string[] = []
     let changed = false
-    for (const agent of rawConfig.disabled_agents as string[]) {
+    for (const agent of copy.disabled_agents as string[]) {
       const newAgent = AGENT_NAME_MAP[agent.toLowerCase()] ?? AGENT_NAME_MAP[agent] ?? agent
       if (newAgent !== agent) {
         changed = true
@@ -77,15 +79,15 @@ export function migrateConfigFile(
       migrated.push(newAgent)
     }
     if (changed) {
-      rawConfig.disabled_agents = migrated
+      copy.disabled_agents = migrated
       needsWrite = true
     }
   }
 
-  if (rawConfig.disabled_hooks && Array.isArray(rawConfig.disabled_hooks)) {
+  if (copy.disabled_hooks && Array.isArray(copy.disabled_hooks)) {
-    const { migrated, changed, removed } = migrateHookNames(rawConfig.disabled_hooks as string[])
+    const { migrated, changed, removed } = migrateHookNames(copy.disabled_hooks as string[])
     if (changed) {
-      rawConfig.disabled_hooks = migrated
+      copy.disabled_hooks = migrated
       needsWrite = true
     }
     if (removed.length > 0) {
@@ -99,13 +101,25 @@ export function migrateConfigFile(
     try {
       const timestamp = new Date().toISOString().replace(/[:.]/g, "-")
       const backupPath = `${configPath}.bak.${timestamp}`
+      try {
         fs.copyFileSync(configPath, backupPath)
+      } catch {
+        // Original file may not exist yet — skip backup
+      }
 
-      fs.writeFileSync(configPath, JSON.stringify(rawConfig, null, 2) + "\n", "utf-8")
+      fs.writeFileSync(configPath, JSON.stringify(copy, null, 2) + "\n", "utf-8")
       log(`Migrated config file: ${configPath} (backup: ${backupPath})`)
     } catch (err) {
       log(`Failed to write migrated config to ${configPath}:`, err)
+      // File write failed — rawConfig is untouched, preserving user's original values
+      return false
     }
+
+    // File write succeeded — apply changes to the original rawConfig
+    for (const key of Object.keys(rawConfig)) {
+      delete rawConfig[key]
+    }
+    Object.assign(rawConfig, copy)
   }
 
   return needsWrite