refactor: remove legacy kb compatibility

Drops the .kb/kb.db migration path, legacy backup filename handling, and
backward-compat test suites. Renames internal kbDir identifiers to
fusionDir and hasKbProject/isValidKbProject to their fusion equivalents.

- Remove needsCentralMigration, autoMigrateToCentral, and the
  "needs-migration" FirstRunState; checkAndMigrate and KB_SKIP_MIGRATION
  env var are gone
- Remove LEGACY_BACKUP_DIR and canonicalizeBackupDir; listBackups no
  longer matches kb-* filenames
- Delete backward-compat.test.ts and store-backward-compat.test.ts;
  update remaining tests to new 3-state first-run model

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/cli/src/bin.test.ts

@@ -189,7 +189,6 @@ vi.mock("./commands/message.js", () => ({
 
 const originalArgv = process.argv;
 const originalExit = process.exit;
-const originalSkipMigration = process.env.KB_SKIP_MIGRATION;
 const originalPiPackageDir = process.env.PI_PACKAGE_DIR;
 
 let importCounter = 0;
@@ -206,7 +205,6 @@ describe("bin command routing and fallbacks", () => {
 
   beforeEach(() => {
     vi.clearAllMocks();
-    process.env.KB_SKIP_MIGRATION = "1";
     delete process.env.PI_PACKAGE_DIR;
     process.exit = vi.fn(((code?: number) => {
       throw new Error(`process.exit:${code ?? 0}`);
@@ -216,11 +214,6 @@ describe("bin command routing and fallbacks", () => {
   afterEach(() => {
     process.argv = originalArgv;
     process.exit = originalExit;
-    if (originalSkipMigration === undefined) {
-      delete process.env.KB_SKIP_MIGRATION;
-    } else {
-      process.env.KB_SKIP_MIGRATION = originalSkipMigration;
-    }
 
     if (originalPiPackageDir === undefined) {
       delete process.env.PI_PACKAGE_DIR;

packages/cli/src/bin.ts

@@ -380,51 +380,6 @@ function getFlagValueNumber(args: string[], flag: string): number | undefined {
   return Number.isFinite(parsed) ? parsed : undefined;
 }
 
-/**
- * Check if migration is needed and run it automatically.
- * This handles the transition from single-project to multi-project mode.
- */
-async function checkAndMigrate(): Promise<void> {
-  // Skip if KB_SKIP_MIGRATION is set
-  if (process.env.KB_SKIP_MIGRATION === "1") {
-    return;
-  }
-
-  try {
-    const { needsCentralMigration, autoMigrateToCentral } = await import("@fusion/core");
-
-    // Check if migration is needed
-    if (!needsCentralMigration(process.cwd())) {
-      return;
-    }
-
-    console.log("\n🔄 Migrating to multi-project mode...");
-
-    // Get CentralCore and run migration
-    const { CentralCore } = await import("@fusion/core");
-    const central = new CentralCore();
-    await central.init();
-
-    try {
-      const result = await autoMigrateToCentral(process.cwd(), central);
-
-      if (result.success) {
-        console.log(`✓ Registered project: ${result.projectsRegistered.join(", ")}`);
-        if (result.errors.length > 0) {
-          console.log(`  Warnings: ${result.errors.join(", ")}`);
-        }
-      } else {
-        console.log(`⚠ Migration warnings: ${result.errors.join(", ")}`);
-      }
-    } finally {
-      await central.close();
-    }
-  } catch (err) {
-    // Migration errors are non-fatal - continue with legacy mode
-    console.log(`⚠ Migration check failed: ${(err as Error).message}`);
-  }
-}
-
 async function main() {
   const { cleanedArgs: args, projectName } = extractGlobalProjectFlag(process.argv.slice(2));
 
@@ -435,12 +390,6 @@ async function main() {
 
   const command = args[0];
 
-  // Migration check: run auto-migration for existing single-project users
-  // Skip for init command itself (user is explicitly initializing)
-  if (command !== "init" && command !== "dashboard") {
-    await checkAndMigrate();
-  }
-
   const {
     runDashboard,
     runServe,

packages/cli/src/commands/backup.test.ts

@@ -21,7 +21,7 @@ vi.mock("@fusion/core", () => ({
   TaskStore: vi.fn().mockImplementation(() => ({
     init: vi.fn().mockResolvedValue(undefined),
     getSettings: mockGetSettings,
-    kbDir: "/cwd/.fusion",
+    fusionDir: "/cwd/.fusion",
   })),
   createBackupManager: vi.fn(() => ({
     listBackups: mockListBackups,
@@ -60,7 +60,7 @@ describe("backup commands", () => {
       projectName: "demo-project",
       projectPath: "/projects/demo",
       isRegistered: true,
-      store: { getSettings: mockGetSettings, kbDir: "/projects/demo/.fusion" },
+      store: { getSettings: mockGetSettings, fusionDir: "/projects/demo/.fusion" },
     });
   });
 

packages/cli/src/commands/backup.ts

@@ -22,14 +22,14 @@ async function resolveBackupStore(projectName?: string): Promise<TaskStore> {
 async function getBackupManager(projectName?: string): Promise<{
   manager: BackupManager;
   store: TaskStore;
-  kbDir: string;
+  fusionDir: string;
 }> {
   const store = await resolveBackupStore(projectName);
-  // Access the private kbDir property via type assertion
-  const kbDir = (store as unknown as { kbDir: string }).kbDir;
+  // Access the private fusionDir property via type assertion
+  const fusionDir = (store as unknown as { fusionDir: string }).fusionDir;
   const settings = await store.getSettings();
-  const manager = createBackupManager(kbDir, settings);
-  return { manager, store, kbDir };
+  const manager = createBackupManager(fusionDir, settings);
+  return { manager, store, fusionDir };
 }
 
 /**
@@ -37,12 +37,12 @@ async function getBackupManager(projectName?: string): Promise<{
  * Usage: fn backup --create
  */
 export async function runBackupCreate(projectName?: string): Promise<void> {
-  const { kbDir, store } = await getBackupManager(projectName);
+  const { fusionDir, store } = await getBackupManager(projectName);
   const settings = await store.getSettings();
   
   console.log("Creating database backup...");
   
-  const result = await runBackupCommand(kbDir, settings);
+  const result = await runBackupCommand(fusionDir, settings);
   
   if (result.success) {
     console.log(result.output);

packages/cli/src/commands/message.ts

@@ -26,8 +26,8 @@ async function getProjectPath(projectName?: string): Promise<string> {
  */
 async function createMessageStore(projectName?: string): Promise<{ store: MessageStore; db: Database }> {
   const projectPath = await getProjectPath(projectName);
-  const kbDir = projectPath + "/.fusion";
-  const db = createDatabase(kbDir);
+  const fusionDir = projectPath + "/.fusion";
+  const db = createDatabase(fusionDir);
   db.init();
   const store = new MessageStore(db);
   return { store, db };

packages/cli/src/project-resolver.ts

@@ -220,12 +220,12 @@ export async function resolveProject(options: ResolveOptions = {}): Promise<Reso
 
   // 2. Walk up from cwd to find .fusion/
   const cwd = options.cwd ? resolve(options.cwd) : process.cwd();
-  const kbDir = findKbDir(cwd);
+  const fusionDir = findKbDir(cwd);
 
-  if (kbDir) {
+  if (fusionDir) {
     // 3. Match path against registered projects
     const allProjects = await central.listProjects();
-    const normalizedKbDir = normalize(kbDir);
+    const normalizedKbDir = normalize(fusionDir);
 
     const match = allProjects.find((p) => normalize(p.path) === normalizedKbDir);
 
@@ -245,12 +245,12 @@ export async function resolveProject(options: ResolveOptions = {}): Promise<Reso
 
     // 4. Has .fusion/ but not registered
     if (interactive) {
-      console.log(`\n  Found fn project at ${kbDir} but it's not registered.`);
+      console.log(`\n  Found fn project at ${fusionDir} but it's not registered.`);
       const shouldRegister = await promptConfirm("Register this project now?", true);
 
       if (shouldRegister) {
         const rl = createInterface({ input: process.stdin, output: process.stdout });
-        const defaultName = kbDir.split("/").pop() || "unnamed";
+        const defaultName = fusionDir.split("/").pop() || "unnamed";
         const name = await rl.question(`  Project name [${defaultName}]: `);
         rl.close();
 
@@ -259,7 +259,7 @@ export async function resolveProject(options: ResolveOptions = {}): Promise<Reso
         try {
           const newProject = await central.registerProject({
             name: finalName,
-            path: kbDir,
+            path: fusionDir,
             isolationMode: "in-process",
           });
 
@@ -272,22 +272,22 @@ export async function resolveProject(options: ResolveOptions = {}): Promise<Reso
           throw new ProjectResolutionError(
             `Failed to register project: ${err.message}`,
             "NOT_REGISTERED",
-            { directory: kbDir, error: err.message }
+            { directory: fusionDir, error: err.message }
           );
         }
       } else {
         throw new ProjectResolutionError(
           "Project not registered. Run `fn project add <path>` to register.",
           "NOT_REGISTERED",
-          { directory: kbDir }
+          { directory: fusionDir }
         );
       }
     } else {
       throw new ProjectResolutionError(
-        `Found fn project at ${kbDir} but it's not registered.\n\n` +
-          "Run `fn project add " + kbDir + "` to register it, or use --project <name>.",
+        `Found fn project at ${fusionDir} but it's not registered.\n\n` +
+          "Run `fn project add " + fusionDir + "` to register it, or use --project <name>.",
         "NOT_REGISTERED",
-        { directory: kbDir }
+        { directory: fusionDir }
       );
     }
   }