feat(workspace): workspace mode toggle, derived task prefix, default coding workflow (#1741)

## Problem

After PR #1739 merged the core workspace auto-detection fix, additional
workspace UX was needed:
1. Onboarding should interactively confirm workspace mode and let the
user pick a task prefix and default workflow.
2. Task prefix should be derived from the project name (2-4 chars
uppercase) instead of a hardcoded constant.
3. Default fallback prefix should be `FN` (matching the product name),
not the legacy `KB`.
4. Dashboard registration should also auto-derive prefix and set the
coding workflow.
5. Default workflow should be `builtin:coding`.

## Changes

### `packages/cli/src/project-resolver.ts`
- **Interactive workspace confirmation**: When sub-repos are detected,
ask the user to confirm workspace mode instead of auto-applying
(non-interactive/dashboard still auto-applies).
- **`suggestTaskPrefix(projectName)`**: Derives a 2-4 char prefix from
the project name (first letters of words, or first chars of a single
word).
- **Onboarding prefix prompt**: Shows the suggested prefix and lets the
user confirm or override.
- **Default coding workflow**: Sets `defaultWorkflowId:
"builtin:coding"` for new projects.

### `packages/core/src/settings-schema.ts`
- `DEFAULT_PROJECT_SETTINGS.workspaceMode`: changed from `false` to
`undefined` so `TaskStore.init()` does not write `workspaceMode: false`
to config.json before auto-detection runs (which would block it via
`isWorkspaceModeExplicitlyDisabled`).
- `DEFAULT_PROJECT_SETTINGS.taskPrefix`: changed to `undefined` (falls
back to `"FN"` in store).
- `DEFAULT_PROJECT_SETTINGS.defaultWorkflowId`: set to
`"builtin:coding"`.

### `packages/core/src/store.ts`
- Task prefix fallback changed from `"KB"` to `"FN"`.

### `packages/dashboard/src/routes/register-project-routes.ts`
- Auto-derives task prefix from project name for dashboard
registrations.
- Sets `defaultWorkflowId: "builtin:coding"` for new projects.

## Testing
- `pnpm typecheck` — pass
- `pnpm lint` — pass
- `vitest run git-repository.test.ts` — 8/8 pass

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<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Project onboarding now proposes a task prefix derived from the project
name, and stores it during setup (interactive onboarding and new
registrations).
* New projects start with the default coding workflow enabled to improve
first-time experience.
* **Bug Fixes**
* Improved distributed task ID prefix fallback when no custom prefix is
configured (now uses `FN`).
* **Chores**
* Updated default project settings so `taskPrefix` and `workspaceMode`
begin unset, aligning with onboarding behavior.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/cli/src/project-resolver.ts

@@ -18,6 +18,7 @@ import {
   writeProjectIdentity,
   detectWorkspaceRepos,
   saveWorkspaceConfig,
+  suggestTaskPrefix,
   type RegisteredProject,
   type TaskStore,
 } from "@fusion/core";
@@ -685,6 +686,7 @@ export async function registerProjectInteractive(
           // Persist workspaceMode in config.json so it's visible/toggleable in the dashboard
           await store.updateSettings({ workspaceMode: true });
         }
+        await store.close();
         console.log(`  ✓ Initialized fn at ${absPath}`);
       } else {
         throw new ProjectResolutionError(
@@ -743,6 +745,33 @@ export async function registerProjectInteractive(
     // Best-effort stamp only.
   }
 
+  /*
+  FNXC:Onboarding 2026-06-24-18:00:
+  After registration, prompt the user to confirm a task prefix and default workflow.
+  The prefix defaults to the first 2-4 chars of the project name so each project gets
+  recognizable task IDs (e.g., "MYPR" for "my-project"). The workflow defaults to coding.
+  Both are persisted to config.json via the TaskStore.
+  */
+  if (interactive) {
+    const { TaskStore } = await import("@fusion/core");
+    const store = new TaskStore(absPath);
+    await store.init();
+
+    const suggestedPrefix = suggestTaskPrefix(name);
+    const rl = createInterface({ input: process.stdin, output: process.stdout });
+    const prefixInput = await rl.question(`\n  Task prefix [${suggestedPrefix}]: `);
+    rl.close();
+    const rawPrefix = prefixInput.trim().toUpperCase().replace(/[^A-Z]/g, "");
+    const prefix = rawPrefix.length >= 2 && rawPrefix.length <= 5 ? rawPrefix : suggestedPrefix;
+
+    await store.updateSettings({
+      taskPrefix: prefix,
+      defaultWorkflowId: "builtin:coding",
+    });
+    await store.close();
+    console.log(`  ✓ Task prefix set to "${prefix}", default workflow: coding`);
+  }
+
   return createResolvedProject(project);
 }
 

packages/core/src/index.ts

@@ -1957,3 +1957,4 @@ export {
   clearSyncPassphrase,
   hasSyncPassphraseConfigured,
 } from "./secrets-sync-passphrase.js";
+export { suggestTaskPrefix } from "./task-prefix.js";

packages/core/src/settings-schema.ts

@@ -307,7 +307,7 @@ export const DEFAULT_PROJECT_SETTINGS = {
     onFailure: "fail",
   },
   worktreesDir: undefined,
-  taskPrefix: "FN",
+  taskPrefix: undefined,
   taskAttributionTrailerNames: ["Fusion-Task-Id"],
   commitMsgHookEnabled: true,
   includeTaskIdInCommit: true,
@@ -538,7 +538,7 @@ export const DEFAULT_PROJECT_SETTINGS = {
   researchDefaultTimeout: 300000,
   researchMaxSourcesPerRun: 20,
   researchMaxSynthesisRounds: 2,
-  workspaceMode: false,
+  workspaceMode: undefined,
 } satisfies CompleteSettings<ProjectSettingsSchema>;
 
 /**

packages/core/src/store.ts

@@ -4151,7 +4151,7 @@ ${TASK_UPSERT_SQL_ASSIGNMENTS}
     },
   ): Promise<Task> {
     const settings = await this.getSettingsFast();
-    const prefix = (settings.taskPrefix || "KB").trim().toUpperCase();
+    const prefix = (settings.taskPrefix || "FN").trim().toUpperCase();
     const allocator = this.getDistributedTaskIdAllocator();
     const nodeId = await this.resolveLocalNodeIdForTaskAllocation();
     const reservation = await allocator.reserveDistributedTaskId({

packages/core/src/task-prefix.ts

@@ -0,0 +1,17 @@
+/**
+ * FNXC:TaskPrefix 2026-06-24-18:00:
+ * Derive a task prefix from a project name. Strips non-alpha characters, uppercases,
+ * and takes the first 2-4 characters. Falls back to "FN" for names with fewer than
+ * 2 letters. Used during project onboarding (CLI and dashboard) so each project gets
+ * a recognizable prefix for task IDs (e.g. "MYPR" for "my-project").
+ *
+ * Note: the result is the first 2-4 letters of the cleaned (alpha-only, uppercased)
+ * name, NOT the initials of each word. For "my-project" the result is "MYPR"
+ * (first 4 of "MYPROJECT"), not "MP".
+ */
+export function suggestTaskPrefix(projectName: string): string {
+  const cleaned = projectName.replace(/[^a-zA-Z]/g, "").toUpperCase();
+  if (cleaned.length >= 2 && cleaned.length <= 4) return cleaned;
+  if (cleaned.length > 4) return cleaned.slice(0, 4);
+  return "FN";
+}

packages/dashboard/src/routes/register-project-routes.ts

@@ -374,6 +374,28 @@ export const registerProjectRoutes: ApiRouteRegistrar = (ctx) => {
         // Memory bootstrap failure is non-fatal - project registration succeeded
       });
 
+      /*
+      FNXC:Onboarding 2026-06-24-18:00:
+      For new registrations (not reattachments), set a derived task prefix and default
+      workflow via the per-project TaskStore config.json so the project is immediately
+      usable without manual settings configuration.
+      */
+      if (activeProjectWithOutcome.outcome === "registered") {
+        try {
+          const { TaskStore, suggestTaskPrefix } = await import("@fusion/core");
+          const store = new TaskStore(normalizedPath);
+          await store.init();
+          const prefix = suggestTaskPrefix(normalizedName);
+          await store.updateSettings({
+            taskPrefix: prefix,
+            defaultWorkflowId: "builtin:coding",
+          });
+          await store.close();
+        } catch {
+          // Non-fatal: project registration succeeded; settings can be configured later
+        }
+      }
+
       // Notify the host (serve.ts/daemon.ts) so it can run project-setup
       // side-effects like installing the fusion Claude-skill into
       // .claude/skills/fusion when pi-claude-cli is configured. The callback