feat(mosaic): route prdy and mission --plan through PrdService (#1275)

- mosaic prdy becomes a thin adapter: --init/--update (wizard for TTY,
  service otherwise), --import with --accept-successor, --export
- mosaic mission --plan persists the mission↔PRD linkage (mission id +
  version marker, PRD id + version) through the service instead of invoking
  the wizard as a second writer; non-TTY runs create non-interactively

packages/mosaic/src/commands/mission.ts

@@ -256,14 +256,41 @@ async function planMission(
   console.log(`Planning mission: ${mission.name}\n`);
 
   try {
-    const { runPrdWizard } = await import('@mosaicstack/prdy');
-    await runPrdWizard({
+    // Thin adapter: the PRD authority (create + mission↔PRD linkage) lives in
+    // PrdService — no second writer path. The mission's updatedAt serves as
+    // its version marker (the gateway exposes no numeric mission version).
+    const { PrdService, runPrdWizard } = await import('@mosaicstack/prdy');
+    const service = new PrdService({ projectPath: process.cwd() });
+
+    if (process.stdout.isTTY) {
+      const created = await runPrdWizard({
+        name: mission.name,
+        projectPath: process.cwd(),
+        interactive: true,
+      });
+      const linked = await service.linkMission({
+        prdId: created.id,
+        missionId: mission.id,
+        missionVersion: mission.updatedAt,
+        requirementIds: [],
+      });
+      console.log(
+        `\nMission ${mission.id} linked to PRD ${linked.id} v${linked.version} (docs/prdy/).`,
+      );
+      return;
+    }
+
+    const doc = await service.planForMission({
       name: mission.name,
-      projectPath: process.cwd(),
-      interactive: true,
+      missionId: mission.id,
+      missionVersion: mission.updatedAt,
+      requirementIds: [],
     });
+    console.log(
+      `PRD created and linked: ${doc.id} v${doc.version} — mission ${mission.id} (docs/prdy/).`,
+    );
   } catch (err) {
-    console.error(`PRD wizard failed: ${err instanceof Error ? err.message : String(err)}`);
+    console.error(`PRD planning failed: ${err instanceof Error ? err.message : String(err)}`);
     process.exit(1);
   }
 }