feat(extensions): establish canonical goal source (#54, #55)

extensions/mosaic-core/lib/reconcile.ts

@@ -0,0 +1,28 @@
+// lib/reconcile.ts — pure exact active-tool reconciliation (PRD R3 core, AC2).
+//
+// The reconciliation output is the COMPLETE target state: applying it makes
+// the active tool set EXACTLY the manifest's set — no more (an injected
+// third-party tool is removed), no less (a manifest tool missing from the
+// active set is listed for addition). NG-2 binds this to setActiveTools();
+// this module never touches Pi state.
+
+export interface ReconcilePlan {
+  /** the exact target active set (sorted manifest tools) */
+  exact: string[];
+  /** active tools absent from the manifest — must be removed */
+  toRemove: string[];
+  /** manifest tools absent from the active set — must be added */
+  toAdd: string[];
+  /** true when the active set already equals the manifest set */
+  unchanged: boolean;
+}
+
+export function reconcileActiveTools(manifestTools: string[], activeTools: string[]): ReconcilePlan {
+  const target = [...new Set(manifestTools)].sort();
+  const active = [...new Set(activeTools)].sort();
+  const inManifest = new Set(target);
+  const inActive = new Set(active);
+  const toRemove = active.filter((t) => !inManifest.has(t));
+  const toAdd = target.filter((t) => !inActive.has(t));
+  return { exact: target, toRemove, toAdd, unchanged: toRemove.length === 0 && toAdd.length === 0 };
+}