diff --git a/packages/core/src/__tests__/postgres/duplicate-and-sibling-lanes.pg.test.ts b/packages/core/src/__tests__/postgres/duplicate-and-sibling-lanes.pg.test.ts
new file mode 100644
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+/*
+FNXC:WorkflowResolvedColumns 2026-07-31-23:15:
+TWO CREATE-TIME DUPLICATE GUARDS, on a RENAMED board.
+
+Both decide "is this candidate still LIVE?" by excluding finished lanes, and both were converted to
+`resolveProjectColumnsForRoles`:
+
+  findRecentTasksByContentFingerprint  — excludes ARCHIVED (unless includeArchived)
+  findRecentTasksBySourceParentTaskId  — excludes COMPLETE and ARCHIVED
+
+Blinding either back to its literals left the whole 16-file lane-detector set green: no test in
+`packages/core` reaches either method.
+
+WHAT BREAKS WITHOUT THEM. They fail in OPPOSITE directions, which is why both are here.
+
+  Fingerprint guard — a renamed board leaves archived cards in the candidate set, so filing a new
+  task is REFUSED as a duplicate of one the operator already archived. The operator cannot create
+  the card and the thing blocking them is invisible.
+
+  Sibling guard — a renamed board leaves finished siblings in the "recent live siblings" set, so a
+  completed sibling keeps counting as active work.
+
+Each is a silent wrong answer on a create path, and neither surfaces an error.
+
+DIFFERENTIAL. The same seeded rows are queried under two vocabularies whose traits are identical and
+only the ids differ; `shipped`/`vaulted` collide with no legacy id. The default-vocabulary cases are
+controls — they pass with or without the conversion.
+
+WINDOWED. Both queries cut off at `Date.now() - windowMs` with `windowMs` capped at 24h, so fixtures
+are seeded at the current time rather than at a fixed past instant; a frozen timestamp falls outside
+the window and every case passes vacuously with an empty result.
+*/
+
+import { afterAll, afterEach, beforeAll, beforeEach, expect, it } from "vitest";
+import { sql } from "drizzle-orm";
+import {
+  createSharedPgTaskStoreTestHarness,
+  pgDescribe,
+  type SharedPgTaskStoreHarness,
+} from "../../__test-utils__/pg-test-harness.js";
+import { BUILTIN_CODING_WORKFLOW_IR } from "../../builtin-coding-workflow-ir.js";
+
+pgDescribe("create-time duplicate guards under a renamed board vocabulary", () => {
+  const h: SharedPgTaskStoreHarness = createSharedPgTaskStoreTestHarness({
+    prefix: "fusion_dup_sibling_lanes",
+  });
+
+  beforeAll(h.beforeAll);
+  beforeEach(h.beforeEach);
+  afterEach(h.afterEach);
+  afterAll(h.afterAll);
+
+  async function seedRenamedWorkflow(): Promise<void> {
+    const RENAME: Record<string, string> = {
+      todo: "drafting",
+      "in-progress": "building",
+      "in-review": "checking",
+      done: "shipped",
+      archived: "vaulted",
+    };
+    const rename = (id: string | undefined) => (id && RENAME[id]) ?? id;
+    const ir = JSON.parse(JSON.stringify(BUILTIN_CODING_WORKFLOW_IR)) as {
+      id: string;
+      nodes?: { column?: string }[];
+      columns?: { id: string }[];
+    };
+    ir.id = "custom:renamed-dup-guards";
+    for (const node of ir.nodes ?? []) node.column = rename(node.column);
+    for (const column of ir.columns ?? []) column.id = rename(column.id) as string;
+
+    const ids = (ir.columns ?? []).map((column) => column.id);
+    expect(ids).toContain("vaulted");
+    expect(ids).not.toContain("archived");
+
+    await h.store().createWorkflowDefinition({ name: "Renamed", kind: "workflow", ir } as never);
+  }
+
+  /** A row carrying `contentFingerprint`, parked in `lane`, created inside the 24h window. */
+  async function seedFingerprintRow(id: string, lane: string): Promise<void> {
+    const store = h.store();
+    const now = new Date().toISOString();
+    await store.createTaskWithReservedId(
+      { description: id, column: "todo" },
+      { taskId: id, createdAt: now, updatedAt: now, applyDefaultWorkflowSteps: false },
+    );
+    await h.adminDb().execute(sql`
+      UPDATE project.tasks
+         SET "column" = ${lane}, source_metadata = ${JSON.stringify({ contentFingerprint: "FP-1" })}::jsonb
+       WHERE id = ${id}`);
+    store.taskCache.delete(id);
+  }
+
+  /** A row parented to KB-PARENT, parked in `lane`, created inside the 24h window. */
+  async function seedSiblingRow(id: string, lane: string): Promise<void> {
+    const store = h.store();
+    const now = new Date().toISOString();
+    await store.createTaskWithReservedId(
+      { description: id, column: "todo" },
+      { taskId: id, createdAt: now, updatedAt: now, applyDefaultWorkflowSteps: false },
+    );
+    await h.adminDb().execute(sql`
+      UPDATE project.tasks
+         SET "column" = ${lane}, source_parent_task_id = 'KB-PARENT'
+       WHERE id = ${id}`);
+    store.taskCache.delete(id);
+  }
+
+  // ── Guard 1: content-fingerprint duplicate ────────────────────────────────
+
+  it("default vocabulary: an ARCHIVED fingerprint match is not a duplicate candidate", async () => {
+    await seedFingerprintRow("KB-FP", "archived");
+
+    expect(await h.store().findRecentTasksByContentFingerprint("FP-1")).toEqual([]);
+  });
+
+  it("renamed vocabulary: a fingerprint match in the RENAMED archived lane is not a candidate", async () => {
+    await seedRenamedWorkflow();
+    await seedFingerprintRow("KB-FP", "vaulted");
+
+    expect(await h.store().findRecentTasksByContentFingerprint("FP-1")).toEqual([]);
+  });
+
+  it("renamed vocabulary: a LIVE fingerprint match is still a duplicate candidate", async () => {
+    /* The paired positive: excluding archived must not degrade into excluding everything, or the
+       duplicate guard stops guarding. */
+    await seedRenamedWorkflow();
+    await seedFingerprintRow("KB-FP", "building");
+
+    const found = await h.store().findRecentTasksByContentFingerprint("FP-1");
+    expect(found.map((task) => task.id)).toEqual(["KB-FP"]);
+  });
+
+  it("renamed vocabulary: includeArchived opts the RENAMED archived lane back in", async () => {
+    await seedRenamedWorkflow();
+    await seedFingerprintRow("KB-FP", "vaulted");
+
+    const found = await h.store().findRecentTasksByContentFingerprint("FP-1", { includeArchived: true });
+    expect(found.map((task) => task.id)).toEqual(["KB-FP"]);
+  });
+
+  // ── Guard 2: recent live siblings ─────────────────────────────────────────
+
+  it("default vocabulary: a FINISHED sibling is not a recent live sibling", async () => {
+    await seedSiblingRow("KB-SIB", "done");
+
+    expect(await h.store().findRecentTasksBySourceParentTaskId("KB-PARENT")).toEqual([]);
+  });
+
+  it("renamed vocabulary: a sibling in the RENAMED complete lane is not live", async () => {
+    await seedRenamedWorkflow();
+    await seedSiblingRow("KB-SIB", "shipped");
+
+    expect(await h.store().findRecentTasksBySourceParentTaskId("KB-PARENT")).toEqual([]);
+  });
+
+  it("renamed vocabulary: a sibling in the RENAMED archived lane is not live", async () => {
+    await seedRenamedWorkflow();
+    await seedSiblingRow("KB-SIB", "vaulted");
+
+    expect(await h.store().findRecentTasksBySourceParentTaskId("KB-PARENT")).toEqual([]);
+  });
+
+  it("renamed vocabulary: a WORKING sibling IS live", async () => {
+    await seedRenamedWorkflow();
+    await seedSiblingRow("KB-SIB", "building");
+
+    const found = await h.store().findRecentTasksBySourceParentTaskId("KB-PARENT");
+    expect(found.map((task) => task.id)).toEqual(["KB-SIB"]);
+  });
+});