diff --git a/components/reasoning-workspace.jsx b/components/reasoning-workspace.jsx
index 429459d..4cac47c 100644
--- a/components/reasoning-workspace.jsx
+++ b/components/reasoning-workspace.jsx
@@ -581,6 +581,10 @@ function ThreadContributionsBadge({ nodeId, contributions }) {
 
   return (
     <div className="mt-3">
+      {/* Thread activity cue: visible when this node has focused investigation history */}
+      <span className="mb-1 block text-[9px] uppercase tracking-widest font-semibold text-amber-500/70">
+        INVESTIGATING
+      </span>
       {/* Thread learning indicator — collapsed by default; user can expand to inspect history */}
       <details open={false} className="rounded-lg border border-gray-200/80 bg-white/60">
         <summary className="cursor-pointer px-3 py-1.5 text-xs font-medium text-gray-600 hover:text-gray-800 select-none">
diff --git a/tests/open-questions-vs-assumptions.test.jsx b/tests/open-questions-vs-assumptions.test.jsx
index 3f14275..0bf92aa 100644
--- a/tests/open-questions-vs-assumptions.test.jsx
+++ b/tests/open-questions-vs-assumptions.test.jsx
@@ -744,3 +744,116 @@ describe("same-node focused result reopen", () => {
     expect(hasCompletedInvestigation("u5")).toBe(true);
   });
 });
+
+// ── INVESTIGATING cue on Open Question cards ───
+
+describe("Focused investigation history cue", () => {
+  function getThreadContribs(nodeId, contributions) {
+    return (contributions || []).filter((c) => c.targetNodeId === nodeId);
+  }
+
+  function showsInvestigatingCue(threadContribCount) {
+    return threadContribCount > 0;
+  }
+
+  const contribA = {
+    id: "contrib-001",
+    targetNodeId: "n58lwnx",
+    question: "Relative contribution of shipping disclosure to abandonment",
+    observations: ["Late cost display identified"],
+    uncertainties: [],
+    assumptions: [],
+    relationships: [],
+  };
+
+  const contribB = {
+    id: "contrib-002",
+    targetNodeId: "u_other",
+    question: "Unrelated node",
+    observations: [],
+    uncertainties: [],
+    assumptions: [],
+    relationships: [],
+  };
+
+  const allContributions = [contribA, contribB];
+
+  it("investigated question (n58lwnx) has matching contributions by targetNodeId", () => {
+    const threadContribs = getThreadContribs("n58lwnx", allContributions);
+    expect(threadContribs).toHaveLength(1);
+    expect(threadContribs[0].id).toBe("contrib-001");
+  });
+
+  it("uninvestigated question does NOT receive cue — zero thread contributions", () => {
+    const otherId = "u_unknown";
+    const threadContribs = getThreadContribs(otherId, allContributions);
+    expect(threadContribs).toHaveLength(0);
+    expect(showsInvestigatingCue(threadContribs.length)).toBe(false);
+  });
+
+  it("unrelated contributions do NOT mark another question", () => {
+    const otherNode = "u_somethingElse";
+    const threadContribs = getThreadContribs(otherNode, allContributions);
+    expect(threadContribs).toHaveLength(0);
+    expect(showsInvestigatingCue(threadContribs.length)).toBe(false);
+  });
+
+  it("investigated question DOES show cue (has 1+ thread contributions)", () => {
+    const threadContribs = getThreadContribs("n58lwnx", allContributions);
+    expect(showsInvestigatingCue(threadContribs.length)).toBe(true);
+  });
+
+  it("UNCLEAR and INVESTIGATING are independent — both can coexist on same node", () => {
+    const uNode = { id: "n58lwnx", kind: "unknown", status: "unclear", label: "U1" };
+    const hasContribs = getThreadContribs(uNode.id, allContributions).length > 0;
+    expect(uNode.status).toBe("unclear");
+    expect(hasContribs).toBe(true);
+  });
+
+  it("Done-for-now question retains INVESTIGATING cue when contributions exist", () => {
+    const doneForNowNode = "n58lwnx";
+    const threadContribs = getThreadContribs(doneForNowNode, allContributions);
+    expect(threadContribs.length).toBeGreaterThan(0);
+    expect(showsInvestigatingCue(threadContribs.length)).toBe(true);
+  });
+
+  it("identity rule distinguishes contributed node from uninvestigated", () => {
+    const invested = getThreadContribs("n58lwnx", allContributions);
+    const uninvested = getThreadContribs("u_unrelated", allContributions);
+    expect(invested.length).toBeGreaterThan(0);
+    expect(uninvested.length).toBe(0);
+    expect(showsInvestigatingCue(invested.length)).not.toBe(showsInvestigatingCue(uninvested.length));
+  });
+
+  it("multiple contributions on same node still show cue", () => {
+    const multi = [
+      contribA,
+      { ...contribA, id: "contrib-003", targetNodeId: "n58lwnx" },
+      { ...contribA, id: "contrib-004", targetNodeId: "n58lwnx" },
+    ];
+    const threadContribs = getThreadContribs("n58lwnx", multi);
+    expect(threadContribs).toHaveLength(3);
+    expect(showsInvestigatingCue(threadContribs.length)).toBe(true);
+  });
+
+  it("null contributions produce no cue", () => {
+    const threadContribs = getThreadContribs("n58lwnx", null);
+    expect(threadContribs).toHaveLength(0);
+    expect(showsInvestigatingCue(threadContribs.length)).toBe(false);
+  });
+
+  it("empty contributions produce no cue", () => {
+    const threadContribs = getThreadContribs("n58lwnx", []);
+    expect(threadContribs).toHaveLength(0);
+    expect(showsInvestigatingCue(threadContribs.length)).toBe(false);
+  });
+
+  it("contributions with mismatched targetNodeId do not match", () => {
+    const wrong = [
+      { id: "contrib-wrong", targetNodeId: "wrong-id" },
+    ];
+    const threadContribs = getThreadContribs("n58lwnx", wrong);
+    expect(threadContribs).toHaveLength(0);
+    expect(showsInvestigatingCue(threadContribs.length)).toBe(false);
+  });
+});