diff --git a/js/app/uiCoordinator.js b/js/app/uiCoordinator.js
index a743ed2f..dce3daeb 100644
--- a/js/app/uiCoordinator.js
+++ b/js/app/uiCoordinator.js
@@ -9,6 +9,7 @@
  * Methods use `this` which is bound to the Application instance.
  */
 import { SHORT_TIMEOUT_MS, DEBOUNCE_DELAY_MS } from "../constants.js";
+import { getActiveSigner } from "../nostrClientRegistry.js";
 
 export function createUiCoordinator(deps) {
   const {
@@ -187,11 +188,52 @@ export function createUiCoordinator(deps) {
     },
 
     syncAuthUiState() {
-      if (this.isUserLoggedIn()) {
+      // Auth-dependent chrome has to follow login/logout/account switches, but
+      // syncAuthUiState() was only ever called at bootstrap — so everything it
+      // gates (notably the share menu's "Share on Nostr" item) kept its
+      // logged-out state for the entire session. Self-install a listener on the
+      // first run rather than adding a call site in js/app.js, which is at its
+      // file-size cap.
+      if (
+        !this.__authUiSyncBound &&
+        typeof window !== "undefined" &&
+        typeof window?.addEventListener === "function"
+      ) {
+        this.__authUiSyncBound = true;
+        window.addEventListener("bitvid:auth-changed", () => {
+          try {
+            this.syncAuthUiState();
+          } catch (error) {
+            devLogger.warn("[Application] Auth UI resync failed:", error);
+          }
+        });
+      }
+
+      const loggedIn = this.isUserLoggedIn();
+      if (loggedIn) {
         this.applyAuthenticatedUiState();
       } else {
         this.applyLoggedOutUiState();
       }
+
+      // Gate the share menu's "Share on Nostr" item. Without this the modal's
+      // shareNostrAuthState stays at its initial `false` forever and the item
+      // renders permanently disabled — indistinguishable from plain text.
+      if (typeof this.videoModal?.setShareNostrAuthState === "function") {
+        let signer = null;
+        try {
+          signer = getActiveSigner();
+        } catch (error) {
+          devLogger.warn("[Application] Failed to read active signer:", error);
+        }
+        this.videoModal.setShareNostrAuthState({
+          isLoggedIn: loggedIn,
+          // Mirrors ShareNostrController.handleShare(): a signer that cannot
+          // sign is no signer at all, and enabling the item would only produce
+          // an error toast on click.
+          hasSigner: !!signer && typeof signer.signEvent === "function",
+        });
+      }
     },
 
     refreshChromeElements() {
diff --git a/js/ui/components/VideoModal.js b/js/ui/components/VideoModal.js
index b56ea6ba..9d7f5ab8 100644
--- a/js/ui/components/VideoModal.js
+++ b/js/ui/components/VideoModal.js
@@ -3453,6 +3453,32 @@ export class VideoModal {
   // Delegated click handler for the share popover's menu-action buttons
   // (Copy URL / Copy Magnet / Copy CDN / Share on Nostr). The forced-source
   // test links self-wire their own copy, so they are skipped here.
+  /**
+   * Update the login/signer gate for the share menu's "Share on Nostr" item.
+   *
+   * This state was initialized to `false` and never written, so
+   * `createVideoShareMenuPanel` always rendered the item disabled — the entry
+   * looked like inert text no matter who was logged in, and the click
+   * delegation in bindShareMenuActions() bails on `button.disabled`. The app
+   * pushes real state here from syncAuthUiState().
+   */
+  setShareNostrAuthState({ isLoggedIn = false, hasSigner = false } = {}) {
+    const next = { isLoggedIn: !!isLoggedIn, hasSigner: !!hasSigner };
+    const changed =
+      next.isLoggedIn !== this.shareNostrAuthState.isLoggedIn ||
+      next.hasSigner !== this.shareNostrAuthState.hasSigner;
+    this.shareNostrAuthState = next;
+
+    // The popover renders its panel on open, so a menu that is already open
+    // would keep showing the stale (disabled) item. Close it so the next open
+    // renders against current state.
+    if (changed) {
+      this.modalSharePopover?.close?.();
+    }
+
+    return changed;
+  }
+
   bindShareMenuActions(panel) {
     if (!panel || typeof panel.addEventListener !== "function") {
       return;
diff --git a/tests/share-nostr-auth-gate.test.mjs b/tests/share-nostr-auth-gate.test.mjs
new file mode 100644
index 00000000..2a39a3ef
--- /dev/null
+++ b/tests/share-nostr-auth-gate.test.mjs
@@ -0,0 +1,173 @@
+// SCN-share-nostr-gate
+//
+// The share menu's "Share on Nostr" item is gated on `isLoggedIn && hasSigner`
+// (js/ui/components/videoMenuRenderers.js). VideoModal initialized
+// `shareNostrAuthState` to {false, false} and NOTHING ever wrote to it, so the
+// item rendered permanently disabled — it looked like inert text, and the click
+// delegation in bindShareMenuActions() bails on `button.disabled`.
+//
+// Two halves have to hold for the button to work:
+//   1. VideoModal.setShareNostrAuthState() records the state.
+//   2. syncAuthUiState() pushes real auth state in, and re-runs on auth change
+//      (it previously ran only once at bootstrap).
+
+import test from "node:test";
+import assert from "node:assert/strict";
+import { createUiCoordinator } from "../js/app/uiCoordinator.js";
+import { VideoModal } from "../js/ui/components/VideoModal.js";
+import {
+  clearActiveSigner,
+  registerSigner,
+  setActiveSigner,
+} from "../js/nostrClientRegistry.js";
+
+const PUBKEY = "b".repeat(64);
+
+// --- VideoModal setter ----------------------------------------------------
+
+function makeModal() {
+  const modal = Object.create(VideoModal.prototype);
+  modal.shareNostrAuthState = { isLoggedIn: false, hasSigner: false };
+  modal.closedPopover = 0;
+  modal.modalSharePopover = {
+    close: () => {
+      modal.closedPopover += 1;
+    },
+  };
+  return modal;
+}
+
+test("setShareNostrAuthState records the gate", () => {
+  const modal = makeModal();
+  assert.equal(modal.setShareNostrAuthState({ isLoggedIn: true, hasSigner: true }), true);
+  assert.deepEqual(modal.shareNostrAuthState, { isLoggedIn: true, hasSigner: true });
+});
+
+test("setShareNostrAuthState is idempotent and only closes a stale menu once", () => {
+  const modal = makeModal();
+  modal.setShareNostrAuthState({ isLoggedIn: true, hasSigner: true });
+  assert.equal(modal.closedPopover, 1, "open menu must re-render against new state");
+
+  // No change -> no churn. Closing the popover on every no-op sync would slam
+  // the menu shut under the user.
+  assert.equal(modal.setShareNostrAuthState({ isLoggedIn: true, hasSigner: true }), false);
+  assert.equal(modal.closedPopover, 1);
+});
+
+test("setShareNostrAuthState coerces and defaults safely", () => {
+  const modal = makeModal();
+  modal.setShareNostrAuthState({ isLoggedIn: "yes", hasSigner: 1 });
+  assert.deepEqual(modal.shareNostrAuthState, { isLoggedIn: true, hasSigner: true });
+
+  modal.setShareNostrAuthState();
+  assert.deepEqual(modal.shareNostrAuthState, { isLoggedIn: false, hasSigner: false });
+});
+
+test("setShareNostrAuthState tolerates no popover", () => {
+  const modal = makeModal();
+  modal.modalSharePopover = null;
+  assert.doesNotThrow(() =>
+    modal.setShareNostrAuthState({ isLoggedIn: true, hasSigner: true })
+  );
+});
+
+// --- syncAuthUiState wiring ----------------------------------------------
+
+function makeApp({ loggedIn }) {
+  const coordinator = createUiCoordinator({
+    devLogger: { warn() {}, error() {}, log() {} },
+  });
+  const pushed = [];
+  const app = {
+    ...coordinator,
+    isUserLoggedIn: () => loggedIn,
+    // Stub the DOM-touching branches; this test is about the share gate.
+    applyAuthenticatedUiState() {},
+    applyLoggedOutUiState() {},
+    videoModal: {
+      setShareNostrAuthState(state) {
+        pushed.push({ ...state });
+      },
+    },
+  };
+  return { app, pushed };
+}
+
+test("syncAuthUiState pushes the gate into the video modal", () => {
+  const { app, pushed } = makeApp({ loggedIn: true });
+  app.syncAuthUiState();
+  assert.equal(pushed.length, 1);
+  assert.equal(pushed[0].isLoggedIn, true);
+});
+
+test("logged out propagates as a closed gate", () => {
+  const { app, pushed } = makeApp({ loggedIn: false });
+  app.syncAuthUiState();
+  assert.deepEqual(pushed[0], { isLoggedIn: false, hasSigner: false });
+});
+
+test("hasSigner reflects a registered, signing-capable signer", () => {
+  clearActiveSigner();
+  const { app, pushed } = makeApp({ loggedIn: true });
+
+  app.syncAuthUiState();
+  assert.equal(pushed[0].hasSigner, false, "no signer registered yet");
+
+  registerSigner(PUBKEY, { pubkey: PUBKEY, signEvent: async (e) => e });
+  setActiveSigner(PUBKEY);
+  app.syncAuthUiState();
+  assert.equal(pushed[1].hasSigner, true);
+
+  clearActiveSigner();
+  app.syncAuthUiState();
+  assert.equal(pushed[2].hasSigner, false, "logout must close the gate again");
+});
+
+test("a signer that cannot sign does not open the gate", () => {
+  // Mirrors ShareNostrController.handleShare(): enabling the item for a signer
+  // without signEvent would only produce an error toast on click.
+  clearActiveSigner();
+  registerSigner(PUBKEY, { pubkey: PUBKEY });
+  setActiveSigner(PUBKEY);
+
+  const { app, pushed } = makeApp({ loggedIn: true });
+  app.syncAuthUiState();
+  assert.equal(pushed[0].hasSigner, false);
+  clearActiveSigner();
+});
+
+test("syncAuthUiState re-runs on bitvid:auth-changed, and binds only once", () => {
+  // The original bug's second half: the gate was computed once at bootstrap and
+  // never again, so logging in mid-session left the button disabled.
+  const listeners = [];
+  const originalWindow = globalThis.window;
+  globalThis.window = {
+    addEventListener(type, handler) {
+      listeners.push({ type, handler });
+    },
+  };
+
+  try {
+    const { app, pushed } = makeApp({ loggedIn: false });
+    app.syncAuthUiState();
+    assert.equal(pushed.length, 1);
+
+    const bound = listeners.filter((l) => l.type === "bitvid:auth-changed");
+    assert.equal(bound.length, 1, "listener installed on first sync");
+
+    bound[0].handler();
+    assert.equal(pushed.length, 2, "auth change re-syncs the gate");
+
+    // Re-entrancy: the resync must not stack a new listener every time.
+    assert.equal(
+      listeners.filter((l) => l.type === "bitvid:auth-changed").length,
+      1
+    );
+  } finally {
+    if (originalWindow === undefined) {
+      delete globalThis.window;
+    } else {
+      globalThis.window = originalWindow;
+    }
+  }
+});