diff --git a/desktop/src/app/App.tsx b/desktop/src/app/App.tsx
index 0f311f3a650..f0dec3dee88 100644
--- a/desktop/src/app/App.tsx
+++ b/desktop/src/app/App.tsx
@@ -45,7 +45,10 @@ import { ResetFailedScreen } from "@/features/onboarding/ui/ResetFailedScreen";
 import { loadCommunityDiscoveryAfterLeave } from "@/features/communities/communityStorage";
 import { useCommunityInit } from "@/features/communities/useCommunityInit";
 import { useNestNotifications } from "@/features/communities/useNestNotifications";
-import { useCommunities } from "@/features/communities/useCommunities";
+import {
+  hasCommunityForRelay,
+  useCommunities,
+} from "@/features/communities/useCommunities";
 import {
   loadCommunityDestination,
   markPendingCommunityRestore,
@@ -387,8 +390,13 @@ function CommunityApp({
       return;
     }
     const previousCommunityId = activeCommunity?.id;
-    const relayAlreadyExists = communities.some(
-      (community) => community.relayUrl === transaction.relayUrl,
+    // Must match how `addCommunity` decides the relay is already here: it
+    // folds a storage-equivalent spelling into the existing community, so a
+    // raw string compare would record `addedCommunity: true` for a community
+    // the connect did not create, and cancelling would then delete it.
+    const relayAlreadyExists = hasCommunityForRelay(
+      communities,
+      transaction.relayUrl,
     );
     const id = addCommunity({
       id: crypto.randomUUID(),
diff --git a/desktop/src/features/communities/resolveCommunityUpdateResult.test.mjs b/desktop/src/features/communities/resolveCommunityUpdateResult.test.mjs
index 0a52ef845d4..4f9cab50132 100644
--- a/desktop/src/features/communities/resolveCommunityUpdateResult.test.mjs
+++ b/desktop/src/features/communities/resolveCommunityUpdateResult.test.mjs
@@ -5,7 +5,12 @@
 import assert from "node:assert/strict";
 import test from "node:test";
 
-import { resolveCommunityUpdateResult } from "./useCommunities.tsx";
+import {
+  hasCommunityForRelay,
+  isSameRelay,
+  resolveCommunityUpdateResult,
+} from "./useCommunities.tsx";
+import { storageKey } from "@/features/profile/lib/selfProfileStorage";
 
 const COMMUNITIES = [
   {
@@ -105,3 +110,129 @@ test("resolveCommunityUpdateResult_same_relay_url_is_not_duplicate_of_self", ()
   });
   assert.deepEqual(result, { kind: "unchanged" });
 });
+
+// ---------------------------------------------------------------------------
+// Relay identity is the storage notion of sameness, not string equality
+// ---------------------------------------------------------------------------
+//
+// Every per-relay slot — self profile, read state, channel sections, sort
+// preference, sidebar watermark, thread activity, observed unread — is keyed
+// through `normalizeRelayUrl` (trim, strip trailing slashes, lowercase). Two
+// communities whose URLs normalize alike therefore already share all of that
+// data, so admitting the second one does not separate them, it hides that
+// they are one.
+
+test("isSameRelay_treatsStorageEquivalentSpellingsAsOneRelay", () => {
+  const canonical = "wss://relay-a.example.com";
+  for (const spelling of [
+    "wss://relay-a.example.com/",
+    "wss://relay-a.example.com//",
+    "WSS://Relay-A.Example.com",
+    "  wss://relay-a.example.com  ",
+  ]) {
+    assert.equal(
+      isSameRelay(canonical, spelling),
+      true,
+      `${spelling} keys to the same storage slot and must be the same relay`,
+    );
+    assert.equal(
+      storageKey(canonical, "pk") === storageKey(spelling, "pk"),
+      true,
+      `${spelling} must actually collide in storage — the premise of this test`,
+    );
+  }
+});
+
+test("isSameRelay_keepsGenuinelyDifferentRelaysApart", () => {
+  assert.equal(
+    isSameRelay("wss://relay-a.example.com", "wss://relay-b.example.com"),
+    false,
+  );
+  assert.equal(
+    isSameRelay("wss://relay-a.example.com", "ws://relay-a.example.com"),
+    false,
+  );
+});
+
+test("resolveCommunityUpdateResult_trailingSlashOfAnotherRelay_isADuplicate", () => {
+  // Before: raw === missed this, so the edit was accepted and the two
+  // communities silently shared every per-relay storage slot.
+  const result = resolveCommunityUpdateResult(COMMUNITIES, "ws-1", "ws-1", {
+    relayUrl: "wss://relay-b.example.com/",
+  });
+  assert.deepEqual(result, { kind: "duplicate-relay" });
+});
+
+test("resolveCommunityUpdateResult_caseOnlyEditOfAnotherRelay_isADuplicate", () => {
+  const result = resolveCommunityUpdateResult(COMMUNITIES, "ws-1", "ws-1", {
+    relayUrl: "WSS://Relay-B.Example.com",
+  });
+  assert.deepEqual(result, { kind: "duplicate-relay" });
+});
+
+test("resolveCommunityUpdateResult_reSpellingOwnRelay_isStillAnUpdate", () => {
+  // Editing your own relay to an equivalent spelling is not a duplicate of
+  // yourself — it stays a normal update, and on the active community it still
+  // reinitialises the backend, because the connection URL really did change.
+  const result = resolveCommunityUpdateResult(COMMUNITIES, "ws-1", "ws-1", {
+    relayUrl: "wss://relay-a.example.com/",
+  });
+  assert.deepEqual(result, { kind: "updated", requiresReinit: true });
+});
+
+// ---------------------------------------------------------------------------
+// The onboarding rollback flag must agree with addCommunity
+// ---------------------------------------------------------------------------
+//
+// `handleCommunityOnboardingConnect` records `addedCommunity` from this
+// predicate and `handleCommunityOnboardingCancel` acts on it: a true flag lets
+// cancel remove the community, or `clearCommunities()` it when it is the only
+// one. Since `addCommunity` folds an equivalent spelling into the existing
+// community rather than creating a new one, asking with raw `===` here would
+// arm that rollback against a community the connect never created.
+
+test("hasCommunityForRelay_reportsAnEquivalentSpellingAsAlreadyPresent", () => {
+  for (const spelling of [
+    "wss://relay-a.example.com/",
+    "wss://relay-a.example.com//",
+    "WSS://Relay-A.Example.com",
+    "  wss://relay-a.example.com  ",
+  ]) {
+    assert.equal(
+      hasCommunityForRelay(COMMUNITIES, spelling),
+      true,
+      `${spelling} is the existing relay, so the connect added nothing`,
+    );
+  }
+});
+
+test("hasCommunityForRelay_reportsAGenuinelyNewRelayAsAbsent", () => {
+  assert.equal(
+    hasCommunityForRelay(COMMUNITIES, "wss://relay-c.example.com"),
+    false,
+  );
+  assert.equal(
+    hasCommunityForRelay(COMMUNITIES, "ws://relay-a.example.com"),
+    false,
+  );
+  assert.equal(hasCommunityForRelay([], "wss://relay-a.example.com"), false);
+});
+
+test("hasCommunityForRelay_agreesWithTheMatchAddCommunityUses", () => {
+  // addCommunity folds via isSameRelay; the rollback flag must not disagree
+  // with it for any spelling, or cancel deletes a pre-existing community.
+  for (const spelling of [
+    "wss://relay-a.example.com",
+    "WSS://Relay-A.Example.com/",
+    "wss://relay-b.example.com//",
+    "wss://relay-c.example.com",
+  ]) {
+    assert.equal(
+      hasCommunityForRelay(COMMUNITIES, spelling),
+      COMMUNITIES.some((community) =>
+        isSameRelay(community.relayUrl, spelling),
+      ),
+      `${spelling} must resolve the same way for both`,
+    );
+  }
+});
diff --git a/desktop/src/features/communities/useCommunities.tsx b/desktop/src/features/communities/useCommunities.tsx
index e0a10017883..05969868347 100644
--- a/desktop/src/features/communities/useCommunities.tsx
+++ b/desktop/src/features/communities/useCommunities.tsx
@@ -16,6 +16,7 @@ import {
   saveActiveCommunityId,
   saveCommunities,
 } from "./communityStorage";
+import { normalizeRelayUrl } from "@/shared/lib/normalizeRelayUrl";
 import { removeSelfProfileCachesForRelay } from "@/features/profile/lib/selfProfileStorage";
 import { removeUserLabelCacheForRelay } from "@/features/profile/lib/userLabelStorage";
 import { removeChannelSnapshotForRelay } from "@/features/channels/channelSnapshot";
@@ -32,6 +33,42 @@ export type UpdateCommunityResult =
   | { kind: "duplicate-relay" }
   | { kind: "not-found" };
 
+/**
+ * Whether two relay URLs identify the same community.
+ *
+ * Deliberately the *storage* notion of sameness, not string equality: every
+ * per-relay slot — self profile, read state, channel sections, sort
+ * preference, sidebar watermark, thread activity, observed unread — is keyed
+ * through `normalizeRelayUrl`, so two URLs that normalize alike already share
+ * all of that data. Letting them exist as two communities does not separate
+ * them; it just hides that they are one.
+ *
+ * `wss://relay.example`, `wss://relay.example/`, `WSS://Relay.Example` and
+ * `wss://relay.example//` are all one relay by that measure.
+ */
+export function isSameRelay(left: string, right: string): boolean {
+  return normalizeRelayUrl(left) === normalizeRelayUrl(right);
+}
+
+/**
+ * Whether the community list already holds the relay `relayUrl` names.
+ *
+ * Callers that decide *whether an add created a community* must ask this, not
+ * compare raw strings: `addCommunity` folds a storage-equivalent spelling into
+ * the existing community and hands back its id, so a raw comparison marks a
+ * pre-existing community as freshly added. Onboarding's rollback then treats
+ * it as temporary and can remove it — or `clearCommunities()` when it is the
+ * only one. Keep this predicate and `addCommunity`'s match in lockstep.
+ */
+export function hasCommunityForRelay(
+  communities: readonly Pick<Community, "relayUrl">[],
+  relayUrl: string,
+): boolean {
+  return communities.some((community) =>
+    isSameRelay(community.relayUrl, relayUrl),
+  );
+}
+
 /**
  * Pure decision logic for updateCommunity — determines the outcome from a
  * synchronous snapshot of communities without side effects.  Extracted so the
@@ -48,10 +85,14 @@ export function resolveCommunityUpdateResult(
   const current = communities.find((w) => w.id === id);
   if (!current) return { kind: "not-found" };
 
+  // Hoisted so the narrowing survives into the callback below.
+  const nextRelayUrl = updates.relayUrl;
   if (
-    updates.relayUrl !== undefined &&
-    updates.relayUrl !== current.relayUrl &&
-    communities.some((w) => w.id !== id && w.relayUrl === updates.relayUrl)
+    nextRelayUrl !== undefined &&
+    nextRelayUrl !== current.relayUrl &&
+    communities.some(
+      (w) => w.id !== id && isSameRelay(w.relayUrl, nextRelayUrl),
+    )
   ) {
     return { kind: "duplicate-relay" };
   }
@@ -187,12 +228,12 @@ function useCommunitiesInternal(): UseCommunitiesReturn {
   );
 
   const addCommunity = useCallback((community: Community): string => {
-    const existing = communitiesRef.current.find(
-      (w) => w.relayUrl === community.relayUrl,
+    const existing = communitiesRef.current.find((w) =>
+      isSameRelay(w.relayUrl, community.relayUrl),
     );
     const resolvedId = existing?.id ?? community.id;
     setCommunitiesState((prev) => {
-      const dup = prev.find((w) => w.relayUrl === community.relayUrl);
+      const dup = prev.find((w) => isSameRelay(w.relayUrl, community.relayUrl));
       let next: Community[];
       if (dup) {
         next = prev.map((w) =>