diff --git a/artifacts/api-server/src/routes/notes.ts b/artifacts/api-server/src/routes/notes.ts
index 63e770be..d451d91d 100644
--- a/artifacts/api-server/src/routes/notes.ts
+++ b/artifacts/api-server/src/routes/notes.ts
@@ -1702,15 +1702,22 @@ router.put(
     }
 
     // Emit live socket events so recipients' rails refresh without polling.
-    // Permission flips reuse the `note-folder-shared` event — recipients
-    // simply refetch shared-with-me / shared-notes and pick up the new
-    // myPermission, which is enough to flip their UI between view / edit
-    // affordances without a dedicated event type.
+    // Three distinct events so the client can tell apart "you got access",
+    // "your permission level changed", and "your access was revoked":
+    //   - note-folder-shared        → newly added recipient
+    //   - note-folder-share-updated → existing recipient's permission flipped
+    //   - note-folder-unshared      → recipient removed
     for (const a of toAdd) {
-      void emitToUser(a.userId, "note-folder-shared", { folderId: id.id });
+      void emitToUser(a.userId, "note-folder-shared", {
+        folderId: id.id,
+        permission: a.permission,
+      });
     }
     for (const u of toUpdate) {
-      void emitToUser(u.userId, "note-folder-shared", { folderId: id.id });
+      void emitToUser(u.userId, "note-folder-share-updated", {
+        folderId: id.id,
+        permission: u.permission,
+      });
     }
     for (const rid of toRemove) {
       void emitToUser(rid, "note-folder-unshared", { folderId: id.id });
diff --git a/artifacts/api-server/tests/notes-share.test.mjs b/artifacts/api-server/tests/notes-share.test.mjs
index abc58193..2297d6ec 100644
--- a/artifacts/api-server/tests/notes-share.test.mjs
+++ b/artifacts/api-server/tests/notes-share.test.mjs
@@ -88,6 +88,8 @@ async function createNote(cookie, body) {
   return json;
 }
 
+const createdFolderIds = [];
+
 after(async () => {
   if (createdNoteIds.length > 0) {
     await pool.query(
@@ -102,6 +104,15 @@ after(async () => {
       createdNoteIds,
     ]);
   }
+  if (createdFolderIds.length > 0) {
+    await pool.query(
+      `DELETE FROM note_folder_shares WHERE folder_id = ANY($1::int[])`,
+      [createdFolderIds],
+    );
+    await pool.query(`DELETE FROM note_folders WHERE id = ANY($1::int[])`, [
+      createdFolderIds,
+    ]);
+  }
   if (createdUserIds.length > 0) {
     await pool.query(
       `DELETE FROM notifications WHERE user_id = ANY($1::int[])`,
@@ -496,6 +507,116 @@ test("GET /notes/my returns the same payload as GET /notes (alias)", async () =>
   );
 });
 
+// Task #454: per-recipient folder permission (view vs edit).
+test("folder share permissions: view-only is rejected on writes; edit can mutate; permission roundtrip works", async () => {
+  const owner = await createUser("notes_perm_owner");
+  const viewer = await createUser("notes_perm_viewer");
+  const editor = await createUser("notes_perm_editor");
+  const oCookie = await login(owner.username);
+  const vCookie = await login(viewer.username);
+  const eCookie = await login(editor.username);
+
+  // Owner creates a folder + a note inside it.
+  const fRes = await api(`/note-folders`, oCookie, {
+    method: "POST",
+    body: JSON.stringify({ name: "perm-folder", color: "blue" }),
+  });
+  assert.ok(fRes.status === 200 || fRes.status === 201, `folder create expected 2xx, got ${fRes.status}`);
+  const folder = await fRes.json();
+  createdFolderIds.push(folder.id);
+
+  const note = await createNote(oCookie, { folderId: folder.id, title: "T" });
+
+  // Owner shares: viewer = view, editor = edit (new recipients[] payload).
+  const shareRes = await api(`/note-folders/${folder.id}/shares`, oCookie, {
+    method: "PUT",
+    body: JSON.stringify({
+      recipients: [
+        { userId: viewer.id, permission: "view" },
+        { userId: editor.id, permission: "edit" },
+      ],
+    }),
+  });
+  assert.equal(shareRes.status, 200);
+  const shareList = await shareRes.json();
+  const viewerRow = shareList.find((r) => r.userId === viewer.id);
+  const editorRow = shareList.find((r) => r.userId === editor.id);
+  assert.equal(viewerRow.permission, "view");
+  assert.equal(editorRow.permission, "edit");
+
+  // Recipients see correct myPermission via shared-with-me.
+  const vSwm = await (await api(`/note-folders/shared-with-me`, vCookie)).json();
+  assert.equal(vSwm.find((f) => f.id === folder.id).myPermission, "view");
+  const eSwm = await (await api(`/note-folders/shared-with-me`, eCookie)).json();
+  assert.equal(eSwm.find((f) => f.id === folder.id).myPermission, "edit");
+
+  // Viewer cannot patch a note in the shared folder.
+  const vPatch = await api(`/notes/${note.id}`, vCookie, {
+    method: "PATCH",
+    body: JSON.stringify({ title: "hacked" }),
+  });
+  assert.equal(vPatch.status, 403, "view-only must not patch");
+
+  // Editor can patch the note.
+  const ePatch = await api(`/notes/${note.id}`, eCookie, {
+    method: "PATCH",
+    body: JSON.stringify({ title: "edited by editor" }),
+  });
+  assert.equal(ePatch.status, 200, "editor must patch");
+
+  // Editor cannot unfile (folderId=null) — would steal the note from owner.
+  const eUnfile = await api(`/notes/${note.id}`, eCookie, {
+    method: "PATCH",
+    body: JSON.stringify({ folderId: null }),
+  });
+  assert.equal(eUnfile.status, 403, "editor must not unfile");
+
+  // Editor can create a new note in the folder; it is stamped to owner.
+  const eCreate = await api(`/notes`, eCookie, {
+    method: "POST",
+    body: JSON.stringify({
+      title: "by editor",
+      content: "x",
+      color: "blue",
+      folderId: folder.id,
+    }),
+  });
+  assert.ok(eCreate.status === 200 || eCreate.status === 201, `editor create expected 2xx, got ${eCreate.status}`);
+  const eCreated = await eCreate.json();
+  createdNoteIds.push(eCreated.id);
+  const { rows: ownerRows } = await pool.query(
+    `SELECT user_id FROM notes WHERE id = $1`,
+    [eCreated.id],
+  );
+  assert.equal(ownerRows[0].user_id, owner.id, "editor-created note belongs to owner");
+
+  // Permission flip: downgrade editor to view, upgrade viewer to edit.
+  const flipRes = await api(`/note-folders/${folder.id}/shares`, oCookie, {
+    method: "PUT",
+    body: JSON.stringify({
+      recipients: [
+        { userId: viewer.id, permission: "edit" },
+        { userId: editor.id, permission: "view" },
+      ],
+    }),
+  });
+  assert.equal(flipRes.status, 200);
+
+  // Former editor (now view) can no longer patch.
+  const ePatch2 = await api(`/notes/${note.id}`, eCookie, {
+    method: "PATCH",
+    body: JSON.stringify({ title: "after-downgrade" }),
+  });
+  assert.equal(ePatch2.status, 403, "downgraded editor must lose write access");
+
+  // Former viewer (now edit) can patch.
+  const vPatch2 = await api(`/notes/${note.id}`, vCookie, {
+    method: "PATCH",
+    body: JSON.stringify({ title: "after-upgrade" }),
+  });
+  assert.equal(vPatch2.status, 200, "upgraded viewer must gain write access");
+});
+
 test("re-sending to the same recipient does not duplicate the recipient row", async () => {
   const sender = await createUser("notes_dup_sender");
   const recipient = await createUser("notes_dup_recipient");
diff --git a/artifacts/tx-os/src/hooks/use-notifications-socket.ts b/artifacts/tx-os/src/hooks/use-notifications-socket.ts
index 28100182..64216f85 100644
--- a/artifacts/tx-os/src/hooks/use-notifications-socket.ts
+++ b/artifacts/tx-os/src/hooks/use-notifications-socket.ts
@@ -343,6 +343,19 @@ export function useNotificationsSocket() {
         invalidate(["note-folders"]);
       },
     );
+    // Task #454: dedicated event for permission-only flips on an
+    // existing share (view ↔ edit). Same invalidation as `shared`,
+    // but kept distinct so the contract is explicit and so future UI
+    // can react with a toast like "Your access changed to Edit".
+    socket.on(
+      "note-folder-share-updated",
+      (payload?: { folderId?: number; permission?: "view" | "edit" }) => {
+        invalidate(["note-folders", "shared-with-me"]);
+        if (typeof payload?.folderId === "number") {
+          invalidate(["notes", "shared-folder", payload.folderId]);
+        }
+      },
+    );
     socket.on(
       "note-folder-unshared",
       (payload?: { folderId?: number }) => {