m4: global API-error surface (no more silent failures)

The api client now catches network failures and non-JSON bodies robustly,
and routes unexpected errors (offline / 5xx) to a global toast — 4xx stay
with the caller so forms keep their inline messages. Toast actions are now
optional (undo toasts keep their button; error toasts are message-only), and
ToastHost moved from AppShell to the app root so toasts show everywhere,
including the login screen.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FRgehjoz7Yv8LkUfADxACm

frontend/src/App.vue

@@ -1,3 +1,8 @@
+<script setup lang="ts">
+import ToastHost from "./components/ToastHost.vue";
+</script>
+
 <template>
   <RouterView />
+  <ToastHost />
 </template>

frontend/src/api/client.ts

@@ -1,25 +1,52 @@
+import { useUiStore } from "../stores/ui";
+
 export interface ApiError {
   error: string;
   status: number;
 }
 
+// Surface infra / unexpected failures (network, 5xx) globally. 4xx are left to
+// the caller — forms and views show their own inline messages for those.
+function notifyError(err: ApiError) {
+  try {
+    useUiStore().showToast(err.error);
+  } catch {
+    /* pinia not active yet (very early boot) — skip the toast */
+  }
+}
+
 async function request<T>(method: string, path: string, body?: unknown): Promise<T> {
-  const resp = await fetch(path, {
+  let resp: Response;
+  try {
+    resp = await fetch(path, {
       method,
       credentials: "include", // send/receive the signed session cookie
       headers: body !== undefined ? { "Content-Type": "application/json" } : undefined,
       body: body !== undefined ? JSON.stringify(body) : undefined,
     });
+  } catch {
+    const err: ApiError = { error: "Can't reach the server. Check your connection.", status: 0 };
+    notifyError(err);
+    throw err;
+  }
 
   const text = await resp.text();
-  const data: unknown = text ? JSON.parse(text) : {};
+  let data: unknown = {};
+  if (text) {
+    try {
+      data = JSON.parse(text);
+    } catch {
+      data = {}; // non-JSON body (e.g. a proxy error page) — fall through to status handling
+    }
+  }
 
   if (!resp.ok) {
     const message =
       typeof data === "object" && data !== null && "error" in data
         ? String((data as { error: unknown }).error)
-        : "Request failed.";
+        : "Something went wrong. Please try again.";
     const err: ApiError = { error: message, status: resp.status };
+    if (resp.status >= 500) notifyError(err);
     throw err;
   }
 

frontend/src/components/AppShell.vue

@@ -8,7 +8,6 @@ import { useUiStore } from "../stores/ui";
 import CommandPalette from "./CommandPalette.vue";
 import Icon from "./Icon.vue";
 import LabelsModal from "./LabelsModal.vue";
-import ToastHost from "./ToastHost.vue";
 import { NOTE_SWATCH_CLASSES, type NoteColor } from "../notes/colors";
 
 const route = useRoute();
@@ -297,8 +296,6 @@ async function signOut() {
 
     <CommandPalette v-if="paletteOpen" @close="paletteOpen = false" />
 
-    <ToastHost />
-
     <div
       v-if="showShortcuts"
       class="fixed inset-0 z-50 flex items-center justify-center bg-black/40 p-4"

frontend/src/components/ToastHost.vue

@@ -19,11 +19,12 @@ const ui = useUiStore();
     >
       <span>{{ ui.toast.message }}</span>
       <button
+        v-if="ui.toast.action"
         type="button"
         class="font-semibold text-brand hover:underline focus:outline-none focus-visible:ring-2 focus-visible:ring-brand"
         @click="ui.runToastAction()"
       >
-        {{ ui.toast.actionLabel }}
+        {{ ui.toast.action.label }}
       </button>
       <button
         type="button"

frontend/src/stores/notes.ts

@@ -106,7 +106,8 @@ export const useNotesStore = defineStore("notes", () => {
   const setPinned = (id: string, pinned: boolean) => mutate(id, { pinned });
   const setArchived = async (id: string, archived: boolean): Promise<void> => {
     await mutate(id, { archived });
-    if (archived) useUiStore().showToast("Note archived", "Undo", () => void setArchived(id, false));
+    if (archived)
+      useUiStore().showToast("Note archived", { label: "Undo", run: () => void setArchived(id, false) });
   };
   const setColor = (id: string, color: NoteColor) => mutate(id, { color });
   const setKind = (id: string, kind: NoteKind) => mutate(id, { kind });
@@ -176,7 +177,7 @@ export const useNotesStore = defineStore("notes", () => {
 
   async function trash(id: string): Promise<void> {
     reconcile(await api.post<Note>(`/api/notes/${id}/trash`));
-    useUiStore().showToast("Note moved to trash", "Undo", () => void restore(id));
+    useUiStore().showToast("Note moved to trash", { label: "Undo", run: () => void restore(id) });
   }
 
   async function restore(id: string): Promise<void> {

frontend/src/stores/ui.ts

@@ -1,11 +1,15 @@
 import { defineStore } from "pinia";
 import { ref } from "vue";
 
+interface ToastAction {
+  label: string;
+  run: () => void;
+}
+
 interface Toast {
   id: number;
   message: string;
-  actionLabel: string;
+  action?: ToastAction;
-  action: () => void;
 }
 
 // Cross-component UI signals that don't belong to any single view (e.g. a
@@ -22,10 +26,10 @@ export const useUiStore = defineStore("ui", () => {
   let toastTimer: ReturnType<typeof setTimeout> | undefined;
   let toastSeq = 0;
 
-  function showToast(message: string, actionLabel: string, action: () => void) {
+  function showToast(message: string, action?: ToastAction) {
     toastSeq += 1;
     const id = toastSeq;
-    toast.value = { id, message, actionLabel, action };
+    toast.value = { id, message, action };
     clearTimeout(toastTimer);
     toastTimer = setTimeout(() => {
       if (toast.value?.id === id) toast.value = null;
@@ -38,9 +42,9 @@ export const useUiStore = defineStore("ui", () => {
   }
 
   function runToastAction() {
-    const action = toast.value?.action;
+    const run = toast.value?.action?.run;
     dismissToast();
-    action?.();
+    run?.();
   }
 
   return { composeTick, requestCompose, toast, showToast, dismissToast, runToastAction };