feat(notes): show loading and failed states for stacked notes

A note that couldn't load rendered a silent blank div. Add a calm
NoteState placeholder (spinner while loading, message + retry on
failure) and gate the read view on it; content still wins when present.

DESIGN.md

@@ -407,6 +407,7 @@ Cells: link strength (9/3/1/blank). Importance row = Σ(weight × strength).
 - **Asymmetric file index:** `addFile` deduped by SHA only, `registerUploadedFile` by PATH — so an edit (same path, new SHA) left a stale duplicate entry. **Fixed** — `addFile` now dedups by SHA *and* path (a path is unique), with a regression test in `userRepo.store.spec.ts`. (Full bidirectional index C3 still the longer-term direction.)
 - **ADR-0001 over-absolute:** it called SHA-keyed references "a fragility". **Refined** by ADR-0002 into two intentional modes (Live/Snapshot).
 - **`CLAUDE.md` "edit history tracking"** mislabels the visited-repos History; no edit-history feature exists. (Flagged in CONTEXT.md.)
+- **Snapshot cache not immutable:** editing writes new content under the *viewed* (old) SHA's cache key (`prepareNoteCache` keys by the viewed sha), so a re-opened old-SHA snapshot can serve new content from cache. **Decided fix (ADR-0002):** key the immutable store by the content's *own* SHA (write-once), keep the Path key as the latest pointer. *(Not yet implemented — the C3/C4 cache slice; unlocks the snapshot banner.)*
 - **Naming drift carried from the language session:** `Flux`→`Igarapé`, `HistoricNotes`→`Index`, `Repetition`→`Card`, `PublicNote*`→`PublishedNote*`, `useNotes()` returns Files not Notes. (Tracked in CONTEXT.md "Flagged ambiguities".)
 
 ---

docs/adr/0002-two-reference-modes.md

@@ -17,4 +17,5 @@ This refines ADR-0001, which framed SHA-keyed references as "a fragility." That
 ## Consequences
 
 - The system **pre-caches** aggressively (content is cached by both SHA and Path on every fetch / freshness pull) so the pinned version is usually present, including offline.
+- **Cache shape (C3/C4):** content is cached under two keys — its own **content SHA** (write-once, immutable → the snapshot store) and its **Path** (overwritten with the latest content → the live pointer). Both hold the full content, so the latest survives even if a SHA entry is evicted, maximizing offline availability for any version already encountered. (Today the code violates this by writing edited content under the *viewed* old SHA key; the fix is to write under the content's *new* SHA and never overwrite an existing SHA entry.)
 - When a Snapshot reference's pinned content is genuinely unavailable (never-fetched + offline — common on a flaky mobile connection), the system **falls back to the most up-to-date cached version and shows a banner** disclosing "this is the latest available, not the exact shared version." Integrity is preserved by **disclosure, not refusal**: the reader is never silently shown different content, but is also never dead-ended on the metro. (This chooses graceful continuity over a hard "unavailable" stop, given mobile is the primary read context.)

src/components/NoteState.spec.ts

@@ -0,0 +1,29 @@
+import { mount } from "@vue/test-utils"
+import { describe, expect, it } from "vitest"
+
+import NoteState from "./NoteState.vue"
+
+describe("NoteState", () => {
+  it("shows a spinner while loading and no retry", () => {
+    const wrapper = mount(NoteState, { props: { status: "loading" } })
+
+    expect(wrapper.find(".loading-spinner").exists()).toBe(true)
+    expect(wrapper.find(".note-state-retry").exists()).toBe(false)
+  })
+
+  it("shows a message and retry button when failed", () => {
+    const wrapper = mount(NoteState, { props: { status: "failed" } })
+
+    expect(wrapper.find(".loading-spinner").exists()).toBe(false)
+    expect(wrapper.text()).toContain("Couldn't load this note")
+    expect(wrapper.find(".note-state-retry").exists()).toBe(true)
+  })
+
+  it("emits retry when the retry button is clicked", async () => {
+    const wrapper = mount(NoteState, { props: { status: "failed" } })
+
+    await wrapper.find(".note-state-retry").trigger("click")
+
+    expect(wrapper.emitted("retry")).toHaveLength(1)
+  })
+})

src/components/NoteState.vue

@@ -0,0 +1,48 @@
+<script lang="ts" setup>
+defineProps<{ status: "loading" | "failed" }>()
+defineEmits<{ retry: [] }>()
+</script>
+
+<template>
+  <div class="note-state">
+    <span
+      v-if="status === 'loading'"
+      class="loading loading-spinner loading-md"
+      aria-label="Loading note"
+    ></span>
+    <template v-else>
+      <p class="note-state-message">Couldn't load this note.</p>
+      <button type="button" class="note-state-retry" @click="$emit('retry')">
+        Retry
+      </button>
+    </template>
+  </div>
+</template>
+
+<style scoped lang="scss">
+.note-state {
+  display: flex;
+  flex: 1;
+  flex-direction: column;
+  align-items: center;
+  justify-content: center;
+  gap: 0.75rem;
+  padding: 2rem 1rem;
+  color: var(--color-base-content);
+  opacity: 0.55;
+  text-align: center;
+}
+
+.note-state-message {
+  margin: 0;
+}
+
+.note-state-retry {
+  padding: 0.25rem 0.85rem;
+  border: 1px solid currentColor;
+  border-radius: 0.375rem;
+  background: transparent;
+  color: inherit;
+  cursor: pointer;
+}
+</style>

src/components/StackedNote.vue

@@ -40,6 +40,10 @@ const EditNote = defineAsyncComponent(
   () => import("@/modules/note/components/EditNote.vue")
 )
 
+const NoteState = defineAsyncComponent(
+  () => import("@/components/NoteState.vue")
+)
+
 const props = defineProps<{
   user: string
   repo: string
@@ -154,10 +158,21 @@ const {
 })
 
 const conflictOpen = ref(false)
+const loadStatus = ref<"loading" | "ready" | "failed">("loading")
 
-onMounted(async () => {
-  initialRawContent.value = await getRawContent()
-})
+const loadNote = async () => {
+  loadStatus.value = "loading"
+  const raw = await getRawContent()
+  if (raw === null) {
+    loadStatus.value = "failed"
+    return
+  }
+  rawContent.value = raw
+  initialRawContent.value = raw
+  loadStatus.value = "ready"
+}
+
+onMounted(loadNote)
 
 watch(
   path,
@@ -412,11 +427,18 @@ const onBadgeClick = async () => {
       <div v-if="mode === 'edit' && isMarkdown" class="edit">
         <edit-note :key="editKey" v-model="rawContent" />
       </div>
-      <div
-        v-if="mode === 'read'"
-        class="note-content"
-        v-html="displayedContent"
-      ></div>
+      <template v-else-if="mode === 'read'">
+        <div
+          v-if="displayedContent"
+          class="note-content"
+          v-html="displayedContent"
+        ></div>
+        <note-state
+          v-else
+          :status="loadStatus === 'failed' ? 'failed' : 'loading'"
+          @retry="loadNote"
+        />
+      </template>
     </section>
     <linked-notes v-if="hasBacklinks && content" :sha="sha" />
     <note-conflict-modal