feat(plugin): knowledge auto-inject (Path A) — title-first per-turn awareness

New UserPromptSubmit hook (scribe_autoinject.sh) + GET /api/plugin/retrieve that
surface the TITLES (never bodies) of the few notes clearing four anti-bloat
gates: a per-user confidence threshold (stricter than pull search), a margin
gate, per-session dedup (exclude_ids), and a top-k ceiling. Each retrieval is
logged to retrieval_logs as source=auto_inject so the threshold can be tuned
from data. Per-user config (enable / threshold / top-k) is DB-backed via
/api/settings with a Settings UI card; defaults enabled, threshold 0.55,
top-k 3 (conservative — tune once auto_inject telemetry accrues).

Scribe: project 2, milestone 93, task 1033.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Xz4j1H7pjYSjKsEpgcNH5E

frontend/src/views/SettingsView.vue

@@ -17,6 +17,13 @@ const timezoneSaved = ref(false);
 const trashRetentionDays = ref("90");
 const savingRetention = ref(false);
 const retentionSaved = ref(false);
+// Knowledge auto-inject (per-user). Defaults mirror the backend
+// (services/plugin_context: enabled, threshold 0.55, top-k 3).
+const kbInjectEnabled = ref(true);
+const kbInjectThreshold = ref("0.55");
+const kbInjectTopK = ref("3");
+const savingKbInject = ref(false);
+const kbInjectSaved = ref(false);
 
 // think_enabled setting removed 2026-05-23. The chat+curator architecture
 // has tools=[] on the chat model; think on a no-tools conversational pass
@@ -56,6 +63,28 @@ async function saveRetention() {
     savingRetention.value = false;
   }
 }
+
+async function saveKbInject() {
+  const t = Math.min(1, Math.max(0, Number(kbInjectThreshold.value) || 0));
+  const k = Math.min(10, Math.max(1, Math.floor(Number(kbInjectTopK.value) || 1)));
+  kbInjectThreshold.value = String(t);
+  kbInjectTopK.value = String(k);
+  savingKbInject.value = true;
+  kbInjectSaved.value = false;
+  try {
+    await apiPut('/api/settings', {
+      kb_autoinject_enabled: kbInjectEnabled.value ? 'true' : 'false',
+      kb_autoinject_threshold: String(t),
+      kb_autoinject_top_k: String(k),
+    });
+    kbInjectSaved.value = true;
+    setTimeout(() => (kbInjectSaved.value = false), 2000);
+  } catch {
+    toastStore.show('Failed to save auto-inject settings', 'error');
+  } finally {
+    savingKbInject.value = false;
+  }
+}
 const newEmail = ref("");
 const emailPassword = ref("");
 const changingEmail = ref(false);
@@ -435,6 +464,13 @@ onMounted(async () => {
   const allSettings = await apiGet<Record<string, string>>("/api/settings");
   userTimezone.value = allSettings.user_timezone ?? "";
   trashRetentionDays.value = allSettings.trash_retention_days ?? "90";
+  kbInjectEnabled.value = allSettings.kb_autoinject_enabled !== "false";
+  if (allSettings.kb_autoinject_threshold !== undefined) {
+    kbInjectThreshold.value = allSettings.kb_autoinject_threshold;
+  }
+  if (allSettings.kb_autoinject_top_k !== undefined) {
+    kbInjectTopK.value = allSettings.kb_autoinject_top_k;
+  }
   if (allSettings.notify_task_reminders !== undefined) {
     notifyTaskReminders.value = allSettings.notify_task_reminders !== "false";
   }
@@ -1165,6 +1201,58 @@ function formatUserDate(iso: string): string {
         </div>
       </section>
 
+      <section class="settings-section full-width">
+        <h2>Knowledge auto-inject</h2>
+        <p class="section-desc">
+          When enabled, the Scribe plugin quietly surfaces the titles of your most
+          relevant notes on each prompt — never their full text — so Claude can pull
+          one in with <code>get_note(id)</code> only when it helps. Titles only, each
+          note at most once per session, and nothing is shown unless it clears the
+          confidence bar below.
+        </p>
+        <div class="checkbox-field">
+          <label>
+            <input type="checkbox" v-model="kbInjectEnabled" />
+            Surface relevant note titles each prompt
+          </label>
+          <p class="field-hint">Off = notes reach context only when Claude searches for them.</p>
+        </div>
+        <div class="field">
+          <label for="kb-inject-threshold">Confidence threshold (0–1)</label>
+          <input
+            id="kb-inject-threshold"
+            v-model="kbInjectThreshold"
+            type="number"
+            min="0"
+            max="1"
+            step="0.05"
+            class="input"
+            style="max-width: 8rem"
+          />
+          <p class="field-hint">Minimum similarity to surface a note. Higher = stricter (fewer, more certain). Deliberately above the 0.45 used for searches you trigger yourself.</p>
+        </div>
+        <div class="field">
+          <label for="kb-inject-topk">Max notes per prompt</label>
+          <input
+            id="kb-inject-topk"
+            v-model="kbInjectTopK"
+            type="number"
+            min="1"
+            max="10"
+            step="1"
+            class="input"
+            style="max-width: 8rem"
+          />
+          <p class="field-hint">Ceiling on titles surfaced at once (1–10).</p>
+        </div>
+        <div class="actions">
+          <button class="btn-save" @click="saveKbInject" :disabled="savingKbInject">
+            {{ savingKbInject ? 'Saving…' : 'Save' }}
+          </button>
+          <span v-if="kbInjectSaved" class="saved-msg">Saved!</span>
+        </div>
+      </section>
+
     </div>
 
     <!-- ── Account ── -->