diff --git a/docs/frameworks/MEMORY.md b/docs/frameworks/MEMORY.md
index 306eac9ca0..14f35f68a6 100644
--- a/docs/frameworks/MEMORY.md
+++ b/docs/frameworks/MEMORY.md
@@ -223,7 +223,13 @@ chronological order if the FTS table is missing or the FTS query throws.
 ### Optional: Qdrant (vector store tier 2)
 
 `src/lib/memory/qdrant.ts` implements an optional Qdrant integration as tier 2
-vector store. Enabled via `qdrantEnabled` in settings / toggle in Engine tab.
+vector store. Retrieval only routes to Qdrant when the engine selector
+`memoryVectorStore === "qdrant"` — the default `"auto"` (and `"sqlite-vec"`)
+**never** select Qdrant. The Engine-tab toggle sets **both** `qdrantEnabled` and
+`memoryVectorStore` together: enabling makes Qdrant the primary store, disabling
+resets to `"auto"` (#5597 — before that fix, enabling was inert because nothing
+wrote the engine selector). If Qdrant is unreachable or returns nothing, retrieval
+falls back to sqlite-vec → FTS5.
 
 - `upsertSemanticMemoryPoint()` — embed `key + content` with the configured
   embedding model, ensure the collection exists (creates cosine-distance
@@ -251,6 +257,26 @@ routes under `src/app/api/settings/qdrant/` are all wired as of v3.8.6:
 | `/api/settings/qdrant/cleanup`          | `POST`        | Remove expired / old points     |
 | `/api/settings/qdrant/embedding-models` | `GET`         | List available embedding models |
 
+**Behavior notes (what to expect):**
+
+- **Engine selection** — enabling Qdrant in the Engine tab makes it the primary
+  store (sets `memoryVectorStore="qdrant"`); disabling resets to `"auto"` (#5597).
+- **No back-fill** — only memories created/updated **after** Qdrant is enabled are
+  written to it (fire-and-forget dual-write). Pre-existing SQLite memories are **not**
+  migrated; "Reindex Now" rebuilds the sqlite-vec index only, not Qdrant.
+- **Vector dimension is auto-detected** from the actual embedding on first use — there
+  is no dimension field to fill in. Changing the embedding model after a collection
+  exists is **not** auto-handled: the existing collection is left untouched, dimension-
+  mismatched writes/searches fail and fall back to sqlite-vec. Recreate the collection
+  (new name, or delete it in Qdrant) to switch embedders.
+- **Distance metric** — always **Cosine** (hardcoded on collection creation; not
+  configurable).
+- **Auth** — API key only (sent as the `api-key` header; optional for unauthenticated
+  local Docker). JWT/RBAC are not used.
+- **Config fields** — the UI exposes `host`, `port`, `collection`, `embeddingModel`,
+  `apiKey`. `vectorSize` / `hnswEfConstruct` are env/DB only and `vectorSize` is not
+  used for collection creation (dimension comes from the embedding).
+
 ### Vector quantization (int8 — opt-in, both backends)
 
 Both vector backends support **opt-in int8 quantization** to cut the memory
diff --git a/src/app/(dashboard)/dashboard/memory/components/QdrantConfigCard.tsx b/src/app/(dashboard)/dashboard/memory/components/QdrantConfigCard.tsx
index 30b44ffeca..68ab2231d1 100644
--- a/src/app/(dashboard)/dashboard/memory/components/QdrantConfigCard.tsx
+++ b/src/app/(dashboard)/dashboard/memory/components/QdrantConfigCard.tsx
@@ -205,6 +205,11 @@ export default function QdrantConfigCard() {
         </span>
       </div>
 
+      {/* Tier 1 vs Tier 2 guidance */}
+      <div className="mb-4 p-3 rounded-lg bg-emerald-500/5 border border-emerald-500/20 text-xs text-text-muted leading-relaxed">
+        {t("qdrant.banner")}
+      </div>
+
       {/* Enable toggle + test connection */}
       <div className="flex items-center justify-between p-4 rounded-lg bg-surface/30 border border-border/30 mb-4">
         <div>
@@ -271,6 +276,7 @@ export default function QdrantConfigCard() {
             placeholder="http://127.0.0.1"
             className="w-full px-3 py-2 rounded-lg bg-background border border-border text-sm font-mono focus:outline-none focus:ring-1 focus:ring-emerald-500"
           />
+          <p className="text-[11px] text-text-muted mt-1.5">{t("qdrant.hostHelp")}</p>
         </div>
         <div className="p-3 rounded-lg bg-surface/30 border border-border/30">
           <label className="text-xs font-medium block mb-1.5">{t("qdrant.portLabel")}</label>
@@ -292,6 +298,7 @@ export default function QdrantConfigCard() {
             placeholder="omniroute_memory"
             className="w-full px-3 py-2 rounded-lg bg-background border border-border text-sm font-mono focus:outline-none focus:ring-1 focus:ring-emerald-500"
           />
+          <p className="text-[11px] text-text-muted mt-1.5">{t("qdrant.collectionHelp")}</p>
         </div>
         <div className="p-3 rounded-lg bg-surface/30 border border-border/30">
           <label className="text-xs font-medium block mb-1.5">
@@ -319,6 +326,7 @@ export default function QdrantConfigCard() {
             placeholder="openai/text-embedding-3-small"
             className="w-full px-3 py-2 rounded-lg bg-background border border-border text-sm font-mono focus:outline-none focus:ring-1 focus:ring-emerald-500"
           />
+          <p className="text-[11px] text-text-muted mt-1.5">{t("qdrant.embeddingModelHelp")}</p>
         </div>
         <div className="p-3 rounded-lg bg-surface/30 border border-border/30 md:col-span-2">
           <label className="text-xs font-medium block mb-1.5">
diff --git a/src/app/api/settings/qdrant/route.ts b/src/app/api/settings/qdrant/route.ts
index 78ea9c0dcb..eff1e2ab01 100644
--- a/src/app/api/settings/qdrant/route.ts
+++ b/src/app/api/settings/qdrant/route.ts
@@ -4,6 +4,7 @@ import { validateBody, isValidationFailure } from "@/shared/validation/helpers";
 import { QdrantSettingsUpdateSchema } from "@/shared/schemas/qdrant";
 import { getQdrantConfig, normalizeQdrantConfig } from "@/lib/memory/qdrant";
 import { updateSettings, getSettings } from "@/lib/localDb";
+import { invalidateMemorySettingsCache } from "@/lib/memory/settings";
 import { sanitizeErrorMessage } from "@omniroute/open-sse/utils/error.ts";
 
 function maskApiKey(apiKey: string | null): { hasApiKey: boolean; apiKeyMasked: string | null } {
@@ -68,7 +69,14 @@ export async function PUT(request: NextRequest) {
 
   try {
     const updates: Record<string, unknown> = {};
-    if (body.enabled !== undefined) updates.qdrantEnabled = body.enabled;
+    if (body.enabled !== undefined) {
+      updates.qdrantEnabled = body.enabled;
+      // #5597: enabling Qdrant here was inert — retrieval only routes to Qdrant when
+      // memoryVectorStore === "qdrant" (the default "auto" never selects it), and no UI
+      // wrote that. Activate/deactivate the engine alongside the toggle so "enabled"
+      // actually means "Qdrant is the primary vector store" (matching the UI copy).
+      updates.memoryVectorStore = body.enabled ? "qdrant" : "auto";
+    }
     if (body.host !== undefined) updates.qdrantHost = body.host;
     if (body.port !== undefined) updates.qdrantPort = body.port;
     if (body.collection !== undefined) updates.qdrantCollection = body.collection;
@@ -80,6 +88,10 @@ export async function PUT(request: NextRequest) {
     }
 
     const newSettings = (await updateSettings(updates)) as Record<string, unknown>;
+    // #5597 follow-up: bust the module-level memory-settings cache so the retrieval
+    // layer (getMemorySettings) picks up the new vectorStore/qdrant config without a
+    // process restart — mirrors src/app/api/settings/memory/route.ts.
+    invalidateMemorySettingsCache();
     return NextResponse.json(buildQdrantSettingsResponse(newSettings));
   } catch (err: unknown) {
     const message = sanitizeErrorMessage(err instanceof Error ? err.message : String(err));
diff --git a/src/i18n/messages/en.json b/src/i18n/messages/en.json
index 4ddab05d11..2380f8725d 100644
--- a/src/i18n/messages/en.json
+++ b/src/i18n/messages/en.json
@@ -3425,6 +3425,10 @@
       "description": "Optional Qdrant integration for scalable semantic search",
       "enableLabel": "Enable Qdrant",
       "enableDesc": "When enabled, Qdrant is used as the primary vector store",
+      "banner": "Tier 2 vector store — an external, scalable alternative to the built-in sqlite-vec (Tier 1). Enable it only if you have a very large memory set or want shared memory across instances; most users are fine on sqlite-vec. When enabled it becomes the primary store and automatically falls back to sqlite-vec if unreachable.",
+      "hostHelp": "Local Docker: http://localhost:6333 · Qdrant Cloud: your cluster URL",
+      "collectionHelp": "Any name — OmniRoute creates it on first use",
+      "embeddingModelHelp": "Sets the vector dimension automatically on first use. Existing memories are not back-filled, and changing the model after data exists needs a fresh collection.",
       "testConnection": "Test connection",
       "testing": "Testing...",
       "statusActive": "Active",
diff --git a/tests/integration/qdrant-routes.test.ts b/tests/integration/qdrant-routes.test.ts
index 462aa9e6e7..8028b9a94a 100644
--- a/tests/integration/qdrant-routes.test.ts
+++ b/tests/integration/qdrant-routes.test.ts
@@ -27,6 +27,7 @@ process.env.API_KEY_SECRET = "test-secret-qdrant-routes";
 
 const core = await import("../../src/lib/db/core.ts");
 const localDb = await import("../../src/lib/localDb.ts");
+const memorySettings = await import("../../src/lib/memory/settings.ts");
 
 // ── Route imports ──
 const qdrantSettingsRoute = await import("../../src/app/api/settings/qdrant/route.ts");
@@ -49,6 +50,9 @@ async function resetStorage() {
   core.resetDbInstance();
   fs.rmSync(TEST_DATA_DIR, { recursive: true, force: true });
   fs.mkdirSync(TEST_DATA_DIR, { recursive: true });
+  // #5597 follow-up: the memory-settings cache is a module-level singleton that
+  // survives per-test DB resets — bust it so each test starts from a clean read.
+  memorySettings.invalidateMemorySettingsCache();
 }
 
 async function makeAuthRequest(
@@ -143,6 +147,99 @@ test("PUT /api/settings/qdrant — updates settings and returns new masked shape
   assert.strictEqual(body.apiKey, undefined, "raw apiKey must not be in response");
 });
 
+// ── #5597: enabling Qdrant must also activate it as the engine ──
+// Regression: retrieval only routes to Qdrant when memoryVectorStore === "qdrant"
+// (retrieval.ts:342/470/694). The card only wrote `qdrantEnabled` and never the
+// engine selector, so enabling Qdrant was inert — it stayed on the default "auto"
+// (which never selects Qdrant). Enabling now also sets memoryVectorStore=qdrant.
+
+test("PUT enabled=true also activates Qdrant as the engine (memoryVectorStore=qdrant)", async () => {
+  const req = await makeAuthRequest("PUT", "http://localhost/api/settings/qdrant", {
+    enabled: true,
+    host: "qdrant-server",
+    collection: "c",
+  });
+  const res = await qdrantSettingsRoute.PUT(req as any);
+  assert.strictEqual(res.status, 200);
+
+  const s = (await localDb.getSettings()) as Record<string, unknown>;
+  assert.strictEqual(
+    s.memoryVectorStore,
+    "qdrant",
+    "enabling Qdrant must select it as the active vector store, else it stays inert"
+  );
+});
+
+test("PUT enabled=false resets the engine back to auto (sqlite-vec)", async () => {
+  await qdrantSettingsRoute.PUT(
+    (await makeAuthRequest("PUT", "http://localhost/api/settings/qdrant", {
+      enabled: true,
+      host: "qdrant-server",
+      collection: "c",
+    })) as any
+  );
+  await qdrantSettingsRoute.PUT(
+    (await makeAuthRequest("PUT", "http://localhost/api/settings/qdrant", {
+      enabled: false,
+    })) as any
+  );
+
+  const s = (await localDb.getSettings()) as Record<string, unknown>;
+  assert.strictEqual(
+    s.memoryVectorStore,
+    "auto",
+    "disabling Qdrant must fall back to auto (sqlite-vec), not stay on qdrant"
+  );
+});
+
+test("PUT without the enabled field must not change memoryVectorStore", async () => {
+  // User already on qdrant; editing only the collection must not reset the engine.
+  await localDb.updateSettings({ memoryVectorStore: "qdrant", qdrantEnabled: true });
+  await qdrantSettingsRoute.PUT(
+    (await makeAuthRequest("PUT", "http://localhost/api/settings/qdrant", {
+      collection: "renamed",
+    })) as any
+  );
+
+  const s = (await localDb.getSettings()) as Record<string, unknown>;
+  assert.strictEqual(
+    s.memoryVectorStore,
+    "qdrant",
+    "editing other fields must leave the engine selection untouched"
+  );
+});
+
+// #5597 follow-up: writing memoryVectorStore to the DB is not enough — retrieval reads
+// through getMemorySettings(), a module-level cache. The PUT handler must invalidate it
+// so the engine switch takes effect without a process restart.
+test("PUT enabled=true invalidates the memory-settings cache (retrieval sees qdrant, no restart)", async () => {
+  // Warm the cache with the pre-toggle value (default auto → not qdrant).
+  const before = await memorySettings.getMemorySettings();
+  assert.notStrictEqual(
+    before.vectorStore,
+    "qdrant",
+    "precondition: cache warmed with a non-qdrant vectorStore"
+  );
+
+  const res = await qdrantSettingsRoute.PUT(
+    (await makeAuthRequest("PUT", "http://localhost/api/settings/qdrant", {
+      enabled: true,
+      host: "qdrant-server",
+      collection: "c",
+    })) as any
+  );
+  assert.strictEqual(res.status, 200);
+
+  // Without the cache invalidation, getMemorySettings() would still return the stale
+  // "auto" value and retrieval would keep routing to sqlite-vec until a restart.
+  const after = await memorySettings.getMemorySettings();
+  assert.strictEqual(
+    after.vectorStore,
+    "qdrant",
+    "PUT must invalidate the memory-settings cache so retrieval routes to Qdrant without a restart"
+  );
+});
+
 test("PUT /api/settings/qdrant — 400 invalid settings (invalid port type in strict schema)", async () => {
   const req = await makeAuthRequest("PUT", "http://localhost/api/settings/qdrant", {
     port: "not-a-number",