Warn about vectors written before the marker existed

The embedder moved from paraphrase-multilingual-MiniLM-L12-v2 to
multilingual-e5-small. Both are 384-dimensional, so nothing in the code
noticed: cosine between an old stored vector and a new query vector is
noise, and recall degrades silently.

So the DB now records the embedder that wrote its vectors. One value for
the whole DB (migration #11, a small `meta` key/value table) rather than a
column on every vector row: the backfill re-embeds every note and fact in
one pass, so a per-row marker would hold the same string in every row and
cost a column on two tables for nothing.

The identity comes from the embedder itself via a new optional ID() method
("multilingual-e5-small@384", model file name plus dimension), so pointing
the config at another model changes the string without anyone editing a
constant. mavend logs a loud WARNING at startup naming both the stored and
the configured embedder when they differ.

Detection only — recall behaviour is unchanged. TODO(#378) in
store.CheckEmbedder marks where the backfill will hook in.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CGeSZxh1DCtRxmFVSYVGvJ

RECALL-EVAL-31-07-2026.md

@@ -75,6 +75,14 @@ same vector. A note is indexed in both places with the same embedding, so if it
 `QueryNotes` it fails again here — the branch can only ever return a **fact**. Its comment calls it
 "additive"; for notes it is not.
 
+**Fixed (Vikunja #373).** The memory pass now runs *first*, as one search over notes and facts with
+one gate, so whichever memory is clearly the best match answers — note or fact. The notes-only pass
+stays behind it for notes the vector index does not hold. No threshold changed, so the set of
+questions Maven answers is the same; only which memory answers them. The fixture gained two mixed
+note+fact cases (`ru-mixed-031`, `ru-mixed-032`), which is why the counts below are out of 27
+answerable cases and not 25: hash recall@1 36.0% (9/25) → 37.0% (10/27), e5 recall@1 72.0% (18/25) →
+70.4% (19/27) with answered-after-gate 68.0% → 66.7% and false recall unchanged at 1/5.
+
 ### 5. Ranking has no recency or type signal, and the store is not the bottleneck
 
 `internal/store/notes.go:67` sorts by cosine and uses `ts` only to break an exact float tie, which

cmd/mavend/query_recall_test.go

@@ -0,0 +1,158 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"math"
+	"testing"
+	"time"
+
+	"github.com/kami/maven/internal/ipc"
+	"github.com/kami/maven/internal/memory"
+	"github.com/kami/maven/internal/phraser"
+	"github.com/kami/maven/internal/router"
+	"github.com/kami/maven/internal/voice"
+)
+
+// fixedEmbedder hands back a vector chosen per text, so a test can say exactly
+// how close each stored memory is to the question. The real embedders make
+// scores that are realistic but not controllable, and this test is about the
+// gate, not about the embedder.
+type fixedEmbedder struct{ vecs map[string][]float32 }
+
+func (f *fixedEmbedder) Dim() int     { return 4 }
+func (f *fixedEmbedder) Close() error { return nil }
+
+func (f *fixedEmbedder) Embed(_ context.Context, text string) ([]float32, error) {
+	v, ok := f.vecs[text]
+	if !ok {
+		return nil, fmt.Errorf("fixedEmbedder: no vector for %q", text)
+	}
+	return v, nil
+}
+
+// scoreVec builds a unit vector whose cosine against the query vector
+// (1,0,0,0) is exactly score.
+func scoreVec(score float64) []float32 {
+	rest := math.Sqrt(1 - score*score)
+	return []float32{float32(score), float32(rest), 0, 0}
+}
+
+// recordingPhraser remembers what the query path handed it to phrase, which is
+// how the test can tell which pass produced the answer.
+type recordingPhraser struct {
+	*phraser.Stub
+	notes []string
+}
+
+func (r *recordingPhraser) PhraseQuery(ctx context.Context, utterance string, notes []string) (string, error) {
+	r.notes = notes
+	return r.Stub.PhraseQuery(ctx, utterance, notes)
+}
+
+// recallCase — one stored memory: its text, how close it is to the question,
+// whether it is a note or a fact, and whether the notes table holds it too.
+type recallCase struct {
+	text  string
+	score float64
+	kind  string
+}
+
+// buildRecallHandler stores the given memories and returns a handler whose
+// query path can be run directly. Notes go into BOTH the notes table and the
+// vector index, which is what the daemon does (voice.go's IntentNote).
+func buildRecallHandler(t *testing.T, question string, mems []recallCase) (*reactiveHandler, *recordingPhraser) {
+	t.Helper()
+	ctx := context.Background()
+	st := newTestStore(t)
+	emb := &fixedEmbedder{vecs: map[string][]float32{question: {1, 0, 0, 0}}}
+	mem := memory.NewInMemoryStore()
+	now := time.Now()
+
+	for i, m := range mems {
+		vec := scoreVec(m.score)
+		emb.vecs[m.text] = vec
+		id := fmt.Sprintf("%s:%d", m.kind, i)
+		if m.kind == "note" {
+			if _, err := st.WriteNote(ctx, now, m.text, vec, "tap:voice"); err != nil {
+				t.Fatalf("WriteNote: %v", err)
+			}
+		}
+		if err := mem.Insert(ctx, id, vec, map[string]string{"text": m.text, "type": m.kind}); err != nil {
+			t.Fatalf("memory insert: %v", err)
+		}
+	}
+
+	phr := &recordingPhraser{Stub: phraser.NewStub()}
+	h := &reactiveHandler{
+		api:             ipc.NewStoreAPI(st),
+		embedder:        emb,
+		replier:         voice.NewStubReplier(),
+		phraser:         phr,
+		now:             func() time.Time { return now },
+		memStore:        mem,
+		dataStore:       st,
+		queryMinScore:   0.55,
+		queryMinMargin:  0.008,
+		weatherProvider: nil,
+	}
+	return h, phr
+}
+
+func askQuery(t *testing.T, h *reactiveHandler, question string) string {
+	t.Helper()
+	return h.applyAction(context.Background(), router.Decision{
+		Intent:    router.IntentQuery,
+		Utterance: question,
+	})
+}
+
+// TestQueryRecallNoteCanWin — the note-recall regression (Vikunja #373). Notes
+// and facts share one vector index, and a note that clearly beats everything
+// else must be the answer. Before the fix the memory pass only ran after the
+// notes-only gate had already rejected the same note at the same score, so only
+// a fact could ever come back from it.
+func TestQueryRecallNoteCanWin(t *testing.T) {
+	const q = "где молоко"
+
+	t.Run("a clearly best note answers", func(t *testing.T) {
+		h, phr := buildRecallHandler(t, q, []recallCase{
+			{text: "молоко стоит в холодильнике", score: 0.90, kind: "note"},
+			{text: "выучил пару аккордов", score: 0.50, kind: "note"},
+		})
+		reply := askQuery(t, h, q)
+		if want := "вот что я нашла: молоко стоит в холодильнике"; reply != want {
+			t.Errorf("reply %q, want %q", reply, want)
+		}
+		// One text, the winning memory's — the answer came from the memory
+		// pass, not from handing the phraser every note in the table.
+		if len(phr.notes) != 1 || phr.notes[0] != "молоко стоит в холодильнике" {
+			t.Errorf("phraser got %q, want just the recalled note", phr.notes)
+		}
+	})
+
+	// The other half of "one gate over everything": a fact that matches better
+	// than the best note now answers, instead of losing to a note that only had
+	// to beat other notes.
+	t.Run("the better-matching fact answers", func(t *testing.T) {
+		h, _ := buildRecallHandler(t, q, []recallCase{
+			{text: "молоко стоит в холодильнике", score: 0.80, kind: "note"},
+			{text: "купил молоко в среду", score: 0.95, kind: "fact"},
+		})
+		if reply := askQuery(t, h, q); reply != "купил молоко в среду" {
+			t.Errorf("reply %q, want the fact read back", reply)
+		}
+	})
+
+	// The gate is untouched: two memories this close mean the embedder cannot
+	// tell them apart, and silence still beats a coin flip.
+	t.Run("no clear best stays silent", func(t *testing.T) {
+		h, _ := buildRecallHandler(t, q, []recallCase{
+			{text: "молоко стоит в холодильнике", score: 0.860, kind: "note"},
+			{text: "молоко закончилось", score: 0.858, kind: "note"},
+		})
+		if reply := askQuery(t, h, q); reply != "не знаю." {
+			t.Errorf("reply %q, want silence", reply)
+		}
+	})
+}

cmd/mavend/recall.go

@@ -2,21 +2,24 @@ package main
 
 import "github.com/kami/maven/internal/memory"
 
-// bestRecall is the read side of the long-term memory store: the top hit's
-// stored text when it clears the confidence gate. This recalls across BOTH
-// notes and facts (facts aren't in the notes table, so this is the only path
-// that can answer "when did I last …?" from a captured fact). A note hit here
-// is redundant with the notes-RAG path — by design; the two indexes can diverge
-// once the backend is swapped for a persistent/external store. ok=false when
-// the hit fails the confidence gate (see memory.Confident: an absolute floor
-// plus a margin over the runner-up) or carries no text.
-func bestRecall(results []memory.Result, minScore, minMargin float64) (string, bool) {
+// bestRecall is the read side of the long-term memory store: the top hit when
+// it clears the confidence gate. The index holds BOTH notes and facts, and
+// either can win — the caller looks at the returned hit's meta["type"] to see
+// which. Facts aren't in the notes table, so this is the only path that can
+// answer "when did I last …?" from a captured fact.
+//
+// The whole hit is returned, not just its text, because "which memory answered"
+// decides how the answer is said: a note gets phrased in Maven's voice, a fact
+// is read back as stored.
+//
+// ok=false when the hit fails the confidence gate (see memory.Confident: an
+// absolute floor plus a margin over the runner-up) or carries no text.
+func bestRecall(results []memory.Result, minScore, minMargin float64) (memory.Result, bool) {
 	if !memory.Confident(results, minScore, minMargin) {
-		return "", false
+		return memory.Result{}, false
 	}
-	text := results[0].Meta["text"]
-	if text == "" {
-		return "", false
+	if results[0].Meta["text"] == "" {
+		return memory.Result{}, false
 	}
-	return text, true
+	return results[0], true
 }

cmd/mavend/recall_test.go

@@ -39,8 +39,27 @@ func TestBestRecall(t *testing.T) {
 		if !ok {
 			t.Fatal("clearing hit not returned")
 		}
-		if got != "выпил воды в три часа" {
-			t.Errorf("wrong text: %q", got)
+		if got.Meta["text"] != "выпил воды в три часа" {
+			t.Errorf("wrong text: %q", got.Meta["text"])
+		}
+		if got.Meta["type"] != "fact" {
+			t.Errorf("kind lost: %q", got.Meta["type"])
+		}
+	})
+
+	// The index holds notes and facts together, so a note has to be able to win
+	// it — for a long time it could not (Vikunja #373).
+	t.Run("a note can win", func(t *testing.T) {
+		res := []memory.Result{
+			{Score: 0.86, Meta: map[string]string{"text": "молоко в холодильнике", "type": "note"}},
+			{Score: 0.61, Meta: map[string]string{"text": "выпил воды", "type": "fact"}},
+		}
+		got, ok := bestRecall(res, min, margin)
+		if !ok {
+			t.Fatal("clearly-best note not returned")
+		}
+		if got.Meta["type"] != "note" || got.Meta["text"] != "молоко в холодильнике" {
+			t.Errorf("got %v, want the note", got.Meta)
 		}
 	})
 

cmd/mavend/voice.go

@@ -171,6 +171,7 @@ func wireVoice(cfg *config.Config, coreAPI ipc.CoreAPI, phr phraser.Phraser, mem
 		emb = router.NewHashEmbedder(1024)
 	}
 	w.embedder = emb
+	checkStoredEmbedder(dataStore, emb)
 
 	// ----- tool executor (the enabled act allowlist, store-backed) -----
 	// Config tools are the declarative bootstrap: seed them into the store as
@@ -786,11 +787,43 @@ func (h *reactiveHandler) applyAction(ctx context.Context, dec router.Decision)
 			log.Printf("voice: embed query: %v", err)
 			return "не получилось найти ответ."
 		}
+		// Long-term memory first: ONE search over everything Maven remembers
+		// (notes and facts share this index) and ONE confidence gate, so the
+		// memory that is clearly the best match answers — a note just as much
+		// as a fact.
+		//
+		// This used to run only after the notes-only gate below had already
+		// rejected the same note at the same score, which no note could ever
+		// survive a second time: the branch could only return a fact (#373).
+		// Order, not the gate, was the bug — the set of questions Maven answers
+		// is unchanged, only which memory gets to answer them.
+		if h.memStore != nil {
+			if hits, herr := h.memStore.Search(ctx, vec, 3); herr == nil {
+				if hit, ok := bestRecall(hits, h.queryMinScore, h.queryMinMargin); ok {
+					text := hit.Meta["text"]
+					// A note is phrased in Maven's voice; a fact is read back
+					// as it was stored.
+					if hit.Meta["type"] == "note" {
+						if reply, perr := h.phraser.PhraseQuery(ctx, dec.Utterance, []string{text}); perr == nil && reply != "" {
+							return reply
+						}
+					}
+					return text
+				}
+			} else {
+				log.Printf("voice: memory search: %v", herr)
+			}
+		}
+
 		notes, err := h.api.QueryNotes(ctx, vec, 5)
 		if err != nil {
 			log.Printf("voice: query notes: %v", err)
 			return "не получилось найти ответ."
 		}
+		// Notes-only pass, for notes the vector index above does not hold (an
+		// older note written before it existed). Same gate, notes-only
+		// candidates.
+		//
 		// Confidence gate: below it, say "I don't know" rather than read back
 		// the least-unrelated note — a confident wrong recall is worse than a
 		// gap (spec's "not a guesser-of-truth"). Same instinct as the loop's
@@ -802,16 +835,6 @@ func (h *reactiveHandler) applyAction(ctx context.Context, dec router.Decision)
 			noteScores[i] = n.Score
 		}
 		if !memory.ConfidentScores(noteScores, h.queryMinScore, h.queryMinMargin) {
-			// Long-term memory recall (notes + facts) before general knowledge:
-			// the notes table can't answer fact questions, but the memory store
-			// indexes both. Only runs when notes-RAG already gave up → additive.
-			if h.memStore != nil {
-				if hits, herr := h.memStore.Search(ctx, vec, 3); herr == nil {
-					if text, ok := bestRecall(hits, h.queryMinScore, h.queryMinMargin); ok {
-						return text
-					}
-				}
-			}
 			// Try general knowledge from the phraser before giving up
 			reply, err := h.phraser.PhraseQuery(ctx, dec.Utterance, nil)
 			if err != nil || reply == "" {
@@ -1745,3 +1768,27 @@ func jsonStringImpl(s string) string {
 	b = append(b, '"')
 	return string(b)
 }
+
+// checkStoredEmbedder compares the embedder we just loaded with the one that
+// wrote the vectors already in the DB (Vikunja #378).
+//
+// The two models we have both make 384-dim vectors, so a size check catches
+// nothing: after a swap, recall silently compares vectors from different
+// spaces and the scores are noise. So we say it out loud. Nothing is changed
+// here — recall keeps running exactly as before until the backfill lands.
+func checkStoredEmbedder(dataStore *store.Store, emb router.Embedder) {
+	if dataStore == nil {
+		return
+	}
+	current := router.EmbedderID(emb)
+	stored, mismatch, err := dataStore.CheckEmbedder(context.Background(), current)
+	if err != nil {
+		log.Printf("voice: embedder marker check failed: %v", err)
+		return
+	}
+	if mismatch {
+		log.Printf("voice: WARNING embedder MISMATCH — stored vectors were written by %q but the configured embedder is %q; recall scores are noise until the notes and facts are re-embedded (Vikunja #378)", stored, current)
+		return
+	}
+	log.Printf("voice: embedder marker ok (%s)", current)
+}

internal/memory/recalleval/recalleval.go

@@ -422,6 +422,8 @@ func rankNote(inTop3 bool) string {
 // bestRecall mirrors cmd/mavend/recall.go — the gate the daemon actually
 // applies to a memory hit. Duplicated rather than imported because package main
 // is not importable; recalleval_test.go asserts the two agree in behaviour.
+// The daemon returns the whole hit (a note and a fact are said differently);
+// the harness only scores what came back, so it keeps returning the text.
 func bestRecall(results []memory.Result, minScore, minMargin float64) string {
 	if !memory.Confident(results, minScore, minMargin) {
 		return ""

internal/memory/recalleval/recalleval_test.go

@@ -197,7 +197,8 @@ func TestHashRecallBaseline(t *testing.T) {
 	t.Log("\n" + rep.String() + rep.Failures())
 	t.Log("\ngate sweep:\n" + sweep(t, router.NewHashEmbedder(hashDim), f))
 
-	// 0.32 sits under the observed 0.360 recall@1.
+	// 0.32 sits under the observed 0.370 recall@1 (was 0.360 over 25 answerable
+	// cases; the two mixed note+fact cases added with #373 make it 27).
 	const floorRecall1 = 0.32
 	if rep.Recall1() < floorRecall1 {
 		t.Errorf("recall@1 %.3f below ratchet %.2f — note recall regressed", rep.Recall1(), floorRecall1)

internal/memory/recalleval/ru_recall_v1.json

@@ -387,6 +387,32 @@
         {"id": "n2", "text": "wifi channel is 6", "kind": "note"},
         {"id": "n3", "text": "the guest network is off", "kind": "note"}
       ]
+    },
+    {
+      "id": "ru-mixed-031",
+      "lang": "ru",
+      "tags": ["mixed", "paraphrase", "hard"],
+      "note": "notes and facts in one store and the note is the answer — the daemon indexes both (Vikunja #373)",
+      "query": "куда я спрятал второй ключ от квартиры",
+      "want": "n1",
+      "notes": [
+        {"id": "n1", "text": "запасной ключ от квартиры лежит в синей коробке на полке", "kind": "note"},
+        {"id": "x1", "text": "поменял замок в двери двадцатого июня", "kind": "fact"},
+        {"id": "x2", "text": "отдал ключ соседке в мае", "kind": "fact"}
+      ]
+    },
+    {
+      "id": "ru-mixed-032",
+      "lang": "ru",
+      "tags": ["mixed", "distractor"],
+      "note": "the mirror of ru-mixed-031: the fact answers and the notes are the distractors",
+      "query": "когда я в последний раз заливал бензин",
+      "want": "x1",
+      "notes": [
+        {"id": "x1", "text": "залил полный бак в четверг вечером", "kind": "fact"},
+        {"id": "n1", "text": "на заправке у моста дешевле бензин", "kind": "note"},
+        {"id": "n2", "text": "надо поменять зимние шины", "kind": "note"}
+      ]
     }
   ]
 }

internal/router/embedder.go

@@ -2,6 +2,7 @@ package router
 
 import (
 	"context"
+	"fmt"
 	"math"
 	"unicode"
 )
@@ -19,6 +20,24 @@ type Embedder interface {
 	Close() error
 }
 
+// IdentifiedEmbedder — an embedder that can name itself. The name goes into
+// the DB next to the vectors it wrote, so a later model swap is caught instead
+// of silently returning nonsense scores (Vikunja #378).
+type IdentifiedEmbedder interface {
+	Embedder
+	ID() string
+}
+
+// EmbedderID is the stable string stored alongside the vectors. It comes from
+// the embedder itself — nobody hand-types a model name twice — and changes
+// whenever the model or its dimension changes.
+func EmbedderID(e Embedder) string {
+	if i, ok := e.(IdentifiedEmbedder); ok {
+		return i.ID()
+	}
+	return fmt.Sprintf("unknown@%d", e.Dim())
+}
+
 // AsymmetricEmbedder — an embedder that wants to know whether a text is a
 // search query or a stored passage. Recall is asymmetric: a short question
 // goes in, a longer note comes out. The e5 family is trained for exactly that
@@ -70,6 +89,10 @@ func NewHashEmbedder(dim int) *HashEmbedder {
 
 func (h *HashEmbedder) Dim() int { return h.dim }
 
+// ID names this embedder for the DB marker. The dimension is part of it
+// because a HashEmbedder of another width is a different vector space.
+func (h *HashEmbedder) ID() string { return fmt.Sprintf("hash@%d", h.dim) }
+
 func (h *HashEmbedder) Close() error { return nil }
 
 func (h *HashEmbedder) Embed(_ context.Context, text string) ([]float32, error) {

internal/router/embedderid_test.go

@@ -0,0 +1,24 @@
+package router
+
+import "testing"
+
+func TestEmbedderIDFromModelPath(t *testing.T) {
+	got := modelIDFromPath("/opt/maven/models/embedder/multilingual-e5-small.onnx")
+	if got != "multilingual-e5-small@384" {
+		t.Fatalf("modelIDFromPath = %q", got)
+	}
+	// A different model file must produce a different id, even at 384 dim.
+	old := modelIDFromPath("/opt/maven/models/embedder/paraphrase-multilingual-MiniLM-L12-v2.onnx")
+	if old == got {
+		t.Fatal("two different models share one id")
+	}
+}
+
+func TestEmbedderIDIncludesDim(t *testing.T) {
+	if id := EmbedderID(NewHashEmbedder(1024)); id != "hash@1024" {
+		t.Fatalf("EmbedderID = %q", id)
+	}
+	if EmbedderID(NewHashEmbedder(1024)) == EmbedderID(NewHashEmbedder(384)) {
+		t.Fatal("dimension not part of the id")
+	}
+}

internal/router/onnxembedder.go

@@ -33,6 +33,7 @@ const (
 type onnxEmbedder struct {
 	tokenizer *unigramTokenizer
 	session   *ort.DynamicSession[int64, float32]
+	id        string
 }
 
 func NewONNXEmbedder(modelPath, tokenizerPath, libPath string) (*onnxEmbedder, error) {
@@ -58,11 +59,31 @@ func NewONNXEmbedder(modelPath, tokenizerPath, libPath string) (*onnxEmbedder, e
 	return &onnxEmbedder{
 		tokenizer: tok,
 		session:   session,
+		id:        modelIDFromPath(modelPath),
 	}, nil
 }
 
 func (e *onnxEmbedder) Dim() int { return embedDim }
 
+// ID names the loaded model for the DB marker (Vikunja #378): the model file's
+// own name plus the dimension, so pointing the config at another model changes
+// the string on its own.
+func (e *onnxEmbedder) ID() string { return e.id }
+
+// modelIDFromPath turns /opt/.../multilingual-e5-small.onnx into
+// "multilingual-e5-small@384".
+func modelIDFromPath(modelPath string) string {
+	name := modelPath
+	if i := strings.LastIndexAny(name, "/\\"); i >= 0 {
+		name = name[i+1:]
+	}
+	name = strings.TrimSuffix(name, ".onnx")
+	if name == "" {
+		name = "onnx"
+	}
+	return fmt.Sprintf("%s@%d", name, embedDim)
+}
+
 // Embed treats the text as a query. The classifier compares one short
 // utterance to another short seed phrase, so both sides get the same prefix
 // and the comparison stays fair. The recall path must call EmbedQuery and

internal/store/meta.go

@@ -0,0 +1,97 @@
+package store
+
+import (
+	"context"
+	"database/sql"
+	"errors"
+	"fmt"
+)
+
+// metaKeyEmbedderID names the embedder that wrote the stored vectors.
+//
+// Why one value for the whole DB and not a column on every vector row: the
+// vectors are only ever rewritten all at once (one backfill re-embeds every
+// note and fact together), so a per-row marker would hold the same string in
+// every row and cost a column on two tables for nothing.
+const metaKeyEmbedderID = "embedder_id"
+
+// Meta reads a single value from the meta table. Missing key ⇒ empty string.
+func (s *Store) Meta(ctx context.Context, key string) (string, error) {
+	var v string
+	err := s.db.QueryRowContext(ctx, `SELECT value FROM meta WHERE key = ?`, key).Scan(&v)
+	if errors.Is(err, sql.ErrNoRows) {
+		return "", nil
+	}
+	if err != nil {
+		return "", fmt.Errorf("read meta %s: %w", key, err)
+	}
+	return v, nil
+}
+
+// SetMeta writes (or overwrites) a single meta value.
+func (s *Store) SetMeta(ctx context.Context, key, value string) error {
+	_, err := s.db.ExecContext(ctx,
+		`INSERT INTO meta (key, value) VALUES (?,?)
+		 ON CONFLICT(key) DO UPDATE SET value = excluded.value`, key, value)
+	if err != nil {
+		return fmt.Errorf("write meta %s: %w", key, err)
+	}
+	return nil
+}
+
+// EmbedderUnknown is the stored id reported for a DB that already holds
+// vectors but never recorded who wrote them.
+const EmbedderUnknown = "unknown (written before this marker existed)"
+
+// CheckEmbedder compares the embedder now configured against the one that
+// wrote the stored vectors. Returns the stored id and whether it differs.
+//
+// Vectors from two different models live in different spaces, so cosine
+// between them is noise rather than a low score — and both of our models are
+// 384-dimensional, so nothing else catches it.
+//
+// Three cases, and the middle one is the one that actually matters:
+//
+//   - marker present ⇒ compare the two ids.
+//   - marker absent but vectors already stored ⇒ this is a DB from before the
+//     marker, so we cannot know who wrote them. Report a mismatch. This is the
+//     real case on the deployed box: those vectors came from the old embedder,
+//     and claiming them for the current one would hide the exact problem the
+//     marker was added to catch.
+//   - marker absent and no vectors ⇒ fresh DB, claim it, nothing to fix.
+//
+// TODO(#378): on a mismatch, run the one-shot backfill here — re-embed every
+// stored note and fact text with the current embedder (EmbedPassage side),
+// write the vectors back, then SetMeta the current id.
+func (s *Store) CheckEmbedder(ctx context.Context, currentID string) (stored string, mismatch bool, err error) {
+	stored, err = s.Meta(ctx, metaKeyEmbedderID)
+	if err != nil {
+		return "", false, err
+	}
+	if stored != "" {
+		return stored, stored != currentID, nil
+	}
+	n, err := s.countVectors(ctx)
+	if err != nil {
+		return "", false, err
+	}
+	if n > 0 {
+		return EmbedderUnknown, true, nil
+	}
+	return currentID, false, s.SetMeta(ctx, metaKeyEmbedderID, currentID)
+}
+
+// countVectors — how many stored rows carry an embedding. Used only to tell a
+// fresh DB apart from one that predates the marker.
+func (s *Store) countVectors(ctx context.Context) (int, error) {
+	var notes, vecs int
+	if err := s.db.QueryRowContext(ctx,
+		`SELECT count(*) FROM notes WHERE embedding IS NOT NULL`).Scan(&notes); err != nil {
+		return 0, fmt.Errorf("count note vectors: %w", err)
+	}
+	if err := s.db.QueryRowContext(ctx,
+		`SELECT count(*) FROM memory_vectors`).Scan(&vecs); err != nil {
+		return 0, fmt.Errorf("count memory vectors: %w", err)
+	}
+	return notes + vecs, nil
+}

internal/store/meta_test.go

@@ -0,0 +1,100 @@
+package store
+
+import (
+	"context"
+	"testing"
+	"time"
+)
+
+// A fresh DB has no marker yet, so the current embedder is recorded and
+// nothing is flagged.
+func TestCheckEmbedderFreshDBRecords(t *testing.T) {
+	s := newTestStore(t)
+	ctx := context.Background()
+
+	stored, mismatch, err := s.CheckEmbedder(ctx, "multilingual-e5-small@384")
+	if err != nil {
+		t.Fatalf("CheckEmbedder: %v", err)
+	}
+	if mismatch {
+		t.Fatal("fresh DB reported a mismatch")
+	}
+	if stored != "multilingual-e5-small@384" {
+		t.Fatalf("stored = %q", stored)
+	}
+	got, err := s.Meta(ctx, metaKeyEmbedderID)
+	if err != nil {
+		t.Fatalf("Meta: %v", err)
+	}
+	if got != "multilingual-e5-small@384" {
+		t.Fatalf("marker not persisted, got %q", got)
+	}
+}
+
+// The deployed box: notes were written by the old embedder, before the marker
+// existed. Claiming them for the current one would hide exactly the problem
+// the marker is for, so an unmarked DB that already holds vectors is a
+// mismatch.
+func TestCheckEmbedderUnmarkedDBWithVectorsIsMismatch(t *testing.T) {
+	s := newTestStore(t)
+	ctx := context.Background()
+
+	if _, err := s.WriteNote(ctx, time.Now(), "молоко в холодильнике", []float32{0.1, 0.2}, "voice"); err != nil {
+		t.Fatalf("WriteNote: %v", err)
+	}
+
+	stored, mismatch, err := s.CheckEmbedder(ctx, "multilingual-e5-small@384")
+	if err != nil {
+		t.Fatalf("CheckEmbedder: %v", err)
+	}
+	if !mismatch {
+		t.Fatal("an unmarked DB with stored vectors should report a mismatch")
+	}
+	if stored != EmbedderUnknown {
+		t.Fatalf("stored = %q, want %q", stored, EmbedderUnknown)
+	}
+	// It must NOT claim the DB — that would silence the warning on restart.
+	got, err := s.Meta(ctx, metaKeyEmbedderID)
+	if err != nil {
+		t.Fatalf("Meta: %v", err)
+	}
+	if got != "" {
+		t.Fatalf("marker written despite unknown provenance: %q", got)
+	}
+}
+
+// Both models are 384-dim, so this is the only thing that catches the swap.
+func TestCheckEmbedderDifferentModelMismatch(t *testing.T) {
+	s := newTestStore(t)
+	ctx := context.Background()
+
+	if err := s.SetMeta(ctx, metaKeyEmbedderID, "paraphrase-multilingual-MiniLM-L12-v2@384"); err != nil {
+		t.Fatalf("SetMeta: %v", err)
+	}
+	stored, mismatch, err := s.CheckEmbedder(ctx, "multilingual-e5-small@384")
+	if err != nil {
+		t.Fatalf("CheckEmbedder: %v", err)
+	}
+	if !mismatch {
+		t.Fatal("different embedder not detected")
+	}
+	if stored != "paraphrase-multilingual-MiniLM-L12-v2@384" {
+		t.Fatalf("stored = %q", stored)
+	}
+}
+
+// The same embedder must never raise a false alarm, including on re-check.
+func TestCheckEmbedderSameModelNoAlarm(t *testing.T) {
+	s := newTestStore(t)
+	ctx := context.Background()
+
+	for i := 0; i < 2; i++ {
+		_, mismatch, err := s.CheckEmbedder(ctx, "multilingual-e5-small@384")
+		if err != nil {
+			t.Fatalf("CheckEmbedder: %v", err)
+		}
+		if mismatch {
+			t.Fatalf("false alarm on pass %d", i)
+		}
+	}
+}

internal/store/migrations.go

@@ -83,6 +83,11 @@ ALTER TABLE reminders ADD COLUMN next_fire_ts INTEGER;`, // #2
 		expires_ts INTEGER NOT NULL
 	);
 	CREATE INDEX IF NOT EXISTS idx_dialogue_sessions_expires ON dialogue_sessions (expires_ts);`, // #10 — the follow-up session survives a restart (Vikunja #363); small, TTL-pruned table, not a history log
+
+	`CREATE TABLE IF NOT EXISTS meta (
+		key   TEXT PRIMARY KEY,
+		value TEXT NOT NULL
+	);`, // #11 — small key/value table for facts about the DB itself; first key is embedder_id (Vikunja #378)
 }
 
 // migrate applies every migration with a number greater than the DB's current