The garden learns which language a card is in, and read-aloud stops guessing

Phase 28 (c), the last of the phase. A word met inside a Portuguese
document is a Portuguese card: migration 0018 mirrors documents.doc_lang
onto vocab_words, set server-side from the ownership lookup capture was
already making. Every card still reviews — filtering the queue to the
half she is learning would drop the words she actually met.

Read-aloud was the larger surprise. detectLang routed Han/kana to
Chinese and everything else to en-US, so the zh pair was accidentally
right and every Latin pair wrong. doc_lang now reaches the client
read-only on the document JSON, and docLang(text, verdict) answers for a
passage taken out of it — with the script test still winning, because
quoted Chinese must never be spelled out one "Chinese letter" at a time.

Claude-Session: https://claude.ai/code/session_01GJHNvirh7Hzhc9RL3HAvz7

internal/vocab/handlers_test.go

@@ -253,3 +253,89 @@ func TestDocLinkSurvivesDocDelete(t *testing.T) {
 		t.Fatalf("doc_id should be nulled after doc delete, got %v", *all[0].DocID)
 	}
 }
+
+// TestCaptureTakesLanguageFromItsDocument is the garden's half of Phase 28: a
+// word met inside a document written in her own language is a card in that
+// language, and the server reads that off the document rather than being told.
+//
+// The three cases are the three the client can actually produce: a lookup inside
+// a flipped document, a lookup inside an English one, and a lookup with no
+// document at all (the search box) — the last of which is '', which reads as
+// English everywhere this value is used.
+func TestCaptureTakesLanguageFromItsDocument(t *testing.T) {
+	srv, database := newTestServer(t)
+
+	seed := func(lang string) string {
+		t.Helper()
+		var id string
+		if err := database.QueryRow(
+			`INSERT INTO documents (user_id, content_text, doc_lang) VALUES (?, 'hi', ?) RETURNING id`,
+			db.LocalUserID, lang,
+		).Scan(&id); err != nil {
+			t.Fatalf("seed doc: %v", err)
+		}
+		return id
+	}
+	pairDoc, enDoc := seed("pair"), seed("en")
+
+	capture := func(word, body string) Word {
+		t.Helper()
+		rec := do(t, srv, http.MethodPost, "/vocab", body)
+		if rec.Code != http.StatusCreated {
+			t.Fatalf("capture %s: code=%d body=%s", word, rec.Code, rec.Body)
+		}
+		var w Word
+		if err := json.Unmarshal(rec.Body.Bytes(), &w); err != nil {
+			t.Fatalf("decode %s: %v", word, err)
+		}
+		return w
+	}
+
+	if got := capture("comum", `{"word":"comum","doc_id":"`+pairDoc+`"}`); got.Lang != "pair" {
+		t.Fatalf("word from a flipped document: lang=%q, want pair", got.Lang)
+	}
+	if got := capture("reception", `{"word":"reception","doc_id":"`+enDoc+`"}`); got.Lang != "en" {
+		t.Fatalf("word from an English document: lang=%q, want en", got.Lang)
+	}
+	if got := capture("orphan", `{"word":"orphan"}`); got.Lang != "" {
+		t.Fatalf("word with no document: lang=%q, want empty", got.Lang)
+	}
+
+	// A client that names a language is ignored: the document is the authority,
+	// the same way runPass never lets the request pick its own target.
+	if got := capture("comum", `{"word":"comum","lang":"en","doc_id":"`+pairDoc+`"}`); got.Lang != "pair" {
+		t.Fatalf("client-supplied lang should not win: lang=%q, want pair", got.Lang)
+	}
+}
+
+// TestRecaptureOutsideADocumentKeepsItsLanguage pins the one asymmetry in the
+// upsert. Re-looking-up a word refreshes its context, but a lookup made with no
+// document carries no verdict — and relabelling a Portuguese card English
+// because she checked the word again from the search box would silently move it
+// to the wrong voice. lang travels with doc_id, or it doesn't travel.
+func TestRecaptureOutsideADocumentKeepsItsLanguage(t *testing.T) {
+	srv, database := newTestServer(t)
+	var docID string
+	if err := database.QueryRow(
+		`INSERT INTO documents (user_id, content_text, doc_lang) VALUES (?, 'olá', 'pair') RETURNING id`,
+		db.LocalUserID,
+	).Scan(&docID); err != nil {
+		t.Fatalf("seed doc: %v", err)
+	}
+	if rec := do(t, srv, http.MethodPost, "/vocab",
+		`{"word":"saudade","gloss":"","doc_id":"`+docID+`"}`); rec.Code != http.StatusCreated {
+		t.Fatalf("capture: code=%d body=%s", rec.Code, rec.Body)
+	}
+	rec := do(t, srv, http.MethodPost, "/vocab", `{"word":"saudade","gloss":"longing"}`)
+	if rec.Code != http.StatusCreated {
+		t.Fatalf("recapture: code=%d body=%s", rec.Code, rec.Body)
+	}
+	var w Word
+	_ = json.Unmarshal(rec.Body.Bytes(), &w)
+	if w.Lang != "pair" {
+		t.Fatalf("recapture outside a document: lang=%q, want pair held", w.Lang)
+	}
+	if w.Gloss != "longing" {
+		t.Fatalf("recapture should still refresh the gloss, got %q", w.Gloss)
+	}
+}