Curated against English had quietly become curated against writing

Seen live: "Esta manhã acordei cedo e fui correr ao longo da marginal.
O ar estava fresco e havia poucas pessoas na rua." — unremarkable
Portuguese, two marker hits, zero English hits, and a verdict of
English. Corrected as English, read aloud in an American voice.

The list was missing the ordinary machinery of the language: the
contractions (ao, à, num), the tenses a diary is written in (estava,
havia, fomos), the words that join two clauses (até, depois, então,
onde). Each clears the bar the list already set — an English sentence
has no reason to contain them — so their absence bought nothing.

The floor stays at three. What changed is that three is now reachable
by prose rather than only by a paragraph that argues its own case. fr
and es get the same additions by analogy; neither has an account yet to
catch it live, which is exactly how this one survived. "sin" and "tan"
stay out of the es list: both are English words.

Two regression tests, pointed in opposite directions — ordinary
Portuguese must read as hers, and English about Portugal, English
quoting Portuguese, and a plain English diary must all still read as
English, held verdict included.

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

internal/suggestions/doclang_test.go

@@ -446,3 +446,55 @@ func TestPassAnnouncesItsVerdict(t *testing.T) {
 		t.Fatal("empty document answered with no verdict header at all")
 	}
 }
+
+// TestOrdinaryProseIsEnoughEvidence is the regression for what the marker lists
+// were caught doing on 2026-07-29, live, in a browser: unremarkable Portuguese
+// read as English, because the list was curated against English so tightly that
+// it had also been curated against ordinary writing. The document below scored
+// two pair markers and zero English ones, and two is below the corroboration
+// floor — so a paragraph with no evidence of English in it at all came back
+// English, and was corrected and read aloud as English.
+//
+// Every sample here is prose a person might actually write, not prose chosen to
+// contain markers. That is the whole point of the test: the failure was invisible
+// to a suite whose fixtures all argued their own case.
+func TestOrdinaryProseIsEnoughEvidence(t *testing.T) {
+	samples := []struct{ name, text string }{
+		{"the one seen live", "Esta manhã acordei cedo e fui correr ao longo da marginal. O ar estava fresco e havia poucas pessoas na rua. Depois comprei um jornal e li-o sentado num banco ao sol."},
+		{"an afternoon out", "Hoje o céu estava limpo e fomos até ao jardim junto ao rio. A minha mãe trouxe uma manta velha e sentámos-nos debaixo de uma árvore."},
+		{"plans", "Amanhã vamos ao cinema depois do trabalho. Ontem estava demasiado cansada para sair de casa."},
+	}
+	for _, s := range samples {
+		if got := documentLang(s.text, "pt-PT", ""); got != docLangPair {
+			t.Errorf("%s: documentLang = %q, want %q — ordinary Portuguese must not read as English\n%s",
+				s.name, got, docLangPair, s.text)
+		}
+	}
+}
+
+// TestEnglishDidNotGetEasierToMistake is the other half, and the reason the
+// additions were held to "a word an English sentence has no reason to contain".
+// Widening a marker list is only safe if it widens in one direction: these are
+// English documents, including ones about Portugal and ones quoting Portuguese,
+// and every one of them must still come back English.
+func TestEnglishDidNotGetEasierToMistake(t *testing.T) {
+	samples := []struct{ name, text string }{
+		{"plain English", "This morning I woke up early and went for a run along the seafront. The air was fresh and there were few people about. Afterwards I bought a newspaper and read it on a bench."},
+		{"English about Portugal", "We spent a week in Lisbon last summer. The trams were crowded but the food was wonderful, and we walked up to the castle every evening."},
+		{"English quoting her", "My mother always says \"até amanhã\" when she leaves, never goodbye. I asked her why once and she said it sounded less final to her."},
+		{"an English diary", "Today was long. I had two meetings before lunch and another one after, and by the time I got home I could not think straight. Tomorrow should be quieter."},
+	}
+	for _, s := range samples {
+		if got := documentLang(s.text, "pt-PT", ""); got != docLangEnglish {
+			t.Errorf("%s: documentLang = %q, want %q — the widened list must not pull English across\n%s",
+				s.name, got, docLangEnglish, s.text)
+		}
+	}
+	// And the same document must not flip once it is already sitting in English:
+	// the hysteresis band is only a safety net if the low side holds too.
+	for _, s := range samples {
+		if got := documentLang(s.text, "pt-PT", docLangEnglish); got != docLangEnglish {
+			t.Errorf("%s: held verdict flipped to %q", s.name, got)
+		}
+	}
+}

internal/suggestions/language.go

@@ -155,6 +155,19 @@ func distinctMarkers(s string, markers map[string]bool) int {
 //
 // A single marker is not enough (see readsAsPairLang), so these lists are read
 // as evidence to be corroborated rather than as a decision.
+//
+// **Curated against English is not the same as curated thinly**, and the first
+// version of these lists confused the two. Seen live 2026-07-29: "Esta manhã
+// acordei cedo e fui correr ao longo da marginal. O ar estava fresco e havia
+// poucas pessoas na rua." — unremarkable Portuguese, two marker hits, *zero*
+// English hits, and a verdict of English, because the document-level floor wants
+// three. The list was missing the ordinary machinery of the language: the
+// contractions (ao, à, num), the past tenses a diary is written in (estava,
+// havia, fomos), and the words that join two clauses (até, depois, então,
+// onde). Every one of them clears the bar above — an English sentence has no
+// reason to contain them — so their absence bought nothing and cost the verdict.
+// The floor stays at three; what changed is that three is now reachable by
+// prose rather than only by a paragraph that happens to argue with itself.
 var latinMarkers = map[string]map[string]bool{
 	"fr": words(
 		"je", "tu", "il", "elle", "ils", "elles", "nous", "vous", "est", "sont",
@@ -164,6 +177,10 @@ var latinMarkers = map[string]map[string]bool{
 		"beaucoup", "toujours", "jamais", "quand", "bien", "chose", "temps",
 		"moi", "toi", "lui", "peux", "veux", "sais", "faire", "dit", "aujourd",
 		"hui", "quelque", "chez", "tout", "tous", "rien", "déjà", "encore",
+		// The same gap the pt-PT list was caught with, closed by analogy rather
+		// than by observation — no fr account exists yet to catch it live.
+		"aux", "après", "où", "avait", "étaient", "depuis", "jusqu", "chaque",
+		"autre", "même", "hier", "demain", "matin", "soir", "nôtre", "leurs",
 	),
 	"pt-PT": words(
 		"eu", "você", "ele", "ela", "eles", "elas", "nós", "são", "uma", "os",
@@ -173,6 +190,18 @@ var latinMarkers = map[string]map[string]bool{
 		"nunca", "bem", "obrigado", "obrigada", "gosto", "tenho", "tem", "foi",
 		"ser", "ter", "mais", "já", "ainda", "aqui", "ali", "nada", "tudo",
 		"todos", "para", "pela", "pelo", "sobre", "assim",
+		// The contractions, which no English sentence has any use for.
+		"ao", "aos", "à", "às", "num", "numa", "dum", "duma", "pelos", "pelas",
+		"neste", "nesta", "disso", "deste", "desta",
+		// The tenses a journal is actually written in.
+		"estava", "estavam", "estão", "estamos", "havia", "houve", "era", "eram",
+		"fui", "fomos", "foram", "vai", "vamos", "tinha", "tinham",
+		// The joins between two clauses.
+		"até", "depois", "antes", "onde", "então", "enquanto", "embora",
+		"sem", "quem", "entre",
+		// And the everyday determiners and time words a diary can hardly avoid.
+		"nosso", "nossa", "outro", "outra", "mesmo", "mesma", "tão",
+		"muitos", "muitas", "poucos", "poucas", "hoje", "ontem", "amanhã",
 	),
 	"es": words(
 		"yo", "él", "ella", "ellos", "ellas", "nosotros", "una", "los", "las",
@@ -181,6 +210,12 @@ var latinMarkers = map[string]map[string]bool{
 		"hacer", "siempre", "nunca", "bien", "gracias", "tengo", "tiene", "fue",
 		"ser", "tener", "más", "aquí", "allí", "nada", "todos",
 		"para", "sobre", "así", "hola", "señor", "usted", "muchas",
+		// Likewise by analogy: no es account exists yet either. "sin" and "tan"
+		// stay out — both are English words, which is the one disqualification.
+		"al", "después", "antes", "donde", "entonces", "mientras", "aunque",
+		"estaba", "estaban", "están", "había", "hubo", "fuimos", "fueron",
+		"nuestro", "nuestra", "otro", "otra", "mismo", "misma", "quién", "quien",
+		"muchos", "pocas", "pocos", "hoy", "ayer", "mañana",
 	),
 }