phraser: report the failure next to the fallback (V-397)

PhraseChat and PhraseQuery returned canned text with a nil error, so a dead
or OOM-killed server was indistinguishable from bad phrasing — "не знаю." is
also a legitimate answer.

Both now return the fallback text AND the error. The daemon keeps using the
text, so the turn still survives; a measuring caller counts a real failure.
An empty response is its own error: the model is up and said nothing.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

internal/phraser/failure_test.go

@@ -0,0 +1,72 @@
+package phraser
+
+import (
+	"context"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+)
+
+// A dead server must be distinguishable from bad phrasing. Both PhraseChat and
+// PhraseQuery keep the turn alive with canned text — "поговорили.", "не знаю.",
+// "вот что я нашла: …" — and every one of those is also a legitimate reply, so
+// the text alone cannot say which happened. The error is the only signal, and
+// before Vikunja #397 it was dropped: the talk scorer reported a full run with
+// zero errors off a server that answered nothing.
+func TestPhrasingReportsTheFailureWithTheFallback(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		http.Error(w, "model not loaded", http.StatusServiceUnavailable)
+	}))
+	t.Cleanup(srv.Close)
+	p := NewLLMPhraserAt(srv.URL, Config{})
+
+	cases := []struct {
+		name string
+		call func() (string, error)
+		want string
+	}{
+		{"chat", func() (string, error) {
+			return p.PhraseChat(context.Background(), "как дела", nil)
+		}, "поговорили."},
+		{"knowledge", func() (string, error) {
+			return p.PhraseQuery(context.Background(), "кто написал войну и мир", nil)
+		}, "не знаю."},
+		{"evidence", func() (string, error) {
+			return p.PhraseQuery(context.Background(), "сколько воды я выпил", []string{"два литра"})
+		}, "вот что я нашла: два литра"},
+	}
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			got, err := c.call()
+			if err == nil {
+				t.Fatalf("no error from a dead server; the scorer would count this as bad phrasing")
+			}
+			if got != c.want {
+				t.Errorf("fallback text = %q, want %q — the daemon still has to say something", got, c.want)
+			}
+		})
+	}
+}
+
+// An empty answer is a failure too: the server is up and produced no tokens,
+// which is not an answer and must not score as one.
+func TestEmptyKnowledgeAnswerIsAnError(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		w.Write([]byte(`{"choices":[{"message":{"content":""}}]}`))
+	}))
+	t.Cleanup(srv.Close)
+	p := NewLLMPhraserAt(srv.URL, Config{})
+
+	got, err := p.PhraseQuery(context.Background(), "кто написал войну и мир", nil)
+	if err == nil {
+		t.Fatal("an empty response scored as an answer")
+	}
+	if got != "не знаю." {
+		t.Errorf("fallback text = %q, want \"не знаю.\"", got)
+	}
+	if !strings.Contains(err.Error(), "empty") {
+		t.Errorf("error = %v; want it to name the empty response", err)
+	}
+}

internal/phraser/llmphraser.go

@@ -428,8 +428,11 @@ func (p *LLMPhraser) PhraseNudge(ctx context.Context, c loop.Candidate) (deliver
 }
 
 // PhraseQuery prompts the LLM with the user's utterance and matching notes to
-// compose a natural answer. Falls back to "вот что я нашла: <notes>" on any
-// LLM error — better to give the raw data than silence.
+// compose a natural answer. On any LLM error it returns BOTH the fallback text
+// ("вот что я нашла: <notes>", or "не знаю." with no notes) AND the error, so a
+// caller that wants to keep the turn alive uses the text and a caller that is
+// measuring counts the failure. Until Vikunja #397 the error was swallowed and a
+// dead server scored as bad phrasing.
 func (p *LLMPhraser) PhraseQuery(ctx context.Context, utterance string, notes []string) (string, error) {
 	// Blank sources are no sources. A caller that hands over one empty string —
 	// a page that fetched to nothing, a snippet trimmed away — used to take the
@@ -439,13 +442,15 @@ func (p *LLMPhraser) PhraseQuery(ctx context.Context, utterance string, notes []
 	if len(notes) == 0 {
 		sys, prompt := p.knowledgePrompt(utterance)
 		resp, err := p.chatWithSystem(ctx, sys, prompt, 768)
-		if err != nil || resp == "" {
-			return "не знаю.", nil
+		if err != nil {
+			return "не знаю.", fmt.Errorf("phrase query (knowledge): %w", err)
+		}
+		if resp == "" {
+			return "не знаю.", errEmptyResponse
 		}
 		text, _, perr := parseResponseMood(resp)
 		if perr != nil {
-			log.Printf("phraser: PhraseQuery: %v", perr)
-			return "не знаю.", nil
+			return "не знаю.", fmt.Errorf("phrase query (knowledge): %w", perr)
 		}
 		if text != "" {
 			return text, nil
@@ -457,13 +462,12 @@ func (p *LLMPhraser) PhraseQuery(ctx context.Context, utterance string, notes []
 	text, _, perr := parseResponseMood(resp)
 	if err != nil || perr != nil {
 		// Read the notes out rather than ship a broken fragment.
-		if perr != nil {
-			log.Printf("phraser: PhraseQuery: %v", perr)
+		cause := err
+		if cause == nil {
+			cause = perr
 		}
-		if len(notes) == 1 {
-			return "вот что я нашла: " + notes[0], nil
-		}
-		return "вот что я нашла: " + strings.Join(notes, "; "), nil
+		return "вот что я нашла: " + strings.Join(notes, "; "),
+			fmt.Errorf("phrase query (evidence): %w", cause)
 	}
 	if text != "" {
 		return text, nil
@@ -472,8 +476,9 @@ func (p *LLMPhraser) PhraseQuery(ctx context.Context, utterance string, notes []
 }
 
 // PhraseChat uses the LLM to respond conversationally, building a multi-turn
-// message array from dialogue history + the current user utterance. Falls back
-// to a simple greeting on any LLM error — better to say something than nothing.
+// message array from dialogue history + the current user utterance. On any LLM
+// error it returns both "поговорили." and the error, on the same rule as
+// PhraseQuery: the fallback keeps the turn alive, the error stays visible.
 func (p *LLMPhraser) PhraseChat(ctx context.Context, utterance string, history []dialogue.Turn) (string, error) {
 	sys := chatSystemPrompt(p.cfg.ContextBlock)
 	msgs := []chatMsg{
@@ -490,13 +495,11 @@ func (p *LLMPhraser) PhraseChat(ctx context.Context, utterance string, history [
 
 	resp, err := p.chatWithMessages(ctx, msgs, 768)
 	if err != nil {
-		log.Printf("phraser: PhraseChat: %v", err)
-		return "поговорили.", nil
+		return "поговорили.", fmt.Errorf("phrase chat: %w", err)
 	}
 	text, _, perr := parseResponseMood(resp)
 	if perr != nil {
-		log.Printf("phraser: PhraseChat: %v", perr)
-		return "поговорили.", nil
+		return "поговорили.", fmt.Errorf("phrase chat: %w", perr)
 	}
 	if text != "" {
 		return text, nil

internal/phraser/swap_test.go

@@ -215,10 +215,12 @@ func TestSwap_RollbackFailureLeavesNoBackendAndDegrades(t *testing.T) {
 	if _, _, aerr := p.acquire(); !errors.Is(aerr, ErrNoBackend) {
 		t.Errorf("acquire error = %v; want ErrNoBackend", aerr)
 	}
-	// Phrasing degrades to its fallback instead of failing the turn.
+	// Phrasing degrades to its fallback instead of failing the turn, and since
+	// Vikunja #397 it reports the error next to that fallback so a measuring
+	// caller can tell "no model" from "bad phrasing".
 	got, err := p.PhraseChat(context.Background(), "привет", nil)
-	if err != nil {
-		t.Fatalf("PhraseChat after a total failure returned an error: %v", err)
+	if !errors.Is(err, ErrNoBackend) {
+		t.Errorf("PhraseChat error = %v; want ErrNoBackend alongside the fallback", err)
 	}
 	if got == "" {
 		t.Error("PhraseChat returned empty; the fallback must still say something")

internal/phraser/world.go

@@ -37,6 +37,11 @@ type Remote interface {
 // (docs/evals/2026-08-02-workstation-gemma4-12b.md).
 var ErrNoWorldModel = errors.New("phraser: no world model available")
 
+// errEmptyResponse — the server answered and said nothing. A separate error from
+// a transport failure because it means the model is up and produced no tokens,
+// which is still not an answer and must not score as one.
+var errEmptyResponse = errors.New("phraser: empty response from the model")
+
 // chatTemperature — what the phraser's own transport has always sampled at.
 // Named so the remote path cannot drift from it silently. Whether 0.7 is right
 // at all is Vikunja #402, and answering that here would hide a phrasing change