feat(chat): stored-transcript QA service (ADR-027)

A read-only deeper-dive over a video's already-stored transcript (ADR-021). Safe by construction: the Service has no VideoSource and no caption-fetch dependency — only a Completer factory over the existing LiteLLM gateway — so it cannot reach YouTube or the rate gate. Reuses the summarizer's truncation discipline (TAPIR_MAX_TRANSCRIPT_CHARS), reporting the cut so the UI can be honest about a bounded transcript. Model defaults to the summary's model and is switchable among an offered, local-first list; an un-offered alias is forced back to the default so chat can never call the gateway with an arbitrary model. Ephemeral: history is carried per-request, nothing persisted. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
2026-06-11 09:16:45 +02:00
parent 69a49bc603
commit cc3cda4ab8
2 changed files with 335 additions and 0 deletions
@@ -0,0 +1,164 @@
+package chat
+
+import (
+	"context"
+	"errors"
+	"strings"
+	"testing"
+)
+
+// recordingCompleter captures the system+user it was asked with and returns a
+// canned answer (or error). It also records which model alias built it.
+type recordingCompleter struct {
+	model      string
+	lastSystem string
+	lastUser   string
+	answer     string
+	err        error
+	calls      *int
+}
+
+func (c *recordingCompleter) Complete(_ context.Context, system, user string) (string, error) {
+	*c.calls++
+	c.lastSystem = system
+	c.lastUser = user
+	if c.err != nil {
+		return "", c.err
+	}
+	return c.answer, nil
+}
+
+// factory builds a recordingCompleter per model and records the last one built so
+// the test can assert which model alias was actually used for the gateway call.
+type factory struct {
+	answer string
+	err    error
+	calls  int
+	used   *recordingCompleter
+}
+
+func (f *factory) make(model string) Completer {
+	c := &recordingCompleter{model: model, answer: f.answer, err: f.err, calls: &f.calls}
+	f.used = c
+	return c
+}
+
+func TestModelsAreOfferedLocalFirstAndCopied(t *testing.T) {
+	f := &factory{answer: "ok"}
+	s := New(f.make, []string{"koala/phi4-mini", "iguana/gemma4-26b"}, 0)
+
+	got := s.Models()
+	want := []string{"koala/phi4-mini", "iguana/gemma4-26b"}
+	if len(got) != len(want) || got[0] != want[0] || got[1] != want[1] {
+		t.Fatalf("Models() = %v, want %v", got, want)
+	}
+	// Mutating the returned slice must not corrupt the Service's list.
+	got[0] = "tampered"
+	if s.Models()[0] != "koala/phi4-mini" {
+		t.Fatal("Models() leaked its backing slice")
+	}
+}
+
+func TestDefaultModelIsTheSummarysModelWhenOffered(t *testing.T) {
+	f := &factory{answer: "ok"}
+	s := New(f.make, []string{"koala/phi4-mini", "iguana/gemma4-26b", "berget/mistral-small"}, 0)
+
+	if got := s.DefaultModel("iguana/gemma4-26b"); got != "iguana/gemma4-26b" {
+		t.Fatalf("DefaultModel(summary) = %q, want the summary's model", got)
+	}
+	// A summary model no longer offered (e.g. cloud disabled) falls back to first.
+	if got := s.DefaultModel("berget/old-model"); got != "koala/phi4-mini" {
+		t.Fatalf("DefaultModel(un-offered) = %q, want the first offered model", got)
+	}
+	// No summary model recorded → first offered.
+	if got := s.DefaultModel(""); got != "koala/phi4-mini" {
+		t.Fatalf("DefaultModel(\"\") = %q, want the first offered model", got)
+	}
+}
+
+func TestAnswerGroundsOnTranscriptAndCarriesHistory(t *testing.T) {
+	f := &factory{answer: "  The video is about attention.  "}
+	s := New(f.make, []string{"koala/phi4-mini"}, 0)
+
+	reply, err := s.Answer(context.Background(), Request{
+		Model:      "koala/phi4-mini",
+		Transcript: "ATTENTION-TRANSCRIPT-MARKER",
+		History:    []Turn{{Question: "who", Answer: "the host"}},
+		Question:   "what is it about",
+	})
+	if err != nil {
+		t.Fatalf("Answer: %v", err)
+	}
+	if reply.Answer != "The video is about attention." {
+		t.Fatalf("answer not trimmed: %q", reply.Answer)
+	}
+	if reply.Truncated {
+		t.Fatal("short transcript must not report truncated")
+	}
+	// The transcript rides in the system prompt; the conversation in the user msg.
+	if !strings.Contains(f.used.lastSystem, "ATTENTION-TRANSCRIPT-MARKER") {
+		t.Fatal("transcript not grounded into the system prompt")
+	}
+	if !strings.Contains(f.used.lastUser, "Q: who") || !strings.Contains(f.used.lastUser, "A: the host") {
+		t.Fatalf("history not carried into the user message: %q", f.used.lastUser)
+	}
+	if !strings.Contains(f.used.lastUser, "what is it about") {
+		t.Fatal("new question missing from the user message")
+	}
+}
+
+func TestAnswerTruncatesLongTranscriptAndReportsIt(t *testing.T) {
+	f := &factory{answer: "answer"}
+	s := New(f.make, []string{"koala/phi4-mini"}, 10)
+
+	reply, err := s.Answer(context.Background(), Request{
+		Model:      "koala/phi4-mini",
+		Transcript: strings.Repeat("x", 500),
+		Question:   "summarize",
+	})
+	if err != nil {
+		t.Fatalf("Answer: %v", err)
+	}
+	if !reply.Truncated {
+		t.Fatal("a transcript past maxChars must report Truncated")
+	}
+	if strings.Count(f.used.lastSystem, "x") != 10 {
+		t.Fatalf("transcript not bounded to maxChars: got %d x's", strings.Count(f.used.lastSystem, "x"))
+	}
+}
+
+func TestAnswerForcesAnUnofferedModelBackToDefault(t *testing.T) {
+	f := &factory{answer: "answer"}
+	s := New(f.make, []string{"koala/phi4-mini", "iguana/gemma4-26b"}, 0)
+
+	// A forged/un-offered model must never reach the gateway as-is — it is forced
+	// to the default offered model (the cloud-absent guarantee depends on this).
+	_, err := s.Answer(context.Background(), Request{
+		Model:      "berget/secret-cloud-model",
+		Transcript: "t",
+		Question:   "q",
+	})
+	if err != nil {
+		t.Fatalf("Answer: %v", err)
+	}
+	if f.used.model != "koala/phi4-mini" {
+		t.Fatalf("un-offered model reached the gateway as %q, want the default", f.used.model)
+	}
+}
+
+func TestAnswerPropagatesCompleterError(t *testing.T) {
+	f := &factory{err: errors.New("gateway down")}
+	s := New(f.make, []string{"koala/phi4-mini"}, 0)
+
+	_, err := s.Answer(context.Background(), Request{Model: "koala/phi4-mini", Transcript: "t", Question: "q"})
+	if err == nil {
+		t.Fatal("expected the gateway error to propagate")
+	}
+}
+
+func TestAnswerRejectsEmptyModelSet(t *testing.T) {
+	s := New(func(string) Completer { return nil }, nil, 0)
+	if _, err := s.Answer(context.Background(), Request{Question: "q"}); err == nil {
+		t.Fatal("expected an error when no models are configured")
+	}
+}