test(chat): a request may carry its own transcript budget (red)

The 18,000-char default is ~22 min of speech and keeps only the head; an
uploaded hour is ~50,000 chars. Red: Request.MaxChars is undefined.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

internal/adapters/chat/maxchars_test.go

@@ -0,0 +1,53 @@
+package chat
+
+import (
+	"context"
+	"strings"
+	"testing"
+)
+
+// A Request may carry its own transcript budget. The Service's cap (18,000 chars by
+// default) is sized for YouTube captions; an uploaded recording is much longer
+// (~50,000 chars an hour), and keeping only the head of it would answer questions
+// about the last two-thirds of a meeting from text that does not contain them
+// (ADR-033). The per-request value overrides; zero means "the service default".
+
+func TestAnswerMaxCharsOverridesTheServiceCap(t *testing.T) {
+	tests := []struct {
+		name          string
+		serviceCap    int
+		requestCap    int
+		transcriptLen int
+		wantKept      int
+		wantTruncated bool
+	}{
+		{"request cap above the service cap keeps the whole transcript", 10, 100, 50, 50, false},
+		{"request cap below the service cap bounds tighter", 100, 10, 50, 10, true},
+		{"zero request cap falls back to the service cap", 20, 0, 50, 20, true},
+		{"negative request cap is treated as unset", 20, -1, 50, 20, true},
+		{"request cap exceeded is reported as truncated", 10, 30, 50, 30, true},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			f := &factory{answer: "answer"}
+			s := New(f.make, []string{"koala/phi4-mini"}, tt.serviceCap)
+
+			reply, err := s.Answer(context.Background(), Request{
+				Model:      "koala/phi4-mini",
+				Transcript: strings.Repeat("x", tt.transcriptLen),
+				Question:   "what was decided?",
+				MaxChars:   tt.requestCap,
+			})
+
+			if err != nil {
+				t.Fatalf("Answer: %v", err)
+			}
+			if got := strings.Count(f.used.lastSystem, "x"); got != tt.wantKept {
+				t.Errorf("transcript chars sent = %d, want %d", got, tt.wantKept)
+			}
+			if reply.Truncated != tt.wantTruncated {
+				t.Errorf("Truncated = %v, want %v", reply.Truncated, tt.wantTruncated)
+			}
+		})
+	}
+}