Add transcript description prompt context

internal/core/config/config_test.go

@@ -51,6 +51,9 @@ func TestDefaultConfigValues(t *testing.T) {
 	if cfg.WorkDir != DefaultWorkDir {
 		t.Fatalf("unexpected default work dir: %q", cfg.WorkDir)
 	}
+	if cfg.TranscriptDescription != "" {
+		t.Fatalf("expected default transcript description to be empty, got %q", cfg.TranscriptDescription)
+	}
 	if cfg.WorkDirRetention != DefaultWorkDirRetention {
 		t.Fatalf("unexpected default work dir retention: %q", cfg.WorkDirRetention)
 	}
@@ -214,6 +217,29 @@ func TestApplyCLIOverridesPrecedence(t *testing.T) {
 	}
 }
 
+func TestApplyCLIOverridesTrimsTranscriptDescription(t *testing.T) {
+	cfg := Default()
+	description := "   background context about speakers   "
+	if err := cfg.ApplyCLIOverrides(CLIOverrides{TranscriptDescription: &description}); err != nil {
+		t.Fatalf("ApplyCLIOverrides failed: %v", err)
+	}
+	if cfg.TranscriptDescription != "background context about speakers" {
+		t.Fatalf("unexpected transcript description trim result: %q", cfg.TranscriptDescription)
+	}
+}
+
+func TestValidationRejectsOverlyLongTranscriptDescription(t *testing.T) {
+	cfg := Default()
+	cfg.TranscriptDescription = strings.Repeat("a", DefaultTranscriptDescriptionMaxChars+1)
+	err := cfg.Validate()
+	if err == nil {
+		t.Fatalf("expected transcript description length validation error")
+	}
+	if !strings.Contains(err.Error(), "transcript description must be 500 characters or fewer") {
+		t.Fatalf("unexpected validation error: %v", err)
+	}
+}
+
 func TestApplyCLIOverridesLegacyLLMConcurrencyAlias(t *testing.T) {
 	cfg := Default()
 	aliasConcurrency := 6