feat(sources)!: split source contracts into PollSource/StreamSource and add mode-aware source config

- Introduce explicit source interfaces: sources.PollSource and sources.StreamSource, with shared sources.Input (Name() only).
- Remove mandatory Kind() from the base source contract to support sources that emit multiple kinds.
- Add config.SourceMode (poll, stream, or omitted/auto) and SourceConfig.Kinds (plural expected kinds), while keeping legacy SourceConfig.Kind for compatibility.
- Enforce mode semantics in config validation (poll requires every, stream forbids every) and detect mode/driver mismatches in sources.Registry.
- Update docs and tests for the new source model and config behavior.

config/validate_test.go

@@ -46,3 +46,119 @@ func TestValidate_RouteKindsRejectsBlankEntries(t *testing.T) {
 		t.Fatalf("expected error to mention blank kind entry, got: %v", err)
 	}
 }
+
+func TestValidate_SourceModePollRequiresEvery(t *testing.T) {
+	cfg := &Config{
+		Sources: []SourceConfig{
+			{Name: "src1", Driver: "driver1", Mode: SourceModePoll},
+		},
+		Sinks: []SinkConfig{
+			{Name: "sink1", Driver: "stdout"},
+		},
+	}
+
+	err := cfg.Validate()
+	if err == nil {
+		t.Fatalf("expected error, got nil")
+	}
+	if !strings.Contains(err.Error(), `sources[0].every`) {
+		t.Fatalf("expected error to mention sources[0].every, got: %v", err)
+	}
+}
+
+func TestValidate_SourceModeStreamRejectsEvery(t *testing.T) {
+	cfg := &Config{
+		Sources: []SourceConfig{
+			{
+				Name:   "src1",
+				Driver: "driver1",
+				Mode:   SourceModeStream,
+				Every:  Duration{Duration: time.Minute},
+			},
+		},
+		Sinks: []SinkConfig{
+			{Name: "sink1", Driver: "stdout"},
+		},
+	}
+
+	err := cfg.Validate()
+	if err == nil {
+		t.Fatalf("expected error, got nil")
+	}
+	if !strings.Contains(err.Error(), `sources[0].every`) {
+		t.Fatalf("expected error to mention sources[0].every, got: %v", err)
+	}
+}
+
+func TestValidate_SourceModeRejectsUnknownValue(t *testing.T) {
+	cfg := &Config{
+		Sources: []SourceConfig{
+			{
+				Name:   "src1",
+				Driver: "driver1",
+				Mode:   SourceMode("batch"),
+				Every:  Duration{Duration: time.Minute},
+			},
+		},
+		Sinks: []SinkConfig{
+			{Name: "sink1", Driver: "stdout"},
+		},
+	}
+
+	err := cfg.Validate()
+	if err == nil {
+		t.Fatalf("expected error, got nil")
+	}
+	if !strings.Contains(err.Error(), `sources[0].mode`) {
+		t.Fatalf("expected error to mention sources[0].mode, got: %v", err)
+	}
+}
+
+func TestValidate_SourceKindAndKindsConflict(t *testing.T) {
+	cfg := &Config{
+		Sources: []SourceConfig{
+			{
+				Name:   "src1",
+				Driver: "driver1",
+				Every:  Duration{Duration: time.Minute},
+				Kind:   "observation",
+				Kinds:  []string{"forecast"},
+			},
+		},
+		Sinks: []SinkConfig{
+			{Name: "sink1", Driver: "stdout"},
+		},
+	}
+
+	err := cfg.Validate()
+	if err == nil {
+		t.Fatalf("expected error, got nil")
+	}
+	if !strings.Contains(err.Error(), `sources[0].kind`) {
+		t.Fatalf("expected error to mention sources[0].kind, got: %v", err)
+	}
+}
+
+func TestValidate_SourceKindsRejectBlankEntries(t *testing.T) {
+	cfg := &Config{
+		Sources: []SourceConfig{
+			{
+				Name:   "src1",
+				Driver: "driver1",
+				Every:  Duration{Duration: time.Minute},
+				Kinds:  []string{"observation", "   "},
+			},
+		},
+		Sinks: []SinkConfig{
+			{Name: "sink1", Driver: "stdout"},
+		},
+	}
+
+	err := cfg.Validate()
+	if err == nil {
+		t.Fatalf("expected error, got nil")
+	}
+	if !strings.Contains(err.Error(), `sources[0].kinds[1]`) {
+		t.Fatalf("expected error to mention sources[0].kinds[1], got: %v", err)
+	}
+}