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/config.go

@@ -21,20 +21,56 @@ type Config struct {
 	Routes  []RouteConfig  `yaml:"routes"`
 }
 
-// SourceConfig describes one polling job.
+// SourceMode selects how a source receives upstream input.
+//
+// Empty mode means "auto": feedkit infers mode from the registered driver type.
+type SourceMode string
+
+const (
+	SourceModeAuto   SourceMode = ""
+	SourceModePoll   SourceMode = "poll"
+	SourceModeStream SourceMode = "stream"
+)
+
+// Normalize lowercases and trims the mode.
+func (m SourceMode) Normalize() SourceMode {
+	switch strings.ToLower(strings.TrimSpace(string(m))) {
+	case "":
+		return SourceModeAuto
+	case string(SourceModePoll):
+		return SourceModePoll
+	case string(SourceModeStream):
+		return SourceModeStream
+	default:
+		return SourceMode(strings.ToLower(strings.TrimSpace(string(m))))
+	}
+}
+
+// SourceConfig describes one input source.
 //
 // This is intentionally generic:
 //   - driver-specific knobs belong in Params.
-//   - "kind" is allowed (useful for safety checks / routing), but feedkit does not
-//     restrict the allowed values.
+//   - mode controls polling vs streaming behavior.
+//   - expected emitted kinds are optional and domain-defined.
 type SourceConfig struct {
 	Name   string `yaml:"name"`
 	Driver string `yaml:"driver"` // e.g. "openmeteo_observation", "rss_feed", etc.
 
-	Every Duration `yaml:"every"` // "15m", "1m", etc.
+	// Mode is optional:
+	//   - "poll": Every must be set (>0)
+	//   - "stream": Every must be omitted/zero
+	//   - empty: infer from driver registration type (poll vs stream)
+	Mode SourceMode `yaml:"mode"`
 
-	// Kind is optional and domain-defined. If set, it should be a non-empty string.
-	// Domains commonly use it to enforce "this source should only emit kind X".
+	// Every is the poll cadence for poll-mode sources ("15m", "1m", etc.).
+	Every Duration `yaml:"every"`
+
+	// Kinds is optional and domain-defined.
+	// If set, it describes the expected emitted event kinds for this source.
+	Kinds []string `yaml:"kinds"`
+
+	// Kind is the legacy singular form. Prefer "kinds".
+	// If both kind and kinds are set, validation fails.
 	Kind string `yaml:"kind"`
 
 	// Params are driver-specific settings (URL, headers, station IDs, API keys, etc.).
@@ -42,6 +78,26 @@ type SourceConfig struct {
 	Params map[string]any `yaml:"params"`
 }
 
+// ExpectedKinds returns normalized expected kinds from config.
+// "kinds" takes precedence; "kind" is used as a legacy fallback.
+func (cfg SourceConfig) ExpectedKinds() []string {
+	if len(cfg.Kinds) > 0 {
+		out := make([]string, 0, len(cfg.Kinds))
+		for _, k := range cfg.Kinds {
+			k = strings.TrimSpace(k)
+			if k == "" {
+				continue
+			}
+			out = append(out, k)
+		}
+		return out
+	}
+	if k := strings.TrimSpace(cfg.Kind); k != "" {
+		return []string{k}
+	}
+	return nil
+}
+
 // SinkConfig describes one output sink adapter.
 type SinkConfig struct {
 	Name   string         `yaml:"name"`