feat: escalate brain search to web when facts cannot confirm

internal/brain/rank/escalate.go

@@ -0,0 +1,43 @@
+package rank
+
+// SecondSource is the web-search block on a deduction answer.
+// Kept apart from graph hits so "ours" and "not ours" stay visible.
+type SecondSource struct {
+	Status  string            `json:"status"`
+	Note    string            `json:"note,omitempty"`
+	Cached  bool              `json:"cached,omitempty"`
+	Results []SecondSourceHit `json:"results,omitempty"`
+}
+
+type SecondSourceHit struct {
+	Rank    int    `json:"rank"`
+	Title   string `json:"title"`
+	URL     string `json:"url"`
+	Snippet string `json:"snippet"`
+	Engine  string `json:"engine"`
+}
+
+type WebFn func(query string) SecondSource
+
+// ShouldEscalate is true when the default deduction path has no facts hit.
+// `--root facts|info` is a single-root ask: do not mix in the web.
+func ShouldEscalate(hits []Hit, rootFilter string) bool {
+	if rootFilter != "" {
+		return false
+	}
+	for _, h := range hits {
+		if h.Root == "facts" {
+			return false
+		}
+	}
+	return true
+}
+
+// Deduce returns the second-source block, or nil when web must not run.
+func Deduce(hits []Hit, query, rootFilter string, noWeb bool, web WebFn) *SecondSource {
+	if noWeb || web == nil || !ShouldEscalate(hits, rootFilter) {
+		return nil
+	}
+	out := web(query)
+	return &out
+}