p3: search API, pinned sources, cache, CLI

POST /v1/search and /v2/search fan in SearXNG, Brave LLM Context, and
Tavily from config-fixed endpoints. Public sources refuse private A
records; SearXNG is a loopback-only client, not the fetch guard.

Cache keys include caller class. Restricted callers search like the
fleet; logs omit query, hosts, URLs, and upstream errors. Degraded
results are not stored. Tavily sends search_depth=basic and drops
answer. Missing keys surface in /healthz.

Default-on sources stay off until the bake-off. Query harvest is not
in this commit.

internal/search/rank.go

@@ -0,0 +1,81 @@
+package search
+
+import (
+	"context"
+	"math"
+	"strings"
+)
+
+type Embedder interface {
+	Embed(ctx context.Context, inputs []string) ([][]float64, error)
+	Acquire(ctx context.Context) (ok bool, reason string)
+	Release()
+}
+
+func Cosine(a, b []float64) float64 {
+	if len(a) == 0 || len(a) != len(b) {
+		return 0
+	}
+	var dot, na, nb float64
+	for i := range a {
+		dot += a[i] * b[i]
+		na += a[i] * a[i]
+		nb += b[i] * b[i]
+	}
+	if na == 0 || nb == 0 {
+		return 0
+	}
+	return dot / (math.Sqrt(na) * math.Sqrt(nb))
+}
+
+func rankHits(ctx context.Context, query string, hits []Hit, emb Embedder) (out []Hit, fallback string) {
+	if emb == nil || len(hits) == 0 {
+		if emb == nil {
+			return hits, "no embed"
+		}
+		return hits, ""
+	}
+	ok, reason := emb.Acquire(ctx)
+	if !ok {
+		if reason == "" {
+			reason = "queue_full"
+		}
+		return hits, reason
+	}
+	defer emb.Release()
+	inputs := make([]string, 0, 1+len(hits))
+	inputs = append(inputs, query)
+	for _, h := range hits {
+		s := strings.TrimSpace(h.Title + " " + h.Snippet)
+		if s == "" {
+			s = h.URL
+		}
+		inputs = append(inputs, s)
+	}
+	vecs, err := emb.Embed(ctx, inputs)
+	if err != nil || len(vecs) != len(inputs) {
+		return hits, "embed error"
+	}
+	q := vecs[0]
+	type pair struct {
+		h Hit
+		s float64
+	}
+	ps := make([]pair, len(hits))
+	for i := range hits {
+		ps[i] = pair{h: hits[i], s: Cosine(q, vecs[i+1])}
+		ps[i].h.Score = ps[i].s
+	}
+	for i := 1; i < len(ps); i++ {
+		j := i
+		for j > 0 && ps[j].s > ps[j-1].s {
+			ps[j], ps[j-1] = ps[j-1], ps[j]
+			j--
+		}
+	}
+	out = make([]Hit, len(ps))
+	for i := range ps {
+		out[i] = ps[i].h
+	}
+	return out, ""
+}