feat(search): P3.1 filters and multi-query merge

Native include/exclude domains, time_range, topic, exact_match, min_score,
and up to 4 queries fused with RRF. Honesty notes stay off the Warn/fail
path. Tavily keeps include_answer false and sets auto_parameters false.
Cache key is canonical JSON. CLI flags and skill recipe included.

internal/dcache/dcache.go

@@ -11,8 +11,6 @@ import (
 	"log/slog"
 	"math"
 	"os"
-	"sort"
-	"strconv"
 	"strings"
 	"sync"
 	"time"
@@ -181,17 +179,6 @@ func QuestionEmbedKey(question, embedModel, callerClass string) string {
 	return hex.EncodeToString(sum[:])
 }
 
-func SearchKey(query string, sources []string, k int, hour time.Time, callerClass string) string {
-	if callerClass == "" {
-		callerClass = ClassFleet
-	}
-	src := append([]string(nil), sources...)
-	sort.Strings(src)
-	bucket := hour.UTC().Format("2006-01-02T15")
-	sum := sha256.Sum256([]byte(NormalizeQuestion(query) + "\x00" + strings.Join(src, ",") + "\x00" + strconv.Itoa(k) + "\x00" + bucket + "\x00" + callerClass))
-	return hex.EncodeToString(sum[:])
-}
-
 type DigestHit struct {
 	Text       string
 	ChunksUsed int

internal/dcache/dcache_test.go

@@ -109,6 +109,12 @@ func TestSearchKeyPartitions(t *testing.T) {
 	if SearchKey("hello", []string{"searxng", "tavily"}, 8, now.Add(time.Hour), ClassFleet) == a {
 		t.Fatal("hour")
 	}
+	if EncodeSearchKey(SearchKeyInput{Queries: []string{"hello"}, Sources: []string{"searxng"}, K: 8, Hour: now, CallerClass: ClassFleet}) == EncodeSearchKey(SearchKeyInput{Queries: []string{"hello"}, Sources: []string{"searxng"}, K: 8, Hour: now, CallerClass: ClassFleet, IncludeDomains: []string{"a.com"}}) {
+		t.Fatal("include_domains")
+	}
+	if EncodeSearchKey(SearchKeyInput{Queries: []string{"hello"}, Sources: []string{"searxng"}, K: 8, Hour: now, CallerClass: ClassFleet}) != EncodeSearchKey(SearchKeyInput{Queries: []string{"hello"}, Sources: []string{"searxng"}, K: 8, Hour: now, CallerClass: ClassFleet, Topic: "general"}) {
+		t.Fatal("topic general")
+	}
 }
 
 func TestCorruptDBBypass(t *testing.T) {

internal/dcache/searchkey.go

@@ -0,0 +1,108 @@
+package dcache
+
+import (
+	"crypto/sha256"
+	"encoding/hex"
+	"encoding/json"
+	"sort"
+	"strconv"
+	"time"
+)
+
+// SearchKeyInput is the canonical cache identity for a search. Callers pass
+// already-normalised filter fields (long time_range, sorted domains optional).
+type SearchKeyInput struct {
+	Queries            []string
+	Sources            []string
+	K                  int
+	Hour               time.Time
+	CallerClass        string
+	IncludeDomains     []string
+	ExcludeDomains     []string
+	IncludeDomainsMode string
+	TimeRange          string
+	StartDate          string
+	EndDate            string
+	Topic              string
+	ExactMatch         bool
+	MinScore           float64
+}
+
+func SearchKey(query string, sources []string, k int, hour time.Time, callerClass string) string {
+	return EncodeSearchKey(SearchKeyInput{
+		Queries:     []string{query},
+		Sources:     sources,
+		K:           k,
+		Hour:        hour,
+		CallerClass: callerClass,
+	})
+}
+
+func EncodeSearchKey(in SearchKeyInput) string {
+	if in.CallerClass == "" {
+		in.CallerClass = ClassFleet
+	}
+	src := append([]string(nil), in.Sources...)
+	sort.Strings(src)
+	qs := make([]string, len(in.Queries))
+	for i, q := range in.Queries {
+		qs[i] = NormalizeQuestion(q)
+	}
+	topic := in.Topic
+	if topic == "" {
+		topic = "general"
+	}
+	m := map[string]any{
+		"caller_class": in.CallerClass,
+		"exact_match":  in.ExactMatch,
+		"hour":         in.Hour.UTC().Format("2006-01-02T15"),
+		"k":            in.K,
+		"min_score":    strconv.FormatFloat(in.MinScore, 'f', -1, 64),
+		"queries":      qs,
+		"sources":      src,
+		"topic":        topic,
+	}
+	if inc := sortedUnique(in.IncludeDomains); len(inc) > 0 {
+		m["include_domains"] = inc
+		mode := in.IncludeDomainsMode
+		if mode == "" {
+			mode = "restrict"
+		}
+		m["include_domains_mode"] = mode
+	}
+	if exc := sortedUnique(in.ExcludeDomains); len(exc) > 0 {
+		m["exclude_domains"] = exc
+	}
+	if in.TimeRange != "" {
+		m["time_range"] = in.TimeRange
+	}
+	if in.StartDate != "" {
+		m["start_date"] = in.StartDate
+	}
+	if in.EndDate != "" {
+		m["end_date"] = in.EndDate
+	}
+	b, _ := json.Marshal(m)
+	sum := sha256.Sum256(b)
+	return hex.EncodeToString(sum[:])
+}
+
+func sortedUnique(in []string) []string {
+	if len(in) == 0 {
+		return nil
+	}
+	out := append([]string(nil), in...)
+	sort.Strings(out)
+	n := 0
+	for _, s := range out {
+		if s == "" {
+			continue
+		}
+		if n > 0 && out[n-1] == s {
+			continue
+		}
+		out[n] = s
+		n++
+	}
+	return out[:n]
+}