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/search/filter.go

@@ -0,0 +1,254 @@
+package search
+
+import (
+	"strings"
+	"time"
+	"unicode/utf8"
+)
+
+const (
+	maxDomainList = 20
+	maxHostLen    = 253
+	searxSiteCap  = 3
+)
+
+var timeRangeLong = map[string]string{
+	"day": "day", "d": "day",
+	"week": "week", "w": "week",
+	"month": "month", "m": "month",
+	"year": "year", "y": "year",
+}
+
+// NormalizeSearch checks query-vs-queries and filter fields. errMsg is
+// "invalid query" or "invalid search"; hint is empty or a field name.
+func NormalizeSearch(query string, queries []string, f Filter) (qs []string, out Filter, errMsg, hint string) {
+	qs, errMsg = normalizeQueries(query, queries)
+	if errMsg != "" {
+		return nil, Filter{}, errMsg, ""
+	}
+	out, hint = normalizeFilter(f)
+	if hint != "" {
+		return nil, Filter{}, "invalid search", hint
+	}
+	if out.ExactMatch {
+		for _, q := range qs {
+			if !hasQuotedPhrase(q) {
+				return nil, Filter{}, "invalid search", "exact_match"
+			}
+		}
+	}
+	return qs, out, "", ""
+}
+
+func normalizeQueries(query string, queries []string) ([]string, string) {
+	q := strings.TrimSpace(query)
+	qs := make([]string, 0, len(queries))
+	for _, s := range queries {
+		qs = append(qs, strings.TrimSpace(s))
+	}
+	hasQ := q != ""
+	hasQS := len(qs) > 0
+	if hasQ && hasQS {
+		return nil, "invalid query"
+	}
+	if !hasQ && !hasQS {
+		return nil, "invalid query"
+	}
+	if hasQ {
+		qs = []string{q}
+	}
+	if len(qs) < 1 || len(qs) > 4 {
+		return nil, "invalid query"
+	}
+	for _, s := range qs {
+		if s == "" || utf8.RuneCountInString(s) > MaxQueryRunes {
+			return nil, "invalid query"
+		}
+	}
+	return qs, ""
+}
+
+func normalizeFilter(f Filter) (Filter, string) {
+	inc, hint := normalizeDomains(f.IncludeDomains, "include_domains")
+	if hint != "" {
+		return Filter{}, hint
+	}
+	exc, hint := normalizeDomains(f.ExcludeDomains, "exclude_domains")
+	if hint != "" {
+		return Filter{}, hint
+	}
+	mode := strings.TrimSpace(f.IncludeDomainsMode)
+	switch mode {
+	case "", "restrict", "prefer":
+	default:
+		return Filter{}, "include_domains_mode"
+	}
+	if mode != "" && len(inc) == 0 {
+		return Filter{}, "include_domains_mode"
+	}
+	if len(inc) > 0 && mode == "" {
+		mode = "restrict"
+	}
+
+	tr := strings.TrimSpace(f.TimeRange)
+	if tr != "" {
+		long, ok := timeRangeLong[tr]
+		if !ok {
+			return Filter{}, "time_range"
+		}
+		tr = long
+	}
+	start := strings.TrimSpace(f.StartDate)
+	end := strings.TrimSpace(f.EndDate)
+	if start != "" {
+		if !validDay(start) {
+			return Filter{}, "start_date"
+		}
+	}
+	if end != "" {
+		if !validDay(end) {
+			return Filter{}, "end_date"
+		}
+	}
+	if (start != "" || end != "") && tr != "" {
+		return Filter{}, "time_range"
+	}
+	if start != "" && end != "" {
+		st, _ := time.Parse("2006-01-02", start)
+		en, _ := time.Parse("2006-01-02", end)
+		if en.Before(st) {
+			return Filter{}, "end_date"
+		}
+	}
+
+	topic := strings.TrimSpace(f.Topic)
+	switch topic {
+	case "", "general", "news", "finance":
+	default:
+		return Filter{}, "topic"
+	}
+
+	ms := f.MinScore
+	if ms < 0 || ms > 1 {
+		return Filter{}, "min_score"
+	}
+
+	return Filter{
+		IncludeDomains:     inc,
+		ExcludeDomains:     exc,
+		IncludeDomainsMode: mode,
+		TimeRange:          tr,
+		StartDate:          start,
+		EndDate:            end,
+		Topic:              topic,
+		ExactMatch:         f.ExactMatch,
+		MinScore:           ms,
+	}, ""
+}
+
+func normalizeDomains(in []string, hint string) ([]string, string) {
+	if len(in) == 0 {
+		return nil, ""
+	}
+	out := make([]string, 0, len(in))
+	seen := map[string]bool{}
+	for _, raw := range in {
+		s := strings.TrimSpace(raw)
+		if s == "" {
+			continue
+		}
+		d, ok := normalizeDomain(s)
+		if !ok {
+			return nil, hint
+		}
+		if seen[d] {
+			continue
+		}
+		seen[d] = true
+		out = append(out, d)
+	}
+	if len(out) == 0 {
+		return nil, ""
+	}
+	if len(out) > maxDomainList {
+		return nil, hint
+	}
+	return out, ""
+}
+
+func normalizeDomain(s string) (string, bool) {
+	s = strings.ToLower(strings.TrimSpace(s))
+	s = strings.TrimSuffix(s, ".")
+	if s == "" || len(s) > maxHostLen {
+		return "", false
+	}
+	if strings.ContainsAny(s, " :/@*?#[]") {
+		return "", false
+	}
+	labels := strings.Split(s, ".")
+	if len(labels) == 0 {
+		return "", false
+	}
+	for _, lab := range labels {
+		if !validLabel(lab) {
+			return "", false
+		}
+	}
+	return s, true
+}
+
+func validLabel(lab string) bool {
+	if lab == "" || len(lab) > 63 {
+		return false
+	}
+	if lab[0] == '-' || lab[len(lab)-1] == '-' {
+		return false
+	}
+	for i := 0; i < len(lab); i++ {
+		c := lab[i]
+		if c >= 'a' && c <= 'z' || c >= '0' && c <= '9' || c == '-' {
+			continue
+		}
+		return false
+	}
+	return true
+}
+
+func validDay(s string) bool {
+	t, err := time.Parse("2006-01-02", s)
+	return err == nil && t.Format("2006-01-02") == s
+}
+
+// hasQuotedPhrase reports a balanced ASCII "…" pair with ≥1 rune inside and no unpaired quotes.
+func hasQuotedPhrase(q string) bool {
+	in := false
+	n := 0
+	pairs := 0
+	for _, r := range q {
+		if r != '"' {
+			if in {
+				n++
+			}
+			continue
+		}
+		if !in {
+			in = true
+			n = 0
+			continue
+		}
+		if n == 0 {
+			return false
+		}
+		in = false
+		pairs++
+	}
+	return !in && pairs >= 1
+}
+
+func QueryRuneLen(qs []string) int {
+	n := 0
+	for _, q := range qs {
+		n += utf8.RuneCountInString(q)
+	}
+	return n
+}