Rewrite a Russian question into English Kiwix keywords (#403)

Kiwix ranks by keyword, not meaning, so a translated question finds song and TV titles. This asks the resident model for the TOPIC instead: a short English noun phrase, like a Wikipedia article title. Locked down three ways, because a wrong query is silently wrong: - A GBNF grammar, same idea as routeGrammar and responseGrammar. The reply must be {"query":"..."} with Latin words only. The JSON wrapper matters: this model always thinks out loud and this llama-server build ignores the thinking switch, so a bare word-list grammar just captured "Let me analyze this request carefully" for every question. - max_tokens 32, since the answer is a few words. - CleanQuery, which throws away empty, Russian and prose replies rather than passing them to Kiwix, and drops question words like "why" and "how much" that a keyword ranker cannot use anyway. Client side only. Nothing is wired into the daemon or any config. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01CGeSZxh1DCtRxmFVSYVGvJ
2026-07-31 18:19:42 +04:00
parent ddb658ffbb
commit b300ac5c70
2 changed files with 288 additions and 0 deletions
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+package kiwix
+
+// Turning a Russian question into an English Kiwix search.
+//
+// Kiwix ranks by keyword, not by meaning. "why is the sky blue" returns a TV
+// episode; "Rayleigh scattering sky blue" returns the right article. So the
+// model's job here is NOT translation — it is naming the English article the
+// answer lives in.
+//
+// The output space is a handful of words, so it is worth locking down hard: a
+// GBNF grammar for the shape, a tiny token cap, and a cleanup pass that throws
+// away anything odd rather than handing junk to Kiwix.
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"strings"
+	"unicode"
+
+	"github.com/kami/maven/internal/llm"
+)
+
+// Completer — the LLM seam, so tests can fake it. *llm.Client satisfies it.
+type Completer interface {
+	Complete(ctx context.Context, r llm.Req) (string, error)
+}
+
+// queryGrammar — one JSON object holding 1..6 keyword words. Latin letters,
+// digits and hyphens only, so the model physically cannot answer the question
+// or reply in Russian.
+//
+// Why the JSON wrapper: this model always thinks out loud and this llama-server
+// build ignores the thinking switch (see ROUTING-EVAL-31-07-2026.md). A bare
+// word-list grammar just captured the reasoning — every case came back as
+// "Let me analyze this request carefully". Demanding JSON, like routeGrammar and
+// responseGrammar already do, gives the reasoning nowhere to go.
+const queryGrammar = `
+root ::= "{" ws "\"query\"" ws ":" ws "\"" word (" " word){0,5} "\"" ws "}"
+word ::= [A-Za-z0-9] [A-Za-z0-9-]{0,23}
+ws   ::= [ \t\n]*
+`
+
+// rewriteSystem — asks for search keywords, not an answer and not a translation.
+const rewriteSystem = `You turn a question into a search query for English Wikipedia.
+
+Rules:
+- Output ONLY English search keywords. Never an answer, never an explanation.
+- Do NOT translate the sentence. Name the thing the answer is about.
+- The output must be a noun phrase, like a Wikipedia article title.
+- Never use question words: no why, how, what, when, which, "how much",
+  "how long", "how to", "vs", "reason", "difference".
+- 2 to 4 words.
+
+Reply with JSON: {"query":"<keywords>"}
+
+Good:
+"почему листья желтеют осенью?" -> {"query":"leaf senescence autumn"}
+"как работает микроволновка?" -> {"query":"microwave oven"}
+"не могли бы вы объяснить, что такое блокчейн?" -> {"query":"blockchain"}
+"сколько живут собаки?" -> {"query":"dog lifespan"}
+"как избавиться от комаров в квартире?" -> {"query":"mosquito control"}
+"чем чай отличается от кофе?" -> {"query":"tea"}
+
+Only JSON, no explanation.`
+
+// maxQueryTokens — the output is a few words plus the JSON wrapper. A tight cap
+// is the cheapest guard against the model rambling into an answer.
+const maxQueryTokens = 32
+
+// Rewriter asks the resident model for English search keywords.
+type Rewriter struct{ c Completer }
+
+func NewRewriter(c Completer) *Rewriter { return &Rewriter{c: c} }
+
+// Rewrite returns English keywords for a question in any language.
+// It errors rather than returning something Kiwix should not see.
+func (r *Rewriter) Rewrite(ctx context.Context, question string) (string, error) {
+	raw, err := r.c.Complete(ctx, llm.Req{
+		System:        rewriteSystem,
+		User:          strings.TrimSpace(question),
+		Grammar:       queryGrammar,
+		MaxTokens:     maxQueryTokens,
+		RepeatPenalty: 1.15,
+	})
+	if err != nil {
+		return "", err
+	}
+	return CleanQuery(unwrapJSON(raw))
+}
+
+// unwrapJSON pulls the query out of {"query":"..."}. If the reply is not that
+// shape it is returned as-is, and CleanQuery decides whether it is usable.
+func unwrapJSON(raw string) string {
+	s := strings.TrimSpace(raw)
+	if !strings.HasPrefix(s, "{") {
+		return s
+	}
+	var got struct{ Query string }
+	if err := json.Unmarshal([]byte(s), &got); err != nil {
+		return s
+	}
+	return got.Query
+}
+
+// maxQueryWords matches the grammar's bound. Anything longer is prose.
+const maxQueryWords = 6
+
+// CleanQuery checks and tidies whatever the model produced. The grammar makes
+// bad output unlikely, not impossible (a server without grammar support, a
+// different model), so this is the real gate in front of Kiwix.
+//
+// Exported so it can be tested without a model.
+func CleanQuery(raw string) (string, error) {
+	s := strings.TrimSpace(raw)
+	// Models like to wrap answers in quotes. Drop surrounding ones.
+	s = strings.Trim(s, "\"'`")
+	// Keep the first line only: everything after it is prose.
+	if i := strings.IndexAny(s, "\r\n"); i >= 0 {
+		s = s[:i]
+	}
+	// Keep letters, digits, spaces and hyphens; anything else becomes a space.
+	var b strings.Builder
+	for _, ru := range s {
+		switch {
+		case unicode.IsLetter(ru) || unicode.IsDigit(ru) || ru == '-':
+			b.WriteRune(ru)
+		default:
+			b.WriteRune(' ')
+		}
+	}
+	words := strings.Fields(b.String())
+	if len(words) == 0 {
+		return "", fmt.Errorf("kiwix rewrite: empty query")
+	}
+	if len(words) > maxQueryWords {
+		return "", fmt.Errorf("kiwix rewrite: %d words, want at most %d (looks like prose)", len(words), maxQueryWords)
+	}
+	words = dropStopWords(words)
+	out := strings.Join(words, " ")
+	// The ZIMs are English. Non-Latin letters mean the model ignored the ask.
+	for _, ru := range out {
+		if unicode.IsLetter(ru) && !isLatin(ru) {
+			return "", fmt.Errorf("kiwix rewrite: query is not English: %q", out)
+		}
+	}
+	return out, nil
+}
+
+// stopWords — question words and filler. The model keeps writing question-shaped
+// queries ("why is the sky blue", "how much water to drink daily") no matter how
+// the prompt is worded, and Kiwix ranks on every word, so those words drag in
+// song and episode titles. Dropping them in code is not a style preference: a
+// keyword ranker gets nothing from them.
+var stopWords = map[string]bool{
+	"a": true, "an": true, "the": true, "is": true, "are": true, "was": true,
+	"do": true, "does": true, "did": true, "to": true, "of": true, "in": true,
+	"on": true, "for": true, "and": true, "or": true, "my": true, "me": true,
+	"i": true, "it": true, "its": true, "be": true, "been": true, "get": true,
+	"how": true, "why": true, "what": true, "when": true, "which": true,
+	"who": true, "where": true, "much": true, "many": true, "long": true,
+	"vs": true, "than": true, "rid": true, "from": true, "about": true,
+}
+
+// dropStopWords removes filler, but never everything: if the query was nothing
+// but stop words there is nothing better to search, so the original is kept and
+// the caller sees whatever Kiwix makes of it.
+func dropStopWords(words []string) []string {
+	kept := make([]string, 0, len(words))
+	for _, w := range words {
+		if !stopWords[strings.ToLower(w)] {
+			kept = append(kept, w)
+		}
+	}
+	if len(kept) == 0 {
+		return words
+	}
+	return kept
+}
+
+func isLatin(ru rune) bool {
+	return (ru >= 'a' && ru <= 'z') || (ru >= 'A' && ru <= 'Z')
+}
@@ -0,0 +1,105 @@
+package kiwix
+
+import (
+	"context"
+	"testing"
+
+	"github.com/kami/maven/internal/llm"
+)
+
+// Bad model output must never reach Kiwix. No model needed for this.
+func TestCleanQueryRejectsJunk(t *testing.T) {
+	bad := []struct{ name, raw string }{
+		{"empty", ""},
+		{"blank", "   \n  "},
+		{"russian came back", "почему небо синее"},
+		{"mixed russian", "sky синее scattering"},
+		{"full sentence", "The sky looks blue because of the scattering of sunlight by air molecules"},
+		{"prose with quotes", `Sure! Here is a good search query: "Rayleigh scattering", which explains it.`},
+	}
+	for _, c := range bad {
+		if got, err := CleanQuery(c.raw); err == nil {
+			t.Errorf("%s: want rejection, got %q", c.name, got)
+		}
+	}
+}
+
+func TestCleanQueryCleans(t *testing.T) {
+	ok := []struct{ raw, want string }{
+		{"Rayleigh scattering sky", "Rayleigh scattering sky"},
+		{"  boiled   egg  cooking \n", "boiled egg cooking"},
+		{`"virtual private network"`, "virtual private network"},
+		{"solid-state drive", "solid-state drive"},
+		{"cat purr.", "cat purr"},
+		{"hiccup\nAlso: hiccough", "hiccup"},
+		// Question words are filler to a keyword ranker, so they go.
+		{"why is the sky blue", "sky blue"},
+		{"how much water to drink daily", "water drink daily"},
+		{"SSD vs HDD comparison", "SSD HDD comparison"},
+		// Nothing but filler: keep it rather than return nothing.
+		{"what is it", "what is it"},
+	}
+	for _, c := range ok {
+		got, err := CleanQuery(c.raw)
+		if err != nil {
+			t.Errorf("%q: %v", c.raw, err)
+			continue
+		}
+		if got != c.want {
+			t.Errorf("%q -> %q, want %q", c.raw, got, c.want)
+		}
+	}
+}
+
+type fakeCompleter struct {
+	out string
+	req llm.Req
+}
+
+func (f *fakeCompleter) Complete(_ context.Context, r llm.Req) (string, error) {
+	f.req = r
+	return f.out, nil
+}
+
+func TestRewriteConstrainsTheCall(t *testing.T) {
+	f := &fakeCompleter{out: `{"query":"Rayleigh scattering sky"}`}
+	got, err := NewRewriter(f).Rewrite(context.Background(), "почему небо синее?")
+	if err != nil {
+		t.Fatalf("rewrite: %v", err)
+	}
+	if got != "Rayleigh scattering sky" {
+		t.Errorf("query = %q", got)
+	}
+	if f.req.Grammar == "" {
+		t.Error("no grammar sent")
+	}
+	if f.req.MaxTokens == 0 || f.req.MaxTokens > 32 {
+		t.Errorf("max_tokens = %d, want a small cap", f.req.MaxTokens)
+	}
+}
+
+func TestRewriteRejectsBadModelOutput(t *testing.T) {
+	bad := []string{
+		`{"query":"почему небо синее"}`, // never translated
+		`{"query":""}`,                  // empty
+		`{"query":"the sky is blue because sunlight is scattered by air"}`, // an answer
+		// Note: a SHORT English prose fragment ("Let me analyze this request")
+		// is under the word cap and cannot be caught here. The grammar is what
+		// stops that one.
+	}
+	for _, out := range bad {
+		f := &fakeCompleter{out: out}
+		if got, err := NewRewriter(f).Rewrite(context.Background(), "почему небо синее?"); err == nil {
+			t.Errorf("%s: want rejection, got %q", out, got)
+		}
+	}
+}
+
+// A reply that is not the JSON shape but is still usable keywords should pass.
+func TestRewriteFallsBackToPlainText(t *testing.T) {
+	f := &fakeCompleter{out: "Rayleigh scattering sky"}
+	got, err := NewRewriter(f).Rewrite(context.Background(), "почему небо синее?")
+	if err != nil || got != "Rayleigh scattering sky" {
+		t.Errorf("got %q, %v", got, err)
+	}
+}