label seeds with the stage 0 grammars and gemma, and measure both (V-546)

The plan calls the labeled set the whole project and names the stage 0
grammars as the label functions. cmd/labelgen runs them, the real ones in
buildRouter order, so a rule change moves the training data with it.

Gemma labels the rest at 334ms/call with nothing unparsed, which matches the
plan's estimate. It agrees with the seed files on 197/277, and reading the
disagreements is the finding: the seeds and the router prompt hold different
definitions of system, of a world question and of a bare verb. V-626.

cmd/labelgen/main.go

@@ -0,0 +1,113 @@
+// Command labelgen labels utterances with the stage 0 grammars and prints JSONL.
+//
+// docs/plans/18-routing-heads-on-e5-small.md calls the labeled set the whole
+// project, and it names the stage 0 grammars as the high-precision label
+// functions to start from. This runs them — the real ones, in the real
+// buildRouter order — rather than a reimplementation, so a rule change moves
+// the training data with it.
+//
+// A grammar that declines leaves the line unlabeled. Those go to the model, and
+// keeping them is the point: a set labeled only by the rules teaches only the
+// rules.
+//
+//	go run ./cmd/labelgen < utterances.txt > labeled.jsonl
+//
+// The wakeword-act grammar is absent, because its allowlist is the deployment's
+// enabled tool names and this tool has no deployment. Every other rule is here.
+package main
+
+import (
+	"bufio"
+	"encoding/json"
+	"fmt"
+	"os"
+	"strings"
+
+	"github.com/kami/maven/internal/router"
+)
+
+// label is one output row. The grammar name rides along so a reviewer can see
+// which rule made the claim, and so a rule that turns out to be wrong can have
+// its rows pulled without re-running everything.
+type label struct {
+	Utterance string `json:"utterance"`
+	Intent    string `json:"intent,omitempty"`
+	Grammar   string `json:"grammar,omitempty"`
+	Key       string `json:"key,omitempty"`
+	Value     string `json:"value,omitempty"`
+	Fn        string `json:"fn,omitempty"`
+	Text      string `json:"text,omitempty"`
+	Labeled   bool   `json:"labeled"`
+}
+
+// grammars mirrors buildRouter's order in cmd/mavend/voicewire.go. Order is
+// load-bearing there and so it is here: the agenda rules must sit after the
+// clock rules, Praxis before the capture marker, the narrative rules last.
+func grammars() []router.Grammar {
+	var g []router.Grammar
+	g = append(g, router.SystemTimeDateGrammars()...)
+	g = append(g, router.AgendaQueryGrammars()...)
+	g = append(g, router.FeedQueryGrammar())
+	g = append(g, router.TaskListGrammar())
+	g = append(g, router.ListGrammars()...)
+	g = append(g, router.ReminderGrammar())
+	g = append(g, router.PraxisGrammars()...)
+	g = append(g, router.TaskCaptureGrammar())
+	g = append(g, router.NarrativeQueryGrammars()...)
+	return g
+}
+
+func match(gs []router.Grammar, utterance string) label {
+	out := label{Utterance: utterance}
+	for _, g := range gs {
+		m := g.Pattern.FindStringSubmatch(utterance)
+		if m == nil {
+			continue
+		}
+		d, ok := g.Build(m)
+		if !ok {
+			continue // the rule saw its shape and declined it
+		}
+		out.Intent = string(d.Intent)
+		out.Grammar = g.Name
+		out.Key = d.Slots.Key
+		out.Value = d.Slots.Value
+		out.Fn = d.Slots.Fn
+		out.Text = d.Slots.Text
+		out.Labeled = true
+		return out
+	}
+	return out
+}
+
+func main() {
+	gs := grammars()
+	in := bufio.NewScanner(os.Stdin)
+	in.Buffer(make([]byte, 0, 64*1024), 1024*1024)
+	out := bufio.NewWriter(os.Stdout)
+	defer out.Flush()
+
+	enc := json.NewEncoder(out)
+	var seen, labeled int
+	for in.Scan() {
+		line := strings.TrimSpace(in.Text())
+		if line == "" || strings.HasPrefix(line, "#") {
+			continue
+		}
+		seen++
+		l := match(gs, line)
+		if l.Labeled {
+			labeled++
+		}
+		if err := enc.Encode(l); err != nil {
+			fmt.Fprintln(os.Stderr, "labelgen:", err)
+			os.Exit(1)
+		}
+	}
+	if err := in.Err(); err != nil {
+		fmt.Fprintln(os.Stderr, "labelgen:", err)
+		os.Exit(1)
+	}
+	// Coverage on stderr, so the count is visible without polluting the JSONL.
+	fmt.Fprintf(os.Stderr, "labelgen: %d/%d labeled by %d grammars\n", labeled, seen, len(gs))
+}