feat: D24 fact intervals (--as-of) and bin/stack assistant helpers.

Store valid_from/valid_to on leafs and filter search by calendar day without
overloading D16 source staleness; stack start/start-assistant wires brain + PicoClaw.

internal/brain/rank/args.go

@@ -5,10 +5,11 @@ import (
 	"strconv"
 
 	"github.com/eSlider/2dph/internal/cli"
+	"github.com/eSlider/2dph/internal/facts"
 	"github.com/integrii/flaggy"
 )
 
-const Usage = `usage: bin/brain/search.go "query" [--root facts|info] [--repo REPO] [-n N] [--hop N] [--json] [--no-web]
+const Usage = `usage: bin/brain/search.go "query" [--root facts|info] [--repo REPO] [-n N] [--hop N] [--as-of YYYY-MM-DD] [--json] [--no-web]
        bin/brain/search.go serve [port]
        bin/brain/search.go --list-model
        source <(./bin/cli/complete.go bash)`
@@ -19,6 +20,7 @@ type Options struct {
 	Repo      string
 	Limit     int
 	Hop       int
+	AsOf      string
 	JSONOut   bool
 	ListModel bool
 	NoWeb     bool
@@ -35,6 +37,7 @@ func NewParser(opt *Options) *flaggy.Parser {
 	p.String(&opt.Repo, "", "repo", "filter by repo")
 	p.Int(&opt.Limit, "n", "n", "max hits")
 	p.Int(&opt.Hop, "", "hop", "walk FROM_FILE depth 1-3")
+	p.String(&opt.AsOf, "", "as-of", "keep facts active on YYYY-MM-DD (D24)")
 	p.Bool(&opt.JSONOut, "", "json", "JSON output")
 	p.Bool(&opt.NoWeb, "", "no-web", "stay local")
 	p.Bool(&opt.ListModel, "", "list-model", "print embedding model")
@@ -64,6 +67,13 @@ func ParseArgs(args []string) (Options, error) {
 	if opt.Hop > 3 {
 		return opt, fmt.Errorf("--hop max is 3 (File → Commit → Person)")
 	}
+	if opt.AsOf != "" {
+		day := facts.NormalizeDay(opt.AsOf)
+		if len(day) != 10 || day[4] != '-' || day[7] != '-' {
+			return opt, fmt.Errorf("--as-of must be YYYY-MM-DD, got %q", opt.AsOf)
+		}
+		opt.AsOf = day
+	}
 	if opt.Query == "" && !opt.ListModel {
 		return opt, fmt.Errorf("no query given")
 	}