Admin: leases, pin, release, drain, usage, metrics

cmd/crossbar/main.go calls admin.Handler with the new 6-arg signature, passing nil for the not-yet-wired leases/limiter/store/drainer (task 07 wires them) so go vet and go test ./... pass on cmd/crossbar. This is a compile fix, not the task-07 wiring; noted in the implementer-log.

Implemented-By: OpenCode session (model recorded in docs/implementer-log.md)

cmd/crossbar/main.go

@@ -49,7 +49,7 @@ func run() error {
 	go table.Run(ctx)
 
 	mux := http.NewServeMux()
-	mux.Handle("/_crossbar/", admin.Handler(cfg, table))
+	mux.Handle("/_crossbar/", admin.Handler(cfg, table, nil, nil, nil, nil))
 	mux.Handle("/", proxy.New(cfg, table, nil, nil, nil, log))
 
 	srv := &http.Server{

docs/implementer-log.md

@@ -5,6 +5,7 @@ owner fills in the Model column. The reviewer adds findings under "Reviews" once
 
 | Task | Date | Status | Gate runs | First gate | Deviations | Notes | Model |
 |---|---|---|---|---|---|---|---|
+| v1/06-admin | 2026-09-25 | done | 2 | fail | Split `internal/admin/admin.go` (196 lines) + `admin_ops.go` (366 lines) to stay under 400. Updated `cmd/crossbar/main.go`'s `admin.Handler` call from the committed 2-arg `(cfg, table)` to the task's 6-arg signature, passing the health table for `hosts` and `nil` for the not-yet-wired `leases`/`limiter`/`store`/`drainer` (task 07 wires them); this was a compile fix required for `go vet`/`go test ./...` on `cmd/crossbar` to pass — the full wiring is task 07. | First `make gate` failed on `go vet` (`admin.Handler` called with 2 args in `main.go` after the signature changed); fixed `main.go` and the gate passed on the second run. `admin_test.go` and `example.toml` verified byte-identical to `docs/plans/v1/_files/`; `internal/lease` and `internal/store` left untouched except the already-present `Candidates`/`StatusCounts`. | ? |
 | v1/05-proxy | 2026-09-25 | done | 2 | fail | Split `internal/proxy/proxy.go` (411 lines) into `proxy.go` + `forward.go` by moving `forward`, `newReverseProxy`, `forwardState`, `statusRecorder`, `leaseState`, `ttfbMs` and the `writeError`/`writeRecord` helpers to `forward.go`; the one `recorder_test.go` `proxy.New` call changed to `proxy.New(cfg, h, nil, nil, nil, nil)` per the task; `cmd/crossbar/main.go` passes `nil, nil, nil` for the new `leases`/`lim`/`rec` args (task 06 wires them). | The tee in `tee.go` already read the final SSE chunk's (streamed) and the JSON body's (non-streamed) usage/timings, so `TestAccountingRowsFromUsageAndTimings` passed on the first run — the only gate blocker was `proxy.go` at 411 lines. | ? |
 | v1/04-lease | 2026-09-25 | done | 1 | pass | The given `TestPinAndUnpin` was wrong and replaced by the owner mid-task; the corrected `internal/lease/lease_test.go` is byte-identical to `docs/plans/v1/_files/internal/lease/lease_test.go`. A `fmt.Printf("DEBUG …")` line the prior session left in `event` was removed before the gate. | `Acquire` order (pinned, existing, inherit, choose) with memory rolled back only after a successful save; `Pin` writes a pin event, then the pin row, then deletes other-host leases, so the pin event always precedes the unpin's release event in the log. | ? |
 | v1/02-fingerprint-config | 2026-09-25 | done | 1 | pass | Switched the existing `TestBadFiles` unknown-key example from `lease_idle` to `bogus_key`, and updated `testdata/bad-unknown-key.toml` to match: this task makes `lease_idle` a valid key, so the old example was stale. `config_test.go` and that testdata are not `_files`-protected, so the edit was permitted even though the task's file list named only `config.go` and `implementer-log.md`; the unknown-key rejection is still covered. | fingerprint.go truncates each input to its first 4096 bytes and uses a presence flag so an empty first system prompt is not overwritten by a later one; `Duration.UnmarshalText` matches `^[0-9]+d$` (regexp) before falling to `time.ParseDuration`. | ? |

example.toml

@@ -1,19 +1,23 @@
-# crossbar example configuration. Replace <tailnet> and the addresses with your own.
+# crossbar example configuration (v1). Replace <tailnet> and the addresses with your own.
 listen        = "127.0.0.1:17777"   # never 0.0.0.0 — bind the tailnet address in production
+db            = "crossbar.db"       # SQLite: leases + accounting (WAL). /var/lib/crossbar/crossbar.db under systemd
 poll_interval = "1s"                # 60s in production; 1s makes the smoke run quick
-queue_max     = 8
+lease_idle    = "30m"               # a conversation idle this long loses its host
+retention     = "180d"              # per-request rows older than this are rolled up daily
+queue_max     = 1                   # waiting places per (host, model) beyond `parallel`; 503 past that
 
 [hosts.alpha]
 base_url = "http://127.0.0.1:18081"    # e.g. http://straylight.<tailnet>:11434
 weight   = 1.0
-models   = { "ornith-1.5-35b-a3b" = { parallel = 4 }, "small-9b" = { parallel = 6 } }
+models   = { "ornith-1.5-35b-a3b" = { parallel = 1 }, "small-9b" = { parallel = 6 } }
 
 [hosts.beta]
 base_url = "http://127.0.0.1:18082"    # e.g. http://titan.<tailnet>:8081
 weight   = 2.0
-models   = { "ornith-1.5-35b-a3b" = { parallel = 4 } }
+models   = { "ornith-1.5-35b-a3b" = { parallel = 2 } }
 
-# v0: a route is a preference list; the first healthy host that has the model wins.
+# v1: a route is a set of candidate hosts; each conversation gets a sticky lease on the host with
+# the most free slots × weight at the time it starts. Pins and drains come from the admin API.
 [routes.opencode-a]
 hosts         = ["alpha", "beta"]
 default_model = "ornith-1.5-35b-a3b"

internal/admin/admin.go

@@ -1,15 +1,19 @@
-// Package admin serves the operator's view of crossbar: the health table and the routes as JSON,
-// mounted at /_crossbar/ on the same listener as the proxy. The shape of /_crossbar/hosts is
-// fixed so operators can read why a request went where it went.
+// Package admin serves the operator's view of crossbar: the hosts view with
+// slots and drain state, the routes view with leases and pins, the pin/release
+// and drain controls, usage accounting, and Prometheus metrics, all under
+// /_crossbar/.
 package admin
 
 import (
-	"encoding/json"
 	"net/http"
+	"sort"
 	"time"
 
 	"git.wntrmute.dev/kyle/crossbar/internal/config"
 	"git.wntrmute.dev/kyle/crossbar/internal/health"
+	"git.wntrmute.dev/kyle/crossbar/internal/lease"
+	"git.wntrmute.dev/kyle/crossbar/internal/limiter"
+	"git.wntrmute.dev/kyle/crossbar/internal/store"
 )
 
 // Hosts is what the admin handler needs from the health table.
@@ -17,59 +21,93 @@ type Hosts interface {
 	All() map[string]health.Status
 }
 
+// Drainer is what the admin handler needs to steer draining; *proxy.Hosts
+// satisfies it.
+type Drainer interface {
+	Draining(name string) bool
+	SetDraining(name string, on bool)
+}
+
+// HostView is one host's row in the hosts view.
 type HostView struct {
-	Healthy bool     `json:"healthy"`
-	Loaded  []string `json:"loaded"`  // never null: an empty slice when nothing is loaded
-	LastOK  string   `json:"last_ok"` // time.RFC3339 in UTC, or "" if never
-	LastErr string   `json:"last_err"`
+	Healthy   bool     `json:"healthy"`
+	Loaded    []string `json:"loaded"`  // never null
+	LastOK    string   `json:"last_ok"` // RFC 3339 UTC or ""
+	LastErr   string   `json:"last_err"`
+	FreeSlots int      `json:"free_slots"` // lim.FreeSlots(host)
+	InFlight  int      `json:"in_flight"`  // sum over the host's configured models
+	Queued    int      `json:"queued"`     // same
+	Draining  bool     `json:"draining"`
 }
 
+// LeaseView is one lease's row in a route's leases.
+type LeaseView struct {
+	FP       string `json:"fp"`
+	Model    string `json:"model"`
+	Host     string `json:"host"`
+	State    string `json:"state"`
+	Created  string `json:"created"`   // RFC 3339 UTC
+	LastUsed string `json:"last_used"` // RFC 3339 UTC
+}
+
+// RouteView is one route's row in the routes view.
 type RouteView struct {
-	Hosts        []string `json:"hosts"`
-	DefaultModel string   `json:"default_model"`
+	Hosts        []string    `json:"hosts"`
+	DefaultModel string      `json:"default_model"`
+	Pinned       string      `json:"pinned"` // "" when not pinned
+	Leases       []LeaseView `json:"leases"` // never null
 }
 
-// Handler serves GET /_crossbar/hosts and GET /_crossbar/routes. Any other method on those paths is
-// a 405 with an Allow: GET header; anything else under the handler is a 404.
-func Handler(cfg *config.Config, h Hosts) http.Handler {
+// handler implements the operator's endpoints under /_crossbar/.
+type handler struct {
+	cfg *config.Config
+	h   Hosts
+	lt  *lease.Table
+	lim *limiter.Limiter
+	st  *store.Store
+	d   Drainer
+}
+
+// Handler builds the operator's HTTP handler.
+func Handler(cfg *config.Config, h Hosts, lt *lease.Table, lim *limiter.Limiter, st *store.Store, d Drainer) http.Handler {
+	hx := &handler{cfg: cfg, h: h, lt: lt, lim: lim, st: st, d: d}
 	mux := http.NewServeMux()
-	mux.HandleFunc("/_crossbar/hosts", hostsHandler(h))
-	mux.HandleFunc("/_crossbar/routes", routesHandler(cfg))
-	mux.HandleFunc("/", notFound)
+	mux.HandleFunc("/_crossbar/hosts", hx.hostsGet)
+	mux.HandleFunc("/_crossbar/hosts/{host}", hx.hostDrain)
+	mux.HandleFunc("/_crossbar/routes", hx.routesGet)
+	mux.HandleFunc("/_crossbar/routes/{route}", hx.routePin)
+	mux.HandleFunc("/_crossbar/usage", hx.usageGet)
+	mux.HandleFunc("/_crossbar/metrics", hx.metricsGet)
+	mux.HandleFunc("/_crossbar/", hx.unknown)
 	return mux
 }
 
-func hostsHandler(h Hosts) http.HandlerFunc {
-	return func(w http.ResponseWriter, r *http.Request) {
-		if r.Method != http.MethodGet {
-			wrongMethod(w)
-			return
-		}
-		views := make(map[string]HostView, len(h.All()))
-		for name, s := range h.All() {
-			views[name] = hostView(s)
-		}
-		writeJSON(w, http.StatusOK, views)
+func (hx *handler) hostsGet(w http.ResponseWriter, r *http.Request) {
+	if r.Method != http.MethodGet {
+		wrongMethod(w, "GET")
+		return
 	}
+	writeJSON(w, http.StatusOK, hx.hostViews())
 }
 
-func routesHandler(cfg *config.Config) http.HandlerFunc {
-	return func(w http.ResponseWriter, r *http.Request) {
-		if r.Method != http.MethodGet {
-			wrongMethod(w)
-			return
-		}
-		views := make(map[string]RouteView, len(cfg.Routes))
-		for name, route := range cfg.Routes {
-			hosts := make([]string, len(route.Hosts))
-			copy(hosts, route.Hosts)
-			views[name] = RouteView{Hosts: hosts, DefaultModel: route.DefaultModel}
-		}
-		writeJSON(w, http.StatusOK, views)
+// hostViews builds every host's row, keyed by host name.
+func (hx *handler) hostViews() map[string]HostView {
+	all := hx.h.All()
+	out := make(map[string]HostView, len(all))
+	for name, s := range all {
+		out[name] = hx.hostView(name, s)
 	}
+	return out
 }
 
-func hostView(s health.Status) HostView {
+// hostView builds one host's row: concurrency from the limiter summed over the
+// models the host serves, draining from the drainer, and the health snapshot.
+func (hx *handler) hostView(name string, s health.Status) HostView {
+	inflight, queued := 0, 0
+	for _, m := range configuredModels(hx.cfg, name) {
+		inflight += hx.lim.InFlight(name, m)
+		queued += hx.lim.Queued(name, m)
+	}
 	loaded := s.Loaded
 	if loaded == nil {
 		loaded = []string{}
@@ -79,24 +117,80 @@ func hostView(s health.Status) HostView {
 		lastOK = s.LastOK.UTC().Format(time.RFC3339)
 	}
 	return HostView{
-		Healthy: s.Healthy,
-		Loaded:  loaded,
-		LastOK:  lastOK,
-		LastErr: s.LastErr,
+		Healthy:   s.Healthy,
+		Loaded:    loaded,
+		LastOK:    lastOK,
+		LastErr:   s.LastErr,
+		FreeSlots: hx.lim.FreeSlots(name),
+		InFlight:  inflight,
+		Queued:    queued,
+		Draining:  hx.d.Draining(name),
 	}
 }
 
-func wrongMethod(w http.ResponseWriter) {
-	w.Header().Set("Allow", "GET")
-	writeJSON(w, http.StatusMethodNotAllowed, map[string]string{"error": "method not allowed"})
+// configuredModels returns the sorted model ids the host serves, or nil when
+// the host is unknown.
+func configuredModels(cfg *config.Config, name string) []string {
+	h, ok := cfg.Hosts[name]
+	if !ok {
+		return nil
+	}
+	models := make([]string, 0, len(h.Models))
+	for m := range h.Models {
+		models = append(models, m)
+	}
+	sort.Strings(models)
+	return models
 }
 
-func notFound(w http.ResponseWriter, r *http.Request) {
-	writeJSON(w, http.StatusNotFound, map[string]string{"error": "not found"})
+func (hx *handler) routesGet(w http.ResponseWriter, r *http.Request) {
+	if r.Method != http.MethodGet {
+		wrongMethod(w, "GET")
+		return
+	}
+	snap := hx.lt.Snapshot()
+	views := make(map[string]RouteView, len(hx.cfg.Routes))
+	for name, route := range hx.cfg.Routes {
+		hosts := make([]string, len(route.Hosts))
+		copy(hosts, route.Hosts)
+		views[name] = hx.routeView(name, hosts, route.DefaultModel, snap)
+	}
+	writeJSON(w, http.StatusOK, views)
 }
 
-func writeJSON(w http.ResponseWriter, status int, v any) {
-	w.Header().Set("Content-Type", "application/json")
-	w.WriteHeader(status)
-	_ = json.NewEncoder(w).Encode(v)
+// routeView builds one route's row: the pinned host (empty if none) and the
+// active leases on it, in snapshot order.
+func (hx *handler) routeView(route string, hosts []string, defaultModel string, snap []lease.Lease) RouteView {
+	leases := make([]LeaseView, 0)
+	for _, l := range snap {
+		if l.Route == route {
+			leases = append(leases, leaseView(l))
+		}
+	}
+	return RouteView{
+		Hosts:        hosts,
+		DefaultModel: defaultModel,
+		Pinned:       hx.lt.Pinned(route),
+		Leases:       leases,
+	}
+}
+
+// leaseView maps a lease to its operator view.
+func leaseView(l lease.Lease) LeaseView {
+	return LeaseView{
+		FP:       l.FP,
+		Model:    l.Model,
+		Host:     l.Host,
+		State:    string(l.State),
+		Created:  formatTime(l.Created),
+		LastUsed: formatTime(l.LastUsed),
+	}
+}
+
+// formatTime renders t as RFC 3339 in UTC, or "" for the zero time.
+func formatTime(t time.Time) string {
+	if t.IsZero() {
+		return ""
+	}
+	return t.UTC().Format(time.RFC3339)
 }

internal/admin/admin_ops.go

@@ -0,0 +1,366 @@
+package admin
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"sort"
+	"strconv"
+	"strings"
+	"time"
+
+	"git.wntrmute.dev/kyle/crossbar/internal/config"
+	"git.wntrmute.dev/kyle/crossbar/internal/lease"
+	"git.wntrmute.dev/kyle/crossbar/internal/store"
+)
+
+// routePin handles POST /_crossbar/routes/{route}: pin the route to a host or
+// release and unpin it.
+func (hx *handler) routePin(w http.ResponseWriter, r *http.Request) {
+	if r.Method != http.MethodPost {
+		wrongMethod(w, "POST")
+		return
+	}
+	route := r.PathValue("route")
+	routeCfg, ok := hx.cfg.Routes[route]
+	if !ok {
+		writeError(w, http.StatusNotFound, "unknown route")
+		return
+	}
+
+	var raw struct {
+		Host    string `json:"host"`
+		Pin     *bool  `json:"pin"`
+		Release *bool  `json:"release"`
+	}
+	if err := decodeJSON(r, &raw); err != nil {
+		writeError(w, http.StatusBadRequest, "invalid body")
+		return
+	}
+
+	pinSet := raw.Pin != nil
+	releaseSet := raw.Release != nil
+	switch {
+	case pinSet && releaseSet:
+		writeError(w, http.StatusBadRequest, "pin and release at once")
+	case !pinSet && !releaseSet:
+		writeError(w, http.StatusBadRequest, "pin or release required")
+	case pinSet:
+		hx.pin(w, route, routeCfg, raw.Host)
+	default:
+		hx.release(w, route)
+	}
+}
+
+// pin validates the host, records candidates, and pins the route.
+func (hx *handler) pin(w http.ResponseWriter, route string, routeCfg config.Route, host string) {
+	if host == "" {
+		writeError(w, http.StatusBadRequest, "pin requires host")
+		return
+	}
+	if !containsHost(routeCfg.Hosts, host) {
+		writeError(w, http.StatusNotFound, "host not in route")
+		return
+	}
+	// Record the route's hosts as candidates so Pin accepts a host no request
+	// has used yet.
+	hx.lt.Candidates(route, routeCfg.Hosts)
+	if err := hx.lt.Pin(route, host, time.Now()); err != nil {
+		if errors.Is(err, lease.ErrUnknownHost) {
+			writeError(w, http.StatusNotFound, "unknown host")
+			return
+		}
+		writeError(w, http.StatusInternalServerError, err.Error())
+		return
+	}
+	writeJSON(w, http.StatusOK, map[string]bool{"ok": true})
+}
+
+// release drops the route's leases and clears its pin.
+func (hx *handler) release(w http.ResponseWriter, route string) {
+	n := hx.lt.Release(route)
+	hx.lt.Unpin(route)
+	writeJSON(w, http.StatusOK, map[string]any{"ok": true, "released": n})
+}
+
+// hostDrain handles POST /_crossbar/hosts/{host}: set or clear draining.
+func (hx *handler) hostDrain(w http.ResponseWriter, r *http.Request) {
+	if r.Method != http.MethodPost {
+		wrongMethod(w, "POST")
+		return
+	}
+	host := r.PathValue("host")
+	if _, ok := hx.cfg.Hosts[host]; !ok {
+		writeError(w, http.StatusNotFound, "unknown host")
+		return
+	}
+	var body struct {
+		Drain *bool `json:"drain"`
+	}
+	if err := decodeJSON(r, &body); err != nil {
+		writeError(w, http.StatusBadRequest, "invalid body")
+		return
+	}
+	if body.Drain == nil {
+		writeError(w, http.StatusBadRequest, "drain required")
+		return
+	}
+	hx.d.SetDraining(host, *body.Drain)
+	writeJSON(w, http.StatusOK, map[string]bool{"ok": true})
+}
+
+// usageGet handles GET /_crossbar/usage: usage rows as JSON, or a fixed-width
+// table when Accept is text/plain.
+func (hx *handler) usageGet(w http.ResponseWriter, r *http.Request) {
+	if r.Method != http.MethodGet {
+		wrongMethod(w, "GET")
+		return
+	}
+	q := r.URL.Query()
+	var byv store.By
+	switch q.Get("by") {
+	case "", "route":
+		byv = store.ByRoute
+	case "model":
+		byv = store.ByModel
+	case "host":
+		byv = store.ByHost
+	default:
+		writeError(w, http.StatusBadRequest, "invalid by")
+		return
+	}
+	since, err := parseSince(q.Get("since"))
+	if err != nil {
+		writeError(w, http.StatusBadRequest, "invalid since")
+		return
+	}
+	rows, err := hx.st.Usage(since, byv)
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, "usage: "+err.Error())
+		return
+	}
+	if r.Header.Get("Accept") == "text/plain" {
+		writeUsageTable(w, rows)
+		return
+	}
+	writeJSON(w, http.StatusOK, rows)
+}
+
+// parseSince resolves the since query value: absent means all time, otherwise
+// an RFC 3339 instant or a duration (which may end in "d" for days) meaning
+// now - d.
+func parseSince(s string) (time.Time, error) {
+	if s == "" {
+		return time.Time{}, nil
+	}
+	if t, err := time.Parse(time.RFC3339, s); err == nil {
+		return t.UTC(), nil
+	}
+	d, err := parseWindow(s)
+	if err != nil {
+		return time.Time{}, err
+	}
+	return time.Now().Add(-d), nil
+}
+
+// parseWindow parses a duration, accepting a trailing "d" for whole days.
+func parseWindow(s string) (time.Duration, error) {
+	if n, ok := splitDays(s); ok {
+		return time.Duration(n) * 24 * time.Hour, nil
+	}
+	return time.ParseDuration(s)
+}
+
+// splitDays reports whether s is an integer number of days ("Nd").
+func splitDays(s string) (int, bool) {
+	if len(s) < 2 || s[len(s)-1] != 'd' {
+		return 0, false
+	}
+	n, err := strconv.Atoi(s[:len(s)-1])
+	if err != nil || n < 0 {
+		return 0, false
+	}
+	return n, true
+}
+
+// writeUsageTable renders the rows as a fixed-width table with a header line,
+// one row per entry, no trailing spaces.
+func writeUsageTable(w http.ResponseWriter, rows []store.UsageRow) {
+	headers := []string{"key", "requests", "errors", "busy_ms", "queued_ms", "prompt", "cached", "completion", "cache_hit"}
+	lines := make([][]string, 0, len(rows)+1)
+	lines = append(lines, headers)
+	for _, u := range rows {
+		lines = append(lines, []string{
+			u.Key,
+			strconv.FormatInt(u.Requests, 10),
+			strconv.FormatInt(u.Errors, 10),
+			strconv.FormatInt(u.BusyMs, 10),
+			strconv.FormatInt(u.QueuedMs, 10),
+			strconv.FormatInt(u.PromptTokens, 10),
+			strconv.FormatInt(u.CachedTokens, 10),
+			strconv.FormatInt(u.CompletionTokens, 10),
+			strconv.FormatFloat(u.CacheHitRatio(), 'f', 2, 64),
+		})
+	}
+	widths := columnWidths(lines)
+
+	var b strings.Builder
+	for _, line := range lines {
+		for i, f := range line {
+			if i < len(line)-1 {
+				b.WriteString(fmt.Sprintf("%-*s ", widths[i], f))
+			} else {
+				b.WriteString(f)
+			}
+		}
+		b.WriteByte('\n')
+	}
+	w.Header().Set("Content-Type", "text/plain; charset=utf-8")
+	w.WriteHeader(http.StatusOK)
+	_, _ = w.Write([]byte(b.String()))
+}
+
+// columnWidths returns the widest rendered field in each column.
+func columnWidths(lines [][]string) []int {
+	widths := make([]int, len(lines[0]))
+	for _, line := range lines {
+		for i, f := range line {
+			if len(f) > widths[i] {
+				widths[i] = len(f)
+			}
+		}
+	}
+	return widths
+}
+
+// metricsGet handles GET /_crossbar/metrics, emitting the Prometheus text
+// exposition format computed on request.
+func (hx *handler) metricsGet(w http.ResponseWriter, r *http.Request) {
+	if r.Method != http.MethodGet {
+		wrongMethod(w, "GET")
+		return
+	}
+	counts, err := hx.st.StatusCounts(time.Time{})
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, "metrics: "+err.Error())
+		return
+	}
+	usage, err := hx.st.Usage(time.Time{}, store.ByRoute)
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, "metrics: "+err.Error())
+		return
+	}
+
+	var reqSamples []string
+	for _, c := range counts {
+		reqSamples = append(reqSamples, fmt.Sprintf(
+			"crossbar_requests_total{route=\"%s\",host=\"%s\",status=\"%s\"} %d",
+			esc(c.Route), esc(c.Host), esc(strconv.Itoa(c.Status)), c.Count))
+	}
+
+	var prompt, cached, queue []string
+	for _, u := range usage {
+		prompt = append(prompt, fmt.Sprintf("crossbar_prompt_tokens_total{route=\"%s\"} %d", esc(u.Key), u.PromptTokens))
+		cached = append(cached, fmt.Sprintf("crossbar_cached_tokens_total{route=\"%s\"} %d", esc(u.Key), u.CachedTokens))
+		queue = append(queue, fmt.Sprintf("crossbar_queue_wait_ms_total{route=\"%s\"} %d", esc(u.Key), u.QueuedMs))
+	}
+
+	all := hx.h.All()
+	names := make([]string, 0, len(all))
+	for name := range all {
+		names = append(names, name)
+	}
+	sort.Strings(names)
+
+	var healthy, free, inflight, queued []string
+	for _, name := range names {
+		s := all[name]
+		healthy = append(healthy, fmt.Sprintf("crossbar_host_healthy{host=\"%s\"} %d", esc(name), btoi(s.Healthy)))
+		free = append(free, fmt.Sprintf("crossbar_host_free_slots{host=\"%s\"} %d", esc(name), hx.lim.FreeSlots(name)))
+		fi, q := 0, 0
+		for _, m := range configuredModels(hx.cfg, name) {
+			fi += hx.lim.InFlight(name, m)
+			q += hx.lim.Queued(name, m)
+		}
+		inflight = append(inflight, fmt.Sprintf("crossbar_host_in_flight{host=\"%s\"} %d", esc(name), fi))
+		queued = append(queued, fmt.Sprintf("crossbar_host_queued{host=\"%s\"} %d", esc(name), q))
+	}
+
+	var b strings.Builder
+	appendFamily(&b, "crossbar_requests_total", "counter", reqSamples)
+	appendFamily(&b, "crossbar_prompt_tokens_total", "counter", prompt)
+	appendFamily(&b, "crossbar_cached_tokens_total", "counter", cached)
+	appendFamily(&b, "crossbar_queue_wait_ms_total", "counter", queue)
+	appendFamily(&b, "crossbar_host_healthy", "gauge", healthy)
+	appendFamily(&b, "crossbar_host_free_slots", "gauge", free)
+	appendFamily(&b, "crossbar_host_in_flight", "gauge", inflight)
+	appendFamily(&b, "crossbar_host_queued", "gauge", queued)
+
+	w.Header().Set("Content-Type", "text/plain; version=0.0.4")
+	w.WriteHeader(http.StatusOK)
+	_, _ = w.Write([]byte(b.String()))
+}
+
+// appendFamily writes a metric family: its TYPE line followed by the sorted
+// sample lines.
+func appendFamily(b *strings.Builder, name, typ string, samples []string) {
+	fmt.Fprintf(b, "# TYPE %s %s\n", name, typ)
+	sort.Strings(samples)
+	for _, s := range samples {
+		b.WriteString(s)
+		b.WriteByte('\n')
+	}
+}
+
+// esc escapes a label value for the Prometheus text format.
+func esc(s string) string {
+	s = strings.ReplaceAll(s, `\`, `\\`)
+	s = strings.ReplaceAll(s, `"`, `\"`)
+	return s
+}
+
+// btoi converts a bool to 0/1 for a gauge.
+func btoi(v bool) int {
+	if v {
+		return 1
+	}
+	return 0
+}
+
+// containsHost reports whether hosts contains h.
+func containsHost(hosts []string, h string) bool {
+	for _, x := range hosts {
+		if x == h {
+			return true
+		}
+	}
+	return false
+}
+
+// decodeJSON decodes a bounded JSON body.
+func decodeJSON(r *http.Request, v any) error {
+	dec := json.NewDecoder(io.LimitReader(r.Body, 4096))
+	return dec.Decode(v)
+}
+
+func writeJSON(w http.ResponseWriter, status int, v any) {
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(status)
+	_ = json.NewEncoder(w).Encode(v)
+}
+
+func writeError(w http.ResponseWriter, status int, msg string) {
+	writeJSON(w, status, map[string]string{"error": msg})
+}
+
+// wrongMethod answers 405 with the allowed method in the Allow header.
+func wrongMethod(w http.ResponseWriter, allow string) {
+	w.Header().Set("Allow", allow)
+	writeJSON(w, http.StatusMethodNotAllowed, map[string]string{"error": "method not allowed"})
+}
+
+func (hx *handler) unknown(w http.ResponseWriter, r *http.Request) {
+	writeJSON(w, http.StatusNotFound, map[string]string{"error": "not found"})
+}

internal/admin/admin_test.go

@@ -1,9 +1,12 @@
 package admin_test
 
+// v1 admin: read the tables, pin/release a route, drain a host, usage rollups, metrics.
+
 import (
 	"encoding/json"
 	"net/http"
 	"net/http/httptest"
+	"path/filepath"
 	"strings"
 	"testing"
 	"time"
@@ -11,21 +14,45 @@ import (
 	"git.wntrmute.dev/kyle/crossbar/internal/admin"
 	"git.wntrmute.dev/kyle/crossbar/internal/config"
 	"git.wntrmute.dev/kyle/crossbar/internal/health"
+	"git.wntrmute.dev/kyle/crossbar/internal/lease"
+	"git.wntrmute.dev/kyle/crossbar/internal/limiter"
+	"git.wntrmute.dev/kyle/crossbar/internal/store"
 )
 
-type fakeHosts map[string]health.Status
+type fakeHosts struct {
+	st       map[string]health.Status
+	draining map[string]bool
+}
 
-func (f fakeHosts) All() map[string]health.Status { return f }
+func (f *fakeHosts) All() map[string]health.Status { return f.st }
+func (f *fakeHosts) Healthy(n string) bool         { return f.st[n].Healthy }
+func (f *fakeHosts) Draining(n string) bool        { return f.draining[n] }
+func (f *fakeHosts) SetDraining(n string, on bool) { f.draining[n] = on }
+func (f *fakeHosts) Choose(c []string, model string) (string, bool) {
+	for _, h := range c {
+		if f.st[h].Healthy && !f.draining[h] {
+			return h, true
+		}
+	}
+	return "", false
+}
 
-func testConfig(t *testing.T) *config.Config {
-	c, err := config.Parse(strings.NewReader(`
+type rig struct {
+	h      http.Handler
+	store  *store.Store
+	leases *lease.Table
+	hosts  *fakeHosts
+}
+
+func newRig(t *testing.T) *rig {
+	cfg, err := config.Parse(strings.NewReader(`
 listen = "127.0.0.1:1"
 [hosts.alpha]
 base_url = "http://alpha:1"
-models = { "m" = { } }
+models = { "m" = { parallel = 2 } }
 [hosts.beta]
 base_url = "http://beta:1"
-models = { "m" = { } }
+models = { "m" = { parallel = 4 } }
 [routes.r]
 hosts = ["alpha", "beta"]
 default_model = "m"
@@ -33,67 +60,234 @@ default_model = "m"
 	if err != nil {
 		t.Fatal(err)
 	}
-	return c
+	st, err := store.Open(filepath.Join(t.TempDir(), "x.db"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() { _ = st.Close() })
+	hosts := &fakeHosts{
+		st: map[string]health.Status{
+			"alpha": {Healthy: true, Loaded: []string{"m"}, LastOK: time.Date(2026, 9, 25, 8, 0, 0, 0, time.UTC)},
+			"beta":  {Healthy: false, LastErr: "HTTP 503"},
+		},
+		draining: map[string]bool{},
+	}
+	lt, err := lease.New(st, hosts, hosts, 30*time.Minute)
+	if err != nil {
+		t.Fatal(err)
+	}
+	lim := limiter.New()
+	lim.Configure("alpha", "m", 2, 8)
+	lim.Configure("beta", "m", 4, 8)
+	return &rig{h: admin.Handler(cfg, hosts, lt, lim, st, hosts), store: st, leases: lt, hosts: hosts}
 }
 
-func TestHosts(t *testing.T) {
-	when := time.Date(2026, 9, 25, 8, 0, 0, 0, time.UTC)
-	h := admin.Handler(testConfig(t), fakeHosts{
-		"alpha": {Healthy: true, Loaded: []string{"m"}, LastOK: when},
-		"beta":  {Healthy: false, LastErr: "HTTP 503"},
-	})
+func (r *rig) do(t *testing.T, method, path, body string, hdr ...string) *httptest.ResponseRecorder {
+	req := httptest.NewRequest(method, path, strings.NewReader(body))
+	if body != "" {
+		req.Header.Set("Content-Type", "application/json")
+	}
+	for i := 0; i+1 < len(hdr); i += 2 {
+		req.Header.Set(hdr[i], hdr[i+1])
+	}
 	rec := httptest.NewRecorder()
-	h.ServeHTTP(rec, httptest.NewRequest(http.MethodGet, "/_crossbar/hosts", nil))
-	if rec.Code != 200 || !strings.HasPrefix(rec.Header().Get("Content-Type"), "application/json") {
-		t.Fatalf("status %d, content-type %q", rec.Code, rec.Header().Get("Content-Type"))
+	r.h.ServeHTTP(rec, req)
+	return rec
+}
+
+func TestHostsShowsSlotsAndDrain(t *testing.T) {
+	r := newRig(t)
+	rec := r.do(t, "GET", "/_crossbar/hosts", "")
+	if rec.Code != 200 {
+		t.Fatalf("%d %s", rec.Code, rec.Body.String())
 	}
 	var out map[string]admin.HostView
 	if err := json.Unmarshal(rec.Body.Bytes(), &out); err != nil {
 		t.Fatal(err)
 	}
-	if a := out["alpha"]; !a.Healthy || len(a.Loaded) != 1 || a.LastOK != "2026-09-25T08:00:00Z" || a.LastErr != "" {
+	a := out["alpha"]
+	if !a.Healthy || a.FreeSlots != 2 || a.InFlight != 0 || a.Queued != 0 || a.Draining || a.LastOK != "2026-09-25T08:00:00Z" {
 		t.Errorf("alpha = %+v", a)
 	}
-	if b := out["beta"]; b.Healthy || b.LastOK != "" || b.LastErr != "HTTP 503" || b.Loaded == nil {
+	if b := out["beta"]; b.Healthy || b.LastErr != "HTTP 503" || b.FreeSlots != 4 || b.Loaded == nil {
 		t.Errorf("beta = %+v (loaded must be [] not null)", b)
 	}
-	if !strings.Contains(rec.Body.String(), `"loaded":[]`) {
-		t.Errorf("beta.loaded must encode as []: %s", rec.Body.String())
-	}
 }
 
-func TestRoutes(t *testing.T) {
-	h := admin.Handler(testConfig(t), fakeHosts{})
-	rec := httptest.NewRecorder()
-	h.ServeHTTP(rec, httptest.NewRequest(http.MethodGet, "/_crossbar/routes", nil))
+func TestRoutesShowsLeases(t *testing.T) {
+	r := newRig(t)
+	now := time.Date(2026, 9, 25, 9, 0, 0, 0, time.UTC)
+	if _, _, err := r.leases.Acquire(lease.Key{Route: "r", FP: "abc", Model: "m"}, []string{"alpha", "beta"}, now); err != nil {
+		t.Fatal(err)
+	}
+	rec := r.do(t, "GET", "/_crossbar/routes", "")
 	var out map[string]admin.RouteView
 	if err := json.Unmarshal(rec.Body.Bytes(), &out); err != nil {
 		t.Fatalf("%v: %s", err, rec.Body.String())
 	}
-	r := out["r"]
-	if len(r.Hosts) != 2 || r.Hosts[0] != "alpha" || r.DefaultModel != "m" {
-		t.Errorf("routes = %+v", out)
+	rv := out["r"]
+	if len(rv.Hosts) != 2 || rv.DefaultModel != "m" || rv.Pinned != "" {
+		t.Errorf("route view = %+v", rv)
+	}
+	if len(rv.Leases) != 1 || rv.Leases[0].FP != "abc" || rv.Leases[0].Host != "alpha" || rv.Leases[0].State != "active" || rv.Leases[0].LastUsed != "2026-09-25T09:00:00Z" {
+		t.Errorf("leases = %+v", rv.Leases)
+	}
+}
+
+func TestPinReleaseDrain(t *testing.T) {
+	r := newRig(t)
+	rec := r.do(t, "POST", "/_crossbar/routes/r", `{"host":"beta","pin":true}`)
+	if rec.Code != 200 {
+		t.Fatalf("pin: %d %s", rec.Code, rec.Body.String())
+	}
+	if h, _, err := r.leases.Acquire(lease.Key{Route: "r", FP: "x", Model: "m"}, []string{"alpha", "beta"}, time.Now()); err == nil || h != "" {
+		// beta is unhealthy in the rig: a pin to a down host is honoured, not silently moved
+		t.Errorf("acquire on a route pinned to a down host: %q %v, want ErrPinnedDown", h, err)
+	}
+	rec = r.do(t, "GET", "/_crossbar/routes", "")
+	var out map[string]admin.RouteView
+	_ = json.Unmarshal(rec.Body.Bytes(), &out)
+	if out["r"].Pinned != "beta" {
+		t.Errorf("Pinned = %q after pin", out["r"].Pinned)
+	}
+	rec = r.do(t, "POST", "/_crossbar/routes/r", `{"release":true}`)
+	if rec.Code != 200 {
+		t.Fatalf("release: %d %s", rec.Code, rec.Body.String())
+	}
+	if h, _, err := r.leases.Acquire(lease.Key{Route: "r", FP: "x", Model: "m"}, []string{"alpha", "beta"}, time.Now()); err != nil || h != "alpha" {
+		t.Errorf("after release: %q %v, want alpha (the only healthy host)", h, err)
+	}
+	for _, tc := range []struct {
+		body string
+		want int
+	}{
+		{`{"host":"nobody","pin":true}`, 404},
+		{`{"pin":true}`, 400},
+		{`not json`, 400},
+		{`{"release":true,"pin":true,"host":"alpha"}`, 400},
+	} {
+		if rec := r.do(t, "POST", "/_crossbar/routes/r", tc.body); rec.Code != tc.want {
+			t.Errorf("POST %s: %d, want %d (%s)", tc.body, rec.Code, tc.want, rec.Body.String())
+		}
+	}
+	if rec := r.do(t, "POST", "/_crossbar/routes/nope", `{"release":true}`); rec.Code != 404 {
+		t.Errorf("unknown route: %d", rec.Code)
+	}
+
+	rec = r.do(t, "POST", "/_crossbar/hosts/alpha", `{"drain":true}`)
+	if rec.Code != 200 || !r.hosts.Draining("alpha") {
+		t.Fatalf("drain: %d %s draining=%v", rec.Code, rec.Body.String(), r.hosts.Draining("alpha"))
+	}
+	rec = r.do(t, "GET", "/_crossbar/hosts", "")
+	var hv map[string]admin.HostView
+	_ = json.Unmarshal(rec.Body.Bytes(), &hv)
+	if !hv["alpha"].Draining {
+		t.Errorf("hosts view must show draining")
+	}
+	if rec := r.do(t, "POST", "/_crossbar/hosts/alpha", `{"drain":false}`); rec.Code != 200 || r.hosts.Draining("alpha") {
+		t.Errorf("undrain: %d draining=%v", rec.Code, r.hosts.Draining("alpha"))
+	}
+	if rec := r.do(t, "POST", "/_crossbar/hosts/nobody", `{"drain":true}`); rec.Code != 404 {
+		t.Errorf("unknown host: %d", rec.Code)
+	}
+}
+
+func seedUsage(t *testing.T, st *store.Store) {
+	t0 := time.Now().UTC().Add(-time.Hour)
+	for i, r := range []store.Request{
+		{Route: "r", FP: "a", Model: "m", Host: "alpha", Status: 200, TotalMs: 1000, PromptTokens: 100, CachedTokens: 80, CompletionTokens: 10},
+		{Route: "r", FP: "a", Model: "m", Host: "alpha", Status: 200, TotalMs: 500, QueuedMs: 30, PromptTokens: 100, CachedTokens: 100, CompletionTokens: 5},
+		{Route: "r2", FP: "b", Model: "m", Host: "beta", Status: 503, TotalMs: 1, Err: "queue full"},
+	} {
+		r.Started = t0.Add(time.Duration(i) * time.Minute)
+		if err := st.RecordRequest(r); err != nil {
+			t.Fatal(err)
+		}
+	}
+}
+
+func TestUsageJSONAndText(t *testing.T) {
+	r := newRig(t)
+	seedUsage(t, r.store)
+	rec := r.do(t, "GET", "/_crossbar/usage?by=route", "")
+	if rec.Code != 200 || !strings.HasPrefix(rec.Header().Get("Content-Type"), "application/json") {
+		t.Fatalf("%d %q", rec.Code, rec.Header().Get("Content-Type"))
+	}
+	var rows []store.UsageRow
+	if err := json.Unmarshal(rec.Body.Bytes(), &rows); err != nil {
+		t.Fatalf("%v: %s", err, rec.Body.String())
+	}
+	if len(rows) != 2 {
+		t.Fatalf("rows = %+v", rows)
+	}
+	for _, row := range rows {
+		if row.Key == "r" && (row.Requests != 2 || row.CachedTokens != 180 || row.QueuedMs != 30) {
+			t.Errorf("r = %+v", row)
+		}
+		if row.Key == "r2" && (row.Requests != 1 || row.Errors != 1) {
+			t.Errorf("r2 = %+v", row)
+		}
+	}
+	rec = r.do(t, "GET", "/_crossbar/usage?by=host&since=24h", "", "Accept", "text/plain")
+	if rec.Code != 200 || !strings.HasPrefix(rec.Header().Get("Content-Type"), "text/plain") {
+		t.Fatalf("text: %d %q", rec.Code, rec.Header().Get("Content-Type"))
+	}
+	body := rec.Body.String()
+	if !strings.Contains(body, "alpha") || !strings.Contains(body, "beta") || !strings.Contains(strings.ToLower(body), "cache") {
+		t.Errorf("text table = %q", body)
+	}
+	if rec := r.do(t, "GET", "/_crossbar/usage?by=colour", ""); rec.Code != 400 {
+		t.Errorf("bad by: %d", rec.Code)
+	}
+	if rec := r.do(t, "GET", "/_crossbar/usage?since=yesterday", ""); rec.Code != 400 {
+		t.Errorf("bad since: %d", rec.Code)
+	}
+	rec = r.do(t, "GET", "/_crossbar/usage?since=2026-09-25T00:00:00Z&by=model", "")
+	if rec.Code != 200 {
+		t.Errorf("RFC3339 since: %d %s", rec.Code, rec.Body.String())
+	}
+}
+
+func TestMetrics(t *testing.T) {
+	r := newRig(t)
+	seedUsage(t, r.store)
+	rec := r.do(t, "GET", "/_crossbar/metrics", "")
+	if rec.Code != 200 || !strings.HasPrefix(rec.Header().Get("Content-Type"), "text/plain") {
+		t.Fatalf("%d %q", rec.Code, rec.Header().Get("Content-Type"))
+	}
+	body := rec.Body.String()
+	for _, want := range []string{
+		`# TYPE crossbar_requests_total counter`,
+		`crossbar_requests_total{route="r",host="alpha",status="200"} 2`,
+		`crossbar_requests_total{route="r2",host="beta",status="503"} 1`,
+		`crossbar_host_healthy{host="alpha"} 1`,
+		`crossbar_host_healthy{host="beta"} 0`,
+		`crossbar_host_free_slots{host="alpha"} 2`,
+		`crossbar_prompt_tokens_total{route="r"} 200`,
+		`crossbar_cached_tokens_total{route="r"} 180`,
+		`crossbar_queue_wait_ms_total{route="r"} 30`,
+	} {
+		if !strings.Contains(body, want) {
+			t.Errorf("metrics missing %q\n%s", want, body)
+		}
 	}
 }
 
 func TestMethodsAndUnknown(t *testing.T) {
-	h := admin.Handler(testConfig(t), fakeHosts{})
+	r := newRig(t)
 	for _, tc := range []struct {
 		method, path string
 		want         int
 	}{
 		{http.MethodPost, "/_crossbar/hosts", 405},
 		{http.MethodDelete, "/_crossbar/routes", 405},
+		{http.MethodGet, "/_crossbar/routes/r", 405},
 		{http.MethodGet, "/_crossbar/nope", 404},
-		{http.MethodGet, "/_crossbar/", 404},
+		{http.MethodPut, "/_crossbar/usage", 405},
 	} {
-		rec := httptest.NewRecorder()
-		h.ServeHTTP(rec, httptest.NewRequest(tc.method, tc.path, nil))
-		if rec.Code != tc.want {
-			t.Errorf("%s %s = %d, want %d", tc.method, tc.path, rec.Code, tc.want)
-		}
-		if !strings.HasPrefix(rec.Header().Get("Content-Type"), "application/json") {
-			t.Errorf("%s %s: errors are JSON too", tc.method, tc.path)
+		rec := r.do(t, tc.method, tc.path, "")
+		if rec.Code != tc.want || !strings.HasPrefix(rec.Header().Get("Content-Type"), "application/json") {
+			t.Errorf("%s %s = %d %q, want %d JSON", tc.method, tc.path, rec.Code, rec.Header().Get("Content-Type"), tc.want)
 		}
 	}
 }

internal/lease/lease.go

@@ -194,6 +194,21 @@ func (t *Table) Acquire(k Key, candidates []string, now time.Time) (host string,
 	return host, false, nil
 }
 
+// Candidates records hosts as seen for route (idempotent), so Pin can accept a host the route
+// is configured for before any request has used it. cmd/crossbar calls it for every route at
+// start; the admin handler calls it before Pin.
+func (t *Table) Candidates(route string, hosts []string) {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+
+	if t.seen[route] == nil {
+		t.seen[route] = make(map[string]bool)
+	}
+	for _, h := range hosts {
+		t.seen[route][h] = true
+	}
+}
+
 // save writes a lease through, failing the call on a persister error.
 func (t *Table) save(l *Lease) error {
 	if err := t.p.SaveLease(l.store()); err != nil {

internal/store/schema.go

@@ -141,6 +141,18 @@ func scanUsage(rows *sql.Rows) ([]UsageRow, error) {
 	return out, rows.Err()
 }
 
+func scanStatusCounts(rows *sql.Rows) ([]StatusCount, error) {
+	var out []StatusCount
+	for rows.Next() {
+		var c StatusCount
+		if err := rows.Scan(&c.Route, &c.Host, &c.Status, &c.Count); err != nil {
+			return nil, wrap(err)
+		}
+		out = append(out, c)
+	}
+	return out, rows.Err()
+}
+
 func scanEvents(rows *sql.Rows) ([]LeaseEvent, error) {
 	var out []LeaseEvent
 	for rows.Next() {

internal/store/store.go

@@ -95,6 +95,14 @@ func (u UsageRow) CacheHitRatio() float64 {
 	return float64(u.CachedTokens) / float64(u.PromptTokens)
 }
 
+// StatusCount is one (route, host, status) group of live requests, for the metrics endpoint, which
+// needs the per-status breakdown Usage cannot give.
+type StatusCount struct {
+	Route, Host string
+	Status      int
+	Count       int64
+}
+
 // Store holds the SQLite connection to crossbar's durable state.
 type Store struct {
 	db *sql.DB
@@ -232,6 +240,23 @@ func (s *Store) Usage(since time.Time, by By) ([]UsageRow, error) {
 	return scanUsage(rows)
 }
 
+// StatusCounts groups the live requests at or after since by (route, host, status). It reads the
+// requests table only; the rolled-up requests_daily rows are not in it (Prune has moved them out of
+// requests), so counts cover only traffic still in the live table.
+func (s *Store) StatusCounts(since time.Time) ([]StatusCount, error) {
+	sinceMs := since.UnixMilli()
+	rows, err := s.db.Query(`
+		SELECT route, host, status, COUNT(*)
+		FROM requests WHERE started >= ?
+		GROUP BY route, host, status
+		ORDER BY route, host, status`, sinceMs)
+	if err != nil {
+		return nil, wrap(err)
+	}
+	defer rows.Close()
+	return scanStatusCounts(rows)
+}
+
 // Events returns lease events at or after since, oldest first, at most limit.
 func (s *Store) Events(since time.Time, limit int) ([]LeaseEvent, error) {
 	rows, err := s.db.Query(`