LB buckets column + health cascade; VPP dump fix; maglevc strictness

SPA (cmd/frontend/web):
- New "lb buckets" column backed by a 1s-debounced GetVPPLBState
  fetch loop with leading+trailing edge coalesce.
- Per-frontend health icon (✅/⚠️/❗/‼️/❓) in the Zippy header,
  gated by a settling flag that suppresses ‼️ until the next lb-state
  reconciliation after a backend transition or weight change.
- In-place leaf merge on lb-state so stable bucket values (e.g. "0")
  don't retrigger the Flash animation on every refresh.
- Zippy cards remember open state in a cookie, default closed on
  fresh load; fixed-width frontend-title-name + reserved icon slot
  so headers line up across all cards.
- Clock-drift watchdog in sse.ts that forces a fresh EventSource on
  laptop-wake so the broker emits a resync instead of hanging on a
  dead half-open socket.

Frontend service (cmd/frontend):
- maglevClient.lbStateLoop, trigger on backend transitions +
  vpp-connect, best-effort fetch on refreshAll.
- Admin handlers explicitly wake the lb-state loop after lifecycle
  ops and set-weight (the latter emits no transition event on the
  maglevd side, so the WatchEvents path wouldn't have caught it).
- /favicon.ico served from embedded web/public IPng logo.

VPP integration:
- internal/vpp/lbstate.go: dumpASesForVIP drops Pfx from the dump
  request (setting it silently wipes IPv4 replies in the LB plugin)
  and filters results by prefix on the response side instead, which
  also demuxes multi-VIP-on-same-port cases correctly.

maglevc:
- Walk now returns the unconsumed token tail; dispatch and the
  question listener reject unknown commands with a targeted error
  instead of dumping the full command tree prefixed with garbage.
- On '?', echo the current line (including the '?') before the help
  list so the output reads like birdc.

Checker / prober:
- internal/checker: ±10% jitter on NextInterval so probes across
  restart don't all fire on the same tick.
- internal/prober: HTTP User-Agent now carries the build version
  and project URL.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

cmd/maglevc/complete.go

@@ -88,9 +88,25 @@ func (ql *questionListener) OnChange(line []rune, pos int, key rune) (newLine []
 	// Walk the confirmed prefix to the current node, then try to advance one
 	// more step using the partial token (via prefix-match or slot fallback).
 	// This mirrors birdc: "sh?" expands "sh" to "show" and shows show's subtree.
-	node, _ := Walk(ql.root, prefix)
+	node, _, remaining := Walk(ql.root, prefix)
 	displayPrefix := strings.Join(prefix, " ")
-	if partial != "" {
+	var unknownMsg string
+	if len(remaining) > 0 {
+		// One of the confirmed prefix tokens was unknown. Show an
+		// "unknown" banner, then list what's available at the deepest
+		// node we *did* reach so the operator can see what they could
+		// have typed instead. The partial at the cursor is irrelevant
+		// once the left context is already broken.
+		consumed := prefix[:len(prefix)-len(remaining)]
+		bad := remaining[0]
+		if len(consumed) == 0 {
+			unknownMsg = fmt.Sprintf("unknown command: %s", bad)
+		} else {
+			unknownMsg = fmt.Sprintf("unknown subcommand %q after %q", bad, strings.Join(consumed, " "))
+		}
+		displayPrefix = strings.Join(consumed, " ")
+		partial = ""
+	} else if partial != "" {
 		if next := matchFixedChild(node.Children, partial); next != nil {
 			// Partial uniquely matched a fixed child — descend into it.
 			node = next
@@ -127,7 +143,19 @@ func (ql *questionListener) OnChange(line []rune, pos int, key rune) (newLine []
 	}
 
 	// Emit output. Raw terminal mode requires \r\n.
-	fmt.Fprintf(ql.rl.Stderr(), "\r\n")
+	//
+	// readline's wrapWriter wraps every Write in a clean-write-print
+	// cycle: it erases the current input line, runs our closure, and
+	// redraws the prompt+buffer afterwards. That means starting the
+	// output with a bare "\r\n" leaves the original row blank, so the
+	// operator loses sight of what they typed. Instead we echo the
+	// full "maglev> show vpp lb ?" ourselves as the first write —
+	// that lands on the just-cleaned row, birdc-style, and the
+	// subsequent Fprintfs each redraw a fresh prompt below the help.
+	fmt.Fprintf(ql.rl.Stderr(), "%s%s\r\n", ql.rl.Config.Prompt, string(line))
+	if unknownMsg != "" {
+		fmt.Fprintf(ql.rl.Stderr(), "  %s\r\n", unknownMsg)
+	}
 	if len(lines) == 0 {
 		fmt.Fprintf(ql.rl.Stderr(), "  <no completions>\r\n")
 	} else {