feat: SPE amp ON/OFF buttons and Low/Mid/High power-level control (keystroke codes best-guess from APG, pending hw verification)

internal/spe/spe.go

@@ -30,9 +30,17 @@ import (
 )
 
 const (
-	cmdOperate byte = 0x0D // toggles STANDBY ↔ OPERATE
+	cmdOperate byte = 0x0D // toggles STANDBY ↔ OPERATE (confirmed on hw)
 	cmdStatus  byte = 0x90 // request the status string
 
+	// Best-guess keystroke codes reconstructed from the APG command table after
+	// correcting the PDF's note-wrap misalignment (anchored to the confirmed
+	// OPERATE=0x0D): OFF=0x0A, POWER=0x0B. The POWER key doubles as power-on (when
+	// the amp is off) and the output-level cycle L→M→H (when it's on) — same as the
+	// single physical POWER button. To be verified on hardware.
+	cmdOff   byte = 0x0A // OFF key — switch the amplifier off
+	cmdPower byte = 0x0B // POWER key — turn on / cycle output power level
+
 	syncHost = 0x55
 	syncAmp  = 0xAA
 
@@ -138,6 +146,34 @@ func (c *Client) Operate(on bool) error {
 // ToggleOperate flips STANDBY/OPERATE unconditionally.
 func (c *Client) ToggleOperate() error { return c.sendCmd(cmdOperate) }
 
+// PowerOn presses the POWER key (turns the amp on when it's off).
+func (c *Client) PowerOn() error { return c.sendCmd(cmdPower) }
+
+// PowerOff presses the OFF key (switches the amp off).
+func (c *Client) PowerOff() error { return c.sendCmd(cmdOff) }
+
+// SetPowerLevel cycles the output power level (L/M/H) to the requested one by
+// tapping the POWER key until the reported level matches, giving the amp time to
+// report each change. `level` is "L", "M" or "H" (case-insensitive).
+func (c *Client) SetPowerLevel(level string) error {
+	want := strings.ToUpper(strings.TrimSpace(level))
+	if want == "" {
+		return nil
+	}
+	// At most 3 taps to walk the 3-way cycle back around to the target.
+	for i := 0; i < 3; i++ {
+		cur := strings.ToUpper(strings.TrimSpace(c.GetStatus().PowerLevel))
+		if cur == want {
+			return nil
+		}
+		if err := c.sendCmd(cmdPower); err != nil {
+			return err
+		}
+		time.Sleep(1 * time.Second) // let the amp apply it and the poll refresh status
+	}
+	return nil
+}
+
 func (c *Client) pollLoop() {
 	t := time.NewTicker(pollEvery)
 	defer t.Stop()