fix(winkeyer): wake a keyer that will not open, instead of giving up

An operator with a WinKey2 USB had to run K1EL's WKdemo and close it again
before OpsLog could talk to the keyer at all. That workaround is the diagnosis:
closing another program does something to the keyer that opening the port does
not, and whatever state it was stuck in survives a failed connect.

So the second handshake attempt now does what closing WKdemo does, in an order
that survives each step failing:

  - Host Close, in case the keyer is still in host mode from a session that
    ended without one — a crash, a cable pulled, a machine switched off. It has
    been waiting ever since for a host that went away.
  - Admin Reset, which returns it to its power-up state. A parser stuck
    part-way through a command whose parameters will never arrive cannot be
    talked out of it any other way.
  - A DTR pulse, which is what closing a program actually does to the line. On
    a WKUSB and on every Arduino-based clone, DTR runs to the processor's reset:
    it is a power-on reset in all but name.

RTS is left alone throughout — on a serial WinKeyer it is the negative rail the
RS-232 swing comes from, and driving it starves the chip.

A keyer that answers the echo and then refuses to open is the same leftover
session seen from the other side, so that case sends Host Close and asks again
rather than reporting a keyer that demonstrably just spoke to us as absent.

And a port already known to need the slow path gets the wake-up on the FIRST
attempt from then on: making the operator sit through a failure to earn it again
doubles the connect time for no new information.

The handshake bytes are already logged on every connect, so the next report of
this shape says where it stopped.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

internal/winkeyer/hostopen.go

@@ -32,7 +32,9 @@ import (
 const (
 	cmdNull     = 0x13
 	cmdAdmin    = 0x00
+	adminReset  = 0x01
 	adminOpen   = 0x02
+	adminClose  = 0x03
 	adminEcho   = 0x04
 	echoProbe   = 0x55 // K1EL's own choice; any byte works, this one is 0b01010101
 	bootDelay   = 400 * time.Millisecond
@@ -75,7 +77,11 @@ func hostOpen(p serial.Port, slowBoot bool) (ver int, needsSlowBoot bool, err er
 		if attempt > 1 || slowBoot {
 			wait = resetDelay
 		}
-		ver, err := hostOpenOnce(p, wait)
+		// A port already known to need the slow path gets the wake-up on the
+		// FIRST attempt too: it needed it last time, and making the operator
+		// wait through a failure to earn it again is a connect that takes twice
+		// as long for no new information.
+		ver, err := hostOpenOnce(p, wait, attempt > 1 || slowBoot)
 		if err == nil {
 			if attempt > 1 {
 				applog.Printf("winkeyer: answered on attempt %d — this keyer needs %s to boot (a K3NG or another Arduino keyer with auto-reset on); remembering that for this port", attempt, wait)
@@ -90,7 +96,10 @@ func hostOpen(p serial.Port, slowBoot bool) (ver int, needsSlowBoot bool, err er
 	return 0, false, lastErr
 }
 
-func hostOpenOnce(p serial.Port, boot time.Duration) (int, error) {
+func hostOpenOnce(p serial.Port, boot time.Duration, hard bool) (int, error) {
+	if hard {
+		recoverKeyer(p)
+	}
 	// The keyer may still be booting off the DTR line we just raised.
 	time.Sleep(boot)
 	drain(p)
@@ -131,11 +140,59 @@ func hostOpenOnce(p serial.Port, boot time.Duration) (int, error) {
 	ver, ok := readByte(p, openTimeout)
 	traceHandshake("RX", nil, ver, ok)
 	if !ok {
-		return 0, errors.New("host open: the keyer echoed but did not return its firmware version")
+		// It answered the echo, so there IS a keyer on this port — it simply
+		// will not open. A keyer already IN host mode does exactly that: a
+		// previous session that ended badly never sent Host Close, and it has
+		// been waiting ever since for a host that went away. Close it and ask
+		// again.
+		applog.Printf("winkeyer: echoed but did not open — closing a host session left over from last time, and asking again")
+		if _, err := p.Write([]byte{cmdAdmin, adminClose}); err != nil {
+			return 0, fmt.Errorf("host close: %w", err)
+		}
+		time.Sleep(250 * time.Millisecond)
+		drain(p)
+		traceHandshake("TX", open, 0, false)
+		if _, err := p.Write(open); err != nil {
+			return 0, fmt.Errorf("host open: %w", err)
+		}
+		ver, ok = readByte(p, openTimeout)
+		traceHandshake("RX", nil, ver, ok)
+		if !ok {
+			return 0, errors.New("host open: the keyer echoed but did not return its firmware version")
+		}
 	}
 	return int(ver), nil
 }
 
+// recoverKeyer does to the keyer what running K1EL's WKdemo and closing it
+// again does — which is the workaround an operator found for a WKUSB that
+// OpsLog could not open until they had.
+//
+// Three things, in an order that survives each of them failing:
+//
+//   - Host Close, in case the keyer is still in host mode from a session that
+//     ended without one: a crash, a cable pulled, a machine switched off.
+//   - Admin Reset, which returns it to its power-up state. A parser stuck
+//     part-way through a command whose parameters will never arrive cannot be
+//     talked out of it any other way.
+//   - A DTR pulse. That is what closing another program actually does to the
+//     line, and on the boxes that wire DTR to the processor's reset — a WKUSB,
+//     and every Arduino-based clone — it is a power-on reset in all but name.
+//
+// RTS is left alone throughout: on a serial WinKeyer it is the negative rail
+// the RS-232 swing comes from, and driving it starves the chip.
+func recoverKeyer(p serial.Port) {
+	applog.Printf("winkeyer: waking the keyer — host close, reset, then a DTR pulse")
+	_, _ = p.Write([]byte{cmdNull, cmdNull, cmdNull, cmdAdmin, adminClose})
+	time.Sleep(150 * time.Millisecond)
+	_, _ = p.Write([]byte{cmdAdmin, adminReset})
+	time.Sleep(150 * time.Millisecond)
+	_ = p.SetDTR(false)
+	time.Sleep(250 * time.Millisecond)
+	_ = p.SetDTR(true)
+	drain(p)
+}
+
 // traceHandshake puts the opening exchange in the log, ALWAYS — unlike the
 // running trace beside it, which is behind the diagnostic option.
 //