fix(web-ssh): send the physical key, and drop a protocol message nobody sends

Two things the key testing turned up.

Alt was wrong on macOS. Option+a arrives as the composed character "å", so
sending e.key put that in the shell instead of Meta-a. Both Alt and Ctrl now
take the letter from e.code (the physical key), falling back to e.key when a
browser does not report it; non-letters keep the plain ASCII mapping, which is
what makes Ctrl+[ an Escape.

The "bye" message was dead: the page never sends it, so the handler arm could
never run.

src/internal/panel/assets/term.js

@@ -605,11 +605,23 @@
       var ss3 = { 1: "P", 2: "Q", 3: "R", 4: "S" };
       send = ss3[f] ? "\x1bO" + ss3[f] : "\x1b[" + [15, 17, 18, 19, 20, 21, 23, 24][f - 5] + "~";
     } else if (e.ctrlKey && !e.altKey && e.key.length === 1) {
-      var c = e.key.toUpperCase().charCodeAt(0);
-      if (c >= 64 && c < 128) send = String.fromCharCode(c & 0x1f);
+      // The physical key is what a terminal wants: on a layout where Ctrl+A
+      // composes into something else, e.key is that something else.
+      var ck = /^Key([A-Z])$/.exec(e.code || "");
+      if (ck) send = String.fromCharCode(ck[1].charCodeAt(0) - 64);
       else if (e.key === " ") send = "\x00";
-    } else if (e.altKey && e.key.length === 1) {
-      send = "\x1b" + e.key;
+      else {
+        // Non-letters keep the plain ASCII mapping, which is what makes
+        // Ctrl+[ an Escape and Ctrl+6 Ctrl+^.
+        var cc = e.key.toUpperCase().charCodeAt(0);
+        if (cc >= 64 && cc < 128) send = String.fromCharCode(cc & 0x1f);
+      }
+    } else if (e.altKey && !e.metaKey) {
+      // Again the physical key: on macOS Option+a arrives as "å", so sending
+      // e.key would put that in the shell instead of Meta-a.
+      var ak = /^Key([A-Z])$/.exec(e.code || "");
+      if (ak) send = "\x1b" + ak[1].toLowerCase();
+      else if (e.key.length === 1) send = "\x1b" + e.key;
     } else if (!e.ctrlKey && !e.metaKey && e.key.length === 1) {
       send = e.key;
     }

src/internal/panel/terminal.go

@@ -58,7 +58,7 @@ var termJS []byte
 // termIn is a message from the browser. Terminal output travels the other way
 // as raw binary frames; only control messages are JSON.
 type termIn struct {
-	T     string `json:"t"` // hello | input | resize | takeover | cancel | bye
+	T     string `json:"t"` // hello | input | resize | takeover
 	Token string `json:"token,omitempty"`
 	Data  string `json:"data,omitempty"`
 	Cols  int    `json:"cols,omitempty"`
@@ -557,11 +557,6 @@ func (s *Server) serveTermClient(conn *websocket.Conn, sock *termSocket, sess *t
 				_ = s.db.AddAuditLog("000+"+user, "terminal.takeover")
 			}
 			s.notifyOthers(user)
-		case "bye":
-			// The window is going away for good: end the shell now rather than
-			// holding it for the grace period.
-			sess.close()
-			return
 		}
 	}
 }