fix markdown / text-editor jank

* only indicate file-history for markdown files since
   other files won't load into the editor which makes
   that entirely pointless; do file extension instead

* text-editor: in files containing one single line,
   ^C followed by ^V ^Z would accidentally a letter

and fix unhydrated extensions

copyparty/httpcli.py

@@ -152,6 +152,8 @@ RE_HSAFE = re.compile(r"[\x00-\x1f<>\"'&]")  # search always much faster
 RE_HOST = re.compile(r"[^][0-9a-zA-Z.:_-]")  # search faster <=17ch
 RE_MHOST = re.compile(r"^[][0-9a-zA-Z.:_-]+$")  # match faster >=18ch
 RE_K = re.compile(r"[^0-9a-zA-Z_-]")  # search faster <=17ch
+RE_HR = re.compile(r"[<>\"'&]")
+RE_MDV = re.compile(r"(.*)\.([0-9]+\.[0-9]{3})(\.[Mm][Dd])$")
 
 UPARAM_CC_OK = set("doc move tree".split())
 
@@ -5969,7 +5971,7 @@ class HttpCli(object):
         # [num-backups, most-recent, hist-path]
         hist: dict[str, tuple[int, float, str]] = {}
         histdir = os.path.join(fsroot, ".hist")
-        ptn = re.compile(r"(.*)\.([0-9]+\.[0-9]{3})(\.[^\.]+)$")
+        ptn = RE_MDV
         try:
             for hfn in bos.listdir(histdir):
                 m = ptn.match(hfn)
@@ -6002,6 +6004,7 @@ class HttpCli(object):
 
         dirs = []
         files = []
+        ptn_hr = RE_HR
         for fn in ls_names:
             base = ""
             href = fn
@@ -6056,11 +6059,13 @@ class HttpCli(object):
                 zd.second,
             )
 
-            try:
+            if is_dir:
-                ext = "---" if is_dir else fn.rsplit(".", 1)[1]
+                ext = "---"
+            elif "." in fn:
+                ext = ptn_hr.sub("@", fn.rsplit(".", 1)[1])
                 if len(ext) > 16:
                     ext = ext[:16]
-            except:
+            else:
                 ext = "%"
 
             if add_fk and not is_dir:

copyparty/web/md2.js

@@ -1078,26 +1078,28 @@ action_stack = (function () {
         var p1 = from.length,
             p2 = to.length;
 
-        while (p1-- > 0 && p2-- > 0)
+        while (p1 --> 0 && p2 --> 0)
             if (from[p1] != to[p2])
                 break;
 
-        if (car > ++p1) {
+        if (car > ++p1)
             car = p1;
-        }
 
         var txt = from.substring(car, p1)
         return {
             car: car,
-            cdr: ++p2,
+            cdr: p2 + (car && 1),
             txt: txt,
             cpos: cpos
         };
     }
 
     var undiff = function (from, change) {
+        var t1 = from.substring(0, change.car),
+            t2 = from.substring(change.cdr);
+
         return {
-            txt: from.substring(0, change.car) + change.txt + from.substring(change.cdr),
+            txt: t1 + change.txt + t2,
             cpos: change.cpos
         };
     }