fix(input): an unbound skill key is a no-op, not a thread-killing ValueError

Regression from the previous commit. Blanking vigor/holy_shield/cleansing
stopped the stray F4 presses, but exposed that paladin.cast_buffs sends the
holy_shield key with no check:

    keyboard.send(self._skill_hotkeys["holy_shield"])   # -> ValueError: Unknown key:

which killed the bot thread mid-run:

    Uncaught exception in thread Thread-8 (start)
    ...
    File "src/char/paladin/paladin.py", line 33, in cast_buffs
    ValueError: Unknown key:

There are 90+ `keyboard.send(self._skill_hotkeys[x])` call sites across the
paladin classes and almost none check first, so the guard belongs at the
boundary: an empty or None key logs at debug and returns. A genuinely unknown
key still raises — the guard is for unbound optional skills, not for typos.

cast_buffs additionally returns early when holy_shield is unbound: send() now
tolerates the empty key, but the right-click after it would still fire and cast
whatever sits on the right slot instead.

Co-Authored-By: Claude Opus 5 <[email protected]>

src/char/paladin/paladin.py

@@ -30,6 +30,11 @@ class Paladin(IChar):
             self._action_frame = 6
 
     def cast_buffs(self, casting_delay: float):
+        # Skip entirely when Holy Shield is unbound. keyboard.send() tolerates
+        # the empty key now, but the right-click after it would still fire and
+        # cast whatever happens to be on the right slot instead.
+        if not self._skill_hotkeys.get("holy_shield"):
+            return
         keyboard.send(self._skill_hotkeys["holy_shield"])
         wait(0.04, 0.1)
         mouse.click(button="right")

src/input_layer/__init__.py

@@ -12,6 +12,7 @@ On non-Windows (Docker/Linux), uses bridge_input to talk to a Windows host
 via TCP. Set BOTTY_BRIDGE_HOST / BOTTY_BRIDGE_PORT env vars.
 """
 import re as _re
+from logger import Logger
 import os as _os
 import threading as _threading
 
@@ -192,9 +193,19 @@ class _Keyboard:
         """
         Send a key press event with stealth timing.
 
+        An EMPTY key is a no-op, not an error. An unbound optional skill is a
+        legitimate configuration — a FoHdin with no Holy Shield, no Vigor, no
+        Cleansing — and there are 90+ `keyboard.send(self._skill_hotkeys[x])`
+        call sites across the paladin classes alone, almost none of which check
+        first. Raising here kills the whole bot thread for a skill the
+        character was never meant to cast. Guard once, at the boundary.
+
         Supports combo keys like 'shift + a', 'ctrl + alt + del'.
         Supports do_release=False (hold key) and do_press=False (release-only).
         """
+        if key is None or str(key).strip() == "":
+            Logger.debug("keyboard.send: empty key (unbound skill) — skipping")
+            return
         self._stealth_before()
 
         # Handle combo keys (e.g. 'shift + a', 'ctrl + alt + del')