fix(artwork): ignore TMUX/ZELLIJ/STY values that mean 'not set'

Some shells and wrappers export ZELLIJ=0 or TMUX=0 outside a multiplexer.
A plain truthiness check treated that as 'inside tmux/zellij' and
downgraded iTerm2/Kitty to the ANSI mosaic, so real artwork silently
disappeared. Only meaningful values now count.

somafm_tui/artwork.py

@@ -30,6 +30,18 @@ _OFF_VALUES = {"0", "off", "no", "none", "false"}
 _PROTOCOL_VALUES = {"tgp", "iterm2"}
 
 
+def _env_flag(env: Mapping[str, str], name: str) -> bool:
+    """True when an environment variable is set to a meaningful value.
+
+    Multiplexers are inconsistent here (``TMUX`` is a path, ``STY`` a
+    session name) and some wrappers export ``ZELLIJ=0``/``TMUX=0`` when they
+    are *not* running, so a plain truthiness check would wrongly downgrade a
+    perfectly good iTerm2/Kitty to the ANSI mosaic.
+    """
+    value = (env.get(name) or "").strip()
+    return bool(value) and value.lower() not in _OFF_VALUES
+
+
 def detect_protocol(environ: Mapping[str, str] | None = None) -> str | None:
     """Return ``"tgp"``, ``"iterm2"`` or ``None`` for the current terminal."""
     env = os.environ if environ is None else environ
@@ -57,7 +69,7 @@ def detect_protocol(environ: Mapping[str, str] | None = None) -> str | None:
 
     # Kitty inside tmux may not inherit TERM=xterm-kitty/KITTY_*.  Ask tmux
     # what the outer terminal is; TGP is wrapped for tmux passthrough.
-    if env.get("TMUX") and shutil.which("tmux"):
+    if _env_flag(env, "TMUX") and shutil.which("tmux"):
         try:
             result = subprocess.run(
                 ["tmux", "display-message", "-p", "#{client_termname}"],
@@ -76,9 +88,9 @@ def detect_protocol(environ: Mapping[str, str] | None = None) -> str | None:
     # iTerm2/WezTerm inside tmux would need their own passthrough wrapper, so
     # default to the mosaic there.
     if (
-        env.get("TMUX")
-        or env.get("ZELLIJ")
-        or env.get("STY")
+        _env_flag(env, "TMUX")
+        or _env_flag(env, "ZELLIJ")
+        or _env_flag(env, "STY")
         or term.startswith("screen")
         or term.startswith("tmux")
         or program in {"tmux", "screen"}

tests/test_artwork.py

@@ -62,3 +62,14 @@ async def test_fetch_validates_and_caches() -> None:
         fetched = await artwork.fetch(client, url)
     assert fetched == data
     assert artwork.load_cached(url) == data
+
+
+def test_multiplexer_env_values_that_mean_no() -> None:
+    # Some wrappers export ZELLIJ=0 / TMUX=0 outside a multiplexer; that must
+    # not disable iTerm2 or Kitty graphics.
+    assert artwork.detect_protocol({"ZELLIJ": "0", "TERM_PROGRAM": "iTerm.app"}) == "iterm2"
+    assert artwork.detect_protocol({"ZELLIJ": "", "TERM_PROGRAM": "iTerm.app"}) == "iterm2"
+    assert artwork.detect_protocol({"TMUX": "0", "KITTY_WINDOW_ID": "1"}) == "tgp"
+    # ...while a real multiplexer still downgrades to the mosaic.
+    assert artwork.detect_protocol({"TMUX": "/tmp/tmux-501/default,1,0", "TERM_PROGRAM": "iTerm.app"}) is None
+    assert artwork.detect_protocol({"STY": "1234.pts-0.host", "TERM_PROGRAM": "iTerm.app"}) is None