feat(pet): gate Unicode placeholders to kitty and Ghostty

WezTerm speaks kitty APC but not U+10EEEE, so detect_terminal_graphics()
== "kitty" is the wrong gate for the placeholder path.

agent/pet/render.py

@@ -90,6 +90,22 @@ def detect_terminal_graphics() -> str:
     return "unicode"
 
 
+def supports_kitty_placeholders() -> bool:
+    """True when the terminal can paint kitty Unicode placeholders (U+10EEEE).
+
+    Narrower than ``detect_terminal_graphics() == "kitty"``. WezTerm speaks
+    kitty APC transmits but does not implement the placeholder grid, so those
+    cells render as tofu. Ghostty and kitty do. VS Code already falls out of
+    ``detect_terminal_graphics`` as ``unicode``.
+    """
+    if detect_terminal_graphics() != "kitty":
+        return False
+    term_program = os.environ.get("TERM_PROGRAM", "").lower()
+    if term_program == "wezterm" or os.environ.get("WEZTERM_PANE"):
+        return False
+    return True
+
+
 def resolve_mode(configured: str | None, *, stream=None) -> str:
     """Resolve the effective render mode from config + the environment.
 

tests/agent/test_pet_engine.py

@@ -239,13 +239,17 @@ def test_kitty_payload_structure(boba_like):
 
 
 
+def _clear_graphics_env(monkeypatch):
+    for key in ("KITTY_WINDOW_ID", "TERM_PROGRAM", "ITERM_SESSION_ID", "WEZTERM_PANE", "TERM"):
+        monkeypatch.delenv(key, raising=False)
+
+
 def test_vscode_terminal_ignores_leaked_graphics_env(monkeypatch):
     # The VS Code / Cursor integrated terminal can't show inline images by
     # default, yet inherits ITERM_SESSION_ID/KITTY_WINDOW_ID when launched from
     # those terminals. TERM_PROGRAM=vscode must win → unicode, never a protocol
     # whose escapes the embedded terminal would silently drop.
-    for key in ("KITTY_WINDOW_ID", "TERM_PROGRAM", "ITERM_SESSION_ID", "WEZTERM_PANE", "TERM"):
-        monkeypatch.delenv(key, raising=False)
+    _clear_graphics_env(monkeypatch)
     monkeypatch.setenv("TERM_PROGRAM", "vscode")
 
     assert render.detect_terminal_graphics() == "unicode"
@@ -253,3 +257,28 @@ def test_vscode_terminal_ignores_leaked_graphics_env(monkeypatch):
         monkeypatch.setenv(leaked, "1")
         assert render.detect_terminal_graphics() == "unicode"
         monkeypatch.delenv(leaked)
+        assert render.supports_kitty_placeholders() is False
+
+
+def test_kitty_placeholders_on_kitty_and_ghostty(monkeypatch):
+    _clear_graphics_env(monkeypatch)
+    monkeypatch.setenv("TERM", "xterm-kitty")
+    monkeypatch.setenv("KITTY_WINDOW_ID", "1")
+    assert render.supports_kitty_placeholders() is True
+
+    _clear_graphics_env(monkeypatch)
+    monkeypatch.setenv("TERM", "xterm-ghostty")
+    monkeypatch.setenv("TERM_PROGRAM", "ghostty")
+    assert render.supports_kitty_placeholders() is True
+
+
+def test_wezterm_is_not_placeholder_capable(monkeypatch):
+    # WezTerm speaks kitty APC but not U+10EEEE. Placeholders would tofu.
+    _clear_graphics_env(monkeypatch)
+    monkeypatch.setenv("TERM", "xterm-256color")
+    monkeypatch.setenv("TERM_PROGRAM", "WezTerm")
+    assert render.detect_terminal_graphics() == "kitty"
+    assert render.supports_kitty_placeholders() is False
+
+    monkeypatch.setenv("WEZTERM_PANE", "1")
+    assert render.supports_kitty_placeholders() is False