fix: clear error messages when prefs or patch file missing at install time

install.py

@@ -95,16 +95,34 @@ def choose_preset(preset: str, auto_yes: bool) -> str:
 
 def merge_prefs(config_path: Path, preset: str) -> None:
     """Invoke merge_prefs.py to upsert the preferences patch into Inkscape's prefs."""
-    subprocess.run(
-        [
-            sys.executable,
-            str(SCRIPT_DIR / "scripts/merge_prefs.py"),
-            "--prefs", str(config_path / "preferences.xml"),
-            "--patch", str(SCRIPT_DIR / "config/preferences-patch.xml"),
-            "--preset", preset,
-        ],
-        check=True,
-    )
+    patch_path = SCRIPT_DIR / "config/preferences-patch.xml"
+    if not patch_path.exists():
+        sys.exit(
+            f"✗ Installation file missing: {patch_path}\n"
+            "  The repo may be incomplete — try re-cloning."
+        )
+
+    prefs_path = config_path / "preferences.xml"
+    if not prefs_path.exists():
+        print("→ No Inkscape preferences found — seeding from Illuscape defaults")
+        print("  (Inkscape will fill in the rest on first launch)")
+
+    try:
+        subprocess.run(
+            [
+                sys.executable,
+                str(SCRIPT_DIR / "scripts/merge_prefs.py"),
+                "--prefs", str(prefs_path),
+                "--patch", str(patch_path),
+                "--preset", preset,
+            ],
+            check=True,
+        )
+    except subprocess.CalledProcessError:
+        sys.exit(
+            "✗ Could not merge Inkscape preferences.\n"
+            "  Launch Inkscape once to initialise its config, then re-run this installer."
+        )
 
 
 # ── Config file copy ──────────────────────────────────────────────────────────