test: add comprehensive test coverage (35% → 58%, threshold 50%)

Add 180+ new tests across 10 test files covering previously untested modules:
- instructions_cli (0% → 100%), hooks_cli (73% → 96%), spellcheck (28% → 84%)
- palace_graph (9% → 91%), general_extractor (0% → 92%), entity_detector (0% → 69%)
- entity_registry (0% → 70%), room_detector_local (0% → 55%), layers (0% → 28%)
- onboarding (0% → 36%)

Also fixes Windows encoding bug in onboarding.py (write_text without encoding="utf-8").

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/test_layers.py

@@ -0,0 +1,122 @@
+"""Tests for mempalace.layers — focused on Layer0."""
+
+import os
+from unittest.mock import patch
+
+from mempalace.layers import Layer0
+
+
+# ── Layer0 — with identity file ─────────────────────────────────────────
+
+
+def test_layer0_reads_identity_file(tmp_path):
+    identity_file = tmp_path / "identity.txt"
+    identity_file.write_text("I am Atlas, a personal AI assistant for Alice.")
+    layer = Layer0(identity_path=str(identity_file))
+    text = layer.render()
+    assert "Atlas" in text
+    assert "Alice" in text
+
+
+def test_layer0_caches_text(tmp_path):
+    identity_file = tmp_path / "identity.txt"
+    identity_file.write_text("Hello world")
+    layer = Layer0(identity_path=str(identity_file))
+    first = layer.render()
+    # Modify file after first read
+    identity_file.write_text("Changed content")
+    second = layer.render()
+    # Should return cached version
+    assert first == second
+    assert second == "Hello world"
+
+
+def test_layer0_missing_file_returns_default(tmp_path):
+    missing = str(tmp_path / "nonexistent.txt")
+    layer = Layer0(identity_path=missing)
+    text = layer.render()
+    assert "No identity configured" in text
+    assert "identity.txt" in text
+
+
+def test_layer0_token_estimate(tmp_path):
+    identity_file = tmp_path / "identity.txt"
+    content = "A" * 400  # 400 chars ~ 100 tokens
+    identity_file.write_text(content)
+    layer = Layer0(identity_path=str(identity_file))
+    estimate = layer.token_estimate()
+    assert estimate == 100
+
+
+def test_layer0_token_estimate_empty(tmp_path):
+    identity_file = tmp_path / "identity.txt"
+    identity_file.write_text("")
+    layer = Layer0(identity_path=str(identity_file))
+    assert layer.token_estimate() == 0
+
+
+def test_layer0_strips_whitespace(tmp_path):
+    identity_file = tmp_path / "identity.txt"
+    identity_file.write_text("  Hello world  \n\n")
+    layer = Layer0(identity_path=str(identity_file))
+    text = layer.render()
+    assert text == "Hello world"
+
+
+def test_layer0_default_path():
+    layer = Layer0()
+    expected = os.path.expanduser("~/.mempalace/identity.txt")
+    assert layer.path == expected
+
+
+# ── Layer1 — mocked chromadb ────────────────────────────────────────────
+
+
+def test_layer1_no_palace():
+    """Layer1 returns helpful message when no palace exists."""
+    with patch("mempalace.layers.MempalaceConfig") as mock_cfg:
+        mock_cfg.return_value.palace_path = "/nonexistent/palace"
+        from mempalace.layers import Layer1
+
+        layer = Layer1(palace_path="/nonexistent/palace")
+    result = layer.generate()
+    assert "No palace found" in result or "No memories" in result
+
+
+# ── Layer2 — mocked chromadb ────────────────────────────────────────────
+
+
+def test_layer2_no_palace():
+    """Layer2 returns message when no palace exists."""
+    with patch("mempalace.layers.MempalaceConfig") as mock_cfg:
+        mock_cfg.return_value.palace_path = "/nonexistent/palace"
+        from mempalace.layers import Layer2
+
+        layer = Layer2(palace_path="/nonexistent/palace")
+    result = layer.retrieve(wing="test")
+    assert "No palace found" in result
+
+
+# ── Layer3 — mocked chromadb ────────────────────────────────────────────
+
+
+def test_layer3_no_palace():
+    """Layer3 returns message when no palace exists."""
+    with patch("mempalace.layers.MempalaceConfig") as mock_cfg:
+        mock_cfg.return_value.palace_path = "/nonexistent/palace"
+        from mempalace.layers import Layer3
+
+        layer = Layer3(palace_path="/nonexistent/palace")
+    result = layer.search("test query")
+    assert "No palace found" in result
+
+
+def test_layer3_search_raw_no_palace():
+    """Layer3.search_raw returns empty list when no palace exists."""
+    with patch("mempalace.layers.MempalaceConfig") as mock_cfg:
+        mock_cfg.return_value.palace_path = "/nonexistent/palace"
+        from mempalace.layers import Layer3
+
+        layer = Layer3(palace_path="/nonexistent/palace")
+    result = layer.search_raw("test query")
+    assert result == []