fix: get_symbol_info returns wrong data for every small symbol

Parser used a 5000-char heuristic slice per symbol; any symbol block
shorter than 5000 chars bled into the next one, and last-write-wins in
the properties dict ensured the neighbor's data clobbered the target.
Reported as Simulation_SPICE:OPAMP returning PJFET data.

Switch to parenthesis-depth tracking to find the true end of each
(symbol ...) block. Also surface Sim.Pins so agents can read opamp pin
numbering without inferring it from schematic placement.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tests/test_symbol_library.py

@@ -0,0 +1,117 @@
+"""
+Regression tests for symbol library parsing.
+
+Covers:
+- The 5000-char heuristic bug where PJFET properties bled into the OPAMP block.
+- The sim_pins field exposed from Sim.Pins properties.
+"""
+
+import sys
+from pathlib import Path
+
+import pytest
+
+sys.path.insert(0, str(Path(__file__).parent.parent / "python"))
+
+from commands.library_symbol import SymbolLibraryCommands, SymbolLibraryManager
+
+FIXTURE = Path(__file__).parent / "fixtures" / "Simulation_SPICE_minimal.kicad_sym"
+SPICE_LIB = Path("/usr/share/kicad/symbols/Simulation_SPICE.kicad_sym")
+
+
+def _manager_for_fixture() -> SymbolLibraryManager:
+    manager = SymbolLibraryManager.__new__(SymbolLibraryManager)
+    manager.project_path = None
+    manager.libraries = {"Simulation_SPICE": str(FIXTURE)}
+    manager.symbol_cache = {}
+    return manager
+
+
+@pytest.mark.unit
+class TestSymbolLibraryManagerParsing:
+    """Unit tests using the minimal fixture file (no disk I/O to system libs)."""
+
+    def test_both_symbols_present(self):
+        manager = _manager_for_fixture()
+        symbols = manager.list_symbols("Simulation_SPICE")
+        names = [s.name for s in symbols]
+        assert "OPAMP" in names
+        assert "PJFET" in names
+        assert len(symbols) == 2
+
+    def test_opamp_description_is_not_pjfet(self):
+        manager = _manager_for_fixture()
+        symbols = manager.list_symbols("Simulation_SPICE")
+        opamp = next(s for s in symbols if s.name == "OPAMP")
+        assert "JFET" not in opamp.description
+
+    def test_opamp_description_correct(self):
+        manager = _manager_for_fixture()
+        symbols = manager.list_symbols("Simulation_SPICE")
+        opamp = next(s for s in symbols if s.name == "OPAMP")
+        assert opamp.description == "Operational amplifier, single"
+
+    def test_opamp_value_correct(self):
+        manager = _manager_for_fixture()
+        symbols = manager.list_symbols("Simulation_SPICE")
+        opamp = next(s for s in symbols if s.name == "OPAMP")
+        assert opamp.value == "${SIM.PARAMS}"
+
+    def test_opamp_sim_pins_exposed(self):
+        manager = _manager_for_fixture()
+        symbols = manager.list_symbols("Simulation_SPICE")
+        opamp = next(s for s in symbols if s.name == "OPAMP")
+        assert opamp.sim_pins == "1=in+ 2=in- 3=vcc 4=vee 5=out"
+
+    def test_pjfet_description_correct(self):
+        manager = _manager_for_fixture()
+        symbols = manager.list_symbols("Simulation_SPICE")
+        pjfet = next(s for s in symbols if s.name == "PJFET")
+        assert pjfet.description == "P-JFET transistor, for simulation only"
+
+    def test_pjfet_value_correct(self):
+        manager = _manager_for_fixture()
+        symbols = manager.list_symbols("Simulation_SPICE")
+        pjfet = next(s for s in symbols if s.name == "PJFET")
+        assert pjfet.value == "PJFET"
+
+    def test_pjfet_sim_pins_exposed(self):
+        manager = _manager_for_fixture()
+        symbols = manager.list_symbols("Simulation_SPICE")
+        pjfet = next(s for s in symbols if s.name == "PJFET")
+        assert pjfet.sim_pins == "1=D 2=G 3=S"
+
+
+@pytest.mark.integration
+class TestGetSymbolInfoHandler:
+    """Integration tests against the real system Simulation_SPICE library."""
+
+    def test_opamp_via_commands_handler(self):
+        if not SPICE_LIB.exists():
+            pytest.skip(f"System library not found: {SPICE_LIB}")
+        manager = SymbolLibraryManager.__new__(SymbolLibraryManager)
+        manager.project_path = None
+        manager.libraries = {"Simulation_SPICE": str(SPICE_LIB)}
+        manager.symbol_cache = {}
+        commands = SymbolLibraryCommands(library_manager=manager)
+        result = commands.get_symbol_info({"symbol": "Simulation_SPICE:OPAMP"})
+        assert result["success"] is True
+        info = result["symbol_info"]
+        assert info["description"] == "Operational amplifier, single"
+        assert "JFET" not in info["description"]
+        assert info["value"] == "${SIM.PARAMS}"
+        assert info["sim_pins"] == "1=in+ 2=in- 3=vcc 4=vee 5=out"
+
+    def test_pjfet_via_commands_handler(self):
+        if not SPICE_LIB.exists():
+            pytest.skip(f"System library not found: {SPICE_LIB}")
+        manager = SymbolLibraryManager.__new__(SymbolLibraryManager)
+        manager.project_path = None
+        manager.libraries = {"Simulation_SPICE": str(SPICE_LIB)}
+        manager.symbol_cache = {}
+        commands = SymbolLibraryCommands(library_manager=manager)
+        result = commands.get_symbol_info({"symbol": "Simulation_SPICE:PJFET"})
+        assert result["success"] is True
+        info = result["symbol_info"]
+        assert info["description"] == "P-JFET transistor, for simulation only"
+        assert info["value"] == "PJFET"