framework: LED.cathode mandatory + close WaterAlarm regression

[raeq]

Summary

Found while reviewing WaterAlarm's breadboard SVG (from #28): the LEDs in the design had no ground connections drawn. The framework's LED.cathode was declared mandatory=False with a "floating = GND" shortcut that lets demos write electrically-broken circuits and have them pass ERC. A real LED with a dangling cathode does not light — this is exactly the physical-fidelity violation CLAUDE.md lists as disallowed.

• LED.cathode now mandatory=True. The framework raises UnconnectedPinError at Circuit.__init__ if a design declares an LED with an unwired cathode.
• WaterAlarm and WaterAlarmSplit had floating cathodes — both now wire red_led.cathode and green_led.cathode to ground. (Bench builds still need a series current-limit resistor; the logic-level demo doesn't model V_F or current.)
• Two new regression tests in tests/components/test_led.py — the second one (test_floating_cathode_refused_at_circuit_construction) is the end-to-end test that would have caught the WaterAlarm bug originally.
• Touched a handful of unit-test fixtures that had leaned on the broken default.

Test plan

• uv run pytest — 4362 passed.
• uv run mypy src/ demos/ clean.
• Demo docs regenerated for water_alarm + water_alarm_split — the breadboard SVGs now show the ground jumpers to each LED's cathode.

Supersedes the auto-closed #29 (the base branch was deleted when #28 merged).

[Copilot]

Pull request overview

This PR tightens electrical correctness in the component framework by making LED.cathode a required connection, preventing physically invalid “floating cathode” LED circuits from passing ERC and propagating into exports/docs (e.g., the WaterAlarm demo).

Changes:

• Make LED.cathode mandatory (removing the prior “floating = GND” shortcut) so Circuit construction raises UnconnectedPinError for dangling cathodes.
• Fix WaterAlarm / WaterAlarmSplit demos by explicitly wiring LED cathodes to ground, and regenerate their exported docs/assets.
• Add regression tests ensuring LEDs require both terminals and that failures occur at Circuit.__init__.

Reviewed changes

Copilot reviewed 41 out of 46 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tests/golden/yosys/water_alarm.json	Golden updated: LED cathodes now land on GND net.
tests/golden/yosys/water_alarm_assembly.json	Golden updated: assembly variant cathodes now on GND.
tests/golden/spice/water_alarm.cir	Golden updated: LED cathodes now SPICE node 0 (ground).
tests/golden/spice/water_alarm_assembly.cir	Golden updated: assembly variant LED cathodes now SPICE ground.
tests/golden/mermaid/water_alarm.mmd	Golden updated: Mermaid graph shows cathode→gnd edges.
tests/golden/mermaid/water_alarm_assembly.mmd	Golden updated: assembly Mermaid graph shows cathode→gnd edges.
tests/golden/kicad/water_alarm.net	Golden updated: KiCad netlist includes LED cathodes on GND net.
tests/golden/kicad/water_alarm_assembly.net	Golden updated: assembly KiCad netlist includes cathodes on GND.
tests/golden/kicad_sch/water_alarm.kicad_sch	Golden updated: schematic adds GND power symbols for LED cathodes.
tests/golden/dot/water_alarm.dot	Golden updated: DOT graph includes cathode→gnd edges.
tests/golden/dot/water_alarm_assembly.dot	Golden updated: assembly DOT graph includes cathode→gnd edges.
tests/golden/breadboard/water_alarm.breadboard.svg	Golden updated: breadboard SVG adds two ground jumpers for LED cathodes.
tests/golden/assembly_guide/water_alarm.md	Golden updated: assembly steps include LED cathode→rail jumpers.
tests/framework/test_framework.py	Update evaluation-order test to wire LED cathode and include a GND rail part.
tests/framework/test_circuit_autocollect.py	Update fixtures to avoid floating LED cathodes and adjust expected collected parts.
tests/framework/import_kicad/test_import.py	Update minimal-netlist test to include explicit power/ground nets to satisfy mandatory LED ports.
tests/components/test_led.py	Add regression tests for mandatory anode/cathode and construction-time failure on dangling cathode.
src/components/passives/led.py	Make cathode port mandatory and update docstring to reflect physical behavior.
demos/water_alarm/water_alarm.py	Wire both LED cathodes to GND in the demo circuit.
demos/water_alarm/docs/WaterAlarm.yosys.json	Regenerated export reflecting cathodes connected to GND.
demos/water_alarm/docs/WaterAlarm.svg	Regenerated diagram reflecting cathodes connected to GND.
demos/water_alarm/docs/WaterAlarm.net-report.md	Regenerated net report showing LED cathodes as GND readers.
demos/water_alarm/docs/WaterAlarm.net	Regenerated KiCad netlist showing LED cathodes on GND.
demos/water_alarm/docs/WaterAlarm.mmd	Regenerated Mermaid showing cathode→gnd edges.
demos/water_alarm/docs/WaterAlarm.md	Regenerated assembly guide including LED cathode ground jumpers.
demos/water_alarm/docs/WaterAlarm.kicad_sch	Regenerated schematic adding GND symbols for LED cathodes.
demos/water_alarm/docs/WaterAlarm.dot	Regenerated DOT graph including cathode→gnd edges.
demos/water_alarm/docs/WaterAlarm.cir	Regenerated SPICE netlist with LED cathodes on node 0.
demos/water_alarm/docs/WaterAlarm.breadboard.svg	Regenerated breadboard SVG adding cathode ground jumpers.
demos/water_alarm_split/water_alarm_split.py	Wire both LED cathodes to GND in split demo.
demos/water_alarm_split/docs/WaterAlarmAssembly.yosys.json	Regenerated export reflecting cathodes connected to GND.
demos/water_alarm_split/docs/WaterAlarmAssembly.svg	Regenerated diagram reflecting cathodes connected to GND.
demos/water_alarm_split/docs/WaterAlarmAssembly.net-report.md	Regenerated net report showing LED cathodes as GND readers.
demos/water_alarm_split/docs/WaterAlarmAssembly.net	Regenerated KiCad netlist showing LED cathodes on GND.
demos/water_alarm_split/docs/WaterAlarmAssembly.mmd	Regenerated Mermaid showing cathode→gnd edges.
demos/water_alarm_split/docs/WaterAlarmAssembly.dot	Regenerated DOT graph including cathode→gnd edges.
demos/water_alarm_split/docs/WaterAlarmAssembly.cir	Regenerated SPICE netlist with LED cathodes on node 0.
demos/water_alarm_split/docs/WaterAlarmAssembly__ControllerBoard.kicad_sch	Regenerated controller-board schematic adding GND symbols for LED cathodes.
demos/water_alarm_split/docs/ControllerBoard.yosys.json	Regenerated export reflecting cathodes connected to GND.
demos/water_alarm_split/docs/ControllerBoard.svg	Regenerated diagram reflecting cathodes connected to GND.
demos/water_alarm_split/docs/ControllerBoard.net-report.md	Regenerated net report showing LED cathodes as GND readers.
demos/water_alarm_split/docs/ControllerBoard.net	Regenerated KiCad netlist showing LED cathodes on GND.
demos/water_alarm_split/docs/ControllerBoard.mmd	Regenerated Mermaid showing cathode→gnd edges.
demos/water_alarm_split/docs/ControllerBoard.kicad_sch	Regenerated schematic adding GND symbols for LED cathodes.
demos/water_alarm_split/docs/ControllerBoard.dot	Regenerated DOT graph including cathode→gnd edges.
demos/water_alarm_split/docs/ControllerBoard.cir	Regenerated SPICE netlist with LED cathodes on node 0.

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