Warn when chip power pins lack decoupling capacitors

[0hmX]

Summary

This is a cross-package implementation of the chip-power-pin decoupling check:

• @tscircuit/core determines each chip pin's decoupling requirement while rendering JSX and serializes that intent into Circuit JSON.
• @tscircuit/checks reads the serialized metadata, evaluates circuit connectivity, and emits the warning.

This keeps component semantics in core and DRC warning ownership in checks.

End-to-end workflow

1. Core copies explicit JSX pinAttributes onto the generated source_port.
2. Core resolves should_have_decoupling_capacitor using this precedence:
   • An explicit shouldHaveDecouplingCapacitor value wins.
   • providesPower: true resolves to false because a power-source output should not require a local decoupling capacitor.
   • An explicit requiresPower value resolves to the same boolean.
   • Otherwise, a conventional chip power label such as VCC or VDD resolves to true.
   • Unrelated pins remain unset so existing underspecified-pin diagnostics continue to work.
3. The result is present in Circuit JSON on the source port, for example:

{
  "type": "source_port",
  "should_have_decoupling_capacitor": true,
  "recommended_decoupling_capacitor_capacitance": "100nF"
}

4. Checks builds a canonical source connectivity map and indexes source components, source ports, capacitors, and ground ports/nets.
5. For each connected simple_chip port that requires decoupling, checks looks for a two-pin simple_capacitor with:
   • one terminal connected to the chip's power rail; and
   • the other terminal connected to a ground port or ground net.
6. If that capacitor exists, no warning is produced. Otherwise checks emits a source_pin_missing_trace_warning, including the recommended capacitance in the message when supplied.
7. The check is exported and registered in runAllNetlistChecks.

False-positive behavior

• shouldHaveDecouplingCapacitor: false is preserved in Circuit JSON and suppresses the warning.
• Pins with providesPower: true are serialized with the requirement set to false.
• Fully unconnected power pins are skipped here because the existing missing-connection check owns that diagnostic.
• Checks performs no VCC/VDD/GND label inference; it consumes domain metadata from Circuit JSON.
• For older Circuit JSON without the new field, checks falls back to requires_power === true && provides_power !== true.

Cross-repository PRs

• Core metadata producer: Emit decoupling metadata for tscircuit/checks core#2953
• Checks warning consumer: Warn when chip power pins lack decoupling capacitors #175

Both changes are required for the complete JSX → Circuit JSON → connectivity check → warning workflow.

Validation

• Core focused metadata and pin-specification regression tests
• Checks focused decoupling test and full test suite (133 tests)
• TypeScript typechecks in both repositories
• Checks build and formatting validation