Circuit design brief and intake

The design-brief sub-agent converts conversation statements into a machine-readable brief
and an intake sidecar. Requirements use R* ids, assumptions use A* ids, and unresolved
questions use Q* ids. Every part and net maps to one or more requirement or assumption
ids. The sidecar binds to the exact brief bytes with brief_sha256.

Run the intake gate before authoring. It is ready only when the hash matches, all brief
parts and nets are mapped, all source ids exist, and there are no open questions.
Assumption-only mappings are reported for review but do not block authoring.

User-attached images are materialized to intake/attachments/ by a hook (see
manifest.jsonl for sha256 provenance); details read from them belong in A*/Q*
records, which may declare an evidence ref (kind, path, sha256, note) —
declared-but-missing or mismatched evidence fails the gate.

Run the library gate before authoring. It parses the installed .kicad_sym and .pretty
files directly and must be pass for every symbol, footprint, and referenced pin. Both
gates are fail-closed and must be recorded as JSON reports.

When the library report fails with authoring_requests, do not substitute a similar
library item. Return each request in the intake as a Q* open question, retaining its
references, requested identifiers, and reason.

Wire harness contract fields

Parts with connector: true become harness connectors for wire-agent. They can
carry housing plus rated_current_a/rated_voltage_v (omitted values fall
back to wire's defaults of 3 A / 250 V). Nets can declare signal_class
(power|ground|signal|analog|data|highspeed|shield — inferred from the name when
absent), voltage_v, and current_a. Emit the contract with
circuit_connectivity_export (or
python3 "$CIRCUIT_PLUGIN/scripts/circuit_launcher.py" connectivity --brief <brief.json> --out <name>.connectivity-source.json); it writes the
wire ConnectivitySource schema and fails closed when a connector has no pins
in the brief (or in --netlist <path> when given).