G2: specify portable core contracts

[yihanzhu]

Gate

G2 design for the accepted portable-core-contracts intent. G1 was accepted in #156 from intent blob 3ed8bb434c096ec126d680019a9491ab8a113e31.

Problem

The closed, unmerged #154 spec mixed three trust boundaries: core records, Git-backed profile resolution, and an executable fake-adapter runner. Its final review still found open capability arguments and self-reported test proof. The replacement G1 intents split those concerns.

Outcome

Accept one exact work/portable-core-contracts/spec.md that an implementation planner can use without inventing core meaning. It must define:

• seven canonical document kinds and all shared/nested wire shapes;
• total stage status, outcome, evidence, time, and actual-execution rules;
• a closed v1 role/capability/permission/argument registry;
• manifest-offer → profile-request → external-grant → result-use separation;
• pure supplied-document validation and stable errors;
• exact consumer boundaries for the later Git resolver and executable adapter-test runner.

Constraints

• This PR writes only work/portable-core-contracts/spec.md.
• Core validation reads no Git repository, physical path mapping, raw fixture, executable, network, credential, or live configuration.
• It does not run an adapter, authenticate a claim, issue authority, publish, activate a profile, or change current live behavior.
• Git object truth belongs to portable-profile-resolution; independent case execution and 2×2 proof belong to portable-adapter-contract-tests.
• Every v1 capability has exact arguments. No generic command, network, credential, merge, approval, bypass, label, deploy, or unbounded write capability.
• The implementation plan must fit the normal 400-net-line review budget or return to G2; the old spec: portable-control-plane-core #154 size exception is not inherited.
• Constitution-path CI wiring remains operator-owned or goes through proposals/.
• Human merge only. G2 acceptance does not approve a plan, implementation, or activation.

Non-goals

Do not continue #154 or implement under portable-control-plane-core. Do not build the profile resolver, test runner, real/default/native adapters, control foundation, durable orchestrator, neutral manager, packaging, deployment, telemetry, or autonomous writes here. The parent #153 remains open until all children and later real-adapter proof finish.