feat(kernel): register the @hcs/kernel workspace

[verlyn13]

What

First non-.gitkeep file in Ring 1. packages/kernel/ has held an empty marker since the repo was scaffolded.

Three files: a package manifest, an empty public-API barrel, and a test suite that guards the ring boundary.

Change class: D — kernel, read path.

The exports map is the point

charter §Package boundary enforcement:

packages/adapters/** cannot import from packages/kernel/src/** except through the declared public API surface (packages/kernel/src/api/).

That rule now has two independent enforcers:

1. scripts/ci/boundary-check.sh rule 2 — a grep. It went three months without executing once: a PCRE lookahead under grep -E exited rc=2 and 2>/dev/null ate the diagnostic, so it printed ✓ ring boundaries intact while a planted violation passed. Repaired in fix(ci): make grep gates and node-tool gates fail closed #93.
2. This package's exports map, which publishes . and ./api and nothing else.

The second is the durable one. A grep can regress silently; a missing exports entry cannot. Verified on this host:

$ node -e "import('@hcs/kernel/api')"
RESOLVED, exports: []

$ node -e "import('@hcs/kernel/src/policy/rule-resolution')"
BLOCKED by exports map: ERR_PACKAGE_PATH_NOT_EXPORTED

Node refuses the deep import before any CI gate has an opinion.

The test suite asserts the map publishes exactly two entry points, routes both through src/api/, and contains no wildcard and no src path — so a future PR cannot quietly widen it to make a convenient deep import work without turning the suite red.

Why the barrel is empty

Deliberate. This is the workspace scaffold, separated from the first service so that workspace wiring problems surface in a three-file diff rather than inside a six-hundred-line one.

The first service to land here is the read-only policy-snapshot loader, assigned by adr/0060 §Ring-1 policy/gateway loader, with its checkpoint-level test obligation specified by adr/0061 — reject at the digest-verification step, not merely at the final Decision. Both accepted; no new ADR required.

No justfile edit was needed

just test kernel works the moment this package has a tests/ directory, because #93 replaced the hardcoded case "$target" in ""|schemas) with discovery over packages/*/tests:

$ just test kernel
 ✓ packages/kernel/tests/api-surface.test.ts (5 tests) 5ms
   Test Files  1 passed (1)
        Tests  5 passed (5)

That was the stated payoff of the discovery change, and it holds. It also means this PR adds zero merge-collision surface on the justfile.

Boundary checks

• No policy duplicated into adapter/hook
• No universal shell execution added
• No audit-write agent endpoint added
• OperationShape remains upstream of CommandShape — none emitted
• Registers no Capability; exposes no agent-callable surface; mints and consumes no ApprovalGrant
• Adds no dependency (lockfile change is the workspace link only)
• Ring 1 imports Ring 0 and nothing above it
• Citation discipline — adr/0060 §Ring-1 policy/gateway loader and adr/0061's test obligation are cited as forward context, not as authorization for anything in this diff. This PR implements no service.
• Precedence — amends no ADR, relieves no ADR-stated rule

Validation

just verify — green. just test kernel — 5/5. Deep-import block verified on this host, output above.