feat(admission): quota + admission plane — completes placement + quotas + admission

[mdheller]

What

place() decided where a workload runs; admission decides whether a subject may run it right now, under per-account/per-project budgets — the multi-tenant, cost-governance third of the cloud-shell fog spec's Control-Plane Agent (placement + quotas + admission). Without it, the plane would happily schedule infinite workloads; that's not a production platform.

tools/admission.py

• Per-subject quotas (max_concurrent, gpu_max, cost_budget) over a DEFAULT_QUOTA.
• admit() fail-closed: over any budget → denied, naming the exceeded dimensions.
• charge() / release() accounting; spend is cumulative (not released).
• File-backed ledger (ledger_path) — a CLI enforces a real running budget across processes, not a fresh one each invocation.

Wired into the spine

executor.run_spine gains admission/admission_key/cost; the check runs before the Grant is minted, so an over-quota subject never receives a capability (status: denied, nothing placed/granted/dispatched).

CLI

sourceosctl run --cost N enforces the ledger-backed budget (exit 4 on DENIED, prints usage vs quota); new sourceosctl quota shows a subject's quota + usage.

run #1 (gpu) → ran … quota usage: {gpu: 1}
run #2 (gpu) → ran … quota usage: {gpu: 2}
run #3 (gpu) → DENIED (fail-closed): quota exceeded: gpu_max

Tests

+9 admission (budgets, charge/release, per-subject isolation, ledger persistence across processes, spine integration) = 90 tools tests green; validate passes; CLI enforcement verified across invocations. Wired: validate REQUIRED, compute-plane CapD link, ledger gitignored.