feat: support compose resource limits (legacy keys and deploy.resources)

[lesnik512]

Summary

Convert compose CPU/memory resource limits to podman run flags, both forms: the legacy top-level service keys and the modern deploy.resources block. When both forms set the same flag, conversion refuses loudly rather than guessing a precedence the compose spec leaves undefined.

Design: planning/changes/2026-07-11.02-resource-limits.md. This closes the last flat-mappable Bucket B item from the coverage audit.

Legacy keys (registry entries)

All flags verified against podman-run.1. A new _number_scalar factory (accepts int/float/string, rejects bool) backs 12 keys; oom_kill_disable uses _bool:

mem_limit→--memory, memswap_limit→--memory-swap, mem_reservation→--memory-reservation, mem_swappiness→--memory-swappiness, cpus→--cpus, cpu_shares→--cpu-shares, cpu_quota→--cpu-quota, cpu_period→--cpu-period, cpuset→--cpuset-cpus, pids_limit→--pids-limit, shm_size→--shm-size, oom_score_adj→--oom-score-adj, oom_kill_disable→--oom-kill-disable.

Values pass through unchanged (a bare int mem_limit is bytes; "512m" carries a unit; a ${VAR} stays live at run time, via the same _Expand/to_shell path every scalar uses). Because these are SERVICE_KEYS registry entries, the existing parsing/emit loops wire them into validation and emission with no bespoke code.

deploy.resources (new resources.py)

deploy becomes a structural key; only deploy.resources is honored (other deploy subkeys — replicas/placement/… — are refused, per the audit's swarm-key rejection). limits.cpus/memory/pids → --cpus/--memory/--pids-limit; reservations.memory → --memory-reservation. reservations.cpus and reservations.devices have no clean podman flag and are refused.

Refuse on conflict

The four flags reachable from both forms — mem_limit/limits.memory, cpus/limits.cpus, pids_limit/limits.pids, mem_reservation/reservations.memory — refuse loudly when both are set on a service. A single _LIMITS table drives both conflict detection and emission, so no flag can be emitted without being conflict-checked.

Non-goals

blkio_config and the Windows-only cpu_count/cpu_percent remain rejected.

Testing

just test-ci at 100% coverage (328 tests), just lint-ci clean, just check-planning OK. tests/test_resources.py covers each deploy.resources field, every refusal, all four conflict pairs, and empty-block no-ops; legacy-key emission and value-type validation are in test_emit.py/test_parsing.py; the supported-keys snapshot is updated. architecture/supported-subset.md gains a ## Resource limits section (and its stale _Expand-fields enumeration was corrected for the new keys).

An adversarial whole-branch review confirmed value passthrough introduces no new shell-injection surface (mem_limit: "$(touch x)" is escaped by to_shell, identical to every other scalar). Two review Minors were fixed in this branch: empty limits:/reservations: YAML blocks are now no-ops (matching deploy:null/resources:null and the ulimits/pull_policy precedent), and the numeric-check predicate is shared between keys.py and resources.py.