hardening(gateway): define global resource budgets and graceful drain deadlines

[BYK]

Motivation

Lore already has several stream-specific limits, but resource control should be auditable across the whole process. Agent Gateway bounds bodies, pools, caches, windows, handshakes, queues, and shutdown. Lore needs a single inventory and coherent process-wide budget model.

Scope

• Inventory all request/response byte limits, retained stream state, caches, sessions, concurrent distillations/curations, workers, queues, and timers.
• Add missing global caps and explicit admission behavior.
• Define graceful drain plus a hard termination deadline.
• Ensure limits compose across chained recall continuations.

Acceptance criteria

• Every potentially unbounded collection or retained byte stream has a documented owner and limit.
• Limit errors are protocol-correct and do not leak hidden recall data.
• Concurrent sessions cannot each independently exceed the intended process budget.
• Shutdown stops admission, drains active work to a deadline, flushes required state, then terminates.
• Stress tests cover slow clients, large bodies, recall chains, worker saturation, and cache pressure.
• Resource-limit metrics identify the exhausted budget.