## Why

The RC5 tunnel register identifies a bounded sequenced-input flow but does not
define typed input state or provider-to-client feedback. The native Apollo
adapter cannot safely translate keyboard, mouse, UTF-8, controller, termination,
rumble, or HDR state from an untyped payload.

## What Changes

- Define a typed, versioned gateway input envelope for keyboard, mouse, UTF-8,
  and controller state.
- Define bounded provider-feedback and provider-termination envelopes on the
  existing reliable control direction.
- Define a separate typed clipboard envelope and Server-owned per-session
  direction, size, and rate policy so the gateway can prevent reflected loops
  without exposing provider management material.
- Define release semantics so gateway cleanup can emit real provider key/button
  releases without a synthetic provider command.
- Preserve RC5 unchanged; this change requires a new immutable Protocol version
  after its fixtures and consumers are final.

## Capabilities

### New Capabilities

- `gateway-input-feedback`: Typed Phase 3C gateway input, provider feedback,
  termination, and release envelopes.

### Modified Capabilities

- None.

## Impact

- Protocol control and datagram registries, schemas, fixtures, and generated
  Go/Rust/Swift bindings.
- Data Plane gateway input/clipboard translation and host-feedback forwarding.
- Connection Server mints only immutable clipboard policy in authenticated
  provider work; it neither receives clipboard bytes nor inspects provider
  packet payloads.