## MODIFIED Requirements

### Requirement: Typed sequenced input envelope
The `input.sequenced.v1` payload SHALL begin with ASCII `VGI1`, a one-byte
event kind, and one-byte payload length. It SHALL contain exactly one bounded
keyboard, mouse-button, relative-mouse, UTF-8 scalar, controller-state,
absolute-mouse, or high-resolution-scroll event. Absolute mouse kind `0x06`
SHALL contain big-endian u16 x, y, viewport width, and viewport height, reject
zero viewports and coordinates outside the viewport, and require negotiated
`input.absolute.v1`. Scroll kind `0x07` SHALL contain big-endian signed i16
vertical and horizontal deltas and require negotiated `input.scroll.v1`. False
keyboard/mouse state and zeroed controller state are explicit releases.
Unknown or unadvertised kinds, length mismatches, malformed UTF-8, unsupported
controller indices, and reserved fields SHALL be rejected before provider
translation.

#### Scenario: Keyboard state change
- **WHEN** a client sends a valid keyboard press or release envelope
- **THEN** the gateway forwards the corresponding typed provider input on its
  reliable keyboard channel and records the pressed state for cleanup.

#### Scenario: Absolute pointer and scroll
- **WHEN** an advertised client sends an in-viewport absolute coordinate or
  signed scroll delta with the exact body length
- **THEN** the gateway accepts the provider-neutral event without adding it to
  pressed-state cleanup.

#### Scenario: Invalid input envelope
- **WHEN** a client sends an unknown or unadvertised kind, invalid length,
  malformed UTF-8 scalar, zero viewport, out-of-range coordinate, or nonzero
  reserved field
- **THEN** the gateway rejects it without sending provider input or changing
  pressed state.