Limits & protocol notes

C3 Mobile's protocol (v2) is deliberately bounded: every message class has a hard size cap and a short lifetime. The caps below are generous for their purpose; hitting one usually signals a misuse the protocol is refusing.

Message and payload bounds

Thing	Limit
Any wire message	256 KiB
Prompt to an agent	64 KiB
Terminal input per send	16 KiB
Terminal grid	400 columns × 240 rows
Scrollback per request	2,000 lines
Keys per key-send command	64
Topology snapshot	4 MiB, transferred as 96 KiB encrypted chunks
Sessions per snapshot	256
Snapshot transfers	4 per 30 seconds

Terminal frames are coalesced to roughly 20 fps on streaming hosts.

Message expiry

Commands are live-or-dead — a message that can't be delivered promptly expires instead of executing later:

Class	Expiry
Terminal input	~5 s
Mutations (workspace/tab/pane operations, prompts)	~10 s
Reads (snapshots, pane reads)	~30 s

Combined with the app's refusal to send while disconnected, there is no offline command queue anywhere in the system.

Channel lifecycle

Encrypted channels between phone and bridge are re-keyed on every reconnect and at most every 15 minutes; command and event directions use independent keys; sequence numbers are monotonic with replay windows, and duplicate requests are deduplicated for 10 minutes.

Network

Listener	Port	Used by
TLS 1.3	4222	Bridges, C3Sync devices
Pinned WSS	8443	Phones

Both are configurable at hub init (--listen, --ws-listen). Control traffic is ephemeral core NATS — nothing mobile-related is persisted on the hub.

Platform qualification (current beta)

Component	Qualified	Built, pending qualification
App	Android	iOS
Bridge	Linux x64, Linux ARM64	macOS (x64/ARM64), Windows x64
Terminal mode	Stream (Linux/macOS)	Snapshot (Windows)

Expo Go is unsupported by design — certificate pinning requires the native build.