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Documentation / Reference / Protocol compatibility

REFERENCE · PROTOCOL

Versions, capabilities, and compatibility.

The connection version selects framing and authentication; Hello capability negotiation selects the semantic terminal and session features available to that connection.

Version range

The current application protocol is N=2 and supports N-1=1. ALPN astra/1 identifies the framing and authentication family; Hello's version range and capability selection define the actual semantics.

Capability table

CapabilityVersionStatus
terminal.semantic_statev2Enabled
terminal.history_pagingv1Enabled
session.objectsv1Enabled
terminal.input_leasev1Enabled
terminal.state_ack / terminal.semantic_diffv1Enabled
transport.stream_channelsv1Negotiated
terminal.datagram_statev3 / v2Fully negotiated per peer

Version 1.2 uses Quinn by default. DATAGRAM requires semantic state v2, state ACKs, semantic diffs, session objects, and stream channels. Older servers missing dependencies use reliable compatibility; no experimental switch is required.

Compatibility boundary

Only N-1 clients without semantic capability negotiation enter the isolated ANSI path. Standalone SSH/SFTP Hosts are a separate product mode, not Astra-over-SSH stdio fallback.

Evolution rules

Capabilities must be negotiated explicitly. UI code must not guess old-field semantics, and migration paths must be versioned and registered. Clients reject unknown or incomplete state and request a reliable baseline.