AXL Rosetta v4 Kernel

Version: 4.0.2-draft Status: Research draft Tier: NORMATIVE KERNEL License: Apache 2.0

Identity

Model-teachable compression protocol for machine-to-machine communication. Kernel = deterministic syntax. Extensions = compression conventions. Code layer = experimental lossy IR. Thesis = speculation.

Packet Syntax

PKT[VER|CLS|SUB|TAG|ARG1|ARG2|META]

Seven pipe-delimited fields inside PKT[ and ]. Trailing empty fields may be omitted.

Field Constraints

Class Codes

INF (inform), ACT (act), QRY (query), RSP (respond), ERR (error).

Parsing Contract

1. Extract all fields by pipe-split.
2. Parse META first (caret-prefixed ^key:value flags, space-separated).
3. META determines ARG2 dispatch: ^mode:code activates code-body grammar; VER >= 3.1 without ^mode:code activates math-arg grammar; else kernel-arg.
4. TAG dispatch follows the same META/VER logic.
5. Parse legality is separated from interpretation legality. A v3 parser legally extracts all fields from a v4 packet; it does not interpret extension semantics.

Reserved Characters and Escaping

Reserved: | [ ] \ ^ ; Escape with backslash: \| \[ \] \\ \; \^ In kernel-arg and math-arg: pipe, brackets, backslash must be escaped. In code-body: semicolons are statement separators; literal semicolon: \; Caret is literal in ARG fields; flag prefix only in META.

Version Negotiation

VER values: 3, 3.1, 3.2, 4. Senders declare VER in every packet. A receiver must accept any VER <= its own. Unknown VER: PKT[4|ERR|sys|val|unsupported_ver|VER=X]

Error Contract

Validation failure produces ERR packet with TAG indicating error class. Error classes: syntax, version, alias, escape, mode, field. See grammar.bnf ERROR TAXONOMY for full definitions and examples.

Mid-sequence behavior: - Valid packets before the error are accepted (partial sequence is valid). - Malformed packet triggers ERR identifying position via ^ref. - Protocol is best-effort; retransmission is not required.

Alias Scope

^alias:XX registers current SUB as alias XX for the remainder of the current sequence. New sequence resets alias table. Re-registration replaces previous binding. Implementation guidance: alias tables should support at least 64 entries.

Defaults

Missing VER defaults to 4. Missing optional fields default to empty. Unknown ^meta keys are ignored. Verbose uncompressed content is always valid.

Backward Compatibility

All v3 packets parse under v4 rules without modification. Extension content in TAG/ARG2 is opaque text to older parsers. Unknown ^meta flags are ignored by all versions.

Grammar

See spec/grammar.bnf. This document and the grammar are co-authoritative. Conflict: grammar governs syntax; this document governs semantics.