Implementation Status

This tracks what the src/language/ pipeline implements today against the grammar and AST sketched in README.md. The runtime stays declarative: the compiler captures topology and policy in an inspectable [Blueprint], while runnable behaviour is supplied by a Rust-side NodeFactory.

Package shape

Flat files under src/language/:

file	role
span.rs	byte+line/column source spans
source.rs	source files and the source map
diagnostic.rs	structured diagnostics and the caret renderer
ast.rs	source AST node types (Program, GraphDecl, NodeDecl, …)
lexer.rs	source text into spanned tokens
parser.rs	tokens into the AST
compiler.rs	AST into one Blueprint per graph, capability binding, graph build
types.rs	tokens + compiled Blueprint/*Spec types (re-exports ast)

ast.rs is re-exported from types.rs, so existing crate::language::types::{Program, NodeDecl, …} paths keep resolving.

Implemented grammar

Graph-level items

• start <ident> — entry node.
• defaults { key value … } — graph defaults.
• input { name type … } / output { name type … } — graph I/O shape (lowered to Blueprint::input / Blueprint::output as IoFieldSpecs).
• checkpoint <ident> / interrupt <ident> — graph-level checkpoint and interrupt policies (Blueprint::checkpoint / Blueprint::interrupt).
• channel <name> <reducer> <arg>* — state channel bound to a reducer policy. Arguments are string/number literals (e.g. a named aggregate reducer or a barrier arrival count) captured in ChannelSpec::args.
• node <name> { … } — node declarations (see below).
• from -> to — static edges.
• join [a, b] -> c — top-level barrier (Blueprint::joins, JoinSpec).

Node-level items

Common: kind, model, system/prompt, tools [..], next, routes { label -> target }.

Extended (H2):

• agent "name" — sub-agent reference for a subagent node (NodeSpec::agent).
• graph "name" — subgraph reference for a subgraph node (NodeSpec::subgraph; binding prefers it over the legacy model field).
• script "name" — REPL script capability for a repl_agent node (NodeSpec::script). Declaration only — never inline code.
• input "mapping" — input mapping for sub-agent / subgraph nodes.
• command { goto <target> update { key value … } } — typed command (NodeSpec::command, CommandSpec). A bare goto also lowers into the node's routing (precedence: routes > next > command goto > edge > terminal).
• sends [ send <node> ["input"] … ] — fanout (NodeSpec::sends, SendSpec).
• sources [a, b] — upstream nodes for a join node (NodeSpec::join_sources).
• options ["approve", "reject"] — choices for an interrupt node.
• checkpoint <ident>, timeout <literal>, retry { … }, metadata { … } — node-level policies.

Node kinds

The registry-backed binding path (DEFAULT_NODE_KINDS) accepts agent, model, tool_executor, subgraph, graph, subagent, repl_agent, router, interrupt, join, and human.

Validation

compile rejects: duplicate nodes, missing/undefined start, unknown next/route/edge/command goto/send/join targets, duplicate route labels, and mixing static routing with routes. Registry binding additionally checks model/tool/subgraph/router/agent/script/reducer references and node kinds. A single shared policy (CapabilityResolver::classify_reference) maps each node kind to the reference it must resolve, so the compiler blueprint gate and both Resolver paths cannot drift: subagent binds its agent reference against the registered agents and repl_agent binds its script reference against the registered scripts.

Not yet implemented

• State-schema declarations (state Name { … }).
• Steering policy lowering for subagent nodes (parsed shape only is partial).
• Duration literals like 60s (write timeouts as a number or quoted string).
• Formatter and round-trip golden tests (milestone L8).
• Agent-authored review gates and blueprint provenance (milestone L7).
• An agent-name allowlist on CapabilityResolver (sub-agent names are carried in the blueprint but not yet registry-validated).