Module predicate 

Predicates over grains, and boolean gates over triggers.

Both reuse areev_cal::ast::Condition rather than introducing a language. That AST already has And/Or/Not with parenthesised grouping and the right OR < AND < NOT precedence, it already serializes as internally tagged JSON, and areev_cal::executor::grain_matches_condition_tree is a total evaluator for it — a missing field is false, never an error.

Two constraints made this the only workable shape:

• areev_run_core::cond is frozen. Its module doc states “No expression language beyond this in v1: that is a spec-shaped surface and a standing exclusion”, repeated as a hard exclusion in the governed-agents proposal. So Argo Events’ conditions: "(a && b) || c" — the best syntax in the survey — is the one thing that cannot be copied.
• New CAL syntax is an OMS conformance decision. Adding &&/|| tokens to the lexer is a spec-level change against an external standard.

Kestra’s shape is the compatible alternative: a data structure with explicit combinator nodes rather than an infix string. A serialized Condition tree is exactly that. Knative reached the same conclusion independently, shipping its structural all/any/not filters ahead of its SQL dialect because the structural form was “much more stable”.

Functions

from_value

Read a predicate back off a Trigger grain.

gate_satisfied

Evaluate a gate over member triggers that have fired.

grain_matches

Does this grain satisfy the predicate?

parse_predicate

Parse a predicate written as CAL WHERE syntax into a Condition tree.

referenced_members

Every field name a gate expression references.

to_value

Serialize a predicate for storage on a Trigger grain.