GQ: general Boolean OR with explicit grouping and precedence

[ragnorc]

Problem

Read predicates cannot express a general alternative across different properties. For example, this 0.10.0 query fails to parse at or:

query q() {
  match { $p: Person $p.name = "Alice" or $p.name = "Bob" }
  return { $p.slug }
}

Literal-list membership already works for some same-field alternatives (including tested enum membership). It does not provide general Boolean composition across properties or nested predicate groups.

Proposed change

Add typed Boolean disjunction with documented conjunction/negation precedence and grouping. Define null semantics, variable scope and evaluation behavior. Start with read predicates; explicitly decide whether the same expression grammar is shared by update/delete predicates rather than silently making their contracts diverge.

Acceptance criteria

• Same-property and cross-property OR, nested grouping, OR combined with existing conjunction/negation, and nullable comparisons behave consistently.
• Type errors and unsupported variable scopes are rejected during compilation.
• A row matching both alternatives is returned once unless ordinary traversal multiplicity produces additional rows.
• Planner pushdown preserves expression semantics; include indexed and scan paths.

This request concerns Boolean predicates, not choosing alternative edge types. Grammar, type checking.