GitHub Actions expression parsing logic (AST nodes, tokenizer, parser, optimizer, patterns, builders) was spread across 9 files in pkg/workflow with no clear ownership boundary and several obvious pattern duplicates.

New pkg/ghexpr package

Pure expression-parsing infrastructure extracted into a standalone package with full spec documentation:

Tests: parser_test.go, optimizer_test.go, builder_test.go, patterns_test.go, plus white-box internal tests (optimizer_white_box_test.go, parser_white_box_test.go).

pkg/workflow — backward-compatible delegation

All 38+ existing files in pkg/workflow continue to compile unchanged via Go type aliases and function var aliases:

// expression_nodes.go
type ConditionNode = ghexpr.ConditionNode
type AndNode       = ghexpr.AndNode
// …

// expression_optimizer.go
var OptimizeExpression = ghexpr.OptimizeExpression

expression_patterns.go re-exports core patterns from ghexpr and retains only gh-aw–specific context patterns (AWInputsPattern, SecretsExpressionPattern, etc.).

Duplicate patterns eliminated

Internal white-box tests that directly accessed unexported optimizer/parser symbols are migrated to pkg/ghexpr as package ghexpr (non-_test) files.