IR

Tsonic IR is the frontend/backend boundary.

What IR captures

• module identity
• imports and exports
• statements and expressions
• resolved types
• generic substitutions
• backend-relevant semantic decisions that must survive into emission

What IR is not

• not a backend syntax tree
• not raw TypeScript AST
• not Roslyn AST

The backend syntax tree is a later layer: CSharpAst.

Why the split exists

IR keeps frontend reasoning separate from backend syntax concerns.

Examples:

• source-package resolution belongs in the frontend and IR side
• C# keyword escaping belongs in backend AST/printer
• numeric proof belongs before backend emission

Why IR matters in practice

Most tricky bugs in the stack are frontend-to-backend contract bugs:

• a source-package call surface was not fully specialized
• a promise or callback result shape was normalized incorrectly
• a local package boundary carried the wrong ownership mode

IR is where those decisions become explicit and testable before the backend has to print C# syntax.