040 abstract compiler pipeline

// Test: Fractal compiler pipeline - ALREADY EXISTS in compiler.kz!
//
// The real implementation is beautiful:
//
// ~compiler.coordinate.default =
//     compiler.context.create(program_ast: program_ast, allocator: allocator)
//     | created c0 |> compiler.coordinate.frontend(ctx: c0.ctx)
//       | continued c1 |> compiler.coordinate.transform_taps(ctx: c1.ctx)
//         | continued c2 |> compiler.coordinate.analysis(ctx: c2.ctx)
//           | continued c3 |> compiler.coordinate.test_generation(ctx: c3.ctx)
//             | continued c4 |> compiler.coordinate.optimize(ctx: c4.ctx)
//               | continued c5 |> compiler.coordinate.emission(ctx: c5.ctx)
//                 | continued c6 |> compiler.metrics.format(...)
//                   | formatted m |> coordinated { ... }
//           | failed f |> error { message: f.message }
//
// Key insights from the REAL code:
// 1. It's a FLOW, not imperative code - the pipeline IS the continuation chain
// 2. Each step is a separate event (compiler.coordinate.frontend, .analysis, etc.)
// 3. Error handling (| failed f |>) is built into the flow
// 4. compiler.coordinate is INTENTIONALLY unimplemented - users override it!
//
// From the comments in compiler.kz:
// "Users can implement compiler.coordinate to customize compilation, or the system
//  will fall back to compiler.coordinate.default (via main.zig bootstrap logic)."
//
// The fractal pattern is ALREADY THERE:
// - Override compiler.coordinate → replace whole pipeline
// - Override compiler.coordinate.analysis → replace just analysis
// - Override compiler.coordinate.frontend → replace just frontend
//
// What we're adding with abstract events:
// - Make this pattern EXPLICIT with ~abstract event
// - Enable delegation to default impl from within override
// - Compile-time enforcement of single implementation

~import "$std/compiler"

// Example: User overrides just the analysis step to add AI error explanation
// ~compiler.coordinate.analysis =
//     compiler.coordinate.analysis.default(ctx: ctx)  // delegate to default
//     | continued c |>
//         if(c.ctx.errors.items.len > 0)
//         | then |> ai_explain_errors(ctx: c.ctx) |> continued { ctx: c.ctx }
//         | else |> continued { ctx: c.ctx }

// Example: User replaces whole pipeline for debug builds
// ~compiler.coordinate =
//     compiler.context.create(program_ast: program_ast, allocator: allocator)
//     | created c0 |> compiler.coordinate.frontend(ctx: c0.ctx)
//       | continued c1 |> compiler.coordinate.analysis(ctx: c1.ctx)
//         | continued c2 |> compiler.coordinate.emission(ctx: c2.ctx)  // skip optimize!
//           | continued c3 |> coordinated { ast: c3.ctx.ast, code: c3.code, metrics: "debug" }

// Placeholder for test framework
~event test.placeholder {}
| ok {}
~proc test.placeholder { return .{ .ok = {} }; }
~test.placeholder()