dx: consumer build.zig has to reach into merjs internals (src/main.zig, tools/codegen.zig, src/worker.zig)

[justrach]

Problem

When you use merjs as a dependency, your build.zig has to reference internal file paths from the merjs package directly:

const merjs_dep = b.dependency("merjs", .{});
const mer_mod = merjs_dep.module("mer");

// These all reach into merjs internals
const main_mod = b.createModule(.{
    .root_source_file = merjs_dep.path("src/main.zig"),  // <-- internal path
});

// codegen
.root_source_file = merjs_dep.path("tools/codegen.zig"),  // <-- internal path

// worker
.root_source_file = merjs_dep.path("src/worker.zig"),  // <-- internal path

This means:

• If merjs renames or moves src/main.zig, every consumer's build breaks
• The consumer has to know merjs's internal file layout to set up their project
• @import("mer") works great as a module, but the entry points (server, codegen, worker) aren't exposed as proper modules

What I expected

Something like:

const merjs_dep = b.dependency("merjs", .{});
const mer_mod = merjs_dep.module("mer");
const server_mod = merjs_dep.module("server");    // instead of merjs_dep.path("src/main.zig")
const codegen_mod = merjs_dep.module("codegen");   // instead of merjs_dep.path("tools/codegen.zig")
const worker_mod = merjs_dep.module("worker");     // instead of merjs_dep.path("src/worker.zig")

Or even better, merjs's build.zig could export helper functions that set up the full build for consumers:

const merjs = b.dependency("merjs", .{});
merjs.addServer(b, .{ .name = "my-site", .app_dir = "app", .api_dir = "api" });
merjs.addWorker(b, .{ .name = "my-site" });
merjs.addCodegen(b);

Context

Ran into this building the kuri site (justrach/kuri/site). The build.zig is 120 lines of boilerplate that mostly just wires up merjs internals. Related to #61 (the init experience), but this is about the ongoing build DX, not just first setup.

Also: wasm/ directory missing from .paths

The build.zig.zon .paths field doesn't include wasm/, which means wasm/counter_config.zig isn't in the published package. The build system tries to import it and fails with FileNotFound. Had to manually copy it from the git source.

[justrach]

Concrete pain point: adding a new page requires editing src/generated/routes.zig manually

When building the turboapi.trilok.ai frontend (which uses merjs as a dep), adding a new page (app/httpcore.zig) required:

1. Creating the page file in app/ — expected, fine
2. Manually editing src/generated/routes.zig to add the import + route entry — this should be automatic

The build.zig already walks app/ and registers modules via addAppPages(), but the route table in src/generated/routes.zig is a static file that doesn't get regenerated on build. So the build succeeds (Zig sees the module) but the server returns 404 because the route isn't in the table.

What I expected: zig build picks up new .zig files in app/ and the route table updates automatically.

What actually happened: Had to manually add:

const app_httpcore = @import("app/httpcore");
// ... and the route entry in the array

This is exactly the "reaching into merjs internals" problem described in this issue. A consumer shouldn't have to know about src/generated/routes.zig at all.

Additionally: filenames with hyphens (e.g. http-core.zig) don't work because Zig identifiers can't contain -. Had to rename to httpcore.zig. The codegen/route scanner should handle this (e.g. replace - with _ in the identifier, keep the hyphenated URL path).