feat: OpenApiDocument is now a class with built-in file watching and EventTarget

[Copilot]

Summary

OpenApiDocument was a plain interface — loading and watching the spec file were handled by separate loadOpenApiDocument and OpenApiWatcher helpers. This PR collapses all three responsibilities into a single class.

src/server/openapi-document.ts — new class:

• Extends EventTarget; dispatches "reload" whenever the file changes on disk
• new OpenApiDocument(source) — captures source path
• await doc.load() — reads + dereferences the spec, populates paths, basePath, produces
• await doc.watch() / await doc.stopWatching() — file-system watcher (no-op for "_" and HTTP sources)

src/server/load-openapi-document.ts — now just creates an instance and calls load().

src/server/dispatcher.ts — retains the old OpenApiDocument interface for backward-compat; class instances satisfy it structurally so existing tests and consumers pass plain objects unchanged.

src/app.ts — OpenApiWatcher removed; replaced by openApiDocument?.watch() / openApiDocument?.stopWatching().

const doc = new OpenApiDocument("/path/to/openapi.json");
await doc.load();
await doc.watch(); // starts watching; emits "reload" on changes
doc.addEventListener("reload", () => { /* react to live spec updates */ });
await doc.stopWatching();

Original Prompt

OpenAPIDocument should be a class

It should know the location of its source file. It should read the file and initialize itself. It should watch for changes (instead of a separate OpenAPIWatcher). It should extend EventTarget so it can notify others when it has been reloaded (those that formerly relied on OpenAPIWatcher).

Manual acceptance tests

• Edit the OpenAPI spec file while the server is running — routes reflect the new spec without a restart
• loadOpenApiDocument() returns an instance with paths, basePath, and produces populated correctly
• Stopping the server cleanly closes the watcher (no dangling process or unhandled-rejection warnings)
• openApiPath: "_" starts the server with no file watcher active
• Routes that existed before a live reload continue to respond correctly (regression)

Tasks

• Created src/server/openapi-document.ts: OpenApiDocument extends EventTarget with load(), watch(), stopWatching()
• Simplified src/server/load-openapi-document.ts to delegate to the new class
• Removed OpenApiWatcher usage from src/app.ts; wired openApiDocument.watch() / stopWatching() in its place
• Kept the backward-compatible OpenApiDocument interface in dispatcher.ts so plain-object test fixtures continue to compile
• Added test/server/openapi-document.test.ts with 8 tests (EventTarget, load, error handling, reload event, path update after reload, no-op watch paths)
• Added minor changeset