Initial boilerplate scaffold for continuum-common

Adds ts-core (logger, Supabase JWT verification, Elysia error
transformers) and rust-core (thiserror error type, tracing init,
G-code checksum/header parsing) packages.

packages/ts-core/src/errors.ts

@@ -0,0 +1,90 @@
+export abstract class HttpError extends Error {
+  abstract readonly status: number;
+  abstract readonly code: string;
+
+  constructor(message: string, readonly details?: unknown) {
+    super(message);
+    this.name = new.target.name;
+  }
+
+  toJSON() {
+    return {
+      error: {
+        code: this.code,
+        message: this.message,
+        details: this.details,
+      },
+    };
+  }
+}
+
+export class BadRequestError extends HttpError {
+  readonly status = 400;
+  readonly code = "BAD_REQUEST";
+}
+
+export class UnauthorizedError extends HttpError {
+  readonly status = 401;
+  readonly code = "UNAUTHORIZED";
+}
+
+export class ForbiddenError extends HttpError {
+  readonly status = 403;
+  readonly code = "FORBIDDEN";
+}
+
+export class NotFoundError extends HttpError {
+  readonly status = 404;
+  readonly code = "NOT_FOUND";
+}
+
+export class ConflictError extends HttpError {
+  readonly status = 409;
+  readonly code = "CONFLICT";
+}
+
+export class InternalError extends HttpError {
+  readonly status = 500;
+  readonly code = "INTERNAL_ERROR";
+}
+
+interface ElysiaErrorContext {
+  code: string | number;
+  error: unknown;
+  set: { status?: number | string };
+}
+
+/**
+ * Drop-in handler for Elysia's `.onError()`. Maps our HttpError hierarchy,
+ * Elysia's built-in error codes, and anything unrecognized to a consistent
+ * `{ error: { code, message, details? } }` JSON body.
+ */
+export function toErrorResponse({ code, error, set }: ElysiaErrorContext) {
+  if (error instanceof HttpError) {
+    set.status = error.status;
+    return error.toJSON();
+  }
+
+  if (code === "VALIDATION") {
+    set.status = 422;
+    return {
+      error: {
+        code: "VALIDATION",
+        message: error instanceof Error ? error.message : "validation failed",
+      },
+    };
+  }
+
+  if (code === "NOT_FOUND") {
+    set.status = 404;
+    return { error: { code: "NOT_FOUND", message: "not found" } };
+  }
+
+  set.status = 500;
+  return {
+    error: {
+      code: "INTERNAL_ERROR",
+      message: error instanceof Error ? error.message : "internal server error",
+    },
+  };
+}