test(worker): add unit tests for php and swift workers

Extract testable logic from exec.mjs into lib.mjs (preprocessCode,
createIOCallbacks, buildResult) and add vitest tests. Add Go tests
for models, exec helpers, and handlers in worker/swift. Update
justfiles to include test tasks for local dev and CI.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/justfile b/justfile
index fe4c6b2..4825e9d 100644
--- a/justfile
+++ b/justfile
@@ -59,3 +59,5 @@ check:
 
 test:
     cd backend; just test
+    cd worker/swift; just test
+    npm -w worker/php run test