fix: prevent stale vendor/ from triggering inconsistent vendoring in CI

actions/checkout does not always remove previously-tracked files that
were deleted in a later commit. A runner that checked out a commit with
vendor/ and then checks out a commit without it may still find vendor/
on disk, causing Go to auto-activate vendor mode and fail with
'inconsistent vendoring'.

Add GOFLAGS=-mod=mod at workflow level so all jobs explicitly use module
mode regardless of whether a stale vendor/ directory exists on disk.

Also fix an off-by-one in the compile_binary diagnostic: repo_root was
computed 3 levels up from test/helpers/ (reaching the parent of the repo)
instead of 2 levels up (the repo root itself), causing the
vendor/modules.txt presence check to report a false negative.

Author: driv3r

.github/workflows/tests.yml

@@ -6,6 +6,14 @@ on:
       - main
   pull_request:
 
+# Prevent Go from auto-activating vendor mode when a stale vendor/ directory
+# exists in the workspace. Actions/checkout does not always remove previously
+# tracked files that were deleted in a later commit, so a checkout of a commit
+# that removed vendor/ may still find the directory on disk, causing
+# "inconsistent vendoring" build failures.
+env:
+  GOFLAGS: "-mod=mod"
+
 jobs:
   gh-285:
     strategy:

test/helpers/ghostferry_helper.rb

@@ -148,7 +148,7 @@ def compile_binary
       # Captures GOMOD / GOWORK / GOFLAGS to detect unexpected workspace or
       # vendor-mode activation, and checks for a repo-level vendor/modules.txt.
       go_env, _  = Open3.capture2e("go", "env", "GOMOD", "GOWORK", "GOFLAGS")
-      repo_root  = File.expand_path("../../..", __dir__)
+      repo_root  = File.expand_path("../..", __dir__)
       vendor_txt = File.join(repo_root, "vendor", "modules.txt")
       @logger.debug("[compile_binary] go env: #{go_env.strip}")
       @logger.debug("[compile_binary] repo_root: #{repo_root}")