Diff from the live server, not from your git history — when a local repo has drifted from production
An investigation agent flagged "the license API PHP returns Japanese-hardcoded messages" and we sat down to fix it. But something felt off the moment we opened the file — the version running on the production server didn't match the latest commit in the local repo . Stranger still, production had more recent features than our local checkout . A bit of digging turned up the truth: months earlier, someone had hot-patched the production file in response to a different user issue, and that change had never been committed back to git . This post walks through how we detected that drift, and the two-stage strategy we used to merge production back into the local repo safely. How this regression silently slips in If we'd written the fix on top of our local repo and uploaded it to production, here's what would have happened: all the production-only improvements get overwritten and quietly disappear . In our case, the production file had a half-year-old language-handling addition for the "Early Bird Bonus" feature — when a USD customer buys, client_name is set to 'Early Bird Bonus' ; for JPY customers it's '早期利用特典' . None of that existed in our local git. A normal PR-merge-and-deploy cycle would have silently rolled back the Early Bird i18n logic , regressing English users' display back to Japanese. Catching this was half luck. Opening the file to start the fix, I noticed code I didn't recognize, ran git blame , and the lines were nowhere in git history . That's when alarm bells went off. Two-stage rollforward — make production the source of truth first The strategy we landed on was a two-stage merge. Stage 1 (rollforward sync) : Pull the production file straight into the local repo. Apply the diff in the "production → local" direction, not the other way . After this, the local repo's HEAD matches what's actually running on production. # Pull the production file into the local repo scp -i ~/.ssh/key layer2024@host:wpmm.jp/public_html/license/api/register_free.php \ /tmp/regis