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2026-10-26 | 🔌 Surviving Dropped Sync Connections 🤖

🐛 The Problem

🧯 The hourly scheduled tasks workflow had been failing about one run in five, and on October 22 it failed four times in a row.

🔍 Every one of those failures died in the same place: the very first step, where the workflow pulls the whole Obsidian vault before any blog or posting task runs.

📜 The logs all ended the same way, with the Obsidian sync client reporting that it had been disconnected from the server.

🔬 What the Evidence Showed

📦 Each run starts from an empty folder and downloads roughly ten thousand seven hundred files, which takes ten to fifteen minutes on a good day.

🎲 The failures struck at random moments, as early as forty four seconds in and as late as fifty one minutes in, after anywhere from six hundred to seven thousand files.

🚫 There were no rate limit or quota messages, and none of our sync code or the sync client version had changed in months.

🧩 The picture was a long download over a single connection that occasionally gets cut, plus a retry loop that only knew how to handle one kind of failure: two sync processes fighting over a lock.

🔧 The Fix

🏷️ A new pure function reads the failure output and classifies it as one of three things: lock contention, a lost connection, or an unrecoverable failure such as an expired subscription.

🔁 Lock contention and lost connections are both retried with exponential backoff, starting at two seconds and doubling, for up to five retries.

🧹 Before each retry, lingering sync processes are stopped and any stale lock is removed, since a crashed client leaves its lock behind.

📊 Each retry logs how many vault files are already on disk, so the run log shows the download resuming rather than starting over.

🎯 The classifier matches the error text the client writes when it fails, not its progress lines, so a note that happens to be named after a disconnect message cannot trigger a retry.

🛡️ Why Resuming Is Safe

⚠️ This vault has been burned before: in March, syncing a stale partial folder made the client think files had been deleted locally, and it deleted them remotely too.

🔎 So before allowing a retry over a half downloaded folder, we read how the sync client keeps its state.

✅ The client records a remote file in its database only after writing the local copy, and keeps unfinished downloads in a pending queue, so files it has not reached yet stay pending downloads instead of looking like deletions.

🆚 The March incident paired an old folder with fresh state, while a retry within the same run reuses a folder and a database that agree with each other.

🛑 The existing circuit breaker still refuses to push if the vault ever ends up with fewer files than it had right after the pull.

🧪 Testing

🔴 The new tests were written first from real failure logs and failed against the old behavior, which treated every disconnect as fatal.

🟢 After the fix they pass, along with property based tests showing that output with no known failure signature is always unrecoverable and that surrounding noise never hides a lost connection.

👀 Looking Ahead

💾 The bigger win would be not downloading the whole vault every hour at all, by caching the vault and its sync state between runs so each pull fetches only what changed. That needs care given the March incident, so it is a follow up rather than part of this change.

📚 Book Recommendations

• Release It! Design and Deploy Production-Ready Software by Michael Nygard
• Designing Data-Intensive Applications by Martin Kleppmann
• Site Reliability Engineering by Betsy Beyer, Chris Jones, Jennifer Petoff, and Niall Richard Murphy
• Thinking in Systems by Donella Meadows