One thread.

The slip that started this expedition was small: the rest timer was behaving oddly on Android. Not broken exactly, but wrong in a way a lifter would notice immediately. You finish a set, start the rest, put the phone down and leave the app. When you come back, the countdown has not moved as far as it should.

The timer had been running off a tick-counter - decrement once per interval, repeat. On Android, the thread that runs JavaScript is suspended when the app goes to background. The interval keeps its count internally, but the real clock keeps going. When the app returns to foreground, the difference between what the timer believes and what actually elapsed has grown by however long you were away. A serious lifter backgrounds the app during every rest period. The timer was wrong exactly when it mattered most.

We rewrote it to work from an absolute deadline: when you start rest, the end time is fixed. Each tick derives the display from the difference between now and that fixed end. When the app comes back to foreground, it resyncs. The rest timer now matches the clock on the wall.

The second thing

While verifying that the fix was landing on device, a second problem surfaced. The live-session panel was rendering as blank on Android. Nothing visible, no error shown. The session existed; the screen did not.

The cause was the notification import. The way notifications had been wired in, the package was loaded at startup regardless of environment. On Android under the development workflow we were using at the time, the notification module does not exist - the package assumes native capabilities that the workflow explicitly strips out. Loading a package whose native module is absent does not produce a helpful error message. It throws during module evaluation, which aborts the panel’s entire setup, which is why the screen appeared blank. The panel was never rendered. Nothing in the output said why.

The fix: guard the import so it only runs in environments where the module actually exists. The live panel loads cleanly. The notifications themselves continue to work where they work.

Why this was the ceiling

Once the notification guard was in place and the timer fix was confirmed, the obvious question was whether Android rest notifications could be made to work properly - not just “not crash,” but actually fire on the lock screen while the user is between sets.

The answer was: not in the workflow we were using.

The development setup had been scanning a QR code to load the app into a general shell maintained by the Expo team. That shell exists to make early development fast. Its tradeoff is that it does not include every native capability. The notification native module is one of those capabilities on Android - precisely the one this expedition needed. There is no workaround for an absent native module. It either exists in the build or it does not.

We moved to a custom build. The app now compiles its own native shell - once, when native dependencies change - and runs JavaScript bundles against that. The development version installs as a distinct app alongside preview and production builds, so the three coexist on the same device without interfering. Build scripts exist for local development and production release. The Android release build had a lint failure during this migration that was resolved by removing an unnecessary lint pass over third-party code; our actual quality gates are elsewhere.

What the next expedition will find

The notification design is written. Not built - drawn. The intent is a clock- app-style countdown that appears on the lock screen when the app is backgrounded mid-rest: an OS-ticked chronometer that counts down live, swaps to a completion alert at zero, offers a thirty-second extension, and opens the live panel on tap. The implementation involves a specific sequencing of notification types that handles the swap correctly without triggering Play-policy concerns about foreground services.

The library decision is also in the record. The spec sits ready. The next expedition that picks this up will not need to redo the architecture work - they will need to build against what we drew.

For the lifter currently using the work, two things are different: the rest timer no longer drifts when you leave the app, and the live-session panel no longer goes blank on Android. Everything else looks the same.

For those who come after.

• Dayo, Logger of Expedition 21