Keep the espresso machine at brew temperature with a periodic purge

[Vijay Vuyyuru (vijayvuyyuru)]

Summary

prepareDrink pokes the brew button and waits out brew_time_sec without ever checking whether the machine responded. The BES920 sleeps after an hour idle, and a brew on a sleeping machine is refused with three beeps — so the arm waits against a dry group head and serves an empty cup, recorded as a success everywhere downstream. This adds an opt-in loop that periodically holds the 1 CUP button (Breville's own documented group-head purge) to reset the machine's idle timer, so it never leaves brew temperature during working hours.

The purge motion is verified on hardware. Poses are authored and the keepalive_purge action runs clean end to end.

⚠️ Open-loop by design — it cannot recover a machine that is genuinely powered off, so if Auto Start fails to fire, orders still brew cold. Requires has_separate_brew_buttons plus purge_approach/purge_press on the filter switcher; with keepalive unset, nothing changes.

Review guide

Start with coffee/keepalive.go — that's the whole feature. Everything else is wiring.

Changes

• coffee/keepalive.go: schedule parsing, DST-correct window membership, the purge decision, the four-move purge (standoff → press → retreat → home), the ticker, and activity persistence in VIAM_MODULE_DATA.
• coffee/config.go: the KeepAlive block; rejects an unset timezone (LoadLocation("") is UTC, not an error) and a too-tight after_min margin.
• coffee/collisions.go: filterCoffeeButtonCollisions — the filter alone may enter the machine's front buffer and top, on the two linear moves only. The handle, claws, and gripper stay hard obstacles.
• coffee/espresso.go: keepalive_purge added to execute_action for on-demand purges (gated on the machine, not on keepalive, so poses can be verified before the loop is on); actionFuncs split out so registration is assertable; pose requirements gated on keepalive.
• coffee/brew_steps.go: activity recorded in brew(), so a standalone brew_coffee action resets the clock too.
• coffee/module.go, api.go: loop startup and the Keep-alive purge step label.
• README.md: config reference, the new poses, and the operator's Auto Start step.

A purge announces itself through speech_service_name and waits 5 seconds before moving, regardless of conversational — it is the one arm motion nobody requested, so it is a safety notice rather than status narration.

Testing

• go test ./coffee and go test -race ./coffee pass. Subtests cover the window (including an EST/EDT pair proving it is not a fixed UTC offset), validation, persistence, the purge decision table, the collision scope, and action registration across both machine types.
• Verified on hardware: {"execute_action": "keepalive_purge"} presses the button and returns home. Planning needed filter vs coffee-machine-top allowed, which is in the set.
• make lint could not run locally — golangci-lint v1.64.8 against a v2 config, pre-existing and unrelated. gofmt -s and go vet ./... are clean, so CI is the first real lint pass on this code.
• Still to confirm before the loop is switched on: that a 1-second hold actually starts the pump. purge() reports success on motion alone, so too short a hold would reset nothing while looking like it worked. Breville's documented purge is 5 seconds.

Claude Code prompts used

• "We are using a breville machine for making cofee: https://www.breville.com/en-us/product/bes920. I want to solve a problem. The machine auto turns off after some period of inactivity. This is fine overnight and on weekends. However, I think on working days, the arm should turn the machine on by hitting the power button. But we need to also manage the state correctly. I.e it only turns off if its been more than an hour since our last coffee or 4 hours. Also, once we turn it on, the machine has to warm up. The state of the power button is given by the status of the light around the power button. If the machine is off, we should lock the portafilter then hit the button and pick the portafilter after and go home. Use the brainstroming skill and check the manual for the full status. The power button appraoch will be a value on the claw switch while the observe pose is a filter switch. We also need to figure out how to detect this via a realsense attached to the arm. Or maybe a seperate webcam. But vision is important and key. Plan this out, ask questions about unclear and propse how we can do the vision"
• "I think this makes sense but I have a few questions. 1. Are you saying we should have something check on a schedule? Theres a trade off on doing this vs just checking at the start of a brew. What are teh tradeoffs 2. Can you talk about the difference btween power save, standby and off? So the off is handled entirely by the machine itself. But we can tell we're in powersave cause its off and if so, click a single cup button to wake?"
• "What if we change this. Enable auto start on the machine itself. Then, just prevent the machine from going into standby when in certain time windows. We should compare against the last time we brewed something (persisted through reconfigures, maybe by writing smth to disk) every configurable num minutes. If we are brewing or time since is <50 min, sleep until next tick. If time >=50 min, lock portafilter, press manual button twice quickly, then unlock portafilter and go home. That seems simpler overall. Its probably still worth having a machine state sensor later but IDRK if we need this right now."
• "we dont nee da data dir, there should be a Viam enrivonment variable for a dir a module can write to. Check the docs for this. Additionally, we actually dont need the manual. If we press and hold the espresso button for 2 seconds, it does the same w/ no new poses at all."
• "Why do we care about the difference between outside vs not doing anyuthing about it? I also think we should just set it to be the autostart time whenever that is via config param. Also, sure we could do the menu button it just seems easier to not do that. Can you do a scan of the manual or online forums ot check if hitting th emenu buttons resets this time?"
• "Ok great, the hold duration will be quite short. This looks good, create a new worktree"
• "give me the full patht o thes pec"
• "alright looks good, go ahead"
• "whatever is faster"
• "create a pr"
• "remove the spec and plan from this file"
• "What are the new poses"
• "where is this worktree located on disk"
• "alright ive set the pose, on the filter switch what other config changes ar eneeded to test this"
• "Yea add ana ction for this."
• "also, should we edit the logic to be last succesful coffee brew? Some actions have nothign to do w/ keeping the machine on. And that is our strongest guarantee?"
• "Merge in latest main to this branch"
• "what is the do command to trigger the action and to what component?"
• "I got htis error: ConnectError: [unknown] keepalive_purge: move to "purge_press" failed: motion planning failed: all IK solutions failed constraints. Failures: { robot constraint: violation between coffee-machine-top_origin and filter_origin geometries: 100.00% },. Seems like we are hitting the top as well. Can you add this as an allowed collision on the move to purge press pose?"
• "wait i dont want the handle, just the filter."
• "wait a second, did you add the gripper and claws to both? hell now jut let the filter collide w. the top and other allowed collisions during the purge press move"
• "ok great the action itself worked. now give me the config for the auto tracking so I can check that"
• "ok great what are the real values to use"
• "I also think we should add an announcement via voice that its going to move and wait 5 seconds, then move. Something like I am going to keep the coffee machine on to that effect"
• "push this and update the pr"