General: Warn when a pod's listening time drops far below its rating

[d4rken]

What changed

CAPod already estimated how much of its rated listening time each earbud still reaches, but that number sat in the device details sheet behind the info icon, where almost nobody would find it. Now, when one of your pods has dropped to half its rated listening time or less, a warning appears directly on that device's settings screen. Tapping it opens the details sheet with the per-pod figures.

The warning only appears once there is enough recent evidence behind it: at least eight listening sessions for that pod, with the most recent measurement under 60 days old. Until then nothing is shown, exactly as before, and turning off battery estimates for a device hides it entirely.

The wording also changed from "Battery Health" to estimated listening time. The figure compares measured drain against Apple's published listening rating, and a short runtime can come from loud volume, cold weather or a demanding codec just as easily as from a worn-out cell. Calling it "health" claimed more than the measurement supports.

Technical Context

• The promotion gate reuses fields already persisted on DrainProfile.LearnedRate (updateCount, updatedAt), so there is no serialization change and no migration, and existing users qualify on data they already have. A richer per-session evidence store was considered and rejected: it would have changed the persisted shape, reset every user's figure, edited the estimator's most defect-prone code path, and centred on a route-verification signal that does not exist yet (see below).
• The 50% threshold is mid-range rather than late. BatteryEstimator.plausibleForModel rejects any learned listening rate faster than 4x the rated drain (SPEC_BAND_MAX), so the derived figure can never fall below roughly 25%.
• The banner triggers on the minimum across pods and names the affected one. The figure is deliberately per-pod, since a single failing earbud is exactly what a combined number would mask.
• The detail sheet and its detailItems construction moved out of the device_info LazyColumn item up to screen scope. Left inside, the banner's tap would set the visibility flag while the only sheet renderer sat in a disposed lazy item, so nothing would open and the sheet would then appear unprompted when scrolling back to the header.
• Known and deliberately not addressed here: the listening gate in BatteryEstimator uses device.isSystemConnected as a proxy for "audio is routed to these pods", but that flag derives from BluetoothProfile.HEADSET (HFP), not the active A2DP route. A worn-but-unrouted pod can have idle drain learned as listening drain, which biases the figure upward and therefore suppresses warnings rather than causing false ones. Separate change.
• String keys were left unrenamed and only the English values changed, so the existing translated locale files keep their entries and Crowdin marks them for re-translation.
• The banner has not been seen rendering on a device: its trigger needs roughly eight real listening sessions with genuine battery drain, so the gate arithmetic is covered by unit tests while the rendering is covered only by Compose previews.