Here are the data structures with brief descriptions:

C[struct].s_fixed
C[struct].s_handlers
C[struct].s_state
CCalendarConfig	The rules a face hands the store, built from its own settings so the store names no SETTING_*
CCalendarEvent	One event. start and end are absolute epochs so the readouts stay fresh against the watch's own clock. The phone fills end with a sensible default when the feed omits DTEND
CCalendarPersist	The trimmed snapshot saved to flash. Holds only the first few events, not the whole strip
CCalendarSeed	Optional prefill: shown until the first real reading lands, or pinned when live = false
CCalendarStrip	The agenda strip. count is 0 until a reading lands
CCallbackList	A list over storage its owner provides. Start it as {entries, max, 0}
CDevShot	One screenshot's worth of state, so a walk of eight themes is not eight shots of the same numbers
CEngineSlot	One slot of a face. Set zone (+ text) for a text-slot, or frame (+ draw) for a draw-slot. Never both. A text-slot with no text stays empty, and so does a draw-slot with no draw
CHealthConfig	The rules a face hands the store
CHealthSaved	The only part worth keeping across a relaunch
CHealthSeed	Optional prefill, or pinned readings when live = false
CHourLatch	Remembers the hour that last buzzed
CIconEntry	One cached icon. Its resource id, the loaded picture, and the extra state icon_tint and the auto-trim scan keep between calls
CIconMargins	The transparent border around an icon's opaque art, in pixels per side
CLocationConfig	The rules a face hands the store
CLocationSeed	Optional prefill, or pinned coords when live = false. On a live store a seed takes the place of restoring the last real fix, and shows until the phone sends coordinates. A seed is never saved, so the fix on flash stays as it was for the next launch without one
COutboxJob	One job waiting to go out, or already in flight
COutboxQueue	Everything the outbox is holding: what is waiting, what nacked, and what is out
CSettingField	Blueprint for a single setting
CSettingsInbound	Carries what an inbound settings message changed, so the caller can react
CSettingsSchema	A face's persistence identity
CStockConfig	The rules a face hands the store, built from its own settings so the store names no SETTING_*
CStockSeed	Optional prefill: shown until the first real reading lands, or pinned when live = false
CStockSlot	One quote slot. When ok is false the symbol field carries a short status word ("RATE LIMIT" and friends) instead of a ticker so the watch has something to show
CStockStrip	The watchlist strip. count is 0 until a reading lands
CStoreFetch	One store's polling state, its catch-up timer, and how it asks the phone
CStorePoll	One store's polling: its interval, whether it polls at all, and when it is next due
CSystemConfig	The rules a face hands the store
CSystemSeed	Optional prefill, or pinned state when live = false
CTimeBand	The stretch of day a band shows: where it starts and how long it runs
CTimeBandSpan	A span clipped to the window, in minutes past the window's start
CTimeConfig	The rules a face hands the store, built from its own settings so the store names no SETTING_*
CWeatherClock	The watch's clock at the moment a message lands, broken apart
CWeatherConfig	The rules a face hands the store, built from its own settings so the store names no SETTING_*
CWeatherDaily	The 7-day strip. count is 0 until a reading lands
CWeatherDayCol	One daily forecast column: a sky code plus the day's high and low
CWeatherHourCol	One hourly forecast column: a sky code plus a temperature (WEATHER_NO_TEMP for none)
CWeatherHourly	The hourly strip. count is 0 until a reading lands
CWeatherMessage	One weather message as the transport read it, before anything is kept
CWeatherSeed	Optional prefill: shown until the first real reading lands, or pinned when live = false
CWeatherState	The weather a store keeps, laid out as the blob it saves to flash
CZone	Everything needed to present one text slot. Where it sits, and which registered font, alignment, and colour to use, plus up to three smaller font and rect tiers to step down to when the text would overflow