subscription-lifecycle

Creating a subscription is one API call. Everything that follows is where the money is lost.

The state machine nobody draws

trialing ──► active ──► past_due ──► canceled
    │           │  ▲         │
    │           │  └─────────┘  (retry succeeded)
    │           ▼
    │       paused / grace
    └──► canceled (trial abandoned)

past_due is the state that matters. A subscription there is still delivering value and no longer being paid for. How long you tolerate that, and what the customer sees while it lasts, is a product decision the code has to encode explicitly — the default of "keep serving forever because nobody wrote the branch" is the expensive one.