# Notification support matrix

What each channel can actually prove, and what the platform refuses to claim.

## Channels

| Channel | Reference implementation | Grade | Strongest evidence the platform records by default |
|---|---|---|---|
| Email | SMTP, Amazon SES API | Stable | Provider acceptance; recipient mail-server delivery, bounce and complaint when the provider publishes events |
| SMS | Twilio Programmable Messaging | Stable | `accepted`/`queued`, `sent`, and carrier-DLR `delivered`/`undelivered` |
| Mobile push (Android and cross-platform) | FCM, FID-first with legacy registration token compatibility | Stable | FCM acceptance and explicit failures |
| Mobile push (Apple) | APNs HTTP/2 provider API | Stable | APNs acceptance |
| Web Push | RFC 8030, RFC 8291, RFC 8292 | Stable | Push-service acceptance; user-agent acknowledgement only where the service offers receipts |
| In-app inbox | Own database | Optional stable | `PERSISTED`, `SEEN`, `READ` |
| Webhook | HTTP client platform | Extension | Whatever the receiving HTTP contract states |

## Evidence levels

`NONE` → `PLATFORM_QUEUED` → `PROVIDER_ACCEPTED` → `NETWORK_OR_CARRIER_ACCEPTED` →
`DEVICE_DELIVERED` → `USER_AGENT_DISPLAYED` → `USER_READ`

| Provider signal | Highest evidence it may produce |
|---|---|
| Internal queue commit | `PLATFORM_QUEUED` |
| SES `MessageId` | `PROVIDER_ACCEPTED` |
| SES `Delivery` | `NETWORK_OR_CARRIER_ACCEPTED` |
| Twilio `accepted` / `queued` | `PROVIDER_ACCEPTED` |
| Twilio `sent` | `NETWORK_OR_CARRIER_ACCEPTED` |
| Twilio `delivered` | `DEVICE_DELIVERED` |
| FCM send success | `PROVIDER_ACCEPTED` |
| APNs 2xx | `PROVIDER_ACCEPTED` |
| Web Push `201` | `PROVIDER_ACCEPTED` |
| Web Push receipt capability | `DEVICE_DELIVERED` |
| In-app row commit | `PROVIDER_ACCEPTED` |
| In-app `seen` endpoint | `USER_AGENT_DISPLAYED` |
| In-app `read` endpoint, authenticated app receipt | `USER_READ` |

Promotions the platform will not make, in code or in configuration:

- FCM send success is not `DEVICE_DELIVERED`.
- An APNs 2xx is not `DELIVERED`.
- An SES `MessageId` is not `DELIVERED`.
- An SMTP `250` is not inbox delivery.

## Submission outcomes

`NOT_SUBMITTED`, `CONFIRMED_ACCEPTED`, `CONFIRMED_REJECTED`, `AMBIGUOUS`.

`AMBIGUOUS` is a first-class stored state, not an error path. It means the request body was committed
to the provider and the outcome could not be read. While an ambiguous attempt exists on a recipient
delivery, automatic retry and automatic cross-channel fallback are both blocked.

## Not supported

The platform will not claim any of the following, because no channel above can support them:

- guaranteed delivery
- guaranteed read
- exactly-once human notification
- unconditional multi-provider failover after an unread response
- provider SDK types in the public API
- audience selection, campaign segmentation or jurisdiction rulings

## Target model

`FCM_FID` is the primary mobile push target. `FCM_REGISTRATION_TOKEN_LEGACY` and
`APNS_DEVICE_TOKEN` are separate types with separate lifecycles; they are never flattened into one
string field.