docs: add Endorser JWT options for background New Activity prefetch

Document expired-token causes, client limits, and server-side options (TTL,
scoped tokens, refresh, BFF) plus questions for Endorser maintainers.

doc/endorser-jwt-background-prefetch-options.md

@@ -0,0 +1,152 @@
+# Options: expired JWT during background “New Activity” prefetch (mobile)
+
+**Date:** 2026-03-26 17:29 PST  
+**Audience:** TimeSafari / crowd-funder team; **Endorser server** maintainers (auth + API policy)  
+**Context:** Android Capacitor app, `POST /api/v2/report/plansLastUpdatedBetween`, native `TimeSafariNativeFetcher` invoked from WorkManager at **T−5 minutes** before the daily notification.
+
+---
+
+## Problem (short)
+
+New Activity notifications prefetch Endorser data in **background** (no JavaScript, no WebView). The HTTP client uses a **Bearer JWT** supplied earlier via `configureNativeFetcher` / `getHeaders(activeDid)`.
+
+If the **access token’s `exp`** is **before** prefetch time, the API returns **400** with a body like:
+
+```json
+{
+  "error": {
+    "message": "JWT failed verification: ... JWT has expired: exp: … < now: …",
+    "code": "JWT_VERIFY_FAILED"
+  }
+}
+```
+
+We **cannot** rely on the user opening the app immediately before prefetch (T−5), so **client-only** mitigations (e.g. refresh JWT on app resume) **reduce** failures but **do not guarantee** a valid token for headless background work.
+
+---
+
+## Why this is different from normal in-app API calls
+
+| In-app | Background prefetch |
+|--------|----------------------|
+| `getHeaders()` runs in JS when needed; user often recently active | WorkManager runs **without** Capacitor / passkey / session refresh |
+| Short TTL tokens are refreshed as the user uses the app | Same token may sit in native memory until **T−5** (or longer) |
+
+So **server-side** and **architecture** choices matter for this feature.
+
+---
+
+## Options (for decision)
+
+### 1. Increase access token TTL (Endorser / IdP)
+
+**Idea:** Issue access JWTs with a longer `exp` so that **configure time → prefetch time** (often **5+ minutes**, sometimes **24h+** if the user rarely opens the app) usually still falls inside validity.
+
+| Pros | Cons |
+|------|------|
+| Simple to explain; one policy change | Longer-lived bearer tokens increase risk if exfiltrated; mitigate with scope, rotation, monitoring |
+| No client protocol change | May not fit strict security posture without a dedicated scope |
+
+**Endorser owner:** token lifetime, scopes, and whether a **dedicated** lifetime or scope for “mobile background read” is acceptable.
+
+---
+
+### 2. Scoped long-lived token for report reads only (Endorser)
+
+**Idea:** Mint a **separate** access token (or sub-scope) valid only for **read-only report** endpoints (`plansLastUpdatedBetween`, etc.), with a **longer TTL** than the interactive session token.
+
+| Pros | Cons |
+|------|------|
+| Limits blast radius vs “longer JWT for everything” | Requires auth model + issuance path; client must store/use this token only for prefetch |
+
+**Endorser owner:** feasibility of **narrow scope** + **longer TTL** for this use case.
+
+---
+
+### 3. Refresh token or device grant (Endorser + mobile native)
+
+**Idea:** Client stores a **refresh token** (or OAuth **device** grant) in **Android Keystore / iOS Keychain**. Before `plansLastUpdatedBetween`, **native** code (no JS) exchanges it for a **new access token**.
+
+| Pros | Cons |
+|------|------|
+| Standard pattern; short TTL for access tokens remains | Endorser must support refresh (or equivalent); secure storage + rotation; **both** client and server work |
+| Works when app is backgrounded for days | Implementation cost on mobile |
+
+**Endorser owner:** refresh endpoint, token rotation, revocation.  
+**Mobile owner:** native fetch path, secure storage, failure handling.
+
+---
+
+### 4. Backend proxy / BFF (TimeSafari backend + Endorser)
+
+**Idea:** Phone calls **your** backend with a **device session** (or FCM registration id); **server** uses **server-to-server** credentials or a **service account** to call Endorser. The device **never** sends an Endorser JWT for this path.
+
+| Pros | Cons |
+|------|------|
+| No Endorser JWT lifetime problem on device | New service, auth, rate limits, privacy review |
+| Central place for logging, abuse control | Operational cost |
+
+**Endorser owner:** partner / S2S auth model for the BFF.  
+**Product team:** hosting and trust boundaries.
+
+---
+
+### 5. “Cron” or periodic jobs on the device to refresh JWT (JS)
+
+**Idea:** Use something like a **cron** schedule to refresh tokens.
+
+**Reality:** Scheduled **native** jobs can run, but **Capacitor / `getHeaders()` / passkey** do **not** run reliably in that context without waking the **WebView**. So **“cron”** only helps if refresh is **fully native** (see option 3) or you accept **unreliable** wake + JS.
+
+**Not recommended** as the primary fix unless paired with **native refresh** or **server** changes.
+
+---
+
+### 6. Product / UX constraints (no server change)
+
+**Idea:** Accept that **headless** API calls may fail if the session is stale; show **fallback** copy; or require “open app once per day” for best results.
+
+| Pros | Cons |
+|------|------|
+| No Endorser change | Does not meet “API-driven notification” expectation for inactive users |
+
+---
+
+## Client-side mitigations already in play (not sufficient alone)
+
+- **`configureNativeFetcherIfReady()`** after startup and when **Account** / identity is ready.
+- **`appStateChange` → `isActive`:** refresh native fetcher when the app returns to foreground (reduces staleness when the user **does** open the app).
+- **Error logging** of 400 bodies for diagnosis.
+
+These **do not** guarantee a fresh JWT at **T−5** if the user never opens the app before prefetch.
+
+---
+
+## Suggested decision order
+
+1. **Align on security posture:** Is a **longer TTL** or **scoped long-lived read token** acceptable for Endorser?
+2. If not, is **refresh token in native** (option 3) or **BFF** (option 4) on the roadmap?
+3. **Parallel:** UX fallback when API is unavailable (option 6) so the app never silently looks “broken.”
+
+---
+
+## References (this repo)
+
+| Topic | Location |
+|--------|----------|
+| Native fetcher + JWT from `getHeaders` | `src/services/notifications/nativeFetcherConfig.ts` |
+| Android POST + errors | `android/app/src/main/java/app/timesafari/TimeSafariNativeFetcher.java` |
+| Web `plansLastUpdatedBetween` + `afterId` | `src/libs/endorserServer.ts` (`getStarredProjectsWithChanges`) |
+| New Activity / dual schedule | `doc/notification-from-api-call.md`, `doc/plugin-feedback-android-dual-schedule-native-fetch-and-timing.md` |
+
+---
+
+## Open questions for Endorser (server developer)
+
+1. What is the **current access token TTL** and can it be **increased** for mobile clients, or **per-scope**?
+2. Is **refresh token** (or similar) available for **non-interactive** renewal?
+3. Would a **read-only** scope for `plansLastUpdatedBetween` with a **longer** lifetime be acceptable?
+4. Is there an existing **server-to-server** or **partner** path that a **BFF** could use instead of user JWT on device?
+
+---
+
+*This document is for internal planning and decision; update it when the team chooses an approach.*