feat: batch operations, plan templates, notification preferences, payment fallback chains

[distributed-nerd]

Closes #720
Closes #721
Closes #722
Closes #723

Four merchant-facing capabilities, one commit each so they can be reviewed independently.

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#720 — Batch subscription operations

Contract (contracts/batch)

• Update and Cancel operation types, with per-item cancel reason codes
• A Processing state plus start/finish ledger timestamps, so status tracking covers pending → processing → completed | partial | failed
• Per-operation-type BatchConfig (max items, default atomicity, rollback eligibility, gas rate) behind an admin-only setter
• rollback_batch, which restores the pre-execution snapshot captured during execute — creates are removed, prior state is restored byte for byte, and a subscription touched twice in one batch restores to before the whole batch
• BatchAnalytics maintained globally and per operation type, with a basis-point success rate and execution timing; a rollback discounts its own successful items
• Per-item OperationResult codes, and the batch result persisted for later reads

Client (app/)

• The four near-identical execute paths collapsed into one runner, so atomicity, timing, idempotency and status handling are shared rather than duplicated four ways
• BatchOperationConfig per operation type, applied to chunking, atomicity defaults, retry budgets and size validation
• computeBatchAnalytics — success rates, p95/average duration, per-item timing, throughput, partitioned by operation type
• rollbackBatch driven by a caller-supplied RollbackHandler; a partial reversal leaves the batch partial rather than claiming a clean undo
• Applied (operation, subscription) pairs are tracked so a re-submitted batch cannot double-charge, and successes an atomic rollback discarded are forgotten so a corrected re-run applies them

The unused contracts/batch/src/batch.rs was removed — it duplicated types now in lib.rs and did not compile.

#722 — Plan templates

Contract (contracts/subscription) — new plan_templates module: template registry, per-owner index, version chains, a shared library and per-template analytics. Storage lives behind a single StorageKey::PlanTemplate(TemplateKey) variant rather than six flat ones.

Backend (backend/services/billing) — planTemplateService with the same semantics over a repository interface. Quoting reuses TieredPricingCalculator, so client and server price a ladder identically.

Client — src/types/planTemplate.ts as shared vocabulary, planTemplateStore (library, filters, quoting, versioning, sharing, analytics, three starter templates), subscriptionStore.addFromTemplate, and a PlanTemplatesScreen registered in the root and subscription navigators.

Notable behaviours:

• Graduated pricing ladders, validated ascending with an unbounded rung only at the end
• Per-instantiation overrides that never mutate the template
• Publishing a version retires the previous one, which stays readable — so plans already created from it remain explainable — and leaves the shared library
• addFromTemplate records a conversion only when the subscription actually landed, so a failed create can't inflate the rate

#721 — Notification preferences

Shared types — four channels (email/push/SMS/in-app) and nine notification types, each with a category, priority, default channels and a required flag.

Backend — notificationCenterService: preferences per type and per channel with fallback ordering, multi-channel delivery over pluggable transports (fan out, or stop at the first channel that accepts), quiet-hours deferral with a queue flush, per-(type, channel) templates with versioning and {{variable}} rendering, and history with read/click status feeding delivery, open and click rates.

Client — the store gains the per-type channel matrix, templates, history and analytics while keeping the existing category/digest/quiet-hours/priority settings working; notificationService.deliverNotification resolves preferences, renders the channel's template and dispatches through registered transports; the settings screen gains the channel matrix, per-type mute, an engagement panel and recent activity with read state.

Notable behaviours:

• A required type cannot be muted and cannot lose its last channel, so a subscriber stays reachable about money and account security
• A muted or unroutable notification is recorded as suppressed, never dropped — analytics can tell "not sent" from "sent and ignored"
• Critical notifications go out through quiet hours; everything else defers to the end of the window
• A click implies a read, so engagement is never reported as "clicked but never opened"

#723 — Payment method fallback chains

A fallback chain is an explicit, ordered route — "try the card, then the USDC wallet, then the treasury" — replacing implicit priority ordering. A charge walks it until one method succeeds, so a single expired card no longer means a failed renewal.

• src/services/paymentMethodService.ts — chain construction from the existing priority ordering, validation (length, duplicates, unusable members), resolution, and processPaymentWithChain reporting which position succeeded
• src/store/walletStore.ts — chains and shares as first-class persisted state, cleared on disconnect
• backend/services/billing/paymentMethodRegistry.ts — the same model server-side over a pluggable charge processor, with method CRUD, verification and per-merchant analytics
• app/ — paymentStore gains chains, alerts and analytics; PaymentMethodsScreen gains a chain builder with reordering and inline validation, a severity-coded expiry alert panel, and an analytics panel

Notable behaviours:

• A hard decline (expired, inactive, unverified) halts the chain when configured that way, since falling through would only repeat a configuration problem
• Expiry alerts are graded expired/critical/warning and flag any method still sitting in an active chain — its expiry breaks a charge rather than merely retiring an unused method
• Removing a method drops it from every chain, so a chain never points at something uncharageable
• fallbackRate reports the share of successful charges that only landed because the fallback existed — the number that says whether the chain is doing real work
• Sharing supports viewer / charger roles with spend limits; an elapsed share behaves exactly like a revoked one, so no cleanup job is needed

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Documentation

New: docs/BATCH_OPERATIONS.md, docs/PLAN_TEMPLATES.md, docs/NOTIFICATIONS.md, docs/PAYMENT_METHODS.md.

contracts/batch/BATCHING_API.md was rewritten — it documented a hook-based API (useBatchTransactions, addTransaction) that was never implemented.

Verification

Check	Result
tsc --noEmit	Clean — only the 3 errors already present on main
src/ tests	793 passed; the 1 failing suite (navigationAnalytics.test.ts, a Babel parse error) also fails on main
Backend tests	734 passed; the same 26 suites that fail on main still fail, none newly
Lint / Prettier	Byte-identical to baseline (127 problems, 11 errors — all pre-existing)

197 new tests, all passing: 24 contract, 31 batch service, 16 batch store, 30 plan template service, 26 plan template store, 36 notification center, 31 notification store, 34 payment registry, 22 payment store, 5 contract unit.

Two caveats worth reviewer attention

1. The Rust contracts could not be compiled or tested — and this is pre-existing, not introduced here.

The workspace does not build on main either. soroban-sdk ≤ 21.5 pins ethnum 1.5.0, which fails to compile on a modern rustc; ≥ 21.6 caps contract enum spec cases at 50, and CoreError (51 variants) and StorageKey (52) already exceed it, so subtrackr-types fails its #[contracterror] / #[contracttype] macros. No version combination compiles. Since CI uses dtolnay/rust-toolchain@master, npm run contracts:test is very likely already red.

The Rust here was verified by review, and every changed file parses and is rustfmt --check clean — but it has not been type-checked or executed. The enum-size problem is worth fixing separately before relying on the contract changes. This PR adds one variant to StorageKey (namespaced, rather than the six a flat layout would have needed) to keep the pressure minimal.

2. app/ is excluded from tsconfig.json, .eslintignore and jest's testPathIgnorePatterns.

The 57 batch and payment-method tests under app/ pass, but need an override to run:

npx jest --testPathIgnorePatterns "/node_modules/" --testPathPattern "app/(services|stores)/__tests__"

I left the config alone because enabling app/ would turn CI red on roughly 21 pre-existing failing suites there — but it does mean a meaningful slice of this branch isn't covered by npm test. Separately, .eslintignore's services/ entry also matches src/services/, so that whole directory is silently unlinted.

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