PAYG: pay-as-you-go billing — metered automation/AI/API + one-time free grant (#6589)

## Summary

Pay-as-you-go (PAYG) billing for Stirling-PDF SaaS. Manual PDF editing
stays free forever; only **automation, AI, and API** usage is metered.
Every team gets a **one-time lifetime free grant** (default 500 PDFs)
before any billing; past that, a team adds a card and pays per metered
document, with a self-set monthly spending cap.

This branch combines and supersedes the in-flight BE (#6574) and FE
(#6579) work plus the SaaS edge functions (Stirling-PDF-SaaS PR, now on
`v3`), hardened into a single reviewable feature after a pre-merge
dead-code/security review.

## Billing model

- **Always free:** manual / JWT web-tool usage is `BYPASSED` — never
metered, no matter where it's triggered.
- **Billable categories:** `AUTOMATION`, `AI`, `API`.
- **One-time lifetime free grant** (`pricing_policy.free_tier_units`,
default 500): never resets, survives subscribing. It gates unsubscribed
teams (billable API calls hard-stop with a 402 once exhausted) and
decides the free-vs-paid split of every job.
- **Subscribed:** paid documents (beyond the grant) are metered to a
Stripe Billing Meter; an optional monthly spending cap degrades billable
categories when reached.
- **Dedup:** the same file pushed through several steps within a
workflow window counts **once** (lineage join), so API/AI chaining on
one file isn't double-charged.

## What's included

**Database** — Flyway migrations `V11`→`V21` with matching Supabase
twins: pricing policy + per-team sidecar (`payg_team_extensions`:
subscription id, Stripe customer, free-grant counter), append-only
`wallet_ledger`, shadow charges, subscription-state RPCs (`V14`), audit
logs (`V15`), billing category (`V16`), one-time lifetime free grant
(`V19`), launch-grant seed (`V20`), drop of the unused
`wallet_category_summary` view (`V21`).

**Charge pipeline** — `PaygChargeInterceptor` (open/join a process,
split the free grant, write the ledger DEBIT), `JobChargeService`
(consume the grant under a row lock, restore it on a first-step refund,
meter only the paid portion on completion), `StaleJobCloser` fallback
(idempotent close → meter).

**Entitlement** — `EntitlementService` (per-team cached snapshot:
grant-gated for free teams, monthly-cap-gated for subscribed) +
`EntitlementGuard` (401 `SIGNUP_REQUIRED` / 402 `FEATURE_DEGRADED` /
`PAYG_LIMIT_REACHED`).

**Metering** — `PaygMeterReportingService` writes a durable
`payg_meter_event_log` row around every POST to the `meter-payg-units`
edge fn (pending → posted/failed); `PaygMeterReconcileScheduler` retries
unposted events under the same idempotency key inside Stripe's 24h dedup
window.

**Billing facts** — `TeamBillingService` reads the synced `stripe.*`
mirror (subscription window, per-document rate; the unsubscribed-team
estimate resolves the rate by Price `lookup_key = plan:processor`).

**Wallet API** — `PaygWalletController`: `GET /api/v1/payg/wallet`,
`PATCH /api/v1/payg/cap`.

**Frontend** — PAYG Plan page (two-card free layout + subscribed views),
`useWallet`, upgrade modal with lazy-loaded Stripe Embedded Checkout and
a shared `SpendCapControl`, customer-portal link, 402/401 interceptor
toast, en-GB i18n. (Per-member usage shows each teammate's spend; the
activity feed is behind a flag until polished.)

**SaaS edge functions** (`Stirling-PDF-SaaS` `v3`) —
`create-checkout-session`, `create-payg-team-subscription`,
`create-customer-portal-session`, `meter-payg-units`,
`payg-subscription-webhook`, `stripe-sync`, plus the stripe-sync
`migrate` + scoped-`backfill` scripts. All price lookup is DB-driven (no
`STRIPE_PAYG_PRICE_ID_*` env vars).

## Release prerequisites (prod)

1. Apply Flyway migrations (`V11`→`V21`) and the Supabase migration
twins.
2. Stripe Sync Engine: run `stripe-sync:migrate`, then a **scoped**
backfill — `product`, `price`, `customer`, `subscription` only (not
`all`, which rate-limits).
3. Register 2 PAYG webhook endpoints (each its own signing secret):
`stripe-sync` (product/price/customer/subscription `.*`) and
`payg-subscription-webhook` (`customer.subscription.created`/`.deleted`
drive state; `.updated` + `invoice.*` observed). Keep the legacy
`stripe-webhook` only if credits/self-hosted flows still run.
4. Stripe Billing Meter: `event_name = payg_doc_units`, value key
`processed_documents`.
5. Env: `PAYG_METER_ENDPOINT` + `SUPABASE_EDGE_FUNCTION_SECRET`
(backend); the webhook signing secrets (edge fns). The default pricing
policy must point at the PAYG Stripe Price(s); `V20` seeds
`free_tier_units = 500`.

## Testing

- `:saas:test` green, `:saas:spotlessCheck` clean, edge-fn Deno tests
green, FE saas typecheck clean (the remaining errors are pre-existing
`proprietary/*` + `prototypes/*`, untouched here). Cucumber shadow-mode
suite + CI workflow included.

## Pre-merge review

An independent dead-code/security pass came back **clean on security**
(team-derived authz / no IDOR, leader-only cap mutation, no
billing-category downgrade, dev/mock hooks gated to
`import.meta.env.DEV` + `/dev/`, no secrets/injection, fail-open
metering by design). The dead/unwired code it flagged has been removed
in this branch (unenforced sub-cap control, an unused JDBC DAO + its
view, dead methods).

## Follow-ups (tracked, not blocking)

- **Enforce per-member sub-caps** — the control was removed because it
read for display but never gated a request; the per-member usage display
and `cap_units` column are retained for when enforcement is wired.
- **API/AI chaining billing model + `ProcessType` enum** — confirm
same-file dedup covers API chaining; define per-tool AI charging; decide
whether the unused enum values stay.
- **Activity feed** — hidden behind a flag until the meter-event surface
is polished.

---------

Co-authored-by: Reece <[email protected]>

app/common/src/main/java/stirling/software/common/service/InternalApiClient.java

@@ -50,6 +50,16 @@ public class InternalApiClient {
                     "^/api/v1/(general|misc|security|convert|filter)(/[A-Za-z0-9_-]+)+$"
                             + "|^/api/v1/ai/tools(/[A-Za-z0-9_-]+)+$");
 
+    /**
+     * Marker propagated on every internal sub-step dispatch so the saas PAYG interceptor classifies
+     * the call as {@code BillingCategory.AUTOMATION}. By construction every {@link
+     * InternalApiClient#post} caller is an automation surface (pipeline executor, AI workflow,
+     * policy runner) running a child tool inside a parent automation flow — see the saas {@code
+     * PaygChargeInterceptor.determineCategory} precedence chain, where this header dominates any
+     * per-tool {@code @RequiresFeature} annotation.
+     */
+    public static final String AUTOMATION_HEADER = "X-Stirling-Automation";
+
     private final ServletContext servletContext;
     private final UserServiceInterface userService;
     private final TempFileManager tempFileManager;
@@ -96,6 +106,11 @@ public class InternalApiClient {
         if (apiKey != null && !apiKey.isEmpty()) {
             headers.add("X-API-KEY", apiKey);
         }
+        // Tag the sub-step as automation so PAYG bills it under AUTOMATION regardless of which
+        // tool-level @RequiresFeature annotation the dispatched controller carries (e.g. an AI-OCR
+        // step inside a policy run must bill as AUTOMATION, not AI). Set unconditionally because
+        // every caller of this dispatcher is an automation surface by design.
+        headers.add(AUTOMATION_HEADER, "true");
 
         HttpEntity<MultiValueMap<String, Object>> entity = new HttpEntity<>(body, headers);
         RequestCallback requestCallback = restTemplate.httpEntityCallback(entity, Resource.class);

app/common/src/test/java/stirling/software/common/service/InternalApiClientTest.java

@@ -59,6 +59,53 @@ class InternalApiClientTest {
                 servletContext, userService, tempFileManager, environment, applicationProperties);
     }
 
+    @Test
+    void postTagsRequestAsAutomation() throws Exception {
+        // Every InternalApiClient.post() caller is a parent automation flow dispatching a child
+        // tool (pipeline executor, AI workflow, policy runner). Tagging the sub-step here means
+        // the saas PaygChargeInterceptor classifies it as BillingCategory.AUTOMATION regardless of
+        // the dispatched controller's @RequiresFeature — so an AI-OCR step inside a policy run
+        // bills as AUTOMATION, not AI. The header value is the literal string "true" because the
+        // interceptor compares case-insensitively-trimmed against that token.
+        MultiValueMap<String, Object> body = new LinkedMultiValueMap<>();
+        body.add("fileInput", namedResource("input.pdf", "data"));
+
+        Path tempPath = Files.createTempFile("internal-api-automation-test", ".tmp");
+        TempFile tempFile = mock(TempFile.class);
+        when(tempFile.getPath()).thenReturn(tempPath);
+        when(tempFile.getFile()).thenReturn(tempPath.toFile());
+        when(tempFileManager.createManagedTempFile("internal-api")).thenReturn(tempFile);
+
+        HttpHeaders[] captured = {null};
+
+        try (var ignored =
+                mockConstruction(
+                        RestTemplate.class,
+                        (rt, ctx) -> {
+                            when(rt.httpEntityCallback(any(), eq(Resource.class)))
+                                    .thenAnswer(
+                                            inv -> {
+                                                HttpEntity<?> entity = inv.getArgument(0);
+                                                captured[0] = entity.getHeaders();
+                                                return (RequestCallback) req -> {};
+                                            });
+                            when(rt.execute(anyString(), eq(HttpMethod.POST), any(), any()))
+                                    .thenAnswer(inv -> fakeOkResponse(inv.getArgument(3)));
+                        })) {
+
+            InternalApiClient mockedClient = newClient();
+            mockedClient.post("/api/v1/general/merge-pdfs", body);
+
+            assertNotNull(captured[0]);
+            assertEquals(
+                    "true",
+                    captured[0].getFirst(InternalApiClient.AUTOMATION_HEADER),
+                    "Sub-step dispatch must carry the automation marker header");
+        } finally {
+            Files.deleteIfExists(tempPath);
+        }
+    }
+
     @Test
     void postDoesNotForceContentType() throws Exception {
         MultiValueMap<String, Object> body = new LinkedMultiValueMap<>();