core: add billing extension seam

TASKS.md

@@ -167,4 +167,5 @@ Progress:
   - Phase 2 dependency slice: `apps/admin-api` now exposes a reusable lib target (`src/lib.rs`), so downstream private repos can depend on `build_app`, `AppState`, `AdminServiceBuilder`, and auth/state modules without copying the Community admin app
   - Phase 3 dependency slice: added public tenancy seam in `crank-core` — `TenantId`, `TenantResolutionContext`, `TenantController`, `TenancyError`, and `SingleTenantController` — so `cloud` can build hosted tenant routing without bypassing the shared extension model
   - Phase 3 dependency slice: added public metering seam in `crank-core` — `MeteringEvent`, `MeteringSink`, `SharedMeteringSink`, and `NoopMeteringSink` — so `cloud` can add hosted usage capture without introducing private-only contracts
+  - Phase 3 dependency slice: added public billing seam in `crank-core` — `BillingHook`, `BillingGate`, `BillingError`, `SharedBillingHook`, and `NoopBillingHook` — so `cloud` can layer billing policy without private-only contracts in the base repo
   - backward-compatible alias `CommunityMachineCredentialVerifier` сохранен, поведение Community не изменено

crates/crank-core/src/ext/billing.rs

@@ -0,0 +1,75 @@
+use std::sync::Arc;
+
+use async_trait::async_trait;
+
+use crate::{TenantId, UsageRollup};
+
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub enum BillingGate {
+    Allow,
+    Deny { reason: String },
+}
+
+#[derive(Debug, thiserror::Error, PartialEq, Eq)]
+pub enum BillingError {
+    #[error("billing integration is not available in this edition")]
+    NotSupportedInEdition,
+    #[error("billing provider failure: {0}")]
+    Provider(String),
+}
+
+#[async_trait]
+pub trait BillingHook: Send + Sync {
+    async fn on_rollup(&self, rollup: UsageRollup) -> Result<(), BillingError>;
+
+    async fn check_billing_gate(&self, tenant: &TenantId) -> Result<BillingGate, BillingError>;
+}
+
+pub type SharedBillingHook = Arc<dyn BillingHook>;
+
+#[derive(Clone, Copy, Debug, Default)]
+pub struct NoopBillingHook;
+
+#[async_trait]
+impl BillingHook for NoopBillingHook {
+    async fn on_rollup(&self, _rollup: UsageRollup) -> Result<(), BillingError> {
+        Ok(())
+    }
+
+    async fn check_billing_gate(&self, _tenant: &TenantId) -> Result<BillingGate, BillingError> {
+        Ok(BillingGate::Allow)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{BillingGate, BillingHook, NoopBillingHook};
+    use crate::{TenantId, UsagePeriod, UsageRollup, WorkspaceId};
+
+    #[tokio::test]
+    async fn noop_billing_hook_allows_default_gate_and_rollups() {
+        let hook = NoopBillingHook;
+
+        hook.on_rollup(UsageRollup {
+            workspace_id: WorkspaceId::new("ws_01"),
+            agent_id: None,
+            operation_id: None,
+            period: UsagePeriod::Last24Hours,
+            calls_total: 10,
+            calls_ok: 9,
+            calls_error: 1,
+            p50_ms: 12,
+            p95_ms: 42,
+            p99_ms: 77,
+        })
+        .await
+        .unwrap();
+
+        let gate = hook
+            .check_billing_gate(&TenantId::new("tenant_01"))
+            .await
+            .unwrap();
+
+        assert_eq!(gate, BillingGate::Allow);
+    }
+}

crates/crank-core/src/ext/mod.rs

@@ -1,6 +1,7 @@
 pub mod access;
 pub mod audit;
 pub mod auth;
+pub mod billing;
 pub mod capability;
 pub mod metering;
 pub mod protocol;

crates/crank-core/src/lib.rs

@@ -47,6 +47,9 @@ pub use ext::auth::{
     TokenIssuerActor, TokenIssuerError, TwoFactorActivation, TwoFactorChallenge,
     TwoFactorPendingIdentity, TwoFactorSetup, TwoFactorStatus, VerifiedMachineCredential,
 };
+pub use ext::billing::{
+    BillingError, BillingGate, BillingHook, NoopBillingHook, SharedBillingHook,
+};
 pub use ext::capability::{CapabilityProfile, CommunityCapabilityProfile};
 pub use ext::metering::{MeteringEvent, MeteringSink, NoopMeteringSink, SharedMeteringSink};
 pub use ext::protocol::{