Webhook DLQ — list failed deliveries and manually retry

Closes the silent-loss hole in outbound webhook delivery. The worker
in src/webhooks.rs retries failed deliveries with exponential backoff
up to 10 attempts, then sets next_attempt_at = NULL and walks away.
Pre-this-commit, those "dead-lettered" rows sat in webhook_deliveries
forever with no surface for the operator to discover, inspect, or
recover from them — a subscriber that was down for >6h during a
license-issuance burst would silently lose those events forever.

What's new:

- repo::DeliveryStatusFilter — enum with parse() so query strings
  map cleanly to SQL predicates.
- repo::list_deliveries — endpoint_id + status + limit, newest first.
- repo::requeue_delivery — resets attempt_count=0, clears delivered_at
  and last_error, sets next_attempt_at=now. The worker picks it up on
  the next 5s tick.

- src/api/webhook_deliveries.rs — admin module with two handlers:
  - GET /v1/admin/webhook-deliveries?endpoint_id=…&status=…&limit=…
  - POST /v1/admin/webhook-deliveries/:id/retry  (audit-logged as
    webhook_delivery.retry; 404 on missing id)
- Routes registered in src/api/mod.rs alongside the existing
  webhook_endpoints CRUD.

- tests/api.rs gains webhook_dlq_lists_failed_and_retry_requeues:
  seeds three deliveries directly via SQL (one each: delivered,
  pending, dead-lettered), exercises the list filter, runs the retry,
  asserts the row migrates from failed→pending, audit row is written,
  404 on bad id, 400 on bad status filter.

Worker code is unchanged. The DLQ is operator-actionable infrastructure
on top of the existing retry semantics.

Test count: 23 (9 unit + 4 migration + 10 API), up from 22.

licensing-service/src/api/mod.rs

@@ -70,6 +70,7 @@ pub mod session_layer;
 pub mod tier;
 pub mod validate;
 pub mod webhook;
+pub mod webhook_deliveries;
 pub mod webhook_endpoints;
 
 use crate::btcpay::client::BtcpayClient;
@@ -304,6 +305,16 @@ pub fn router(state: AppState) -> Router {
             "/v1/admin/webhook-endpoints/:id",
             axum::routing::delete(webhook_endpoints::delete),
         )
+        // Webhook delivery history (the dead-letter inspection +
+        // manual-retry surface; see webhook_deliveries.rs for why).
+        .route(
+            "/v1/admin/webhook-deliveries",
+            get(webhook_deliveries::list),
+        )
+        .route(
+            "/v1/admin/webhook-deliveries/:id/retry",
+            post(webhook_deliveries::retry),
+        )
         // Discount / referral codes.
         .route(
             "/v1/admin/discount-codes",

licensing-service/src/api/webhook_deliveries.rs

@@ -0,0 +1,104 @@
+//! Admin views over the outbound webhook delivery queue.
+//!
+//! Companion to `webhook_endpoints.rs`: that module manages the
+//! configured subscriber URLs; this one exposes the row-level history
+//! of attempts (success, in-flight retries, dead-lettered failures)
+//! and lets operators manually re-queue a dead delivery for another
+//! pass through the worker.
+//!
+//! Why this exists: the worker in `crate::webhooks` retries failed
+//! deliveries with exponential backoff up to 10 attempts, then sets
+//! `next_attempt_at = NULL` and walks away. Pre-this-module, those
+//! "dead-lettered" rows were invisible — operators had no surface to
+//! discover, inspect, or recover from them. A subscriber endpoint
+//! that was down for >6h during a license-issuance burst would
+//! silently lose those events forever.
+
+use crate::api::admin::{request_context, require_admin};
+use crate::api::AppState;
+use crate::db::repo::{self, DeliveryStatusFilter};
+use crate::error::{AppError, AppResult};
+use axum::{
+    extract::{Path, Query, State},
+    http::HeaderMap,
+    Json,
+};
+use serde::Deserialize;
+use serde_json::{json, Value};
+
+const DEFAULT_LIMIT: i64 = 100;
+const MAX_LIMIT: i64 = 500;
+
+#[derive(Debug, Deserialize)]
+pub struct ListDeliveriesQuery {
+    /// Filter by configured endpoint id. Omit for all endpoints.
+    pub endpoint_id: Option<String>,
+    /// One of `pending` | `delivered` | `failed` | `all`. Defaults to
+    /// `all`. The `failed` filter is the dead-letter queue — rows
+    /// where the worker exhausted retries.
+    pub status: Option<String>,
+    /// Cap on rows returned. Defaults to 100; max 500.
+    pub limit: Option<i64>,
+}
+
+pub async fn list(
+    State(state): State<AppState>,
+    headers: HeaderMap,
+    Query(q): Query<ListDeliveriesQuery>,
+) -> AppResult<Json<Value>> {
+    require_admin(&state, &headers)?;
+    let status = match q.status.as_deref() {
+        Some(s) => DeliveryStatusFilter::parse(s).ok_or_else(|| {
+            AppError::BadRequest(format!(
+                "invalid status filter '{s}'; expected pending|delivered|failed|all"
+            ))
+        })?,
+        None => DeliveryStatusFilter::All,
+    };
+    let limit = q
+        .limit
+        .unwrap_or(DEFAULT_LIMIT)
+        .clamp(1, MAX_LIMIT);
+    let rows = repo::list_deliveries(
+        &state.db,
+        q.endpoint_id.as_deref(),
+        status,
+        limit,
+    )
+    .await?;
+    Ok(Json(json!({ "deliveries": rows })))
+}
+
+/// Manual re-queue for a dead-lettered (or otherwise stuck)
+/// delivery. The worker will pick it up on the next 5s tick.
+///
+/// 404 if the delivery id doesn't exist; 200 on success with the
+/// updated row in the body so the SPA can re-render the list with
+/// the new state immediately.
+pub async fn retry(
+    State(state): State<AppState>,
+    headers: HeaderMap,
+    Path(id): Path<String>,
+) -> AppResult<Json<Value>> {
+    let actor_hash = require_admin(&state, &headers)?;
+    let (ip, ua) = request_context(&headers);
+    let delivery = repo::requeue_delivery(&state.db, &id)
+        .await?
+        .ok_or_else(|| AppError::NotFound(format!("webhook delivery '{id}'")))?;
+    let _ = repo::insert_audit(
+        &state.db,
+        "admin_api_key",
+        Some(&actor_hash),
+        "webhook_delivery.retry",
+        Some("webhook_delivery"),
+        Some(&id),
+        ip.as_deref(),
+        ua.as_deref(),
+        &json!({
+            "endpoint_id": delivery.endpoint_id,
+            "event_type": delivery.event_type,
+        }),
+    )
+    .await;
+    Ok(Json(json!(delivery)))
+}