diff --git a/docs/bookings.md b/docs/bookings.md
index df14963..986b13d 100644
--- a/docs/bookings.md
+++ b/docs/bookings.md
@@ -88,9 +88,9 @@ This:
 - Sets `status = confirmed`
 - Clears `expiresAt` on both the booking and its allocations
 
-Confirm is safe to retry — confirming an already confirmed booking returns the confirmed booking.
+Returns `409 Conflict` with code `booking.hold_expired` if the hold expired before confirmation, or `booking.invalid_transition` if the booking is not in `hold` state.
 
-Returns `409 Conflict` with code `hold_expired` if the hold expired before confirmation.
+Confirm is safe to retry with the same `Idempotency-Key` header.
 
 ## Cancel (release)
 
@@ -105,7 +105,9 @@ This:
 - Sets `status = canceled`
 - Deactivates allocations (`active = false`)
 
-Cancel works on both `hold` and `confirmed` bookings. It's safe to retry — canceling an already canceled booking returns the booking.
+Cancel works on both `hold` and `confirmed` bookings. Returns `409 Conflict` with code `booking.invalid_transition` if the booking is already `canceled` or `expired`.
+
+Cancel is safe to retry with the same `Idempotency-Key` header.
 
 ## Expiration
 
diff --git a/docs/errors.md b/docs/errors.md
index fd82100..b8ec810 100644
--- a/docs/errors.md
+++ b/docs/errors.md
@@ -15,9 +15,9 @@ Response shape:
 ```json
 {
   "error": {
-    "code": "VALIDATION_ERROR",
-    "message": "Invalid request data",
-    "details": { ... }
+    "code": "invalid_input",
+    "message": "Invalid input",
+    "issues": [...]
   }
 }
 ```
@@ -35,25 +35,44 @@ Another active allocation already blocks that time range on that resource.
 ```json
 {
   "error": {
-    "code": "overlap_conflict",
-    "message": "Time slot conflicts with existing allocation"
+    "code": "allocation.overlap",
+    "message": "Conflict",
+    "details": {
+      "conflictingAllocationIds": ["alc_..."]
+    }
   }
 }
 ```
 
 ### Policy rejected
 
-The service's policy rejects the booking request (wrong hours, invalid duration, etc.).
+The service's policy rejects the booking request (wrong hours, invalid duration, etc.). The top-level code is always `policy.rejected`; the specific reason is in `details.code`.
 
 ```json
 {
   "error": {
-    "code": "policy_rejected",
-    "message": "Policy evaluation failed"
+    "code": "policy.rejected",
+    "message": "Conflict",
+    "details": {
+      "code": "policy.blackout",
+      "message": "Blackout window"
+    }
   }
 }
 ```
 
+Policy sub-codes:
+
+| `details.code`                   | Meaning                                     |
+| -------------------------------- | ------------------------------------------- |
+| `policy.blackout`                | Date falls in a blackout window             |
+| `policy.closed`                  | Service is closed at that time              |
+| `policy.invalid_duration`        | Duration not allowed by policy              |
+| `policy.misaligned_start`        | Start time doesn't align to scheduling grid |
+| `policy.lead_time_violation`     | Too short notice                            |
+| `policy.horizon_exceeded`        | Too far in advance                          |
+| `policy.overnight_not_supported` | Overnight bookings not supported            |
+
 ### Resource not in service
 
 The requested resource does not belong to the specified service.
@@ -61,8 +80,25 @@ The requested resource does not belong to the specified service.
 ```json
 {
   "error": {
-    "code": "resource_not_in_service",
-    "message": "Resource does not belong to this service"
+    "code": "service.resource_not_member",
+    "message": "Conflict",
+    "details": {
+      "serviceId": "svc_...",
+      "resourceId": "rsc_..."
+    }
+  }
+}
+```
+
+### Service has no policy
+
+Trying to create a booking against a service that has no policy attached.
+
+```json
+{
+  "error": {
+    "code": "service.no_policy",
+    "message": "Conflict"
   }
 }
 ```
@@ -74,21 +110,29 @@ Trying to confirm a booking whose hold has already expired.
 ```json
 {
   "error": {
-    "code": "hold_expired",
-    "message": "Hold expired"
+    "code": "booking.hold_expired",
+    "message": "Conflict",
+    "details": {
+      "expiresAt": "2026-03-01T10:15:00.000Z",
+      "serverTime": "2026-03-01T10:20:00.000Z"
+    }
   }
 }
 ```
 
 ### Invalid state transition
 
-Trying to confirm a booking that is not in `hold` state.
+Trying to confirm or cancel a booking that is not in the expected state.
 
 ```json
 {
   "error": {
-    "code": "invalid_state_transition",
-    "message": "Cannot transition from current status"
+    "code": "booking.invalid_transition",
+    "message": "Conflict",
+    "details": {
+      "currentStatus": "confirmed",
+      "requestedStatus": "confirmed"
+    }
   }
 }
 ```
@@ -113,60 +157,69 @@ Trying to delete a resource that has allocations or service associations.
 ```json
 {
   "error": {
-    "code": "resource_in_use",
-    "message": "Resource has active allocations or service associations"
+    "code": "resource.in_use",
+    "message": "Conflict",
+    "details": {
+      "message": "Resource has active allocations or service associations"
+    }
   }
 }
 ```
 
-### Service has no policy
+### Policy in use
 
-Trying to create a booking against a service that has no policy attached.
+Trying to delete a policy that is referenced by one or more services or bookings.
 
 ```json
 {
   "error": {
-    "code": "service.no_policy",
-    "message": "Service must have a policy to create bookings"
+    "code": "policy.in_use",
+    "message": "Conflict",
+    "details": {
+      "message": "Policy is referenced by one or more services or bookings"
+    }
   }
 }
 ```
 
-### Policy in use
+### Booking-owned allocation
 
-Trying to delete a policy that is referenced by one or more services or bookings.
+Trying to delete an allocation that belongs to a booking. Use the booking cancel endpoint instead.
 
 ```json
 {
   "error": {
-    "code": "policy.in_use",
-    "message": "Policy is referenced by one or more services or bookings"
+    "code": "allocation.managed_by_booking",
+    "message": "Conflict",
+    "details": {
+      "bookingId": "bkg_..."
+    }
   }
 }
 ```
 
-### Booking-owned allocation
+### Idempotency mismatch
 
-Trying to delete an allocation that belongs to a booking. Use the booking cancel endpoint instead.
+Same `Idempotency-Key` header but different request body or path.
 
 ```json
 {
   "error": {
-    "code": "booking_owned_allocation",
-    "message": "Allocation belongs to a booking"
+    "code": "idempotency_payload_mismatch",
+    "message": "Idempotency key already used with different payload"
   }
 }
 ```
 
-### Idempotency mismatch
+## 425 Too Early
 
-Same `Idempotency-Key` header but different request body.
+A previous request with the same `Idempotency-Key` is still processing. Wait and retry.
 
 ```json
 {
   "error": {
-    "code": "IDEMPOTENCY_MISMATCH",
-    "message": "Idempotency key already used with different parameters"
+    "code": "idempotency_in_progress",
+    "message": "Previous request still in progress"
   }
 }
 ```
@@ -180,4 +233,5 @@ Unexpected failure. Retry with backoff and the same `Idempotency-Key` header whe
 - `200`/`201` - proceed
 - `409` - pick a new time slot, adjust parameters, or ask the user
 - `422` - fix your payload (bug)
+- `425` - wait and retry with the same `Idempotency-Key`
 - `5xx` - retry with backoff + idempotency