fix airprint discovery

openspec/changes/fix-airprint-discovery/specs/printserver/cups/spec.md

@@ -0,0 +1,19 @@
+# Spec Delta
+
+## MODIFIED Requirements
+
+### Requirement: Printer is shared and discoverable
+The system SHALL share the queue over IPP and advertise it via AirPrint
+(mDNS/DNS-SD).
+
+#### Scenario: IPP printer is shared
+- **WHEN** CUPS runs in the container
+- **THEN** the printer is shared via IPP for network clients
+
+#### Scenario: AirPrint discovery
+- **WHEN** Avahi runs alongside CUPS
+- **THEN** the printer is advertised via AirPrint with URF, sides and colour capabilities so macOS and iOS/iPadOS clients can discover it without a driver
+
+#### Scenario: Advertised DNS-SD sub-types
+- **WHEN** the shared queue is advertised over mDNS
+- **THEN** its `_ipp._tcp` and `_ipps._tcp` registrations carry the `_print` and `_universal` sub-types and carry no `_cups` sub-type, so a client that classifies a printer carrying `_cups` as a shared CUPS printer — macOS, in its Add Printer window — still offers its driverless AirPrint driver