Archive the add-cups-printserver-container change

Moves the completed change to openspec/changes/archive/2026-10-18-add-cups-printserver-container/ and syncs the printserver/cups capability into openspec/specs/.
2026-10-18 16:54:54 +02:00
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+# Proposal
+
+## Why
+
+Run a Podman container that shares the Brother HL-4150CDN network printer over
+IPP/AirPrint, so clients on macOS, iOS/iPadOS, Linux and Windows can print.
+
+The HL-4150CDN already emulates BR-Script3 (PostScript 3) and accepts PostScript
+on its AppSocket/LPD ports, so the container can forward PostScript directly to
+the printer instead of shipping Brother's 32-bit Linux CUPS wrapper plus
+Ghostscript rasterisation. This removes the i386 dependency, the multiarch
+runtime and the fragile vendor filter chain.
+
+The previous approach (Brother Linux `.deb` packages) turned out not to work in
+`debian:bookworm-slim`: the vendor filter `filterhl4150cdn` needs `file` (with
+`a2ps` as a fallback), which are not installed, so it exits with an error and
+produces no output. The official BR-Script3 PPD avoids that entire code path.
+
+## What Changes
+
+- Create a Containerfile for Podman based on Debian stable running CUPS, Avahi
+  and D-Bus (no i386 multiarch).
+- Install Brother's official **BR-Script3 PPD** (committed under
+  `assets/Brother HL-4150CDN/ppd/`) so CUPS emits device options — paper source
+  (tray), duplex and colour/mono, plus media type, print quality, toner save and
+  secure print — as PostScript `setpagedevice`.
+- Point the queue at the printer with a raw AppSocket URI (`socket://<ip>:9100`)
+  by default.
+- Convert incoming client formats (URF/Apple Raster, PWG Raster, PDF, PostScript)
+  to PostScript inside CUPS and pass them through to the printer's PostScript
+  interpreter.
+- Share the queue over IPP and advertise it via mDNS/DNS-SD (Avahi/AirPrint).
+- Keep runtime configuration (printer address, protocol, queue name) in
+  environment variables.
+- Document the supported client matrix.
+
+## Capabilities
+
+### New Capabilities
+- `printserver/cups`: Containerised CUPS print server which shares the Brother
+  HL-4150CDN over IPP/AirPrint and prints by sending PostScript (BR-Script3)
+  directly to the printer.
+
+### Modified Capabilities
+None
+
+## Impact
+
+- Containerfile plus supporting `cupsd.conf` and `entrypoint.sh` in the
+  repository root.
+- Uses `assets/Brother HL-4150CDN/ppd/BR4150_2.PPD`.
+- Runtime ports: CUPS/IPP (631/tcp), mDNS/DNS-SD (5353/udp).
+- No 32-bit runtime libraries; the image no longer depends on the host CPU
+  architecture.
+- Windows clients install Brother's own BR-Script3 Windows driver client-side.
+- The unused Brother Linux `.deb` packages previously under
+  `assets/Brother HL-4150CDN/` have been removed.