fix: re-declare ARG TARGETARCH in each Dockerfile stage

Docker automatic platform ARGs are only in scope for FROM instructions.
$TARGETARCH in RUN commands was always empty, so the deadsnakes PPA
conditional never ran and python3.13 could not be found on the Ubuntu
22.04 CUDA base.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

CHANGELOG.md

@@ -7,6 +7,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [0.2.6] - 2026-06-12
+
+### Fixed
+
+- **Dockerfile: `ARG TARGETARCH` re-declared in each stage**: Docker's automatic platform ARGs are only in scope for `FROM` instructions, not `RUN` commands. The `$TARGETARCH` variable in the deadsnakes PPA conditional was silently empty, so the PPA was never added and `python3.13` could not be located on the Ubuntu 22.04 CUDA base. Adding `ARG TARGETARCH` at the top of both the `build` and `runtime` stage bodies fixes the amd64 build.
+
 ## [0.2.5] - 2026-06-12
 
 ### Changed

Dockerfile

@@ -10,6 +10,7 @@ ARG TARGETARCH
 
 FROM base-${TARGETARCH} AS build
 
+ARG TARGETARCH
 ENV DEBIAN_FRONTEND=noninteractive
 
 # amd64 (Ubuntu 22.04 CUDA base): Python 3.13 via deadsnakes PPA
@@ -47,6 +48,7 @@ RUN chmod +x /app/entrypoint.sh
 
 FROM base-${TARGETARCH} AS runtime
 
+ARG TARGETARCH
 ENV DEBIAN_FRONTEND=noninteractive
 
 RUN apt-get update && apt-get install -y --no-install-recommends \

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "winnow"
-version = "0.2.5"
+version = "0.2.6"
 description = "Immich to Frigate training sets"
 license = "MIT"
 requires-python = ">=3.13"