feat: bake build metadata into the image as env vars #minor

.devcontainer/Dockerfile

@@ -286,5 +286,21 @@ RUN echo '\n# === Backup & Git Reminder ===' | tee -a /home/vscode/.zshrc && \
 USER root
 RUN mkdir -p /home/vscode/.kube && chmod 0700 /home/vscode/.kube
 RUN chown -R vscode:vscode /home/vscode
+
+# Build metadata baked into the image as env vars (available in any run path,
+# including the plain `docker run` in developer-setup.sh -- not just when the
+# image is launched as a devcontainer). Values are supplied as build args by
+# .github/workflows/build_and_publish_devcontainer.yml via devcontainer.json.
+# Kept at the very end of the build so these per-commit values don't invalidate
+# the cache of the (expensive) tool-install layers above.
+ARG COMMIT_SHA=UNKNOWN
+ARG SHORT_SHA=UNKNOWN
+ARG BUILD_TIMESTAMP=UNKNOWN
+ARG GIT_REF=UNKNOWN
+ENV COMMIT_SHA=${COMMIT_SHA}
+ENV SHORT_SHA=${SHORT_SHA}
+ENV BUILD_TIMESTAMP=${BUILD_TIMESTAMP}
+ENV GIT_REF=${GIT_REF}
+
 ENTRYPOINT [ "/usr/local/share/docker-init.sh" ]
 CMD [ "sleep", "infinity" ]

.devcontainer/devcontainer.json

@@ -3,10 +3,19 @@
 {
 	"name": "Ubuntu",
 	"build": {
-		"dockerfile": "Dockerfile"
+		"dockerfile": "Dockerfile",
+		// Build metadata forwarded to the Dockerfile as build args, sourced from
+		// the runner environment set in build_and_publish_devcontainer.yml.
+		// Default to empty locally (Dockerfile ARGs fall back to UNKNOWN).
+		"args": {
+			"COMMIT_SHA": "${localEnv:COMMIT_SHA}",
+			"SHORT_SHA": "${localEnv:SHORT_SHA}",
+			"BUILD_TIMESTAMP": "${localEnv:BUILD_TIMESTAMP}",
+			"GIT_REF": "${localEnv:GIT_REF}"
+		}
 		// Update 'VARIANT' to pick an Ubuntu version: jammy / ubuntu-22.04, focal / ubuntu-20.04, bionic /ubuntu-18.04
 		// Use ubuntu-22.04 or ubuntu-18.04 on local arm64/Apple Silicon.
-	
+
 	},
 
 	// Set *default* container specific settings.json values on container create.

.github/workflows/build_and_publish_devcontainer.yml

@@ -33,6 +33,12 @@ jobs:
       - name: Generate Variables for Tags
         uses: rlespinasse/github-slug-action@e6f261660910b273384c5c42b17a0217881b217a # v5.6.0
 
+      - name: Set build variables
+        id: vars
+        run: |
+          echo "short_sha=${GITHUB_SHA::7}" >> $GITHUB_OUTPUT
+          echo "build_timestamp=$(date -u +"%Y-%m-%dT%H:%M:%SZ")" >> $GITHUB_OUTPUT
+
       - name: Build and run dev container task
         uses: devcontainers/ci@513af61f4de4f75d37e4438f184ba4358f0fc1ca # v0.3
         with:
@@ -41,3 +47,7 @@ jobs:
           push: always
         env:
           VERSION: "${{ env.GITHUB_REF_SLUG }}"
+          COMMIT_SHA: "${{ github.sha }}"
+          SHORT_SHA: "${{ steps.vars.outputs.short_sha }}"
+          BUILD_TIMESTAMP: "${{ steps.vars.outputs.build_timestamp }}"
+          GIT_REF: "${{ github.ref_name }}"