ci: pull the courier CLI with the bare OCI protocol; crane:debug has no /bin/sh

Woodpecker's k8s backend runs every step through /bin/sh. crane:debug
carries only /busybox/sh, so the fetch-courier step died at container
init (pipeline 10). The release step now fetches the manifest by digest
from zot, tries each blob as a gzip tar for usr/local/bin/courier and
stops at the one that has it — busybox wget, tar and gzip, which
alpine/git has. Proven in that image before this push.

.woodpecker.yml

@@ -66,22 +66,16 @@ steps:
       branch: main
       event: push
 
-  # The release channel. Two steps because courier's image is distroless — the
-  # binary is exported out of it, then run from an image that has sh and git.
-  # `courier deployed` appends a version to the document releases/hush.prod
-  # (the changelog, `git log <serving>..<this>`) and posts one message on the
-  # `deploys` topic, as the `releases` agent, whose credential can send and do
-  # nothing else. The same call every other substrate makes — see
+  # The release channel. `courier deployed` appends a version to the document
+  # releases/hush.prod (the changelog, `git log <serving>..<this>`) and posts one
+  # message on the `deploys` topic, as the `releases` agent, whose credential can
+  # send and do nothing else. The same call every other substrate makes — see
   # orchard9-k3sf scripts/lib/release.sh; this is the Woodpecker copy.
-  fetch-courier:
-    image: gcr.io/go-containerregistry/crane:debug
-    commands:
-      - crane export registry.threesix.ai/courier/courierd:3d490785@sha256:9d1ce76216a93f3d3808fc208179aaa2eb6c3eda20332095a28c3893b2ff5bdf - | tar -xf - usr/local/bin/courier
-      - mv usr/local/bin/courier ./courier && rmdir -p usr/local/bin 2>/dev/null || true
-    when:
-      branch: main
-      event: push
-
+  #
+  # The CLI comes out of courier's own image, pinned by digest, pulled with the
+  # bare OCI protocol (zot allows anonymous pulls): the image is distroless and
+  # the k8s backend runs steps through /bin/sh, so neither the image itself nor
+  # crane:debug (/busybox/sh only) can be the step — measured on pipeline 10.
   release:
     image: alpine/git
     environment:
@@ -89,6 +83,15 @@ steps:
       COURIER_TOKEN:
         from_secret: courier_releases_token
     commands:
+      - |
+        R=https://registry.threesix.ai/v2/courier/courierd
+        D=sha256:9d1ce76216a93f3d3808fc208179aaa2eb6c3eda20332095a28c3893b2ff5bdf   # courierd:3d490785
+        wget -qO manifest.json --header='Accept: application/vnd.oci.image.manifest.v1+json,application/vnd.docker.distribution.manifest.v2+json' "$$R/manifests/$$D"
+        for l in $$(grep -o '"digest":"sha256:[a-f0-9]*"' manifest.json | cut -d'"' -f4); do
+          wget -qO- "$$R/blobs/$$l" | tar -xzf - usr/local/bin/courier 2>/dev/null && break
+        done
+        test -x usr/local/bin/courier || { echo "courier CLI not found in any layer of courierd@$$D"; exit 1; }
+        mv usr/local/bin/courier ./courier; rm -rf usr manifest.json
       - |
         set -- hush prod ${CI_COMMIT_SHA} \
           -image registry.threesix.ai/hush/api:${CI_COMMIT_SHA:0:8} -substrate k3s \