diff --git a/README.md b/README.md
index 5f1a17b..79dc423 100644
--- a/README.md
+++ b/README.md
@@ -173,6 +173,12 @@ the SHA. This makes branch tags **sortable** so
 newest build — the Git SHA alone is not orderable. The short SHA is kept for
 traceability and Flux sorts on the timestamp only.
 
+> **Note:** with `docker-tag-timestamp: 'true'` the build also pushes the plain
+> `<prefix>-<short-sha>` tag alongside the timestamped one. That stable per-commit
+> tag is what the release step retags into the version tag, so it must continue
+> to exist. It does not match the `^<prefix>-[0-9]+-[0-9a-f]+$` filter below, so
+> Flux ignores it.
+
 With the timestamp enabled, use one `ImagePolicy` per environment, filtering by prefix:
 
 ```yaml
diff --git a/scripts/generate-tags.sh b/scripts/generate-tags.sh
index 8f5b26d..036154a 100755
--- a/scripts/generate-tags.sh
+++ b/scripts/generate-tags.sh
@@ -16,24 +16,34 @@ require_env INPUT_DOCKER_REGISTRY
 require_env INPUT_DOCKER_IMAGE
 
 BUILD="true"
+# ALIAS_TAG is an additional immutable tag pushed alongside TAG (see set_branch_tags).
+ALIAS_TAG=""
 
-# branch_tag builds the immutable tag for an environment branch.
+# set_branch_tags computes the immutable tag(s) for an environment branch and
+# assigns them to the globals TAG and ALIAS_TAG.
 #
-# When INPUT_DOCKER_TAG_TIMESTAMP is "true" the tag gets a UTC timestamp inserted
-# before the short SHA (e.g. dev-20260602143055-abcdef12). This makes branch tags
-# sortable by Flux image automation (numerical policy) — the git SHA alone is not
-# orderable, so Flux cannot otherwise tell which build is newest. The SHA is kept
-# for traceability. When the flag is unset/false the legacy <prefix>-<sha> shape
-# is produced, so existing consumers are unaffected.
+# When INPUT_DOCKER_TAG_TIMESTAMP is "true" the canonical TAG gets a UTC timestamp
+# inserted before the short SHA (e.g. dev-20260602143055-abcdef12). This makes
+# branch tags sortable by Flux image automation (numerical policy) — the Git SHA
+# alone is not orderable, so Flux cannot otherwise tell which build is newest.
+# In that case ALIAS_TAG holds the legacy <prefix>-<short-sha> tag, which is also
+# pushed: it is the stable per-commit handle that retag-image.sh looks up to find
+# the source image for a release, so dropping it would break the release retag.
+# The alias does not match Flux's "<prefix>-<digits>-<hex>" pattern, so Flux
+# ignores it. When the flag is unset/false only the legacy <prefix>-<short-sha>
+# tag is produced, so existing consumers are unaffected.
 #
 # The timestamp is overridable via BUILD_TIMESTAMP for deterministic tests.
-branch_tag() {
+set_branch_tags() {
   local prefix="$1"
+  local sha="${GITHUB_SHA::8}"
   if [[ "${INPUT_DOCKER_TAG_TIMESTAMP:-false}" == "true" ]]; then
     local ts="${BUILD_TIMESTAMP:-$(date -u +%Y%m%d%H%M%S)}"
-    echo "${prefix}-${ts}-${GITHUB_SHA::8}"
+    TAG="${prefix}-${ts}-${sha}"
+    ALIAS_TAG="${prefix}-${sha}"
   else
-    echo "${prefix}-${GITHUB_SHA::8}"
+    TAG="${prefix}-${sha}"
+    ALIAS_TAG=""
   fi
 }
 
@@ -43,15 +53,15 @@ if [[ -n "${INPUT_DOCKER_CUSTOM_TAG:-}" ]]; then
   PUSH="true"
   BUILD="${INPUT_DOCKER_DISABLE_RETAGGING:-false}"
 elif [[ $GITHUB_REF == refs/heads/master ]]; then
-  TAG="$(branch_tag master)"
+  set_branch_tags master
   LATEST="master"
   PUSH="true"
 elif [[ $GITHUB_REF == refs/heads/main ]]; then
-  TAG="$(branch_tag main)"
+  set_branch_tags main
   LATEST="main"
   PUSH="true"
 elif [[ $GITHUB_REF == refs/heads/dev ]]; then
-  TAG="$(branch_tag dev)"
+  set_branch_tags dev
   LATEST="dev"
   PUSH="true"
 elif [[ $GITHUB_REF == refs/tags/v* ]]; then
@@ -71,6 +81,9 @@ else
 fi
 
 TAG_LIST="${INPUT_DOCKER_REGISTRY}/${INPUT_DOCKER_IMAGE}:${TAG}"
+if [[ -n "${ALIAS_TAG:-}" ]]; then
+  TAG_LIST+=",${INPUT_DOCKER_REGISTRY}/${INPUT_DOCKER_IMAGE}:${ALIAS_TAG}"
+fi
 if [[ -n "${LATEST:-}" ]]; then
   TAG_LIST+=",${INPUT_DOCKER_REGISTRY}/${INPUT_DOCKER_IMAGE}:${LATEST}"
 fi
diff --git a/tests/generate-tags.bats b/tests/generate-tags.bats
index 2fdfc92..387a9aa 100644
--- a/tests/generate-tags.bats
+++ b/tests/generate-tags.bats
@@ -69,6 +69,27 @@ teardown() {
   assert_output_value "latest" "dev"
 }
 
+@test "timestamp flag pushes a stable <prefix>-<sha> alias in tag_list" {
+  export INPUT_DOCKER_TAG_TIMESTAMP="true"
+  export GITHUB_REF="refs/heads/main"
+  run "$SCRIPT"
+  assert_success
+  # canonical timestamped tag + stable sha alias (for release retag) + floating tag
+  local tag_list
+  tag_list=$(get_output_value "tag_list")
+  [[ "$tag_list" == "registry.staffbase.com/my-service:main-20260602143055-abcdef12,registry.staffbase.com/my-service:main-abcdef12,registry.staffbase.com/my-service:main" ]]
+}
+
+@test "no <prefix>-<sha> alias is added when timestamp flag is off" {
+  export GITHUB_REF="refs/heads/main"
+  run "$SCRIPT"
+  assert_success
+  local tag_list
+  tag_list=$(get_output_value "tag_list")
+  [[ "$tag_list" != *"my-service:main-abcdef12,"*"my-service:main-abcdef12"* ]]
+  [[ "$tag_list" == "registry.staffbase.com/my-service:main-abcdef12,registry.staffbase.com/my-service:main" ]]
+}
+
 @test "main branch with timestamp flag inserts timestamp before sha" {
   export INPUT_DOCKER_TAG_TIMESTAMP="true"
   export GITHUB_REF="refs/heads/main"