diff --git a/.github/workflows/e2e-tests.yml b/.github/workflows/e2e-tests.yml
index c68b05f2a9..efa5a5ccb0 100644
--- a/.github/workflows/e2e-tests.yml
+++ b/.github/workflows/e2e-tests.yml
@@ -42,6 +42,9 @@ jobs:
         with:
           persist-credentials: false
 
+      - name: Test image stamp
+        run: sh e2e/stamp_test.sh
+
       - name: Set up Go
         uses: actions/setup-go@v7
         with:
diff --git a/e2e/stamp.sh b/e2e/stamp.sh
index 73fb5591d0..9c4ed355be 100755
--- a/e2e/stamp.sh
+++ b/e2e/stamp.sh
@@ -27,16 +27,24 @@ digest() {
 }
 
 {
-	# the content of those paths, not the commit: an e2e-only commit cannot change the image, and
-	# keying on HEAD would rebuild the stack for every one of them
-	# shellcheck disable=SC2086 # the path list is deliberately split into arguments
-	for path in $sources; do
-		git rev-parse "HEAD:$path"
-	done
+	# Hash the files on disk, not HEAD plus a diff: staging or committing the same
+	# content must not invalidate a running stack. Skip deleted files, including
+	# staged deletions, so committing their removal leaves the stamp unchanged too.
+	# shellcheck disable=SC2086,SC2016 # split paths; expand $file in the child shell
+	git ls-files -z -- $sources | xargs -0 sh -c '
+		for file do
+			if [ -f "$file" ]; then
+				if command -v sha256sum >/dev/null 2>&1; then
+					sha256sum "$file"
+				else
+					shasum -a 256 "$file"
+				fi
+			fi
+		done
+	' sh
+	# Only untracked names belong here; porcelain also records index state.
 	# shellcheck disable=SC2086
-	git diff HEAD -- $sources
-	# shellcheck disable=SC2086
-	git status --porcelain -- $sources
+	git ls-files --others --exclude-standard -z -- $sources
 	# an instrumented build is a different binary from the same sources, so it has to be a
 	# different stamp: without this a coverage stack is accepted for a plain run, and a plain
 	# stack for a coverage run, which reports no coverage at all and looks like untested code
diff --git a/e2e/stamp_test.sh b/e2e/stamp_test.sh
new file mode 100644
index 0000000000..b62e3fdee1
--- /dev/null
+++ b/e2e/stamp_test.sh
@@ -0,0 +1,80 @@
+#!/bin/sh
+# Exercise the stamp without building an image or starting the browser stack.
+set -eu
+
+stamp_script=$(cd "$(dirname "$0")" && pwd)/stamp.sh
+work=$(mktemp -d "${TMPDIR:-/tmp}/remark42-stamp.XXXXXX")
+trap 'rm -rf "$work"' EXIT HUP INT TERM
+mkdir -p "$work/e2e/telegramstub" "$work/backend" "$work/frontend"
+cp "$stamp_script" "$work/e2e/stamp.sh"
+cd "$work"
+git init -q
+git config user.name w3lld1
+git config user.email w3lld1@users.noreply.github.com
+printf 'original\n' > backend/source
+printf 'frontend\n' > 'frontend/file with spaces'
+printf 'stub\n' > e2e/telegramstub/source
+printf 'image\n' > Dockerfile
+printf 'init\n' > docker-init.sh
+git add .
+git commit -qm initial
+
+stamp() { E2E_COVERAGE='' sh e2e/stamp.sh; }
+same() {
+	if [ "$1" != "$2" ]; then
+		printf 'FAIL: %s (%s != %s)\n' "$3" "$1" "$2" >&2
+		exit 1
+	fi
+	printf 'PASS: %s\n' "$3"
+}
+different() {
+	if [ "$1" = "$2" ]; then
+		printf 'FAIL: %s (%s == %s)\n' "$3" "$1" "$2" >&2
+		exit 1
+	fi
+	printf 'PASS: %s\n' "$3"
+}
+
+original=$(stamp)
+printf 'edited\n' > backend/source
+edited=$(stamp)
+different "$original" "$edited" 'tracked content changes the stamp'
+git add backend/source
+same "$edited" "$(stamp)" 'staging an edit preserves the stamp'
+git commit -qm edit
+same "$edited" "$(stamp)" 'committing an edit preserves the stamp'
+
+rm backend/source
+deleted=$(stamp)
+different "$edited" "$deleted" 'deleting a tracked file changes the stamp'
+git add backend/source
+same "$deleted" "$(stamp)" 'staging a deletion preserves the stamp'
+git commit -qm deletion
+same "$deleted" "$(stamp)" 'committing a deletion preserves the stamp'
+
+printf 'changed\n' > 'frontend/file with spaces'
+spaced=$(stamp)
+different "$deleted" "$spaced" 'content in a path with spaces is hashed'
+git add frontend
+git commit -qm spaces
+same "$spaced" "$(stamp)" 'committing a path with spaces preserves the stamp'
+
+printf 'new\n' > frontend/untracked
+untracked=$(stamp)
+different "$spaced" "$untracked" 'untracked names change the stamp'
+printf 'later edit\n' > frontend/untracked
+same "$untracked" "$(stamp)" 'untracked contents retain the name-only behavior'
+mv frontend/untracked frontend/renamed
+different "$untracked" "$(stamp)" 'renaming an untracked file changes the stamp'
+rm frontend/renamed
+same "$spaced" "$(stamp)" 'removing an untracked file restores the stamp'
+
+printf 'suite only\n' > e2e/test.txt
+git add e2e/test.txt
+git commit -qm suite
+same "$spaced" "$(stamp)" 'a suite-only commit preserves the stamp'
+printf 'edited stub\n' > e2e/telegramstub/source
+different "$spaced" "$(stamp)" 'the telegram image sources are included'
+plain=$(stamp)
+same "$plain" "$(E2E_COVERAGE=0 sh e2e/stamp.sh)" 'coverage=0 is a plain build'
+different "$plain" "$(E2E_COVERAGE=1 sh e2e/stamp.sh)" 'coverage=1 is a separate build'