diff --git a/.config/migration-gate-floor.txt b/.config/migration-gate-floor.txt
new file mode 100644
index 000000000..1da7a3af2
--- /dev/null
+++ b/.config/migration-gate-floor.txt
@@ -0,0 +1,10 @@
+# Committed floor for the number of tests selected by the migration-critical
+# CI gate (see scripts/check_migration_gate_count.sh, backlog#1153 infra-12).
+#
+# The floor equals the exact count of rustfs-ecstore --lib tests matching the
+# gate filter (name substrings: data_movement, rebalance, decommission,
+# source_cleanup, delete_marker) at the time this file was last updated.
+# CI fails if the selected count drops below this number, so renames or
+# removals that thin the gate must update this file in the same PR.
+# Adding tests does not require a bump, but bumping keeps the guard tight.
+571
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index b55082482..6a0950e32 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -170,13 +170,18 @@ jobs:
       # Explicit gate for migration-critical suites. These tests already ran in
       # the full nextest pass above; a single filtered nextest invocation keeps
       # the named gate without rebuilding or re-running them one package at a time.
+      #
+      # The gate selects tests by name substring (data_movement / rebalance /
+      # decommission / source_cleanup / delete_marker), so renames can silently
+      # thin it. The script owns the filter expression and first verifies the
+      # selected-test count against the committed floor in
+      # .config/migration-gate-floor.txt before running the gate; renames or
+      # removals must update that file consciously (see the script header).
       # Kept on the default profile (no --profile ci): a second --profile ci run
       # would clobber target/nextest/ci/junit.xml, and none of these tests are
       # quarantined so they gain nothing from the ci profile's retry overrides.
       - name: Run rebalance/decommission migration proofs
-        run: |
-          cargo nextest run -p rustfs-ecstore --lib \
-            -E 'test(data_movement) or test(rebalance) or test(decommission) or test(source_cleanup) or test(delete_marker)'
+        run: ./scripts/check_migration_gate_count.sh
 
   test-and-lint-rio-v2:
     name: Test and Lint (rio-v2)
diff --git a/scripts/check_migration_gate_count.sh b/scripts/check_migration_gate_count.sh
new file mode 100755
index 000000000..22c853e71
--- /dev/null
+++ b/scripts/check_migration_gate_count.sh
@@ -0,0 +1,79 @@
+#!/usr/bin/env bash
+# Count-floor guard for the migration-critical test gate (backlog#1153 infra-12).
+#
+# ci.yml's migration gate selects tests BY NAME SUBSTRING. A rename that drops
+# a test out of the filter silently thins the gate — potentially to zero —
+# without any CI signal (this is how the layered gate died when #878 closed).
+# This script owns the filter expression so the count check and the test run
+# cannot drift, and fails fast when the number of selected tests drops below
+# the committed floor in .config/migration-gate-floor.txt.
+#
+# NAMING CONVENTION DEPENDENCY: migration-gate tests are matched by these
+# reserved name substrings:
+#
+#   data_movement, rebalance, decommission, source_cleanup, delete_marker
+#
+# Renaming a test away from all of these substrings removes it from the gate.
+# The floor equals the exact selected-test count at the time it was last
+# committed, so ANY reduction fails CI. To shrink the gate intentionally
+# (test removed or consciously renamed), update the floor file in the same PR
+# so the reduction is visible in the diff. Adding tests never requires a floor
+# bump (the floor is a lower bound), but bumping it keeps the guard tight.
+#
+# Per-pattern floors are deliberately omitted: with an exact-count total floor,
+# a single test dropping out of any pattern already fails the check, so
+# per-pattern bookkeeping would add churn without detection power.
+#
+# Usage:
+#   scripts/check_migration_gate_count.sh          # count check + run the gate
+#   scripts/check_migration_gate_count.sh check    # count check only
+#   scripts/check_migration_gate_count.sh run      # run the gate only
+
+set -euo pipefail
+
+cd "$(dirname "$0")/.."
+
+# Single source of truth for the migration-gate filter. ci.yml must invoke
+# this script instead of inlining the expression.
+MIGRATION_GATE_FILTER='test(data_movement) or test(rebalance) or test(decommission) or test(source_cleanup) or test(delete_marker)'
+FLOOR_FILE=".config/migration-gate-floor.txt"
+
+mode="${1:-all}"
+case "$mode" in
+    all | check | run) ;;
+    *)
+        echo "usage: $0 [all|check|run]" >&2
+        exit 2
+        ;;
+esac
+
+if [[ "$mode" == "all" || "$mode" == "check" ]]; then
+    floor="$(grep -Ev '^[[:space:]]*(#|$)' "$FLOOR_FILE" | head -n1 | tr -d '[:space:]')"
+    if ! [[ "$floor" =~ ^[0-9]+$ ]]; then
+        echo "error: $FLOOR_FILE does not contain a numeric floor (got: '$floor')" >&2
+        exit 1
+    fi
+
+    # Human-format list: binary headers start at column 0, one test per
+    # 4-space-indented line. A nextest failure aborts via set -e with its
+    # stderr visible; an output-format change collapses the count to 0 and
+    # fails loudly rather than silently passing.
+    list_output="$(cargo nextest list -p rustfs-ecstore --lib -E "$MIGRATION_GATE_FILTER")"
+    count="$(printf '%s\n' "$list_output" | grep -c '^    ' || true)"
+
+    if ((count < floor)); then
+        echo "error: migration gate selects $count tests, below the committed floor of $floor." >&2
+        echo "" >&2
+        echo "The gate matches tests by name substring (data_movement / rebalance /" >&2
+        echo "decommission / source_cleanup / delete_marker). A rename or removal has" >&2
+        echo "thinned the selection. Either restore the test names, or — if the" >&2
+        echo "reduction is intentional — update $FLOOR_FILE in this PR so the" >&2
+        echo "gate change is explicit and reviewable." >&2
+        exit 1
+    fi
+    echo "migration gate count OK: $count selected tests (floor: $floor)"
+fi
+
+if [[ "$mode" == "all" || "$mode" == "run" ]]; then
+    cargo nextest run -p rustfs-ecstore --lib -E "$MIGRATION_GATE_FILTER"
+fi