diff --git a/deploy.sh b/deploy.sh
index f34aee8..9922330 100755
--- a/deploy.sh
+++ b/deploy.sh
@@ -56,9 +56,12 @@
 #  Exit Codes:
 #  - 0: The deployment finished.
 #  - 1: A step failed.
+#  - 126: A required command is not executable.
 #  - 127: A required command is missing.
 #
 #  Version History:
+#  v1.1 2026-09-13
+#       Normalize shared usage and command checks across shell scripts.
 #  v1.0 2026-08-14
 #       Initial release.
 #
@@ -72,8 +75,9 @@ DATA_GROUP=${DATA_GROUP:-www-data}
 VENV_DIR="$TARGET_DIR/.venv"
 SOURCE_DIR=$(cd "$(dirname "$0")" && pwd)
 
-# Display this script's header as usage information
+# Display full script header information extracted from the top comment block
 usage() {
+    check_commands awk
     awk '
         BEGIN { in_header = 0 }
         /^#+$/ && length($0) >= 10 { if (!in_header) { in_header = 1; next } else exit }
@@ -82,12 +86,16 @@ usage() {
     exit 0
 }
 
-# Check that the required commands are available
+# Check if required commands are available and executable
 check_commands() {
-    for cmd in "$PYTHON" sudo install; do
-        if ! command -v "$cmd" >/dev/null 2>&1; then
-            echo "[ERROR] Command not found: $cmd" >&2
+    for cmd in "$@"; do
+        cmd_path=$(command -v "$cmd" 2>/dev/null)
+        if [ -z "$cmd_path" ]; then
+            echo "[ERROR] Command '$cmd' is not installed. Please install $cmd and try again." >&2
             exit 127
+        elif [ ! -x "$cmd_path" ]; then
+            echo "[ERROR] Command '$cmd' is not executable. Please check the permissions." >&2
+            exit 126
         fi
     done
 }
@@ -198,7 +206,7 @@ main() {
     case "${1:-}" in
         -h|--help) usage ;;
     esac
-    check_commands
+    check_commands "$PYTHON" sudo install
     check_python
     create_directories
     create_environment_file
diff --git a/doc/POLICY.md b/doc/POLICY.md
index 15e5987..c9d0df3 100644
--- a/doc/POLICY.md
+++ b/doc/POLICY.md
@@ -319,6 +319,16 @@ This repository was left behind by exactly the practices this section forbids.
 - Define `usage()`, `main()`, and call `main "$@"` at the end.
 - An interpreter path is a default that can be overridden, not a constant
   compiled into the script.
+- A helper name shared with other id774 shell scripts is an interface. The same
+  name means the same arguments, exit statuses, side effects and implementation.
+  Do not specialize a shared helper in place.
+- Repository-specific behavior belongs at the call site or in a differently
+  named helper. If the behavior differs, the function name differs.
+- `check_commands()` takes the command names to inspect in `"$@"`, resolves each
+  with `command -v`, exits `127` when a command is unavailable and `126` when the
+  resolved path is not executable.
+- The shared header-extracting `usage()` calls `check_commands awk` before
+  invoking `awk`, prints the header block and exits `0`.
 
 ### 2.7 Documentation and Versioning
 
diff --git a/doc/VERSIONS b/doc/VERSIONS
index f763072..e9e93c5 100644
--- a/doc/VERSIONS
+++ b/doc/VERSIONS
@@ -14,6 +14,8 @@ v1.0.2 (Release Date: TBD)
 - Redact any echoed API key before a provider error reaches logs or stderr.
 - Reject invalid chart/summary ranges and stock-list rows missing code or name.
 - Replace generated CSV/TXT files atomically so failed writes keep good data.
+- Normalize shell helper contracts so missing and non-executable commands
+  report statuses `127` and `126` consistently.
 
 v1.0.1 (2026-08-26)
 -------------------
diff --git a/run.sh b/run.sh
index 553c137..2b8a8c8 100755
--- a/run.sh
+++ b/run.sh
@@ -62,8 +62,12 @@
 #  Exit Codes:
 #  - 0: Every step succeeded.
 #  - 1: At least one step failed.
+#  - 126: A required command is not executable.
+#  - 127: A required command is missing.
 #
 #  Version History:
+#  v1.1 2026-09-13
+#       Normalize shared usage and command checks; keep pipeline checks separate.
 #  v1.0 2026-08-14
 #       Initial release.
 #
@@ -102,8 +106,9 @@ NOTIFY="$VENV_DIR/bin/finance-notify"
 
 failures=0
 
-# Display this script's header as usage information
+# Display full script header information extracted from the top comment block
 usage() {
+    check_commands awk
     awk '
         BEGIN { in_header = 0 }
         /^#+$/ && length($0) >= 10 { if (!in_header) { in_header = 1; next } else exit }
@@ -125,8 +130,22 @@ log() {
     echo "$@" >>"$JOBLOG" 2>&1
 }
 
-# Check that the commands this job drives are installed
+# Check if required commands are available and executable
 check_commands() {
+    for cmd in "$@"; do
+        cmd_path=$(command -v "$cmd" 2>/dev/null)
+        if [ -z "$cmd_path" ]; then
+            echo "[ERROR] Command '$cmd' is not installed. Please install $cmd and try again." >&2
+            exit 127
+        elif [ ! -x "$cmd_path" ]; then
+            echo "[ERROR] Command '$cmd' is not executable. Please check the permissions." >&2
+            exit 126
+        fi
+    done
+}
+
+# Check that the finance pipeline commands are installed
+check_pipeline_commands() {
     for cmd in "$CHARTS" "$SUMMARY" "$NOTIFY"; do
         if [ ! -x "$cmd" ]; then
             echo "[ERROR] Command not found: $cmd" >&2
@@ -134,10 +153,6 @@ check_commands() {
             exit 1
         fi
     done
-    if ! command -v date >/dev/null 2>&1; then
-        echo "[ERROR] Command not found: date" >&2
-        exit 127
-    fi
 }
 
 # Check that the fetching step has the credential it needs
@@ -226,7 +241,8 @@ main() {
         -h|--help) usage ;;
     esac
     load_environment
-    check_commands
+    check_pipeline_commands
+    check_commands date
     check_credential
     check_environment