CI: Enhance common script with strict mode

This adds bash strict mode, color output helpers, ASSERT function, and
cleanup mechanism to improve CI script reliability and debugging.
- Add color output functions (print_success, print_error, print_warning)
- Add ASSERT function for test validation
- Add cleanup function registry with trap handler
- Fix POSIX compliance (use = instead of ==)

Author: jserv

.ci/common.sh

@@ -1,3 +1,8 @@
+# Bash strict mode (enabled only when executed directly, not sourced)
+if ! (return 0 2> /dev/null); then
+    set -euo pipefail
+fi
+
 # Expect host is Linux/x86_64, Linux/aarch64, macOS/arm64
 
 MACHINE_TYPE=$(uname -m)
@@ -15,12 +20,67 @@ check_platform()
     esac
 }
 
-if [[ "${OS_TYPE}" == "Linux" ]]; then
+if [ "${OS_TYPE}" = "Linux" ]; then
     PARALLEL=-j$(nproc)
 else
     PARALLEL=-j$(sysctl -n hw.logicalcpu)
 fi
 
+# Color output helpers
+RED='\033[0;31m'
+GREEN='\033[0;32m'
+YELLOW='\033[1;33m'
+NC='\033[0m' # No Color
+
+print_success()
+{
+    echo -e "${GREEN}[SUCCESS]${NC} $1"
+}
+
+print_error()
+{
+    echo -e "${RED}[ERROR]${NC} $1" >&2
+}
+
+print_warning()
+{
+    echo -e "${YELLOW}[WARNING]${NC} $1"
+}
+
+# Assertion function for tests
+# Usage: ASSERT <condition> <error_message>
+ASSERT()
+{
+    local condition=$1
+    shift
+    local message="$*"
+
+    if ! eval "${condition}"; then
+        print_error "Assertion failed: ${message}"
+        print_error "Condition: ${condition}"
+        return 1
+    fi
+}
+
+# Cleanup function registry
+CLEANUP_FUNCS=()
+
+register_cleanup()
+{
+    CLEANUP_FUNCS+=("$1")
+}
+
+cleanup()
+{
+    local func
+    for func in "${CLEANUP_FUNCS[@]-}"; do
+        [ -n "${func}" ] || continue
+        eval "${func}" || true
+    done
+}
+
+trap cleanup EXIT
+
 # Universal download utility with curl/wget compatibility
 # Provides consistent interface regardless of which tool is available
 
@@ -49,7 +109,7 @@ download_to_stdout()
     local url="$1"
     case "$DOWNLOAD_TOOL" in
         curl)
-            curl -fsSL "$url"
+            curl -fS --retry 5 --retry-delay 2 --retry-max-time 60 -sL "$url"
             ;;
         wget)
             wget -qO- "$url"
@@ -66,7 +126,7 @@ download_to_file()
     local output="$2"
     case "$DOWNLOAD_TOOL" in
         curl)
-            curl -fsSL -o "$output" "$url"
+            curl -fS --retry 5 --retry-delay 2 --retry-max-time 60 -sL -o "$output" "$url"
             ;;
         wget)
             wget -q -O "$output" "$url"
@@ -88,7 +148,7 @@ download_with_headers()
             for header in "$@"; do
                 headers+=(-H "$header")
             done
-            curl -fsSL "${headers[@]}" "$url"
+            curl -fS --retry 5 --retry-delay 2 --retry-max-time 60 -sL "${headers[@]}" "$url"
             ;;
         wget)
             for header in "$@"; do
@@ -107,7 +167,7 @@ download_silent()
     local url="$1"
     case "$DOWNLOAD_TOOL" in
         curl)
-            curl -fsSL "$url"
+            curl -fS --retry 5 --retry-delay 2 --retry-max-time 60 -sL "$url"
             ;;
         wget)
             wget -qO- "$url"
@@ -124,7 +184,7 @@ download_with_progress()
     local output="$2"
     case "$DOWNLOAD_TOOL" in
         curl)
-            curl -fL -# -o "$output" "$url"
+            curl -fS --retry 5 --retry-delay 2 --retry-max-time 60 -L -# -o "$output" "$url"
             ;;
         wget)
             wget -O "$output" "$url"
@@ -141,7 +201,7 @@ check_url()
     local url="$1"
     case "$DOWNLOAD_TOOL" in
         curl)
-            curl -fsSL --head "$url" > /dev/null 2>&1
+            curl -fS --retry 5 --retry-delay 2 --retry-max-time 60 -sL --head "$url" > /dev/null 2>&1
             ;;
         wget)
             wget --spider -q "$url" 2> /dev/null