PLN-228: fix: improve install script error handling and diagnostics

Capture stderr from claude plugin commands instead of discarding it,
add a strip_ansi helper to clean ANSI codes from error output, and
display meaningful error messages when marketplace registration or
plugin install/update fails. Previously errors were silently swallowed,
making installation failures hard to diagnose.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: peterulsteen

install.sh

@@ -20,10 +20,11 @@ BLUE='\033[0;34m'
 BOLD='\033[1m'
 NC='\033[0m'
 
-info()  { echo -e "${GREEN}[✓]${NC} $1"; }
-warn()  { echo -e "${YELLOW}[!]${NC} $1"; }
-err()   { echo -e "${RED}[✗]${NC} $1"; }
-step()  { echo -e "${BLUE}[→]${NC} ${BOLD}$1${NC}"; }
+info()       { echo -e "${GREEN}[✓]${NC} $1"; }
+warn()       { echo -e "${YELLOW}[!]${NC} $1"; }
+err()        { echo -e "${RED}[✗]${NC} $1"; }
+step()       { echo -e "${BLUE}[→]${NC} ${BOLD}$1${NC}"; }
+strip_ansi() { echo "$1" | sed 's/\x1b\[[0-9;]*m//g'; }
 
 # ── Constants ────────────────────────────────────────────────────────────────
 MARKETPLACE_SOURCE="closedloop-ai/claude-plugins"
@@ -73,11 +74,15 @@ echo
 # ── Add marketplace ─────────────────────────────────────────────────────────
 step "Registering closedloop-ai marketplace..."
 
-if claude plugin marketplace add "$MARKETPLACE_SOURCE" 2>/dev/null; then
+if MARKETPLACE_ERR=$(claude plugin marketplace add "$MARKETPLACE_SOURCE" 2>&1); then
     info "Marketplace registered: $MARKETPLACE_SOURCE"
 else
-    # May already be registered — not a fatal error
-    warn "Marketplace may already be registered (continuing)"
+    MARKETPLACE_ERR_CLEAN=$(strip_ansi "$MARKETPLACE_ERR")
+    if echo "$MARKETPLACE_ERR_CLEAN" | grep -qiE 'already|exists'; then
+        warn "Marketplace already registered: $MARKETPLACE_SOURCE (continuing)"
+    else
+        warn "Marketplace registration failed: $MARKETPLACE_ERR_CLEAN"
+    fi
 fi
 
 echo
@@ -90,16 +95,20 @@ FAILED=0
 
 for plugin in "${PLUGINS[@]}"; do
     PLUGIN_REF="${plugin}@${MARKETPLACE_NAME}"
-    if claude plugin install "$PLUGIN_REF" --scope user 2>/dev/null; then
+    if INSTALL_ERR=$(claude plugin install "$PLUGIN_REF" --scope user 2>&1); then
         info "Installed: $plugin"
         INSTALLED=$((INSTALLED + 1))
     else
         # May already be installed — try to update instead
-        if claude plugin update "$PLUGIN_REF" --scope user 2>/dev/null; then
+        if UPDATE_ERR=$(claude plugin update "$PLUGIN_REF" --scope user 2>&1); then
             info "Updated: $plugin"
             INSTALLED=$((INSTALLED + 1))
         else
             warn "Could not install/update: $plugin"
+            INSTALL_ERR_CLEAN=$(strip_ansi "$INSTALL_ERR")
+            UPDATE_ERR_CLEAN=$(strip_ansi "$UPDATE_ERR")
+            [[ -n "$INSTALL_ERR_CLEAN" ]] && warn "install: $INSTALL_ERR_CLEAN"
+            [[ -n "$UPDATE_ERR_CLEAN" ]] && warn "update: $UPDATE_ERR_CLEAN"
             FAILED=$((FAILED + 1))
         fi
     fi