refactor: eliminate plan_credits duplication, _copilot_api wrapper, and test boilerplate (#43)

- Collapse plan_credits() from two identical case blocks (promo/standard)
  into one case keyed by plan type with inline promo check — saves ~16 lines
- Inline gh_api --api-version 2026-03-10 at both call sites and delete the
  _copilot_api() 2-line wrapper that only existed to fix that flag
- Source lib/github-common.sh in install-hooks.sh to reuse color vars
  (RED/GREEN/YELLOW/NC) instead of redeclaring them; keep the [HOOKS]-labelled
  print functions since they differ from the lib's [SUCCESS]/[WARNING]/[ERROR]
- Add _run_script() helper to test_script_validation.bats and replace all 59
  single-line run bash -c invocations — removes the repeated
  "export PATH='${MOCK_BIN}:${PATH}';" boilerplate from every test body

All 91 bats tests pass.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: locus313

install-hooks.sh

@@ -21,12 +21,10 @@
 set -euo pipefail
 
 SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+# shellcheck source=lib/github-common.sh
+source "${SCRIPT_DIR}/lib/github-common.sh"
 
-RED='\033[0;31m'
-GREEN='\033[0;32m'
-YELLOW='\033[1;33m'
-NC='\033[0m'
-
+# Override lib's print functions with [HOOKS] prefix for this script's output.
 print_success() { echo -e "${GREEN}[HOOKS]${NC} $1"; }
 print_warning() { echo -e "${YELLOW}[HOOKS]${NC} $1"; }
 print_error()   { echo -e "${RED}[HOOKS]${NC} $1" >&2; }

reporting/github-copilot-report/github-copilot-report.sh

@@ -77,30 +77,13 @@ if [[ "$_today" -ge "20260601" && "$_today" -lt "20260901" ]]; then
 fi
 
 plan_credits() {
-    # If an explicit override is set, always use it
-    if [[ -n "$CREDITS_PER_SEAT_OVERRIDE" ]]; then
-        echo "$CREDITS_PER_SEAT_OVERRIDE"
-        return
-    fi
-    if [[ "$IN_PROMO_PERIOD" == "true" ]]; then
-        case "${1,,}" in
-            business)          echo "3000" ;;
-            enterprise)        echo "7000" ;;
-            pro_plus|proplus)  echo "7000" ;;
-            free)              echo "50"   ;;
-            pro)               echo "3000" ;;
-            *)                 echo "3000" ;;
-        esac
-    else
-        case "${1,,}" in
-            business)          echo "1900" ;;
-            enterprise)        echo "3900" ;;
-            pro_plus|proplus)  echo "3900" ;;
-            free)              echo "50"   ;;
-            pro)               echo "1900" ;;
-            *)                 echo "1900" ;;
-        esac
-    fi
+    [[ -n "$CREDITS_PER_SEAT_OVERRIDE" ]] && { echo "$CREDITS_PER_SEAT_OVERRIDE"; return; }
+    local promo="$IN_PROMO_PERIOD"
+    case "${1,,}" in
+        enterprise|pro_plus|proplus) [[ "$promo" == "true" ]] && echo "7000" || echo "3900" ;;
+        free)                        echo "50" ;;
+        *)                           [[ "$promo" == "true" ]] && echo "3000" || echo "1900" ;;
+    esac
 }
 
 # ── Help text ─────────────────────────────────────────────────────────────────
@@ -206,22 +189,14 @@ else
     print_warning "az CLI is not logged in — department/division grouping will be skipped."
     print_warning "Run 'az login' to enable Entra ID enrichment, or pass --no-entra."
 fi
-
-# ── GitHub API via curl with Copilot API version ──────────────────────────────
-# The Copilot usage-metrics endpoints require API version 2026-03-10.
-_copilot_api() {
-    local url="$1"; shift
-    gh_api "${url}" --api-version 2026-03-10 "$@"
-}
-
 # fetch_usage_ndjson REPORT_PATH
 # Calls the new usage metrics API (which returns signed download_links to NDJSON
 # files rather than inline JSON), downloads each file, and emits one NDJSON
 # object per line on stdout.  Exits cleanly with empty output if unavailable.
 fetch_usage_ndjson() {
     local path="$1"
     local resp links
-    resp=$(_copilot_api "${path}" 2>/dev/null) || return 0
+    resp=$(gh_api "${path}" --api-version 2026-03-10 2>/dev/null) || return 0
     [[ "${resp}" == "__404__" || "${resp}" == "__422__" ]] && return 0
     links=$(echo "$resp" | jq -r '.download_links[]? // empty' 2>/dev/null) || return 0
     [[ -z "$links" ]] && return 0
@@ -323,8 +298,7 @@ while IFS= read -r _login; do
     [[ -z "$_login" ]] && continue
     _login_i=$(( _login_i + 1 ))
     printf '\r  [%d/%d] %s          ' "$_login_i" "$_LOGIN_COUNT" "$_login" >&2
-    _resp=$(_copilot_api \
-        "/enterprises/${GITHUB_ENTERPRISE}/settings/billing/ai_credit/usage?user=${_login}&year=${_BILLING_YEAR}&month=${_BILLING_MONTH}") || _resp=""
+    _resp=$(gh_api "/enterprises/${GITHUB_ENTERPRISE}/settings/billing/ai_credit/usage?user=${_login}&year=${_BILLING_YEAR}&month=${_BILLING_MONTH}" --api-version 2026-03-10) || _resp=""
     if [[ "${_resp}" == "__404__" || "${_resp}" == "__422__" ]]; then
         # No usage data this month — valid, treat as 0 credits.
         _credits="0"