Pricing: migrate from app_config JSON to relational tables

Replaces the two `pricing_*_tiers_json` blobs and five `first_session_discount_*`
keys in app_config with dedicated `pricing_tiers` and `pricing_promotions`
tables plus matching `_history` audit tables. UUID PKs, UNIQUE(mode, minutes)
natural-key constraint, optimistic-lock via `updated_at` token returning 409
STALE_WRITE on conflicts. Every mutation writes a history row capturing the
operator (changed_by from request.auth.userId) and change_kind.

CC SettingsPage replaces the JSON-textarea editors with per-row tables —
add / edit / soft-delete / reactivate / reorder, plus a buffered first-session
discount form with the same optimistic-lock contract. `minutes` and `mode` are
read-only on edit since they form the natural key; operators soft-delete and
recreate to change duration.

Stage 5 fixes a latent leak: `client.payment.routes.js` had its own local
`readDiscountConfig` that still read from app_config — would have silently
fallen to hardcoded defaults once the legacy rows were deleted. Now reads from
pricing_promotions via the shared service helper, so CC edits to the first-
session discount affect actual payment pricing on the next request.

Customer-facing GET /api/client/chat/pricing shape unchanged (id values are
now UUIDs instead of "5"/"12"/"60" but lookups happen by (mode, minutes), so
no app changes needed). 27 new backend tests, all green.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/src/services/config.service.js

@@ -35,63 +35,47 @@ export const setMaxCustomersPerMitra = async (value) => {
   return { max_customers_per_mitra: value }
 }
 
-// --- Phase 4: First-session discount (replaces Phase 3 free-trial config) ---
+// --- Phase 4: First-session discount config (back-compat shim) ---
+//
+// The canonical source of truth for the first-session discount lives in the
+// `pricing_promotions` table (eligibility = 'first_session'). The CC settings
+// page still calls `/internal/config/free-trial`, which exposes a slim
+// {enabled, duration_minutes} view — kept as a back-compat shim until the CC
+// UI is migrated to the richer /internal/config/first-session-discount handler.
+// Reads and writes go directly against `pricing_promotions` so operator edits
+// stay in sync with the customer-facing pricing payload.
+//
+// The legacy `first_session_discount_*` keys in `app_config` were retired in
+// Stage 5 (deleted by migrate.js) — do NOT reintroduce them.
 
-export const getFirstSessionDiscountConfig = async () => {
-  const rows = await sql`
-    SELECT key, value FROM app_config
-    WHERE key IN (
-      'first_session_discount_enabled',
-      'first_session_discount_actual_price_idr',
-      'first_session_discount_gimmick_price_idr',
-      'first_session_discount_duration_minutes',
-      'first_session_discount_modes'
-    )
-  `
-  const byKey = Object.fromEntries(rows.map((r) => [r.key, r.value?.value]))
-  return {
-    enabled: byKey.first_session_discount_enabled ?? true,
-    actual_price_idr: byKey.first_session_discount_actual_price_idr ?? 2000,
-    gimmick_price_idr: byKey.first_session_discount_gimmick_price_idr ?? 12000,
-    duration_minutes: byKey.first_session_discount_duration_minutes ?? 12,
-    modes: byKey.first_session_discount_modes ?? ['chat'],
-  }
-}
-
-export const setFirstSessionDiscountConfig = async (patch) => {
-  const map = {
-    enabled: 'first_session_discount_enabled',
-    actual_price_idr: 'first_session_discount_actual_price_idr',
-    gimmick_price_idr: 'first_session_discount_gimmick_price_idr',
-    duration_minutes: 'first_session_discount_duration_minutes',
-    modes: 'first_session_discount_modes',
-  }
-  for (const [field, key] of Object.entries(map)) {
-    if (patch[field] === undefined) continue
-    await sql`
-      INSERT INTO app_config (key, value, updated_at)
-      VALUES (${key}, ${sql.json({ value: patch[field] })}, NOW())
-      ON CONFLICT (key) DO UPDATE SET value = EXCLUDED.value, updated_at = NOW()
-    `
-  }
-  return getFirstSessionDiscountConfig()
-}
-
-// Back-compat shim — CC settings page still calls /internal/config/free-trial.
-// Phase 4 routes will be added; until the CC UI is migrated this maps to the new keys.
 export const getFreeTrialConfig = async () => {
-  const cfg = await getFirstSessionDiscountConfig()
+  const [row] = await sql`
+    SELECT enabled, duration_minutes FROM pricing_promotions
+    WHERE eligibility = 'first_session'
+  `
   return {
-    enabled: cfg.enabled,
-    duration_minutes: cfg.duration_minutes,
+    enabled: row?.enabled ?? true,
+    duration_minutes: row?.duration_minutes ?? 12,
   }
 }
 
 export const setFreeTrialConfig = async ({ enabled, duration_minutes }) => {
-  return setFirstSessionDiscountConfig({
-    ...(enabled !== undefined ? { enabled } : {}),
-    ...(duration_minutes !== undefined ? { duration_minutes } : {}),
-  })
+  // Build a sparse UPDATE so undefined fields are left alone (matches the prior
+  // semantics where missing patch fields were no-ops). Use COALESCE on each
+  // column with the sentinel-when-undefined pattern; postgres.js parameterizes
+  // null/undefined identically, so we branch on which fields the caller sent.
+  if (enabled === undefined && duration_minutes === undefined) {
+    return getFreeTrialConfig()
+  }
+
+  await sql`
+    UPDATE pricing_promotions
+    SET enabled          = ${enabled === undefined ? sql`enabled` : enabled},
+        duration_minutes = ${duration_minutes === undefined ? sql`duration_minutes` : duration_minutes},
+        updated_at       = NOW()
+    WHERE eligibility = 'first_session'
+  `
+  return getFreeTrialConfig()
 }
 
 // --- Phase 4: Support handles ---
@@ -120,30 +104,6 @@ export const setSupportHandles = async ({ wa, telegram }) => {
   return next
 }
 
-// --- Phase 4: Pricing tier groups ---
-
-export const getPricingTierGroups = async () => {
-  const rows = await sql`
-    SELECT key, value FROM app_config
-    WHERE key IN ('pricing_chat_tiers_json', 'pricing_call_tiers_json')
-  `
-  const byKey = Object.fromEntries(rows.map((r) => [r.key, r.value]))
-  return {
-    chat: byKey.pricing_chat_tiers_json?.tiers ?? [],
-    call: byKey.pricing_call_tiers_json?.tiers ?? [],
-  }
-}
-
-export const setPricingTierGroup = async (mode, tiers) => {
-  const key = mode === 'call' ? 'pricing_call_tiers_json' : 'pricing_chat_tiers_json'
-  await sql`
-    INSERT INTO app_config (key, value, updated_at)
-    VALUES (${key}, ${sql.json({ tiers })}, NOW())
-    ON CONFLICT (key) DO UPDATE SET value = EXCLUDED.value, updated_at = NOW()
-  `
-  return getPricingTierGroups()
-}
-
 export const getExtensionTimeoutConfig = async () => {
   const [row] = await sql`SELECT value FROM app_config WHERE key = 'extension_timeout_seconds'`
   // Default 10s pairs with the auto-approve-on-timeout flow; raise this if you change the policy to auto-reject.