refactor(api): centralize AnswerPlatform in packages/api/src/platform.ts

PR #298 review: the 'web' | 'ios' | 'android' platform enum was duplicated
across the answers router, trpc Context typing, and the DB schema comment.
Single source of truth now lives in packages/api/src/platform.ts
(ANSWER_PLATFORMS + AnswerPlatform), re-exported from the package root and
used to type answers.ts's zod schema and trpc.ts's Context.recordAnswer.

Also drops the answer_platform_idx index added in migration
0002_answer_platform.sql: the stats page's per-platform counts are a
full-table GROUP BY, which an index on this low-cardinality (3-4 value)
column wouldn't speed up — only add write overhead. Safe to hand-edit since
this migration hasn't been applied to any real database yet (unmerged,
in-PR).

Author: acharlop

apps/website/src/server/db/migrations/0002_answer_platform.sql

@@ -1,2 +1 @@
-ALTER TABLE "answer" ADD COLUMN "platform" text;--> statement-breakpoint
-CREATE INDEX "answer_platform_idx" ON "answer" USING btree ("platform");
+ALTER TABLE "answer" ADD COLUMN "platform" text;

apps/website/src/server/db/migrations/meta/0002_snapshot.json

@@ -346,21 +346,6 @@
           "concurrently": false,
           "method": "btree",
           "with": {}
-        },
-        "answer_platform_idx": {
-          "name": "answer_platform_idx",
-          "columns": [
-            {
-              "expression": "platform",
-              "isExpression": false,
-              "asc": true,
-              "nulls": "last"
-            }
-          ],
-          "isUnique": false,
-          "concurrently": false,
-          "method": "btree",
-          "with": {}
         }
       },
       "foreignKeys": {},

apps/website/src/server/db/schema.ts

@@ -447,11 +447,16 @@ export const answer = pgTable(
     questionId: text('question_id').notNull(),
     language: text('language'),
     type: text('type').notNull().default('answered'),
-    // Nullable, additive (public stats page, issue: analytics page). Rows written
-    // before this column existed — and any client that hasn't updated yet — stay
-    // NULL; the stats aggregation surfaces those as "Unattributed" rather than
-    // guessing. New writes carry 'web' | 'ios' | 'android' from the host transport
+    // Nullable, additive (public stats page). Rows written before this column
+    // existed — and any client that hasn't updated yet — stay NULL; the stats
+    // aggregation surfaces those as "Unattributed" rather than guessing. New
+    // writes carry 'web' | 'ios' | 'android' from the host transport
     // (answer-transport.ts on each client), never guessed server-side.
+    //
+    // No index: the stats page's per-platform counts are a full-table
+    // GROUP BY (see getPlatformCounts in server/stats/query.ts), which an
+    // index on this low-cardinality (3-4 value) column wouldn't speed up —
+    // it would only add write overhead.
     platform: text('platform'),
   },
   (table) => {
@@ -461,7 +466,6 @@ export const answer = pgTable(
         table.questionId
       ),
       answerDeviceIdIdx: index('answer_device_id_idx').on(table.deviceId),
-      answerPlatformIdx: index('answer_platform_idx').on(table.platform),
     }
   }
 )

packages/api/src/index.ts

@@ -10,6 +10,8 @@ export const createCaller = createCallerFactory(appRouter)
 export {appRouter}
 export type {Context} from './trpc'
 export type {AppRouter}
+export {ANSWER_PLATFORMS} from './platform'
+export type {AnswerPlatform} from './platform'
 
 /** Inference helpers for end-to-end typed clients. */
 export type RouterInputs = inferRouterInputs<AppRouter>

packages/api/src/platform.ts

@@ -0,0 +1,9 @@
+/**
+ * Client platforms an Answer (or a catalog event) can originate from — the
+ * single source of truth other packages/derive from, instead of hand-copying
+ * the same three strings (previously duplicated across answers.ts, trpc.ts,
+ * and the stats page's own types/query modules).
+ */
+export const ANSWER_PLATFORMS = ['web', 'ios', 'android'] as const
+
+export type AnswerPlatform = (typeof ANSWER_PLATFORMS)[number]

packages/api/src/routers/answers.ts

@@ -1,17 +1,15 @@
 import {z} from 'zod'
 
+import {ANSWER_PLATFORMS} from '../platform'
 import {createTRPCRouter, publicProcedure} from '../trpc'
 
-/** Client platforms an Answer can originate from — see the stats page's per-platform split. */
-export const ANSWER_PLATFORMS = ['web', 'ios', 'android'] as const
-
 export const answersRouter = createTRPCRouter({
   /**
    * Record one Answer (CONTEXT.md → Answer record): the Device answered a
    * Question. Validates the event, then hands it to the host's `recordAnswer`
    * port (the Drizzle adapter in apps/website). `type` defaults to `'answered'`,
    * today's only kind (a future dwell-timer / Skip may add others). `platform`
-   * is optional (analytics page): each client's transport sets it once, so
+   * is optional (stats page): each client's transport sets it once, so
    * older builds that omit it keep working — those rows land as "Unattributed"
    * in the stats breakdown.
    */

packages/api/src/trpc.ts

@@ -1,5 +1,7 @@
 import {initTRPC} from '@trpc/server'
 
+import type {AnswerPlatform} from './platform'
+
 /**
  * The API context. The content router is public and stateless, but the host
  * supplies a `recordAnswer` port so `answers.record` can persist to the Answer
@@ -15,11 +17,11 @@ export type Context = {
     language: string
     type: string
     /**
-     * Which client sent this Answer — 'web' | 'ios' | 'android'. Optional so
-     * older, not-yet-updated clients keep working; absent/unset means the
-     * stats page buckets the row as "Unattributed" rather than guessing.
+     * Which client sent this Answer. Optional so older, not-yet-updated
+     * clients keep working; absent/unset means the stats page buckets the
+     * row as "Unattributed" rather than guessing.
      */
-    platform?: string
+    platform?: AnswerPlatform
   }) => Promise<void>
 }