refactor(db): extract the P2002 predicate into one shared helper

The Prisma unique-constraint (P2002) narrowing predicate had been
hand-copied into five call sites. Fold them into a single isP2002 in
src/lib/prisma-errors.ts and import it everywhere (the two step-drain
sites keep their local isUniqueConstraintViolation name via an import
alias). Behaviour-identical; one place to chase a future P2002-semantics
change instead of five.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/lib/measurements/consolidate-legacy-steps.ts

@@ -38,6 +38,7 @@
  * `rollup-full-backfill` boot-time converging-backfill pattern.
  */
 import type { PrismaClient } from "@/generated/prisma/client";
+import { isP2002 as isUniqueConstraintViolation } from "@/lib/prisma-errors";
 
 import { dailyStatsExternalId } from "./apple-health-mapping";
 import {
@@ -100,15 +101,6 @@ export interface StepConsolidationSummary {
   };
 }
 
-/** True for a Prisma unique-constraint violation (P2002). */
-function isUniqueConstraintViolation(err: unknown): boolean {
-  return (
-    typeof err === "object" &&
-    err !== null &&
-    "code" in err &&
-    (err as { code?: unknown }).code === "P2002"
-  );
-}
 
 export interface StepConsolidationOptions {
   /** Limit the pass to a single user. Default = every user. */

src/lib/measurements/dense-intraday-retention.ts

@@ -41,6 +41,7 @@
  * production standalone image strips `tsx`, so this can never be a CLI.
  */
 import type { MeasurementType, PrismaClient } from "@/generated/prisma/client";
+import { isP2002 as isUniqueConstraintViolation } from "@/lib/prisma-errors";
 
 import {
   dailyStatsExternalId,
@@ -77,19 +78,6 @@ export const DENSE_INTRADAY_RETENTION_DAYS = 14;
 /** The daily-stats externalId prefix marks an already-collapsed row. */
 const DAILY_STATS_PREFIX = "stats:";
 
-/**
- * True for a Prisma unique-constraint violation (P2002). Mirrors the
- * `consolidate-legacy-steps.ts` precedent verbatim so the two drains
- * classify the same error the same way.
- */
-function isUniqueConstraintViolation(err: unknown): boolean {
-  return (
-    typeof err === "object" &&
-    err !== null &&
-    "code" in err &&
-    (err as { code?: unknown }).code === "P2002"
-  );
-}
 
 export interface DenseIntradayRetentionSummary {
   dryRun: boolean;

src/lib/medications/intake-slot-dedup.ts

@@ -41,6 +41,7 @@
  * unregistered queue silently never drains.
  */
 import { prisma } from "@/lib/db";
+import { isP2002 } from "@/lib/prisma-errors";
 import { annotate } from "@/lib/logging/context";
 import { getGlobalBoss } from "@/lib/jobs/boss-instance";
 import { DEFAULT_TIMEZONE } from "@/lib/tz/format";
@@ -53,16 +54,6 @@ import { recomputeMedicationComplianceForEvent } from "@/lib/rollups/medication-
 
 export const INTAKE_SLOT_DEDUP_QUEUE = "intake-slot-dedup";
 
-/** Narrow a thrown Prisma error to the P2002 unique-constraint code. */
-function isP2002(err: unknown): boolean {
-  return (
-    typeof err === "object" &&
-    err !== null &&
-    "code" in err &&
-    (err as { code: unknown }).code === "P2002"
-  );
-}
-
 /**
  * Serial concurrency — the populator walks a user's intake events and
  * writes per slot; concurrency-1 keeps it from crowding the request

src/lib/medications/scheduling/slot-upsert.ts

@@ -17,21 +17,13 @@
 import type { PrismaClient } from "@/generated/prisma/client";
 
 import { prisma as defaultPrisma } from "@/lib/db";
+import { isP2002 } from "@/lib/prisma-errors";
 import { resolveCanonicalSlotInstant } from "@/lib/medications/scheduling/resolve-slot-instant";
 import type { WorkerScheduleRow } from "@/lib/medications/scheduling/worker-helpers";
 import type { InjectionSiteKey } from "@/lib/medications/injection-sites";
 
 type PrismaLike = Pick<PrismaClient, "medication" | "medicationIntakeEvent">;
 
-/** Narrow a thrown Prisma error to the P2002 unique-constraint code. */
-function isP2002(err: unknown): boolean {
-  return (
-    typeof err === "object" &&
-    err !== null &&
-    "code" in err &&
-    (err as { code: unknown }).code === "P2002"
-  );
-}
 
 /** The minimal intake-row shape the slot upsert reads + returns. */
 export interface SlotIntakeRow {

src/lib/prisma-errors.ts

@@ -0,0 +1,24 @@
+/**
+ * Shared Prisma error narrowing helpers.
+ *
+ * The P2002 (unique-constraint violation) predicate was hand-copied into
+ * five call sites (rollup persist, intake-slot dedup, slot upsert, legacy
+ * step consolidation, dense-intraday retention). v1.11.2 folds them into
+ * this single helper so a future change to the P2002 semantics has one
+ * place to live instead of five.
+ *
+ * Deliberately structural (`typeof === "object"` + `"code" in err` +
+ * `code === "P2002"`) rather than `instanceof Prisma.PrismaClientKnownRequestError`
+ * so it survives client-bundling quirks while staying specific to the
+ * unique-constraint code.
+ */
+
+/** Narrow a thrown Prisma error to the P2002 unique-constraint code. */
+export function isP2002(err: unknown): boolean {
+  return (
+    typeof err === "object" &&
+    err !== null &&
+    "code" in err &&
+    (err as { code: unknown }).code === "P2002"
+  );
+}

src/lib/rollups/measurement-rollups.ts

@@ -30,6 +30,7 @@
 import { prisma } from "@/lib/db";
 import { getGlobalBoss } from "@/lib/jobs/boss-instance";
 import { annotate } from "@/lib/logging/context";
+import { isP2002 } from "@/lib/prisma-errors";
 import {
   collapseRollupRowsBySource,
   loadUserSourcePriority,
@@ -437,16 +438,6 @@ async function runRollupAggregate(input: {
  * with `ON CONFLICT DO UPDATE` so the round-trip count is bounded
  * regardless of fan-out width.
  */
-/** Narrow a thrown Prisma error to the P2002 unique-constraint code. */
-function isP2002(err: unknown): boolean {
-  return (
-    typeof err === "object" &&
-    err !== null &&
-    "code" in err &&
-    (err as { code: unknown }).code === "P2002"
-  );
-}
-
 async function persistRollupRows(
   userId: string,
   granularity: RollupGranularity,