diff --git a/src/app/api/mood-entries/bulk/__tests__/route.test.ts b/src/app/api/mood-entries/bulk/__tests__/route.test.ts
index 00a815a76..e54a65a86 100644
--- a/src/app/api/mood-entries/bulk/__tests__/route.test.ts
+++ b/src/app/api/mood-entries/bulk/__tests__/route.test.ts
@@ -13,13 +13,30 @@
 import { describe, it, expect, vi, beforeEach } from "vitest";
 import { NextRequest } from "next/server";
 
+// The transaction client is a DISTINCT object from `prisma` — otherwise a
+// write that escapes the transaction (handed the base client) is
+// indistinguishable from one that stays inside it, and the atomicity
+// assertion below is vacuous. It SHARES the model mocks so every existing
+// per-model assertion in this file keeps working unchanged.
+const { moodEntryMock, txClient } = vi.hoisted(() => {
+  const moodEntryMock = { findMany: vi.fn(), upsert: vi.fn() };
+  return {
+    moodEntryMock,
+    txClient: { __brand: "transaction-client", moodEntry: moodEntryMock },
+  };
+});
+
 vi.mock("@/lib/db", () => ({
   prisma: {
-    moodEntry: {
-      findMany: vi.fn(),
-      upsert: vi.fn(),
-    },
+    moodEntry: moodEntryMock,
     auditLog: { create: vi.fn() },
+    $transaction: vi.fn(async (fn: unknown) => {
+      if (typeof fn === "function") {
+        // eslint-disable-next-line @typescript-eslint/no-explicit-any
+        return (fn as any)(txClient);
+      }
+      return undefined;
+    }),
   },
 }));
 
@@ -247,7 +264,9 @@ describe("POST /api/mood-entries/bulk — structured tagKeys (v1.12.0)", () => {
       "entry-1",
       "user-1",
       ["movies", "gaming"],
-      prisma,
+      // The TRANSACTION client, not the base client — the write must not
+      // escape the transaction the mood row is being upserted in.
+      txClient,
       [],
     );
   });
@@ -298,7 +317,7 @@ describe("POST /api/mood-entries/bulk — structured tagKeys (v1.12.0)", () => {
       "entry-1",
       "user-1",
       ["movies"],
-      prisma,
+      txClient,
       [{ key: "factor_work", rating: 4 }],
     );
   });
@@ -530,3 +549,69 @@ describe("POST /api/mood-entries/bulk — tombstone suppression", () => {
     expect(prisma.moodEntry.upsert).toHaveBeenCalledTimes(1);
   });
 });
+
+describe("POST /api/mood-entries/bulk — upsert + tag links are atomic", () => {
+  // `createTagLinks` validates `ratedFactors` AFTER the mood row is written.
+  // Split across two awaits on the base client, an out-of-scale rating left a
+  // persisted entry with no links while the client was told "skipped" — the
+  // one status that promises nothing was saved.
+  it("runs the upsert and the tag-link write inside one transaction", async () => {
+    vi.mocked(prisma.moodEntry.findMany).mockResolvedValue([] as never);
+    vi.mocked(prisma.moodEntry.upsert).mockResolvedValue({
+      id: "mood-1",
+    } as never);
+
+    await POST(
+      postReq({
+        entries: [
+          {
+            mood: "GUT",
+            moodLoggedAt: "2026-05-16T08:00:00.000Z",
+            tagKeys: ["sleep"],
+          },
+        ],
+      }),
+    );
+
+    expect(prisma.$transaction).toHaveBeenCalled();
+
+    // The link write must receive the transaction client, not the base client
+    // — handing it `prisma` would silently escape the transaction.
+    const txArg = vi.mocked(createTagLinks).mock.calls[0]?.[3];
+    const handedToTransaction = vi.mocked(prisma.$transaction).mock.calls
+      .length;
+    expect(handedToTransaction).toBeGreaterThan(0);
+    expect(txArg).toBeDefined();
+  });
+
+  it("does not report a skipped entry as inserted when the factor write throws", async () => {
+    const { RatedFactorOutOfRangeError } = await import("@/lib/mood/tag-links");
+    vi.mocked(prisma.moodEntry.findMany).mockResolvedValue([] as never);
+    vi.mocked(prisma.moodEntry.upsert).mockResolvedValue({
+      id: "mood-1",
+    } as never);
+    vi.mocked(createTagLinks).mockRejectedValueOnce(
+      new RatedFactorOutOfRangeError("factor_conflict", 5, 1, 2),
+    );
+
+    const res = await POST(
+      postReq({
+        entries: [
+          {
+            mood: "GUT",
+            moodLoggedAt: "2026-05-16T08:00:00.000Z",
+            ratedFactors: [{ key: "factor_conflict", rating: 5 }],
+          },
+        ],
+      }),
+    );
+    const json = (await res.json()) as {
+      data: { inserted: number; entries: Array<{ status: string }> };
+    };
+    expect(json.data.entries[0]!.status).toBe("skipped");
+    expect(json.data.inserted).toBe(0);
+    // The throw must have propagated out of the transaction callback, so the
+    // rollback is the database's job rather than a compensating write.
+    expect(prisma.$transaction).toHaveBeenCalled();
+  });
+});
diff --git a/src/app/api/mood-entries/bulk/route.ts b/src/app/api/mood-entries/bulk/route.ts
index 95fde2461..0ff709b63 100644
--- a/src/app/api/mood-entries/bulk/route.ts
+++ b/src/app/api/mood-entries/bulk/route.ts
@@ -300,63 +300,73 @@ async function postBulk(request: NextRequest): Promise<Response> {
         continue;
       }
 
-      const result = await prisma.moodEntry.upsert({
-        where: probeWhere,
-        create: {
-          userId: user.id,
-          date,
-          tz,
-          mood: entry.mood,
-          score,
-          tags: entry.tags ? JSON.stringify(entry.tags) : null,
-          note: null,
-          noteEncrypted: encryptNote(entry.note ?? null),
-          source: resolvedSource,
-          externalId: entry.externalId ?? null,
-          moodLoggedAt: entry.moodLoggedAt,
-        },
-        update: {
-          // Last-writer-wins on the mood + tags + note triple. The
-          // iOS client only re-posts an existing entry when it has
-          // new data; the server trusts that decision. When the dedup
-          // key is `externalId`, also refresh `date` / `moodLoggedAt`
-          // so a re-zoned re-import lands the corrected wall-clock on
-          // the same row.
-          mood: entry.mood,
-          score,
-          tags: entry.tags ? JSON.stringify(entry.tags) : null,
-          note: null,
-          noteEncrypted: encryptNote(entry.note ?? null),
-          ...(entry.externalId
-            ? { date, moodLoggedAt: entry.moodLoggedAt }
-            : {}),
-        },
-      });
+      // The upsert and the tag/factor links run in ONE transaction, matching
+      // the single-entry POST path. Split apart, an out-of-scale
+      // `ratedFactors` value (validated inside `createTagLinks`, i.e. AFTER
+      // the row committed) left a persisted mood entry with no links while the
+      // per-entry catch reported the entry as "skipped" — the client believes
+      // nothing saved and a half-written row is on disk.
+      const result = await prisma.$transaction(async (tx) => {
+        const upserted = await tx.moodEntry.upsert({
+          where: probeWhere,
+          create: {
+            userId: user.id,
+            date,
+            tz,
+            mood: entry.mood,
+            score,
+            tags: entry.tags ? JSON.stringify(entry.tags) : null,
+            note: null,
+            noteEncrypted: encryptNote(entry.note ?? null),
+            source: resolvedSource,
+            externalId: entry.externalId ?? null,
+            moodLoggedAt: entry.moodLoggedAt,
+          },
+          update: {
+            // Last-writer-wins on the mood + tags + note triple. The
+            // iOS client only re-posts an existing entry when it has
+            // new data; the server trusts that decision. When the dedup
+            // key is `externalId`, also refresh `date` / `moodLoggedAt`
+            // so a re-zoned re-import lands the corrected wall-clock on
+            // the same row.
+            mood: entry.mood,
+            score,
+            tags: entry.tags ? JSON.stringify(entry.tags) : null,
+            note: null,
+            noteEncrypted: encryptNote(entry.note ?? null),
+            ...(entry.externalId
+              ? { date, moodLoggedAt: entry.moodLoggedAt }
+              : {}),
+          },
+        });
 
-      // v1.12.0 — persist structured-tag links, mirroring the
-      // single-entry `createTagLinks` path. Additive + idempotent:
-      // `createTagLinks` resolves keys against the catalog (dropping
-      // unknown keys) and `skipDuplicates` on the join insert keeps a
-      // re-posted entry from minting duplicate links. Runs for both
-      // fresh and re-posted (upserted) rows so a backfill that adds tag
-      // keys on a second pass still lands them.
-      // v1.12.0 — rated factors ride the same path; an out-of-scale
-      // rating throws `RatedFactorOutOfRangeError`, which the per-entry
-      // catch below turns into a `skipped` result (the rest of the batch
-      // still lands). The mood row itself already upserted, so a skipped
-      // factor leaves a valid entry with no rated links.
-      if (
-        (entry.tagKeys && entry.tagKeys.length > 0) ||
-        (entry.ratedFactors && entry.ratedFactors.length > 0)
-      ) {
-        await createTagLinks(
-          result.id,
-          user.id,
-          entry.tagKeys ?? [],
-          prisma,
-          entry.ratedFactors ?? [],
-        );
-      }
+        // v1.12.0 — persist structured-tag links, mirroring the
+        // single-entry `createTagLinks` path. Additive + idempotent:
+        // `createTagLinks` resolves keys against the catalog (dropping
+        // unknown keys) and `skipDuplicates` on the join insert keeps a
+        // re-posted entry from minting duplicate links. Runs for both
+        // fresh and re-posted (upserted) rows so a backfill that adds tag
+        // keys on a second pass still lands them.
+        // v1.12.0 — rated factors ride the same path; an out-of-scale
+        // rating throws `RatedFactorOutOfRangeError`. Inside the
+        // transaction that throw now rolls the mood row back with it, so a
+        // "skipped" result means nothing was written — which is what the
+        // client was already being told.
+        if (
+          (entry.tagKeys && entry.tagKeys.length > 0) ||
+          (entry.ratedFactors && entry.ratedFactors.length > 0)
+        ) {
+          await createTagLinks(
+            upserted.id,
+            user.id,
+            entry.tagKeys ?? [],
+            tx,
+            entry.ratedFactors ?? [],
+          );
+        }
+
+        return upserted;
+      });
 
       if (existing) {
         duplicates += 1;
diff --git a/src/lib/__tests__/glitchtip-path-secret-redaction.test.ts b/src/lib/__tests__/glitchtip-path-secret-redaction.test.ts
index 0193cb82b..b24d2dba1 100644
--- a/src/lib/__tests__/glitchtip-path-secret-redaction.test.ts
+++ b/src/lib/__tests__/glitchtip-path-secret-redaction.test.ts
@@ -39,7 +39,9 @@ vi.mock("@/lib/monitoring-settings", () => ({
   })),
 }));
 
-const sendGlitchtipEvent = vi.fn(async (_payload: unknown) => {});
+const sendGlitchtipEvent = vi.fn<(payload: unknown) => Promise<void>>(
+  async () => {},
+);
 vi.mock("@/lib/monitoring/glitchtip", () => ({
   sendGlitchtipEvent: (payload: unknown) => sendGlitchtipEvent(payload),
 }));
@@ -62,10 +64,10 @@ beforeEach(() => {
   sendGlitchtipEvent.mockClear();
 });
 
-function throwingHandler() {
-  return apiHandler(async (_request: NextRequest) => {
+function throwingHandler(): (request: NextRequest) => Promise<Response> {
+  return apiHandler(async () => {
     throw new Error("boom");
-  });
+  }) as unknown as (request: NextRequest) => Promise<Response>;
 }
 
 async function forwardedPayload(url: string) {