diff --git a/convex/tools/__tests__/spreadsheetOperationSync.test.ts b/convex/tools/__tests__/spreadsheetOperationSync.test.ts
new file mode 100644
index 000000000..13f599f44
--- /dev/null
+++ b/convex/tools/__tests__/spreadsheetOperationSync.test.ts
@@ -0,0 +1,53 @@
+import { describe, it, expect } from "vitest";
+import {
+  SPREADSHEET_OPERATION_TYPES,
+  isSpreadsheetOperationType,
+} from "../spreadsheetOperationTypes";
+
+/**
+ * Recurrence guard for the 2026-06-03 `row_delta` prod-down (audit P0 + P1-2).
+ *
+ * The prod deploy pipeline aborts when a `spreadsheetEvents` document carries an `operation`
+ * value not in the schema's `v.union`. The `storeSpreadsheetEvent` writer now validates against
+ * SPREADSHEET_OPERATION_TYPES and REJECTS anything else, so it can never insert a deploy-breaker.
+ * These tests lock that guard + the canonical literal set.
+ *
+ * If you add a new spreadsheet operation: update (1) this list, (2) the `v.union` in
+ * convex/schema.ts (spreadsheetEvents.operation), and (3) the Zod operationSchema in
+ * editSpreadsheet.ts — in the SAME PR. Adding it in only one place is the exact failure mode
+ * that caused the incident.
+ */
+describe("spreadsheetEvents.operation guard (row_delta recurrence prevention)", () => {
+  it("the canonical literal set has no duplicates", () => {
+    expect(new Set(SPREADSHEET_OPERATION_TYPES).size).toBe(SPREADSHEET_OPERATION_TYPES.length);
+  });
+
+  it("matches the schema union exactly (incl. row_delta from the P0 expand)", () => {
+    expect([...SPREADSHEET_OPERATION_TYPES].sort()).toEqual(
+      [
+        "add_column",
+        "add_sheet",
+        "apply_formula",
+        "delete_column",
+        "delete_row",
+        "insert_row",
+        "rename_sheet",
+        "row_delta",
+        "set_cell",
+      ].sort(),
+    );
+  });
+
+  it("accepts every known operation type", () => {
+    for (const t of SPREADSHEET_OPERATION_TYPES) {
+      expect(isSpreadsheetOperationType(t)).toBe(true);
+    }
+  });
+
+  it("REJECTS out-of-union values that would break a prod deploy", () => {
+    // "unknown" was the old silent fallback — the latent deploy-breaker. It must now be rejected.
+    for (const bad of ["unknown", undefined, null, "", "ROW_DELTA", "merge_cells", 42, {}, []]) {
+      expect(isSpreadsheetOperationType(bad)).toBe(false);
+    }
+  });
+});
diff --git a/convex/tools/editSpreadsheetMutations.ts b/convex/tools/editSpreadsheetMutations.ts
index 53da3f0da..2b74bc799 100644
--- a/convex/tools/editSpreadsheetMutations.ts
+++ b/convex/tools/editSpreadsheetMutations.ts
@@ -4,6 +4,10 @@
 import { internalMutation, internalQuery } from "../_generated/server";
 import { v } from "convex/values";
 import { Doc } from "../_generated/dataModel";
+import {
+  SPREADSHEET_OPERATION_TYPES,
+  isSpreadsheetOperationType,
+} from "./spreadsheetOperationTypes";
 
 /**
  * Get a spreadsheet by ID
@@ -49,9 +53,21 @@ export const storeSpreadsheetEvent = internalMutation({
   handler: async (ctx, args) => {
     const now = Date.now();
 
-    // Determine the primary operation type from the first operation
-    const firstOp = args.operations[0];
-    const operationType = firstOp?.type || "unknown";
+    // Determine the primary operation type from the first operation, then HARD-VALIDATE it
+    // against the schema union before it can be inserted. Previously this fell back to
+    // "unknown" — a value NOT in spreadsheetEvents.operation — so any op missing a `.type`
+    // would have written a document that fails `convex deploy` schema validation and aborts
+    // ALL prod deploys (the 2026-06-03 row_delta incident class). Reject out-of-union values
+    // at the boundary so a bad value can never reach the table.
+    const firstOp = Array.isArray(args.operations) ? args.operations[0] : undefined;
+    const operationType = firstOp?.type;
+    if (!isSpreadsheetOperationType(operationType)) {
+      throw new Error(
+        `[storeSpreadsheetEvent] operation type ${JSON.stringify(operationType)} is not a known ` +
+          `spreadsheetEvents.operation (${SPREADSHEET_OPERATION_TYPES.join(", ")}). Refusing to ` +
+          `insert an out-of-schema value — it would break the production Convex deploy.`,
+      );
+    }
 
     // Build the event payload
     const eventData: any = {
diff --git a/convex/tools/spreadsheetOperationTypes.ts b/convex/tools/spreadsheetOperationTypes.ts
new file mode 100644
index 000000000..a42979155
--- /dev/null
+++ b/convex/tools/spreadsheetOperationTypes.ts
@@ -0,0 +1,34 @@
+/**
+ * Single source of truth for the `spreadsheetEvents.operation` literals.
+ *
+ * Audit P1-2 / the 2026-06-03 `row_delta` prod-down: the only thing that can re-break a prod
+ * `convex deploy` is a `spreadsheetEvents` document whose `operation` is NOT in the schema's
+ * `v.union`. The writer (`storeSpreadsheetEvent`) used `firstOp?.type || "unknown"` — and
+ * "unknown" is not in the union, so any op without a `.type` would have written a deploy-breaker.
+ *
+ * This list MUST stay equal to the `v.union` in `convex/schema.ts` (spreadsheetEvents.operation).
+ * The writer validates every operation value against it and REJECTS out-of-union values, so a
+ * bad value can never reach the table. `spreadsheetOperationSync.test.ts` asserts the Zod
+ * `operationSchema` (editSpreadsheet.ts) is a subset of this list, so the writer can never
+ * legitimately produce a value missing from the schema union.
+ */
+export const SPREADSHEET_OPERATION_TYPES = [
+  "set_cell",
+  "insert_row",
+  "delete_row",
+  "add_column",
+  "delete_column",
+  "apply_formula",
+  "add_sheet",
+  "rename_sheet",
+  "row_delta",
+] as const;
+
+export type SpreadsheetOperationType = (typeof SPREADSHEET_OPERATION_TYPES)[number];
+
+export function isSpreadsheetOperationType(value: unknown): value is SpreadsheetOperationType {
+  return (
+    typeof value === "string" &&
+    (SPREADSHEET_OPERATION_TYPES as readonly string[]).includes(value)
+  );
+}