diff --git a/.changeset/plugin-storage-range-filter-guard.md b/.changeset/plugin-storage-range-filter-guard.md
new file mode 100644
index 0000000000..9958f2634a
--- /dev/null
+++ b/.changeset/plugin-storage-range-filter-guard.md
@@ -0,0 +1,12 @@
+---
+"emdash": patch
+---
+
+Fixes a plugin storage range filter whose every bound is `undefined` matching every row instead of failing. Building a bound from an optional value — `where: { stock: { gte: minStock } }` where `minStock` is `undefined` — type-checks, but contributed no SQL, so `query()` and `count()` returned the whole collection and `updateIf()` applied its write with no guard at all. A guarded decrement could then drive a counter past the bound the caller asked for.
+
+Such a filter now throws `StorageQueryError` naming the field. Pass a defined bound, or omit the field when you mean to match unconditionally:
+
+```typescript
+const where = minStock === undefined ? {} : { stock: { gte: minStock } };
+await ctx.storage.products.query({ where });
+```
diff --git a/packages/core/src/plugins/storage-query.ts b/packages/core/src/plugins/storage-query.ts
index a60c5df335..56b642a22b 100644
--- a/packages/core/src/plugins/storage-query.ts
+++ b/packages/core/src/plugins/storage-query.ts
@@ -243,6 +243,17 @@ export function buildCondition(
 		if (value.lt !== undefined) pushBound("<", value.lt);
 		if (value.lte !== undefined) pushBound("<=", value.lte);
 
+		// A filter with no defined bound contributes no SQL. Returning it would
+		// widen the caller's predicate to "match everything" — survivable in a
+		// read, but it strips the guard off a conditional write.
+		if (conditions.length === 0) {
+			throw new StorageQueryError(
+				`Range filter for field '${field}' has no defined bound`,
+				field,
+				"Provide at least one of gt, gte, lt, or lte, or omit the field.",
+			);
+		}
+
 		return {
 			sql: conditions.join(" AND "),
 			params,
@@ -268,6 +279,8 @@ export function buildWhereClause(
 
 	for (const [field, value] of Object.entries(where)) {
 		const condition = buildCondition(db, field, value);
+		// An empty slot in the join would emit `<cond> AND ` and fail to parse.
+		if (!condition.sql) continue;
 		conditions.push(condition.sql);
 		params.push(...condition.params);
 	}
diff --git a/packages/core/tests/integration/plugins/storage-updateif.test.ts b/packages/core/tests/integration/plugins/storage-updateif.test.ts
index 35c26679ce..390dacc6d7 100644
--- a/packages/core/tests/integration/plugins/storage-updateif.test.ts
+++ b/packages/core/tests/integration/plugins/storage-updateif.test.ts
@@ -14,6 +14,7 @@ import { it, expect, beforeEach, afterEach } from "vitest";
 
 import { PluginStorageRepository } from "../../../src/database/repositories/plugin-storage.js";
 import type { Database } from "../../../src/database/types.js";
+import { StorageQueryError } from "../../../src/plugins/storage-query.js";
 import {
 	describeEachDialect,
 	setupForDialect,
@@ -191,6 +192,20 @@ describeEachDialect("Plugin storage updateIf", (dialect) => {
 		expect((await repo.get("p1"))?.stock).toBe(5);
 	});
 
+	it("updateIf() with an all-`undefined` guard throws instead of writing unguarded", async () => {
+		// An empty predicate contributes no SQL. Dropped silently, it would leave
+		// the UPDATE unguarded and drive stock past the bound the caller asked for.
+		const repo = productsRepo();
+		await repo.put("p1", { sku: "A", stock: 0, tier: 1, name: "Alpha" });
+		await expect(
+			repo.updateIf("p1", {
+				where: { stock: { gte: undefined } },
+				delta: { stock: { dec: 1 } },
+			}),
+		).rejects.toThrow(StorageQueryError);
+		expect((await repo.get("p1"))?.stock).toBe(0);
+	});
+
 	it("updateIf() with an all-`undefined` set (no delta) throws and never writes", async () => {
 		const repo = productsRepo();
 		await repo.put("p1", { sku: "A", stock: 5, tier: 1, name: "Alpha" });
diff --git a/packages/core/tests/integration/plugins/storage.test.ts b/packages/core/tests/integration/plugins/storage.test.ts
index 3d6e3f59a4..5adb2f9d21 100644
--- a/packages/core/tests/integration/plugins/storage.test.ts
+++ b/packages/core/tests/integration/plugins/storage.test.ts
@@ -155,6 +155,24 @@ describe("Plugin Storage Integration", () => {
 			const plain = await repo.query({ where: { eventType: { startsWith: "sale:" } } });
 			expect(plain.items).toHaveLength(2);
 		});
+
+		it("rejects a range filter with no defined bound instead of matching every row", async () => {
+			// A bound built from an optional value is the common way to reach this;
+			// dropping the predicate would silently widen the query to the whole
+			// collection.
+			const repo = new PluginStorageRepository<AnalyticsEvent>(db, "analytics", "events", [
+				"timestamp",
+			]);
+			await repo.putMany([
+				{ id: "e1", data: { eventType: "a", userId: "u1", timestamp: "2024-01-01", metadata: {} } },
+				{ id: "e2", data: { eventType: "b", userId: "u2", timestamp: "2024-06-01", metadata: {} } },
+			]);
+
+			const since: string | undefined = undefined;
+			await expect(repo.query({ where: { timestamp: { gte: since } } })).rejects.toThrow(
+				/no defined bound/,
+			);
+		});
 	});
 
 	describe("createPluginStorageAccessor", () => {
diff --git a/packages/core/tests/unit/plugins/storage-query.test.ts b/packages/core/tests/unit/plugins/storage-query.test.ts
index 1aa6fba9eb..e5a5cc143f 100644
--- a/packages/core/tests/unit/plugins/storage-query.test.ts
+++ b/packages/core/tests/unit/plugins/storage-query.test.ts
@@ -277,6 +277,15 @@ describe("storage-query", () => {
 			expect(result.sql).toBe(`${ageNum} >= ? AND ${ageNum} < ?`);
 			expect(result.params).toEqual([18, 65]);
 		});
+
+		it("should throw for a range filter whose every bound is undefined", () => {
+			// An empty predicate is silently dropped downstream, which turns a
+			// guard into an unconditional match.
+			expect(() => buildCondition(db, "age", { gte: undefined })).toThrow(StorageQueryError);
+			expect(() => buildCondition(db, "age", { gt: undefined, lte: undefined })).toThrow(
+				StorageQueryError,
+			);
+		});
 	});
 
 	describe("buildWhereClause", () => {
@@ -314,6 +323,14 @@ describe("storage-query", () => {
 			expect(result.sql).toContain(">= ?");
 			expect(result.params).toEqual(["active", "pending", "test%", 5]);
 		});
+
+		it("should never emit a dangling AND", () => {
+			// A condition that contributes no SQL must not leave an empty slot in
+			// the join, which would produce `<cond> AND ` and fail to parse.
+			expect(() => buildWhereClause(db, { count: { gte: -99 }, name: { gte: undefined } })).toThrow(
+				StorageQueryError,
+			);
+		});
 	});
 
 	describe("buildOrderByClause", () => {
diff --git a/skills/creating-plugins/references/storage.md b/skills/creating-plugins/references/storage.md
index 313cc570fb..9b01b9f80e 100644
--- a/skills/creating-plugins/references/storage.md
+++ b/skills/creating-plugins/references/storage.md
@@ -84,7 +84,7 @@ const result = await ctx.storage.submissions.query({
 // Exact match
 where: { status: "pending" }
 
-// Range
+// Range — needs at least one defined bound, or it throws StorageQueryError
 where: { createdAt: { gte: "2024-01-01" } }
 where: { score: { gt: 50, lte: 100 } }
 
@@ -155,6 +155,7 @@ Behavior to account for:
 - `delta` accepts integers. A float throws `TypeError`.
 - Pass at least one of `set` or `delta`. A field cannot appear in both.
 - A `dec` drives a field negative when the guard does not cover it. Pair `dec: k` with a `gte: k` guard to keep the field at or above zero.
+- A range filter in the guard needs at least one defined bound. `{ stock: { gte: undefined } }` throws `StorageQueryError` rather than leaving the write unguarded.
 - A losing writer that aborts instead of returning `{ applied: false }` throws `StorageSerializationError`, carrying the Postgres SQLSTATE (`40001` or `40P01`). Retry the call.
 
 ### Index Design
diff --git a/templates/blank/.agents/skills/creating-plugins/references/storage.md b/templates/blank/.agents/skills/creating-plugins/references/storage.md
index 313cc570fb..9b01b9f80e 100644
--- a/templates/blank/.agents/skills/creating-plugins/references/storage.md
+++ b/templates/blank/.agents/skills/creating-plugins/references/storage.md
@@ -84,7 +84,7 @@ const result = await ctx.storage.submissions.query({
 // Exact match
 where: { status: "pending" }
 
-// Range
+// Range — needs at least one defined bound, or it throws StorageQueryError
 where: { createdAt: { gte: "2024-01-01" } }
 where: { score: { gt: 50, lte: 100 } }
 
@@ -155,6 +155,7 @@ Behavior to account for:
 - `delta` accepts integers. A float throws `TypeError`.
 - Pass at least one of `set` or `delta`. A field cannot appear in both.
 - A `dec` drives a field negative when the guard does not cover it. Pair `dec: k` with a `gte: k` guard to keep the field at or above zero.
+- A range filter in the guard needs at least one defined bound. `{ stock: { gte: undefined } }` throws `StorageQueryError` rather than leaving the write unguarded.
 - A losing writer that aborts instead of returning `{ applied: false }` throws `StorageSerializationError`, carrying the Postgres SQLSTATE (`40001` or `40P01`). Retry the call.
 
 ### Index Design
diff --git a/templates/blog-cloudflare/.agents/skills/creating-plugins/references/storage.md b/templates/blog-cloudflare/.agents/skills/creating-plugins/references/storage.md
index 313cc570fb..9b01b9f80e 100644
--- a/templates/blog-cloudflare/.agents/skills/creating-plugins/references/storage.md
+++ b/templates/blog-cloudflare/.agents/skills/creating-plugins/references/storage.md
@@ -84,7 +84,7 @@ const result = await ctx.storage.submissions.query({
 // Exact match
 where: { status: "pending" }
 
-// Range
+// Range — needs at least one defined bound, or it throws StorageQueryError
 where: { createdAt: { gte: "2024-01-01" } }
 where: { score: { gt: 50, lte: 100 } }
 
@@ -155,6 +155,7 @@ Behavior to account for:
 - `delta` accepts integers. A float throws `TypeError`.
 - Pass at least one of `set` or `delta`. A field cannot appear in both.
 - A `dec` drives a field negative when the guard does not cover it. Pair `dec: k` with a `gte: k` guard to keep the field at or above zero.
+- A range filter in the guard needs at least one defined bound. `{ stock: { gte: undefined } }` throws `StorageQueryError` rather than leaving the write unguarded.
 - A losing writer that aborts instead of returning `{ applied: false }` throws `StorageSerializationError`, carrying the Postgres SQLSTATE (`40001` or `40P01`). Retry the call.
 
 ### Index Design
diff --git a/templates/blog/.agents/skills/creating-plugins/references/storage.md b/templates/blog/.agents/skills/creating-plugins/references/storage.md
index 313cc570fb..9b01b9f80e 100644
--- a/templates/blog/.agents/skills/creating-plugins/references/storage.md
+++ b/templates/blog/.agents/skills/creating-plugins/references/storage.md
@@ -84,7 +84,7 @@ const result = await ctx.storage.submissions.query({
 // Exact match
 where: { status: "pending" }
 
-// Range
+// Range — needs at least one defined bound, or it throws StorageQueryError
 where: { createdAt: { gte: "2024-01-01" } }
 where: { score: { gt: 50, lte: 100 } }
 
@@ -155,6 +155,7 @@ Behavior to account for:
 - `delta` accepts integers. A float throws `TypeError`.
 - Pass at least one of `set` or `delta`. A field cannot appear in both.
 - A `dec` drives a field negative when the guard does not cover it. Pair `dec: k` with a `gte: k` guard to keep the field at or above zero.
+- A range filter in the guard needs at least one defined bound. `{ stock: { gte: undefined } }` throws `StorageQueryError` rather than leaving the write unguarded.
 - A losing writer that aborts instead of returning `{ applied: false }` throws `StorageSerializationError`, carrying the Postgres SQLSTATE (`40001` or `40P01`). Retry the call.
 
 ### Index Design
diff --git a/templates/marketing-cloudflare/.agents/skills/creating-plugins/references/storage.md b/templates/marketing-cloudflare/.agents/skills/creating-plugins/references/storage.md
index 313cc570fb..9b01b9f80e 100644
--- a/templates/marketing-cloudflare/.agents/skills/creating-plugins/references/storage.md
+++ b/templates/marketing-cloudflare/.agents/skills/creating-plugins/references/storage.md
@@ -84,7 +84,7 @@ const result = await ctx.storage.submissions.query({
 // Exact match
 where: { status: "pending" }
 
-// Range
+// Range — needs at least one defined bound, or it throws StorageQueryError
 where: { createdAt: { gte: "2024-01-01" } }
 where: { score: { gt: 50, lte: 100 } }
 
@@ -155,6 +155,7 @@ Behavior to account for:
 - `delta` accepts integers. A float throws `TypeError`.
 - Pass at least one of `set` or `delta`. A field cannot appear in both.
 - A `dec` drives a field negative when the guard does not cover it. Pair `dec: k` with a `gte: k` guard to keep the field at or above zero.
+- A range filter in the guard needs at least one defined bound. `{ stock: { gte: undefined } }` throws `StorageQueryError` rather than leaving the write unguarded.
 - A losing writer that aborts instead of returning `{ applied: false }` throws `StorageSerializationError`, carrying the Postgres SQLSTATE (`40001` or `40P01`). Retry the call.
 
 ### Index Design
diff --git a/templates/marketing/.agents/skills/creating-plugins/references/storage.md b/templates/marketing/.agents/skills/creating-plugins/references/storage.md
index 313cc570fb..9b01b9f80e 100644
--- a/templates/marketing/.agents/skills/creating-plugins/references/storage.md
+++ b/templates/marketing/.agents/skills/creating-plugins/references/storage.md
@@ -84,7 +84,7 @@ const result = await ctx.storage.submissions.query({
 // Exact match
 where: { status: "pending" }
 
-// Range
+// Range — needs at least one defined bound, or it throws StorageQueryError
 where: { createdAt: { gte: "2024-01-01" } }
 where: { score: { gt: 50, lte: 100 } }
 
@@ -155,6 +155,7 @@ Behavior to account for:
 - `delta` accepts integers. A float throws `TypeError`.
 - Pass at least one of `set` or `delta`. A field cannot appear in both.
 - A `dec` drives a field negative when the guard does not cover it. Pair `dec: k` with a `gte: k` guard to keep the field at or above zero.
+- A range filter in the guard needs at least one defined bound. `{ stock: { gte: undefined } }` throws `StorageQueryError` rather than leaving the write unguarded.
 - A losing writer that aborts instead of returning `{ applied: false }` throws `StorageSerializationError`, carrying the Postgres SQLSTATE (`40001` or `40P01`). Retry the call.
 
 ### Index Design
diff --git a/templates/portfolio-cloudflare/.agents/skills/creating-plugins/references/storage.md b/templates/portfolio-cloudflare/.agents/skills/creating-plugins/references/storage.md
index 313cc570fb..9b01b9f80e 100644
--- a/templates/portfolio-cloudflare/.agents/skills/creating-plugins/references/storage.md
+++ b/templates/portfolio-cloudflare/.agents/skills/creating-plugins/references/storage.md
@@ -84,7 +84,7 @@ const result = await ctx.storage.submissions.query({
 // Exact match
 where: { status: "pending" }
 
-// Range
+// Range — needs at least one defined bound, or it throws StorageQueryError
 where: { createdAt: { gte: "2024-01-01" } }
 where: { score: { gt: 50, lte: 100 } }
 
@@ -155,6 +155,7 @@ Behavior to account for:
 - `delta` accepts integers. A float throws `TypeError`.
 - Pass at least one of `set` or `delta`. A field cannot appear in both.
 - A `dec` drives a field negative when the guard does not cover it. Pair `dec: k` with a `gte: k` guard to keep the field at or above zero.
+- A range filter in the guard needs at least one defined bound. `{ stock: { gte: undefined } }` throws `StorageQueryError` rather than leaving the write unguarded.
 - A losing writer that aborts instead of returning `{ applied: false }` throws `StorageSerializationError`, carrying the Postgres SQLSTATE (`40001` or `40P01`). Retry the call.
 
 ### Index Design
diff --git a/templates/portfolio/.agents/skills/creating-plugins/references/storage.md b/templates/portfolio/.agents/skills/creating-plugins/references/storage.md
index 313cc570fb..9b01b9f80e 100644
--- a/templates/portfolio/.agents/skills/creating-plugins/references/storage.md
+++ b/templates/portfolio/.agents/skills/creating-plugins/references/storage.md
@@ -84,7 +84,7 @@ const result = await ctx.storage.submissions.query({
 // Exact match
 where: { status: "pending" }
 
-// Range
+// Range — needs at least one defined bound, or it throws StorageQueryError
 where: { createdAt: { gte: "2024-01-01" } }
 where: { score: { gt: 50, lte: 100 } }
 
@@ -155,6 +155,7 @@ Behavior to account for:
 - `delta` accepts integers. A float throws `TypeError`.
 - Pass at least one of `set` or `delta`. A field cannot appear in both.
 - A `dec` drives a field negative when the guard does not cover it. Pair `dec: k` with a `gte: k` guard to keep the field at or above zero.
+- A range filter in the guard needs at least one defined bound. `{ stock: { gte: undefined } }` throws `StorageQueryError` rather than leaving the write unguarded.
 - A losing writer that aborts instead of returning `{ applied: false }` throws `StorageSerializationError`, carrying the Postgres SQLSTATE (`40001` or `40P01`). Retry the call.
 
 ### Index Design
diff --git a/templates/starter-cloudflare/.agents/skills/creating-plugins/references/storage.md b/templates/starter-cloudflare/.agents/skills/creating-plugins/references/storage.md
index 313cc570fb..9b01b9f80e 100644
--- a/templates/starter-cloudflare/.agents/skills/creating-plugins/references/storage.md
+++ b/templates/starter-cloudflare/.agents/skills/creating-plugins/references/storage.md
@@ -84,7 +84,7 @@ const result = await ctx.storage.submissions.query({
 // Exact match
 where: { status: "pending" }
 
-// Range
+// Range — needs at least one defined bound, or it throws StorageQueryError
 where: { createdAt: { gte: "2024-01-01" } }
 where: { score: { gt: 50, lte: 100 } }
 
@@ -155,6 +155,7 @@ Behavior to account for:
 - `delta` accepts integers. A float throws `TypeError`.
 - Pass at least one of `set` or `delta`. A field cannot appear in both.
 - A `dec` drives a field negative when the guard does not cover it. Pair `dec: k` with a `gte: k` guard to keep the field at or above zero.
+- A range filter in the guard needs at least one defined bound. `{ stock: { gte: undefined } }` throws `StorageQueryError` rather than leaving the write unguarded.
 - A losing writer that aborts instead of returning `{ applied: false }` throws `StorageSerializationError`, carrying the Postgres SQLSTATE (`40001` or `40P01`). Retry the call.
 
 ### Index Design
diff --git a/templates/starter/.agents/skills/creating-plugins/references/storage.md b/templates/starter/.agents/skills/creating-plugins/references/storage.md
index 313cc570fb..9b01b9f80e 100644
--- a/templates/starter/.agents/skills/creating-plugins/references/storage.md
+++ b/templates/starter/.agents/skills/creating-plugins/references/storage.md
@@ -84,7 +84,7 @@ const result = await ctx.storage.submissions.query({
 // Exact match
 where: { status: "pending" }
 
-// Range
+// Range — needs at least one defined bound, or it throws StorageQueryError
 where: { createdAt: { gte: "2024-01-01" } }
 where: { score: { gt: 50, lte: 100 } }
 
@@ -155,6 +155,7 @@ Behavior to account for:
 - `delta` accepts integers. A float throws `TypeError`.
 - Pass at least one of `set` or `delta`. A field cannot appear in both.
 - A `dec` drives a field negative when the guard does not cover it. Pair `dec: k` with a `gte: k` guard to keep the field at or above zero.
+- A range filter in the guard needs at least one defined bound. `{ stock: { gte: undefined } }` throws `StorageQueryError` rather than leaving the write unguarded.
 - A losing writer that aborts instead of returning `{ applied: false }` throws `StorageSerializationError`, carrying the Postgres SQLSTATE (`40001` or `40P01`). Retry the call.
 
 ### Index Design