diff --git a/packages/tools/src/shared/cache.ts b/packages/tools/src/shared/cache.ts
index 15ce16fe..0fe1beed 100644
--- a/packages/tools/src/shared/cache.ts
+++ b/packages/tools/src/shared/cache.ts
@@ -5,6 +5,9 @@ import type { MemoryMode } from "./types"
  * Generic memory cache for storing per-turn memories to avoid redundant API calls.
  * Used to cache memory retrieval results during tool-call loops within the same turn.
  */
+const escapeKeySegment = (segment: string): string =>
+	segment.replace(/%/g, "%25").replace(/:/g, "%3A")
+
 export class MemoryCache<T = string> {
 	private cache: LRUCache<string, T> = new LRUCache({ max: 100 })
 
@@ -25,7 +28,9 @@ export class MemoryCache<T = string> {
 		message: string,
 	): string {
 		const normalizedMessage = message.trim().replace(/\s+/g, " ")
-		return `${containerTag}:${threadId || ""}:${mode}:${normalizedMessage}`
+		const safeContainerTag = escapeKeySegment(containerTag)
+		const safeThreadId = escapeKeySegment(threadId ?? "")
+		return `${safeContainerTag}:${safeThreadId}:${mode}:${normalizedMessage}`
 	}
 
 	/**
diff --git a/packages/tools/src/tools-shared.test.ts b/packages/tools/src/tools-shared.test.ts
index 3cc070ba..718b286b 100644
--- a/packages/tools/src/tools-shared.test.ts
+++ b/packages/tools/src/tools-shared.test.ts
@@ -1,4 +1,5 @@
 import { describe, expect, it } from "vitest"
+import { makeTurnKey } from "./shared/cache"
 import {
 	DEFAULT_VALUES,
 	SEARCH_LIMIT_BOUNDS,
@@ -130,3 +131,39 @@ describe("deduplicateMemoriesForMode", () => {
 		expect(deduplicated.searchResults).toEqual([])
 	})
 })
+
+describe("makeTurnKey", () => {
+	it("generates predictable turn key for standard inputs", () => {
+		expect(makeTurnKey("user-123", "thread-456", "full", "hello world")).toBe(
+			"user-123:thread-456:full:hello world",
+		)
+	})
+
+	it("normalizes and collapses whitespace in message", () => {
+		expect(
+			makeTurnKey("user-123", "thread-456", "full", "  hello   world  \n "),
+		).toBe("user-123:thread-456:full:hello world")
+	})
+
+	it("handles undefined threadId cleanly", () => {
+		expect(makeTurnKey("user-123", undefined, "profile", "test")).toBe(
+			"user-123::profile:test",
+		)
+	})
+
+	it("escapes colons to prevent cache key collisions between tag and threadId", () => {
+		const keyA = makeTurnKey("user:123", "456", "profile", "hi")
+		const keyB = makeTurnKey("user", "123:456", "profile", "hi")
+		expect(keyA).toBe("user%3A123:456:profile:hi")
+		expect(keyB).toBe("user:123%3A456:profile:hi")
+		expect(keyA).not.toBe(keyB)
+	})
+
+	it("escapes percent signs to avoid ambiguity with encoded sequences", () => {
+		const keyA = makeTurnKey("user%3A123", "456", "profile", "hi")
+		const keyB = makeTurnKey("user:123", "456", "profile", "hi")
+		expect(keyA).toBe("user%253A123:456:profile:hi")
+		expect(keyB).toBe("user%3A123:456:profile:hi")
+		expect(keyA).not.toBe(keyB)
+	})
+})