diff --git a/src/agents/sanitize-for-prompt.test.ts b/src/agents/sanitize-for-prompt.test.ts
new file mode 100644
index 0000000000..b79a1250ba
--- /dev/null
+++ b/src/agents/sanitize-for-prompt.test.ts
@@ -0,0 +1,53 @@
+import { describe, expect, it } from "vitest";
+import { sanitizeForPromptLiteral } from "./sanitize-for-prompt.js";
+import { buildAgentSystemPrompt } from "./system-prompt.js";
+
+describe("sanitizeForPromptLiteral (OC-19 hardening)", () => {
+  it("strips ASCII control chars (CR/LF/NUL/tab)", () => {
+    expect(sanitizeForPromptLiteral("/tmp/a\nb\rc\x00d\te")).toBe("/tmp/abcde");
+  });
+
+  it("strips Unicode line/paragraph separators", () => {
+    expect(sanitizeForPromptLiteral(`/tmp/a\u2028b\u2029c`)).toBe("/tmp/abc");
+  });
+
+  it("strips Unicode format chars (bidi override)", () => {
+    // U+202E RIGHT-TO-LEFT OVERRIDE (Cf) can spoof rendered text.
+    expect(sanitizeForPromptLiteral(`/tmp/a\u202Eb`)).toBe("/tmp/ab");
+  });
+
+  it("preserves ordinary Unicode + spaces", () => {
+    const value = "/tmp/my project/日本語-folder.v2";
+    expect(sanitizeForPromptLiteral(value)).toBe(value);
+  });
+});
+
+describe("buildAgentSystemPrompt uses sanitized workspace/sandbox strings", () => {
+  it("sanitizes workspaceDir (no newlines / separators)", () => {
+    const prompt = buildAgentSystemPrompt({
+      workspaceDir: "/tmp/project\nINJECT\u2028MORE",
+    });
+    expect(prompt).toContain("Your working directory is: /tmp/projectINJECTMORE");
+    expect(prompt).not.toContain("Your working directory is: /tmp/project\n");
+    expect(prompt).not.toContain("\u2028");
+  });
+
+  it("sanitizes sandbox workspace/mount/url strings", () => {
+    const prompt = buildAgentSystemPrompt({
+      workspaceDir: "/tmp/test",
+      sandboxInfo: {
+        enabled: true,
+        containerWorkspaceDir: "/work\u2029space",
+        workspaceDir: "/host\nspace",
+        workspaceAccess: "read-write",
+        agentWorkspaceMount: "/mnt\u2028mount",
+        browserNoVncUrl: "http://example.test/\nui",
+      },
+    });
+    expect(prompt).toContain("Sandbox container workdir: /workspace");
+    expect(prompt).toContain("Sandbox host workspace: /hostspace");
+    expect(prompt).toContain("(mounted at /mntmount)");
+    expect(prompt).toContain("Sandbox browser observer (noVNC): http://example.test/ui");
+    expect(prompt).not.toContain("\nui");
+  });
+});
diff --git a/src/agents/sanitize-for-prompt.ts b/src/agents/sanitize-for-prompt.ts
new file mode 100644
index 0000000000..7692cf306d
--- /dev/null
+++ b/src/agents/sanitize-for-prompt.ts
@@ -0,0 +1,18 @@
+/**
+ * Sanitize untrusted strings before embedding them into an LLM prompt.
+ *
+ * Threat model (OC-19): attacker-controlled directory names (or other runtime strings)
+ * that contain newline/control characters can break prompt structure and inject
+ * arbitrary instructions.
+ *
+ * Strategy (Option 3 hardening):
+ * - Strip Unicode "control" (Cc) + "format" (Cf) characters (includes CR/LF/NUL, bidi marks, zero-width chars).
+ * - Strip explicit line/paragraph separators (Zl/Zp): U+2028/U+2029.
+ *
+ * Notes:
+ * - This is intentionally lossy; it trades edge-case path fidelity for prompt integrity.
+ * - If you need lossless representation, escape instead of stripping.
+ */
+export function sanitizeForPromptLiteral(value: string): string {
+  return value.replace(/[\p{Cc}\p{Cf}\u2028\u2029]/gu, "");
+}
diff --git a/src/agents/system-prompt.ts b/src/agents/system-prompt.ts
index 21a176ac8c..f6b4c0625f 100644
--- a/src/agents/system-prompt.ts
+++ b/src/agents/system-prompt.ts
@@ -4,6 +4,7 @@ import type { ResolvedTimeFormat } from "./date-time.js";
 import type { EmbeddedContextFile } from "./pi-embedded-helpers.js";
 import { SILENT_REPLY_TOKEN } from "../auto-reply/tokens.js";
 import { listDeliverableMessageChannels } from "../utils/message-channel.js";
+import { sanitizeForPromptLiteral } from "./sanitize-for-prompt.js";
 
 /**
  * Controls which hardcoded sections are included in the system prompt.
@@ -355,13 +356,17 @@ export function buildAgentSystemPrompt(params: {
   const promptMode = params.promptMode ?? "full";
   const isMinimal = promptMode === "minimal" || promptMode === "none";
   const sandboxContainerWorkspace = params.sandboxInfo?.containerWorkspaceDir?.trim();
+  const sanitizedWorkspaceDir = sanitizeForPromptLiteral(params.workspaceDir);
+  const sanitizedSandboxContainerWorkspace = sandboxContainerWorkspace
+    ? sanitizeForPromptLiteral(sandboxContainerWorkspace)
+    : "";
   const displayWorkspaceDir =
-    params.sandboxInfo?.enabled && sandboxContainerWorkspace
-      ? sandboxContainerWorkspace
-      : params.workspaceDir;
+    params.sandboxInfo?.enabled && sanitizedSandboxContainerWorkspace
+      ? sanitizedSandboxContainerWorkspace
+      : sanitizedWorkspaceDir;
   const workspaceGuidance =
-    params.sandboxInfo?.enabled && sandboxContainerWorkspace
-      ? `For read/write/edit/apply_patch, file paths resolve against host workspace: ${params.workspaceDir}. Prefer relative paths so both sandboxed exec and file tools work consistently.`
+    params.sandboxInfo?.enabled && sanitizedSandboxContainerWorkspace
+      ? `For read/write/edit/apply_patch, file paths resolve against host workspace: ${sanitizedWorkspaceDir}. Prefer relative paths so both sandboxed exec and file tools work consistently.`
       : "Treat this directory as the single global workspace for file operations unless explicitly instructed otherwise.";
   const safetySection = [
     "## Safety",
@@ -480,21 +485,21 @@ export function buildAgentSystemPrompt(params: {
           "Some tools may be unavailable due to sandbox policy.",
           "Sub-agents stay sandboxed (no elevated/host access). Need outside-sandbox read/write? Don't spawn; ask first.",
           params.sandboxInfo.containerWorkspaceDir
-            ? `Sandbox container workdir: ${params.sandboxInfo.containerWorkspaceDir}`
+            ? `Sandbox container workdir: ${sanitizeForPromptLiteral(params.sandboxInfo.containerWorkspaceDir)}`
             : "",
           params.sandboxInfo.workspaceDir
-            ? `Sandbox host workspace: ${params.sandboxInfo.workspaceDir}`
+            ? `Sandbox host workspace: ${sanitizeForPromptLiteral(params.sandboxInfo.workspaceDir)}`
             : "",
           params.sandboxInfo.workspaceAccess
             ? `Agent workspace access: ${params.sandboxInfo.workspaceAccess}${
                 params.sandboxInfo.agentWorkspaceMount
-                  ? ` (mounted at ${params.sandboxInfo.agentWorkspaceMount})`
+                  ? ` (mounted at ${sanitizeForPromptLiteral(params.sandboxInfo.agentWorkspaceMount)})`
                   : ""
               }`
             : "",
           params.sandboxInfo.browserBridgeUrl ? "Sandbox browser: enabled." : "",
           params.sandboxInfo.browserNoVncUrl
-            ? `Sandbox browser observer (noVNC): ${params.sandboxInfo.browserNoVncUrl}`
+            ? `Sandbox browser observer (noVNC): ${sanitizeForPromptLiteral(params.sandboxInfo.browserNoVncUrl)}`
             : "",
           params.sandboxInfo.hostBrowserAllowed === true
             ? "Host browser control: allowed."
diff --git a/src/agents/workspace-run.ts b/src/agents/workspace-run.ts
index 1061a0344e..8ba281c485 100644
--- a/src/agents/workspace-run.ts
+++ b/src/agents/workspace-run.ts
@@ -1,4 +1,5 @@
 import type { OpenClawConfig } from "../config/config.js";
+import { logWarn } from "../logger.js";
 import { redactIdentifier } from "../logging/redact-identifier.js";
 import {
   classifySessionKeyShape,
@@ -8,6 +9,7 @@ import {
 } from "../routing/session-key.js";
 import { resolveUserPath } from "../utils.js";
 import { resolveAgentWorkspaceDir, resolveDefaultAgentId } from "./agent-scope.js";
+import { sanitizeForPromptLiteral } from "./sanitize-for-prompt.js";
 
 export type WorkspaceFallbackReason = "missing" | "blank" | "invalid_type";
 type AgentIdSource = "explicit" | "session_key" | "default";
@@ -84,8 +86,12 @@ export function resolveRunWorkspaceDir(params: {
   if (typeof requested === "string") {
     const trimmed = requested.trim();
     if (trimmed) {
+      const sanitized = sanitizeForPromptLiteral(trimmed);
+      if (sanitized !== trimmed) {
+        logWarn("Control/format characters stripped from workspaceDir (OC-19 hardening).");
+      }
       return {
-        workspaceDir: resolveUserPath(trimmed),
+        workspaceDir: resolveUserPath(sanitized),
         usedFallback: false,
         agentId,
         agentIdSource,
@@ -96,8 +102,12 @@ export function resolveRunWorkspaceDir(params: {
   const fallbackReason: WorkspaceFallbackReason =
     requested == null ? "missing" : typeof requested === "string" ? "blank" : "invalid_type";
   const fallbackWorkspace = resolveAgentWorkspaceDir(params.config ?? {}, agentId);
+  const sanitizedFallback = sanitizeForPromptLiteral(fallbackWorkspace);
+  if (sanitizedFallback !== fallbackWorkspace) {
+    logWarn("Control/format characters stripped from fallback workspaceDir (OC-19 hardening).");
+  }
   return {
-    workspaceDir: resolveUserPath(fallbackWorkspace),
+    workspaceDir: resolveUserPath(sanitizedFallback),
     usedFallback: true,
     fallbackReason,
     agentId,