diff --git a/.env.example b/.env.example
index dcbcd63..1308290 100644
--- a/.env.example
+++ b/.env.example
@@ -17,3 +17,8 @@ ARTEX_LLM_PROVIDER=
 ARTEX_LLM_MODEL=
 ARTEX_LLM_BASE_URL=
 ARTEX_LLM_PROXY=
+
+# Untrusted-output boundary (optional). ARTEX_UNTRUSTED_BOUNDARY=1 frames every tool
+# output between nonce-tagged markers so the model treats it as data, not instructions.
+# Off by default; test it against a local target before enabling it in production.
+# ARTEX_UNTRUSTED_BOUNDARY=1
diff --git a/agent/chat.go b/agent/chat.go
index ae52ee8..02ec298 100644
--- a/agent/chat.go
+++ b/agent/chat.go
@@ -160,6 +160,9 @@ func (c *ChatAgent) Chat(ctx context.Context, agentKey, sessionID, message strin
 		Settlement:   wrapupSettlement(agentKey, nil),
 		NonStreaming: c.nonStreaming(), // when this profile selects non-streaming, use Provider.Complete
 		MaxTokens:    c.maxTokens(),    // 0 = send no cap, the server's default decides
+
+		// Opt-in via ARTEX_UNTRUSTED_BOUNDARY (default off): nonce-frame tool output as untrusted data.
+		UntrustedOutputBoundary: untrustedBoundaryEnabled(),
 	}
 	if c.guard != nil {
 		opts.Hooks = c.guard.Hooks()
diff --git a/agent/mainagent.go b/agent/mainagent.go
index 94585fb..f5b3f7d 100644
--- a/agent/mainagent.go
+++ b/agent/mainagent.go
@@ -169,6 +169,9 @@ func (m *MainAgent) Chat(ctx context.Context, taskID int64, mainSeg int, as *db.
 		Settlement:   wrapupSettlement("mainagent", nil),
 		NonStreaming: m.nonStreaming(), // when this profile selects non-streaming, use Provider.Complete
 		MaxTokens:    m.maxTokens(),    // 0 = send no cap, the server's default decides
+
+		// Opt-in via ARTEX_UNTRUSTED_BOUNDARY (default off): nonce-frame tool output as untrusted data.
+		UntrustedOutputBoundary: untrustedBoundaryEnabled(),
 	}
 	if m.tx != nil { // persist raw human↔AI conversation; one accumulating file per segment
 		opts.Transcript = m.tx
diff --git a/agent/planner.go b/agent/planner.go
index 7f53f80..ddf16be 100644
--- a/agent/planner.go
+++ b/agent/planner.go
@@ -457,6 +457,9 @@ func (p *Planner) Plan(ctx context.Context, taskID int64, as *db.AssetStore, ts
 		Settlement:   settle,
 		NonStreaming: p.nonStreaming(), // when this profile selects non-streaming, use Provider.Complete
 		MaxTokens:    p.maxTokens(),    // 0 = send no cap; the server default decides
+
+		// Opt-in via ARTEX_UNTRUSTED_BOUNDARY (default off): nonce-frame tool output as untrusted data.
+		UntrustedOutputBoundary: untrustedBoundaryEnabled(),
 	}
 	if p.tx != nil { // persist raw LLM conversation; one accumulating file per task's planner
 		opts.Transcript = p.tx
diff --git a/agent/untrusted_boundary.go b/agent/untrusted_boundary.go
new file mode 100644
index 0000000..cf20e93
--- /dev/null
+++ b/agent/untrusted_boundary.go
@@ -0,0 +1,19 @@
+package agent
+
+import (
+	"os"
+	"strings"
+)
+
+// untrustedBoundaryEnabled reports whether ARTEX_UNTRUSTED_BOUNDARY opts in to
+// Norma's untrusted-output boundary (agentcore.Options.UntrustedOutputBoundary:
+// tool results framed between nonce-tagged markers). Only "1", "true" and "on"
+// (case- and space-insensitive) enable it; unset, empty or anything else keeps
+// it off.
+func untrustedBoundaryEnabled() bool {
+	switch strings.ToLower(strings.TrimSpace(os.Getenv("ARTEX_UNTRUSTED_BOUNDARY"))) {
+	case "1", "true", "on":
+		return true
+	}
+	return false
+}
diff --git a/agent/untrusted_boundary_test.go b/agent/untrusted_boundary_test.go
new file mode 100644
index 0000000..c396eb6
--- /dev/null
+++ b/agent/untrusted_boundary_test.go
@@ -0,0 +1,59 @@
+package agent
+
+import (
+	"os"
+	"strings"
+	"testing"
+)
+
+func TestUntrustedBoundaryEnabled(t *testing.T) {
+	for _, tc := range []struct {
+		env  string
+		want bool
+	}{
+		{"", false},
+		{"0", false},
+		{"false", false},
+		{"yes", false},
+		{"1", true},
+		{"true", true},
+		{"on", true},
+		{" TRUE ", true},
+		{"On", true},
+	} {
+		t.Setenv("ARTEX_UNTRUSTED_BOUNDARY", tc.env)
+		if got := untrustedBoundaryEnabled(); got != tc.want {
+			t.Errorf("ARTEX_UNTRUSTED_BOUNDARY=%q: got %v, want %v", tc.env, got, tc.want)
+		}
+	}
+}
+
+func TestUntrustedBoundaryDisabledWhenUnset(t *testing.T) {
+	t.Setenv("ARTEX_UNTRUSTED_BOUNDARY", "1") // registers restoration of the original value
+	os.Unsetenv("ARTEX_UNTRUSTED_BOUNDARY")
+	if untrustedBoundaryEnabled() {
+		t.Fatal("ARTEX_UNTRUSTED_BOUNDARY unset: got true, want false")
+	}
+}
+
+// Structural, not behavioural: the four agentcore.Options literals live inside
+// run methods that need a database and an LLM provider, so this only checks
+// that each source file passes the helper to the option exactly once.
+func TestUntrustedBoundaryWiredInOptionsLiterals(t *testing.T) {
+	const want = "UntrustedOutputBoundary: untrustedBoundaryEnabled(),"
+	for _, f := range []string{"worker.go", "planner.go", "chat.go", "mainagent.go"} {
+		src, err := os.ReadFile(f)
+		if err != nil {
+			t.Fatal(err)
+		}
+		n := 0
+		for _, line := range strings.Split(string(src), "\n") {
+			if strings.TrimSpace(line) == want {
+				n++
+			}
+		}
+		if n != 1 {
+			t.Errorf("%s: %d lines equal to %q, want 1", f, n, want)
+		}
+	}
+}
diff --git a/agent/worker.go b/agent/worker.go
index 93b5863..d69d003 100644
--- a/agent/worker.go
+++ b/agent/worker.go
@@ -526,6 +526,9 @@ func (w *Worker) execute(ctx context.Context, name string, taskID int64, as *db.
 		Todos:         actool.NewTodoStore(),                  // session-level scratch todos (TodoWrite), pure planning, discarded on exit
 		NonStreaming:  w.nonStreaming(),                       // when this profile selects non-streaming, use Provider.Complete
 		MaxTokens:     w.maxTokens(),                          // 0 = send no cap; the server default decides
+
+		// Opt-in via ARTEX_UNTRUSTED_BOUNDARY (default off): nonce-frame tool output as untrusted data.
+		UntrustedOutputBoundary: untrustedBoundaryEnabled(),
 	}
 	if hooks != nil { // typed-nil guard: only set when concrete (avoids harness panic)
 		opts.Hooks = hooks
diff --git a/docker-compose.yml b/docker-compose.yml
index 3870ea7..d343b43 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -36,6 +36,7 @@ services:
       ARTEX_LLM_PROXY: ${ARTEX_LLM_PROXY:-}
       ARTEX_JWT_KEY_DIR: /app/keys
       ARTEX_TRUSTED_PROXIES: ${ARTEX_TRUSTED_PROXIES:-}
+      ARTEX_UNTRUSTED_BOUNDARY: ${ARTEX_UNTRUSTED_BOUNDARY:-}
     ports:
       - "${ARTEX_BIND_ADDR:-127.0.0.1}:8787:8787"
       - "127.0.0.1:8788:8788"