diff --git a/backend/internal/domain/text.go b/backend/internal/domain/text.go
new file mode 100644
index 00000000..3144dfd1
--- /dev/null
+++ b/backend/internal/domain/text.go
@@ -0,0 +1,26 @@
+package domain
+
+import (
+	"strings"
+	"unicode"
+)
+
+// SanitizeControlChars removes control characters that are unsafe to deliver
+// into a live terminal pane, while preserving the whitespace that legitimate
+// multi-line text relies on (newline, carriage return, tab).
+//
+// Any text that reaches an agent's PTY must pass through here. The session
+// runtime pastes messages straight into the live pane, so an unfiltered escape
+// sequence (cursor control, screen clear, OSC) embedded in attacker-influenced
+// content — a GitHub reviewer comment, a CI job log tail — would be interpreted
+// by the terminal instead of read as plain text. Both the HTTP send endpoint
+// and the lifecycle nudge path share this one definition so neither can drift
+// into delivering raw control bytes.
+func SanitizeControlChars(s string) string {
+	return strings.Map(func(r rune) rune {
+		if unicode.IsControl(r) && r != '\n' && r != '\r' && r != '\t' {
+			return -1
+		}
+		return r
+	}, s)
+}
diff --git a/backend/internal/domain/text_test.go b/backend/internal/domain/text_test.go
new file mode 100644
index 00000000..40794e6a
--- /dev/null
+++ b/backend/internal/domain/text_test.go
@@ -0,0 +1,25 @@
+package domain
+
+import "testing"
+
+func TestSanitizeControlChars(t *testing.T) {
+	tests := []struct {
+		name string
+		in   string
+		want string
+	}{
+		{name: "plain text unchanged", in: "hello world", want: "hello world"},
+		{name: "keeps newline tab carriage return", in: "a\nb\tc\rd", want: "a\nb\tc\rd"},
+		{name: "strips ansi escape byte leaving harmless residue", in: "before\x1b[2Jafter", want: "before[2Jafter"},
+		{name: "strips nul and bell", in: "x\x00y\az", want: "xyz"},
+		{name: "strips osc sequence bytes", in: "\x1b]0;title\a", want: "]0;title"},
+		{name: "empty stays empty", in: "", want: ""},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := SanitizeControlChars(tt.in); got != tt.want {
+				t.Fatalf("SanitizeControlChars(%q) = %q, want %q", tt.in, got, tt.want)
+			}
+		})
+	}
+}
diff --git a/backend/internal/httpd/controllers/sessions.go b/backend/internal/httpd/controllers/sessions.go
index bc0a4504..b59d2d0a 100644
--- a/backend/internal/httpd/controllers/sessions.go
+++ b/backend/internal/httpd/controllers/sessions.go
@@ -6,7 +6,6 @@ import (
 	"net/http"
 	"strconv"
 	"strings"
-	"unicode"
 
 	"github.com/go-chi/chi/v5"
 
@@ -274,7 +273,7 @@ func (c *SessionsController) send(w http.ResponseWriter, r *http.Request) {
 		envelope.WriteAPIError(w, r, http.StatusBadRequest, "bad_request", "MESSAGE_TOO_LONG", "Message is too long", nil)
 		return
 	}
-	message := stripUnsafeControlChars(in.Message)
+	message := domain.SanitizeControlChars(in.Message)
 	if err := c.Svc.Send(r.Context(), sessionID(r), message); err != nil {
 		envelope.WriteError(w, r, err)
 		return
@@ -403,15 +402,6 @@ func parseSessionListFilter(r *http.Request) (sessionsvc.ListFilter, error) {
 	return filter, nil
 }
 
-func stripUnsafeControlChars(message string) string {
-	return strings.Map(func(r rune) rune {
-		if unicode.IsControl(r) && r != '\n' && r != '\r' && r != '\t' {
-			return -1
-		}
-		return r
-	}, message)
-}
-
 func writeSessionPRError(w http.ResponseWriter, r *http.Request, err error) {
 	var claimed ports.PRClaimedByActiveSessionError
 	switch {
diff --git a/backend/internal/lifecycle/manager_test.go b/backend/internal/lifecycle/manager_test.go
index 95a753ac..ca33d560 100644
--- a/backend/internal/lifecycle/manager_test.go
+++ b/backend/internal/lifecycle/manager_test.go
@@ -190,6 +190,46 @@ func TestPRObservation_ReviewCommentsNudgeAgent(t *testing.T) {
 	}
 }
 
+func TestPRObservation_CINudgeSanitizesLogTailControlChars(t *testing.T) {
+	m, st, msg := newManager()
+	st.sessions["mer-1"] = working("mer-1")
+	// A CI log tail with an embedded ANSI escape sequence and a NUL byte; the
+	// agent's pane must receive the visible text without the control bytes.
+	o := ports.PRObservation{Fetched: true, URL: "pr1", CI: domain.CIFailing, Checks: []ports.PRCheckObservation{{Name: "build", CommitHash: "c1", Status: domain.PRCheckFailed, LogTail: "line1\x1b[2Jline2\x00\ttabbed"}}}
+	if err := m.ApplyPRObservation(ctx, "mer-1", o); err != nil {
+		t.Fatal(err)
+	}
+	if len(msg.msgs) != 1 {
+		t.Fatalf("want one CI nudge, got %v", msg.msgs)
+	}
+	got := msg.msgs[0]
+	if strings.ContainsRune(got, '\x1b') || strings.ContainsRune(got, '\x00') {
+		t.Fatalf("nudge still carries control bytes: %q", got)
+	}
+	if !strings.Contains(got, "line1") || !strings.Contains(got, "line2") || !strings.Contains(got, "\ttabbed") {
+		t.Fatalf("nudge dropped visible text or tab: %q", got)
+	}
+}
+
+func TestPRObservation_ReviewNudgeSanitizesCommentControlChars(t *testing.T) {
+	m, st, msg := newManager()
+	st.sessions["mer-1"] = working("mer-1")
+	o := ports.PRObservation{Fetched: true, URL: "pr1", Review: domain.ReviewChangesRequest, Comments: []ports.PRCommentObservation{{ID: "1", Body: "please\x1b]0;pwned\afix this"}}}
+	if err := m.ApplyPRObservation(ctx, "mer-1", o); err != nil {
+		t.Fatal(err)
+	}
+	if len(msg.msgs) != 1 {
+		t.Fatalf("want one review nudge, got %v", msg.msgs)
+	}
+	got := msg.msgs[0]
+	if strings.ContainsRune(got, '\x1b') || strings.ContainsRune(got, '\a') {
+		t.Fatalf("review nudge still carries control bytes: %q", got)
+	}
+	if !strings.Contains(got, "please") || !strings.Contains(got, "fix this") {
+		t.Fatalf("review nudge dropped visible text: %q", got)
+	}
+}
+
 func TestSCMObservationProjectsToExistingPRReactions(t *testing.T) {
 	m, st, msg := newManager()
 	st.sessions["mer-1"] = working("mer-1")
diff --git a/backend/internal/lifecycle/reactions.go b/backend/internal/lifecycle/reactions.go
index 540a5064..851f11c0 100644
--- a/backend/internal/lifecycle/reactions.go
+++ b/backend/internal/lifecycle/reactions.go
@@ -70,7 +70,10 @@ func (m *Manager) ApplyPRObservation(ctx context.Context, id domain.SessionID, o
 			if ch.Status == domain.PRCheckFailed {
 				msg := "CI is failing on your PR. Review the output below and push a fix."
 				if ch.LogTail != "" {
-					msg += "\n\nFailing output:\n" + ch.LogTail
+					// LogTail is raw CI job output; sanitize before it reaches the
+					// agent's live pane so embedded escape sequences can't drive the
+					// terminal (the dedup signature stays on the raw bytes).
+					msg += "\n\nFailing output:\n" + domain.SanitizeControlChars(ch.LogTail)
 				}
 				return m.sendOnce(ctx, id, o.URL, "ci:"+o.URL+":"+ch.Name, ch.CommitHash+":"+ch.LogTail, msg, 0)
 			}
@@ -404,7 +407,11 @@ func reviewContent(comments []ports.PRCommentObservation) (string, string) {
 		if c.Resolved {
 			continue
 		}
-		bodies = append(bodies, c.Body)
+		// Comment bodies are attacker-influenced (anyone who can comment on the
+		// PR) and get pasted into the agent's live pane; strip control/escape
+		// chars. The signature is built from comment IDs, not bodies, so dedup is
+		// unaffected.
+		bodies = append(bodies, domain.SanitizeControlChars(c.Body))
 		ids = append(ids, c.ID)
 	}
 	return strings.Join(bodies, "\n\n"), strings.Join(ids, ",")