diff --git a/internal/runtime/executor/codex_executor.go b/internal/runtime/executor/codex_executor.go
index 966a1320d08..04080f35fe8 100644
--- a/internal/runtime/executor/codex_executor.go
+++ b/internal/runtime/executor/codex_executor.go
@@ -1709,7 +1709,7 @@ func normalizeCodexInstructions(body []byte) []byte {
 	if !instructions.Exists() || instructions.Type == gjson.Null {
 		body, _ = sjson.SetBytes(body, "instructions", "")
 	}
-	return body
+	return stripCodexIntermediaryUpdatesFromPayload(body)
 }
 
 var imageGenToolJSON = []byte(`{"type":"image_generation","output_format":"png"}`)
diff --git a/internal/runtime/executor/codex_prompt_patch.go b/internal/runtime/executor/codex_prompt_patch.go
new file mode 100644
index 00000000000..88a328d5a68
--- /dev/null
+++ b/internal/runtime/executor/codex_prompt_patch.go
@@ -0,0 +1,87 @@
+package executor
+
+import (
+	"bytes"
+	"encoding/json"
+	"strings"
+)
+
+const codexIntermediaryUpdatesHeading = "## Intermediary updates"
+
+func stripCodexIntermediaryUpdatesFromPayload(body []byte) []byte {
+	if !bytes.Contains(body, []byte(codexIntermediaryUpdatesHeading)) {
+		return body
+	}
+
+	var payload map[string]any
+	decoder := json.NewDecoder(bytes.NewReader(body))
+	decoder.UseNumber()
+	if err := decoder.Decode(&payload); err != nil {
+		return body
+	}
+
+	instructions, ok := payload["instructions"].(string)
+	if !ok {
+		return body
+	}
+	stripped, changed := stripCodexIntermediaryUpdatesText(instructions)
+	if !changed {
+		return body
+	}
+	payload["instructions"] = stripped
+
+	var out bytes.Buffer
+	encoder := json.NewEncoder(&out)
+	encoder.SetEscapeHTML(false)
+	if err := encoder.Encode(payload); err != nil {
+		return body
+	}
+	return bytes.TrimSpace(out.Bytes())
+}
+
+func stripCodexIntermediaryUpdatesText(text string) (string, bool) {
+	if !strings.Contains(text, codexIntermediaryUpdatesHeading) {
+		return text, false
+	}
+
+	lines := strings.SplitAfter(text, "\n")
+	out := make([]string, 0, len(lines))
+	skipping := false
+	changed := false
+
+	for _, line := range lines {
+		trimmed := strings.TrimSpace(strings.TrimSuffix(strings.TrimSuffix(line, "\n"), "\r"))
+		if !skipping && trimmed == codexIntermediaryUpdatesHeading {
+			skipping = true
+			changed = true
+			continue
+		}
+
+		if skipping {
+			if isCodexIntermediaryUpdatesStopHeading(trimmed) {
+				skipping = false
+				out = append(out, line)
+			}
+			continue
+		}
+
+		out = append(out, line)
+	}
+
+	if !changed {
+		return text, false
+	}
+	return strings.Join(out, ""), true
+}
+
+func isCodexIntermediaryUpdatesStopHeading(trimmedLine string) bool {
+	if trimmedLine == codexIntermediaryUpdatesHeading {
+		return false
+	}
+
+	headingLevel := 0
+	for headingLevel < len(trimmedLine) && headingLevel < 6 && trimmedLine[headingLevel] == '#' {
+		headingLevel++
+	}
+	return headingLevel > 0 && len(trimmedLine) > headingLevel && trimmedLine[headingLevel] == ' '
+}
diff --git a/internal/runtime/executor/codex_prompt_patch_test.go b/internal/runtime/executor/codex_prompt_patch_test.go
new file mode 100644
index 00000000000..e997810da3f
--- /dev/null
+++ b/internal/runtime/executor/codex_prompt_patch_test.go
@@ -0,0 +1,92 @@
+package executor
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/tidwall/gjson"
+)
+
+func TestStripCodexIntermediaryUpdatesFromPayloadTopLevelInstructions(t *testing.T) {
+	payload := []byte(`{"instructions":"before\n\n## Intermediary updates \n- noisy updates\n- more noise\n## Final answer instructions\nkeep this","input":[{"role":"user","content":"hello"}]}`)
+
+	out := stripCodexIntermediaryUpdatesFromPayload(payload)
+	instructions := gjson.GetBytes(out, "instructions").String()
+
+	if strings.Contains(instructions, "Intermediary updates") || strings.Contains(instructions, "noisy updates") {
+		t.Fatalf("intermediary section was not stripped: %q", instructions)
+	}
+	if !strings.Contains(instructions, "before") || !strings.Contains(instructions, "## Final answer instructions") {
+		t.Fatalf("surrounding instructions were not preserved: %q", instructions)
+	}
+}
+
+func TestStripCodexIntermediaryUpdatesFromPayloadLeavesNestedInputText(t *testing.T) {
+	payload := []byte(`{"instructions":"keep","input":[{"content":[{"type":"input_text","text":"alpha\n## Intermediary updates\nremove me"}]}],"reasoning":{"effort":"high"}}`)
+
+	out := stripCodexIntermediaryUpdatesFromPayload(payload)
+	text := gjson.GetBytes(out, "input.0.content.0.text").String()
+
+	if !strings.Contains(text, "Intermediary updates") || !strings.Contains(text, "remove me") {
+		t.Fatalf("nested user text was stripped unexpectedly: %q", text)
+	}
+	if !strings.Contains(text, "alpha") {
+		t.Fatalf("nested prompt prefix was not preserved: %q", text)
+	}
+	if got := gjson.GetBytes(out, "reasoning.effort").String(); got != "high" {
+		t.Fatalf("unrelated fields changed: reasoning.effort=%q", got)
+	}
+}
+
+func TestStripCodexIntermediaryUpdatesFromPayloadOnlyTouchesInstructions(t *testing.T) {
+	payload := []byte(`{"instructions":"keep\n## Intermediary updates\nremove me\n## Final answer instructions\nanswer","input":[{"content":[{"type":"input_text","text":"alpha\n## Intermediary updates\nkeep this user text"}]}]}`)
+
+	out := stripCodexIntermediaryUpdatesFromPayload(payload)
+	instructions := gjson.GetBytes(out, "instructions").String()
+	text := gjson.GetBytes(out, "input.0.content.0.text").String()
+
+	if strings.Contains(instructions, "Intermediary updates") || strings.Contains(instructions, "remove me") {
+		t.Fatalf("instructions intermediary section was not stripped: %q", instructions)
+	}
+	if !strings.Contains(instructions, "## Final answer instructions") {
+		t.Fatalf("following instruction section was not preserved: %q", instructions)
+	}
+	if !strings.Contains(text, "Intermediary updates") || !strings.Contains(text, "keep this user text") {
+		t.Fatalf("nested user text was stripped unexpectedly: %q", text)
+	}
+}
+
+func TestStripCodexIntermediaryUpdatesFromPayloadLeavesUnrelatedPayload(t *testing.T) {
+	payload := []byte(`{"instructions":"inline mention of ## Intermediary updates should stay","input":[]}`)
+
+	out := stripCodexIntermediaryUpdatesFromPayload(payload)
+	if string(out) != string(payload) {
+		t.Fatalf("payload changed unexpectedly:\ngot  %s\nwant %s", string(out), string(payload))
+	}
+}
+
+func TestStripCodexIntermediaryUpdatesTextRemovesLastSection(t *testing.T) {
+	out, changed := stripCodexIntermediaryUpdatesText("before\n## Intermediary updates\n- remove me")
+	if !changed {
+		t.Fatal("expected text to change")
+	}
+	if strings.Contains(out, "Intermediary updates") || strings.Contains(out, "remove me") {
+		t.Fatalf("last section was not stripped: %q", out)
+	}
+	if !strings.Contains(out, "before") {
+		t.Fatalf("prefix was not preserved: %q", out)
+	}
+}
+
+func TestStripCodexIntermediaryUpdatesTextStopsAtMarkdownHeading(t *testing.T) {
+	out, changed := stripCodexIntermediaryUpdatesText("before\n## Intermediary updates\n- remove me\n## Intermediary updates\n- remove me too\n### Keep this\nkeep")
+	if !changed {
+		t.Fatal("expected text to change")
+	}
+	if strings.Contains(out, "Intermediary updates") || strings.Contains(out, "remove me") {
+		t.Fatalf("intermediary sections were not stripped: %q", out)
+	}
+	if !strings.Contains(out, "before") || !strings.Contains(out, "### Keep this\nkeep") {
+		t.Fatalf("surrounding markdown was not preserved: %q", out)
+	}
+}