diff --git a/scripts/check_codex_comments_test.py b/scripts/check_codex_comments_test.py
index 0a6aac6112..8e47649302 100644
--- a/scripts/check_codex_comments_test.py
+++ b/scripts/check_codex_comments_test.py
@@ -141,16 +141,20 @@ def test_observed_comments_only_exempt_completed_informational_reviews(self):
                         cache=data if cached else None,
                     )
 
-    def test_auto_triggered_security_heading_does_not_hide_findings(self):
-        header = "### 🛡️ Codex Security Review · _Automatically triggered_\n\n"
+    def test_security_headings_do_not_hide_findings(self):
         clean = FIXTURES["security_no_findings"]["body"]
-        for body, expected in (
-            (clean, 0),
-            (clean + "\n\n[P1] A security issue still needs fixing.", 1),
-            ("Security review completed. Found a P1 credential disclosure.", 1),
+        for header in (
+            "### 🛡️ Codex Security Review\n\n",
+            "### 🛡️ Codex Security Review · _Automatically triggered_\n\n",
         ):
-            with self.subTest(body=body):
-                self.assert_gate(expected, snapshot([comment(header + body)]))
+            for body, expected in (
+                (clean, 0),
+                (clean + "\n\n[P1] A security issue still needs fixing.", 1),
+                ("Security review completed. Found a P1 credential disclosure.", 1),
+                (header + clean, 1),
+            ):
+                with self.subTest(header=header, body=body):
+                    self.assert_gate(expected, snapshot([comment(header + body)]))
 
     def test_summary_completion_requires_metadata_and_every_review_row(self):
         completed = FIXTURES["summary"]["body"]
diff --git a/scripts/lib/codex_comments.jq b/scripts/lib/codex_comments.jq
index f917e5a48d..9163095a4b 100644
--- a/scripts/lib/codex_comments.jq
+++ b/scripts/lib/codex_comments.jq
@@ -4,7 +4,7 @@
 # Strip only the observed help text: a heading alone must not hide a finding
 # added inside the details section, or a second section appended after it.
 def codex_without_help:
-  ltrimstr("### 🛡️ Codex Security Review · _Automatically triggered_\n\n")
+  sub("^### 🛡️ Codex Security Review( · _Automatically triggered_)?\n\n"; "")
   | rtrimstr("\n\n<details> <summary>ℹ️ About Codex in GitHub</summary>\n<br/>\n\n"
     + "[Your team has set up Codex to review pull requests in this repo](https://chatgpt.com/codex/cloud/settings/general). Reviews are triggered when you\n"
     + "- Open a pull request for review\n- Mark a draft as ready\n- Comment \"@codex review\" or \"@codex security review\".\n\n"
diff --git a/src/node/services/providerModelFactory.test.ts b/src/node/services/providerModelFactory.test.ts
index d88422fba1..7ebbedae99 100644
--- a/src/node/services/providerModelFactory.test.ts
+++ b/src/node/services/providerModelFactory.test.ts
@@ -1187,6 +1187,36 @@ describe("ProviderModelFactory GitHub Copilot", () => {
         expect(headers.get("authorization")).toBe("Bearer test-access-token");
         expect(headers.get("chatgpt-account-id")).toBe("test-account-id");
         expect(headers.get("content-type")).toBe("application/json");
+        expect(headers.get("session-id")).toBeNull();
+
+        for (const [promptCacheKey, sessionId, expectedSessionId] of [
+          ["mux-v1-project-scope", undefined, "mux-v1-project-scope"],
+          ["mux-v1-日本語-scope", undefined, "mux-v1-%E6%97%A5%E6%9C%AC%E8%AA%9E-scope"],
+          ["mux-v1-project\nscope", undefined, "mux-v1-project%0Ascope"],
+          ["mux-v1-\ud800-scope", undefined, "mux-v1-%EF%BF%BD-scope"],
+          ["mux-v1-project-scope", "explicit-session", "explicit-session"],
+        ] as const) {
+          const cacheHeaders = new Headers(request.headers);
+          if (sessionId) cacheHeaders.set("session-id", sessionId);
+          for (let turn = 0; turn < 2; turn++) {
+            await capturedFetch(request.url, {
+              method: "POST",
+              headers: cacheHeaders,
+              body: JSON.stringify({
+                model: "gpt-5.3-codex",
+                input: [{ role: "user", content: `Turn ${turn}` }],
+                prompt_cache_key: promptCacheKey,
+                store: true,
+                truncation: "auto",
+              }),
+            });
+            const outgoing = requests.at(-1);
+            expect(outgoing?.input).toBe(CODEX_ENDPOINT);
+            expect(JSON.parse(outgoing?.init?.body as string)).toMatchObject({ store: false });
+            expect(JSON.parse(outgoing?.init?.body as string)).not.toHaveProperty("truncation");
+            expect(new Headers(outgoing?.init?.headers).get("session-id")).toBe(expectedSessionId);
+          }
+        }
       } finally {
         PROVIDER_REGISTRY.openai = originalOpenAIRegistry;
       }
diff --git a/src/node/services/providerModelFactory.ts b/src/node/services/providerModelFactory.ts
index f5d7fb31bc..f5ddca9e4b 100644
--- a/src/node/services/providerModelFactory.ts
+++ b/src/node/services/providerModelFactory.ts
@@ -1728,6 +1728,22 @@ export class ProviderModelFactory {
                   try {
                     const headers = new Headers(init?.headers);
                     headers.delete("content-length");
+                    // Codex derives its cache routing key from session-id, not the body key.
+                    // Reuse Xum's stable scope so successive OAuth turns reach the same cache.
+                    const { prompt_cache_key: promptCacheKey } = JSON.parse(body) as {
+                      prompt_cache_key?: unknown;
+                    };
+                    if (
+                      !headers.has("session-id") &&
+                      typeof promptCacheKey === "string" &&
+                      promptCacheKey.length > 0
+                    ) {
+                      // UTF-8 replaces lone surrogates before encoding project names for HTTP headers.
+                      headers.set(
+                        "session-id",
+                        encodeURIComponent(Buffer.from(promptCacheKey).toString())
+                      );
+                    }
                     nextInit = {
                       ...init,
                       headers,