diff --git a/memory-bank/change-log.md b/memory-bank/change-log.md
index 9c0af5ec..e93dabc2 100644
--- a/memory-bank/change-log.md
+++ b/memory-bank/change-log.md
@@ -516,3 +516,37 @@ Validation:
 Follow-ups:
 
 - Remaining optional cleanup in these handlers is dead import/unused local pruning (non-behavioral) if we want a final low-risk tidy pass.
+
+---
+
+### CL-013: TASK22224 completion-message route parity closure slice
+
+date: 2026-03-24
+author: Cline
+scope: `pages/api/file/createappealcompletemessage_api.js`, `tests/phase21/file-handler-contract.test.cjs`
+type: change
+rationale: Continue next requested slice by closing the final promise-chain parity outlier in file completion-message flow and strengthening phase21 contract coverage.
+impact: Improves maintainability and async error hygiene while preserving route behavior and existing error contracts.
+status: completed
+
+Summary:
+
+- `pages/api/file/createappealcompletemessage_api.js`
+    - replaced inline `.catch(...)` on fire-and-forget `updateAccount(...)` with explicit async IIFE + `try/catch` and `void` invocation
+    - preserved non-blocking behavior and logging semantics for account-update failure path
+    - preserved primary route contracts and success payload (`{ status: "success" }`)
+- phase21 file contract tests expanded:
+    - success path for encoded hash candidate on `createappealcompletemessage_api`
+    - dependency-failure contract assertion for `CREATE_APPEAL_COMPLETE_MESSAGE_FAILED`
+
+Validation:
+
+- `node tests/phase21/api-contract-slice1.test.cjs` -> pass
+    - helper: 4/4
+    - file-handler: 53/53
+    - email-handler: 12/12
+    - endpoint-handler: 152/152
+
+Follow-ups:
+
+- Optional final low-risk tidy sweep: remove dead imports/unused locals in legacy file handlers now that contract hardening stream is functionally complete.
diff --git a/pages/api/file/createappealcompletemessage_api.js b/pages/api/file/createappealcompletemessage_api.js
index 23455b6b..17c43b1e 100644
--- a/pages/api/file/createappealcompletemessage_api.js
+++ b/pages/api/file/createappealcompletemessage_api.js
@@ -115,15 +115,19 @@ ApiProxy.get(async (req, res) => {
         contactId = contactId.match(/\(([^)]+)\)/);
 
         if (typeofinvolvement != 846040000) {
-            updateAccount(
-                contactId[1],
-                {
-                    pinswg_typeofinvolvement: 846040001
-                },
-                true
-            ).catch((error) => {
-                consoleLogger(error);
-            });
+            void (async () => {
+                try {
+                    await updateAccount(
+                        contactId[1],
+                        {
+                            pinswg_typeofinvolvement: 846040001
+                        },
+                        true
+                    );
+                } catch (error) {
+                    consoleLogger(error);
+                }
+            })();
         }
 
         await createCaseCompleteMessage(containerName, tempCaseRef);
diff --git a/tests/phase21/file-handler-contract.test.cjs b/tests/phase21/file-handler-contract.test.cjs
index 8306a0f4..587cd8ad 100644
--- a/tests/phase21/file-handler-contract.test.cjs
+++ b/tests/phase21/file-handler-contract.test.cjs
@@ -694,6 +694,98 @@ test("createappealcompletemessageproxy dependency failure returns CREATE_APPEAL_
     );
 });
 
+test("createappealcompletemessage_api accepts encoded hash variant and returns success", async () => {
+    const mod = loadModule(
+        "pages/api/file/createappealcompletemessage_api.js",
+        {
+            nextConnect: createNextConnectMock(),
+            middleware: () => {},
+            respondError: respondErrorMock,
+            respondSuccess: respondSuccessMock,
+            hashAPIPath: (queryPath) =>
+                queryPath.includes("tempcaseref=TMP%2F1")
+                    ? "&hash=expected"
+                    : "&hash=other",
+            getProgressBlobs: async () => ({ path: "TMP/1/progress.json" }),
+            downloadProgressFile: async (_container, path) => {
+                if (path.includes("_case.json")) {
+                    return {
+                        "customerid_contact@odata.bind":
+                            "/contacts(00000000-0000-0000-0000-000000000001)"
+                    };
+                }
+
+                return {
+                    pinswg_siteaddressline1: "Line 1",
+                    pinswg_siteaddressline2: "",
+                    pinswg_siteaddresstown: "Town",
+                    pinswg_siteaddresscounty: "County",
+                    pinswg_siteaddresspostcode: "CF1 1AA",
+                    pinswg_lpaapplicationreference: "LPA-1",
+                    pinswg_developmentdescription: "Desc",
+                    pinswg_name: "tmp"
+                };
+            },
+            createBlob: async () => ({}),
+            getCaseBlob: async () => ({}),
+            createCaseCompleteMessage: async () => ({}),
+            updateAccount: async () => ({}),
+            consoleLogger: () => {},
+            _: { isEmpty: (v) => v === undefined || v === null || v === "" }
+        }
+    );
+
+    const req = {
+        query: {
+            container: "cont/1",
+            tempcaseref: "TMP/1",
+            inv: "846040001",
+            hash: "expected"
+        }
+    };
+    const res = createRes();
+    await mod.default.handler(req, res);
+
+    assert.strictEqual(res.state.statusCode, 200);
+    assert.deepStrictEqual(JSON.parse(JSON.stringify(res.state.jsonBody)), {
+        status: "success"
+    });
+});
+
+test("createappealcompletemessage_api dependency failure returns CREATE_APPEAL_COMPLETE_MESSAGE_FAILED", async () => {
+    const mod = loadModule(
+        "pages/api/file/createappealcompletemessage_api.js",
+        {
+            nextConnect: createNextConnectMock(),
+            middleware: () => {},
+            respondError: respondErrorMock,
+            respondSuccess: respondSuccessMock,
+            hashAPIPath: () => "&hash=expected",
+            getProgressBlobs: async () => {
+                throw new Error("progress failed");
+            },
+            consoleLogger: () => {},
+            _: { isEmpty: () => true }
+        }
+    );
+
+    const req = {
+        query: {
+            container: "c1",
+            tempcaseref: "TMP1",
+            hash: "expected"
+        }
+    };
+    const res = createRes();
+    await mod.default.handler(req, res);
+
+    assert.strictEqual(res.state.statusCode, 400);
+    assert.strictEqual(
+        res.state.jsonBody.error.code,
+        "CREATE_APPEAL_COMPLETE_MESSAGE_FAILED"
+    );
+});
+
 test("createcaseinvolvement returns record exists on 412 conflict", async () => {
     const mod = loadModule("pages/api/file/createcaseinvolvement_api.js", {
         respondError: respondErrorMock,