@@ -303,6 +303,7 @@ describe("acpToolCallDiffPatch", () => {
         "-b",
         "+B",
         "",
+        'diff --git "a//repo/c.ts" "b//repo/c.ts"',
         "--- /repo/c.ts",
         "+++ /repo/c.ts",
         "@@ -1,1 +1,1 @@",
@@ -311,6 +312,31 @@ describe("acpToolCallDiffPatch", () => {
         "",
       ].join("\n"),
     );
+    assert.equal(
+      acpToolCallDiffPatch([
+        { type: "diff", path: "/repo/new.txt", oldText: null, newText: "hello\n" },
+        {
+          type: "diff",
+          changes: [{ operation: "modify", path: "/repo/a.ts" }],
+          patch: { format: "git_patch", text: "@@ -1 +1 @@\n-a\n+A\n" },
+        },
+      ]),
+      [
+        'diff --git "a//repo/new.txt" "b//repo/new.txt"',
+        "--- /dev/null",
+        "+++ /repo/new.txt",
+        "@@ -0,0 +1,1 @@",
+        "+hello",
+        "",
+        'diff --git "a//repo/a.ts" "b//repo/a.ts"',
+        '--- "a//repo/a.ts"',
+        '+++ "b//repo/a.ts"',
+        "@@ -1 +1 @@",
+        "-a",
+        "+A",
+        "",
+      ].join("\n"),
+    );
   });
 });
 
 
@@ -908,7 +908,7 @@ export function acpToolCallDiffPatch(content: unknown): string | undefined {
     const diff = unknownRecord(entry);
     return diff?.type === "diff" ? [diff] : [];
   });
-  const patches = diffs.flatMap((diff) => {
+  const patches = diffs.flatMap((diff): ReadonlyArray<{ text: string; path?: string }> => {
     const patch = unknownRecord(diff.patch);
     if (typeof patch?.text === "string") {
       const change =
@@ -925,10 +925,12 @@ export function acpToolCallDiffPatch(content: unknown): string | undefined {
         const after =
           change.operation === "delete" ? "/dev/null" : JSON.stringify(`b/${change.path}`);
         return [
-          `diff --git ${JSON.stringify(`a/${oldPath}`)} ${JSON.stringify(`b/${change.path}`)}\n--- ${before}\n+++ ${after}\n${patch.text.trimStart()}`,
+          {
+            text: `diff --git ${JSON.stringify(`a/${oldPath}`)} ${JSON.stringify(`b/${change.path}`)}\n--- ${before}\n+++ ${after}\n${patch.text.trimStart()}`,
+          },
         ];
       }
-      return [patch.text];
+      return [{ text: patch.text }];
     }
     if (typeof diff.path !== "string" || typeof diff.newText !== "string") return [];
     const oldText = typeof diff.oldText === "string" ? diff.oldText : undefined;
@@ -946,9 +948,19 @@ export function acpToolCallDiffPatch(content: unknown): string | undefined {
     );
     return structured === undefined || structured.hunks.length === 0
       ? []
-      : [formatPatch(structured, FILE_HEADERS_ONLY)];
+      : [{ text: formatPatch(structured, FILE_HEADERS_ONLY), path: diff.path }];
   });
-  return patches.length === 0 ? undefined : patches.join("\n");
+  // Diff parsers split at Git headers once one exists, so every section then needs its own.
+  const hasGitHeader = patches.some(({ text }) => /^diff --git /m.test(text));
+  return patches.length === 0
+    ? undefined
+    : patches
+        .map(({ text, path }) =>
+          hasGitHeader && path !== undefined
+            ? `diff --git ${JSON.stringify(`a/${path}`)} ${JSON.stringify(`b/${path}`)}\n${text}`
+            : text,
+        )
+        .join("\n");
 }
 
 function pathFromToolCall(toolCall: AcpToolCallState): string | undefined {