diff --git a/apps/api/src/decofile/commit-coalescer.ts b/apps/api/src/decofile/commit-coalescer.ts
index e5b3df6a33..f0ba25411a 100644
--- a/apps/api/src/decofile/commit-coalescer.ts
+++ b/apps/api/src/decofile/commit-coalescer.ts
@@ -1,9 +1,5 @@
-import {
-  appendCoAuthorTrailer,
-  type CoAuthorIdentity,
-} from "@decocms/sandbox/shared";
-import { blockKeyToFileStem, mergeBlocks } from "@decocms/shared/decofile";
-import { repoIdentityKey } from "@decocms/shared/git-providers";
+import type { CoAuthorIdentity } from "@decocms/sandbox/shared";
+import { blockKeyToFileStem } from "@decocms/shared/decofile";
 import { exponentialBackoffWithJitter, sleep } from "@decocms/shared/std";
 import {
   type FileChange,
@@ -15,9 +11,9 @@ import {
   blockEntriesInTree,
   blocksDirPath,
   primeBlobCache,
-  resolveBlockContents,
   resolveOrCreateHead,
 } from "./read-decofile";
+import { decofileCommitMessage, regenerateGenArtifact } from "./gen-artifact";
 
 /**
  * Per-(virtualMcpId, branch) commit coalescer. Autosaves arrive every ~700ms
@@ -174,33 +170,24 @@ async function commitBatch(batch: Batch): Promise<string> {
 
     if (writes.length === 0) return headSha;
 
-    // Repos that track the merged artifact get it regenerated in-commit;
-    // gitignored repos (the common case) never have the tree entry.
-    const genPath = packagePath
-      ? `${packagePath}/.deco/blocks.gen.json`
-      : ".deco/blocks.gen.json";
-    if (tree.some((e) => e.type === "blob" && e.path === genPath)) {
-      const files = await resolveBlockContents(
-        client,
-        nextBlocks.values(),
-        blobMemo,
-      );
-      const { decofile: genContent, skipped } = mergeBlocks(files);
-      if (skipped.length > 0) {
-        console.warn("decofile gen: dropped blocks that were not valid JSON", {
-          repo: repoIdentityKey(client.repo),
-          branch,
-          packagePath,
-          blocks: skipped.map((s) => s.key),
-        });
-      }
-      writes.push({ path: genPath, content: genContent });
-    }
+    const gen = await regenerateGenArtifact({
+      client,
+      tree,
+      packagePath,
+      branch,
+      nextBlocks: nextBlocks.values(),
+      memo: blobMemo,
+    });
+    if (gen) writes.push(gen);
 
     try {
       const { sha } = await client.commitFiles({
         branch,
-        message: commitMessage(batch),
+        message: decofileCommitMessage(
+          [...batch.set.keys()],
+          [...batch.del],
+          batch.deps.coAuthor,
+        ),
         expectedHead: headSha,
         changes: writes,
       });
@@ -217,16 +204,3 @@ async function commitBatch(batch: Batch): Promise<string> {
     }
   }
 }
-
-function commitMessage(batch: Batch): string {
-  const summarize = (keys: string[]): string => {
-    const shown = keys.slice(0, 3).join(", ");
-    return keys.length > 3 ? `${shown} (+${keys.length - 3} more)` : shown;
-  };
-  const parts: string[] = [];
-  if (batch.set.size > 0)
-    parts.push(`update ${summarize([...batch.set.keys()])}`);
-  if (batch.del.size > 0) parts.push(`delete ${summarize([...batch.del])}`);
-  const subject = `chore(decofile): ${parts.join("; ")}`;
-  return appendCoAuthorTrailer(subject, batch.deps.coAuthor);
-}
diff --git a/apps/api/src/decofile/gen-artifact.ts b/apps/api/src/decofile/gen-artifact.ts
new file mode 100644
index 0000000000..ed945e9043
--- /dev/null
+++ b/apps/api/src/decofile/gen-artifact.ts
@@ -0,0 +1,71 @@
+import {
+  appendCoAuthorTrailer,
+  type CoAuthorIdentity,
+} from "@decocms/sandbox/shared";
+import { mergeBlocks } from "@decocms/shared/decofile";
+import { repoIdentityKey } from "@decocms/shared/git-providers";
+import type { FileChange, RepoContentClient, TreeEntry } from "@/git-providers";
+import { type BlockSource, resolveBlockContents } from "./read-decofile";
+
+/** Repo-relative path of the merged `blocks.gen.json` artifact. */
+function genArtifactPath(packagePath: string | null): string {
+  return packagePath
+    ? `${packagePath}/.deco/blocks.gen.json`
+    : ".deco/blocks.gen.json";
+}
+
+/**
+ * The regenerated `blocks.gen.json`, for a commit that changes `.deco/blocks`.
+ *
+ * Repos that track the merged artifact get it rewritten in the same commit, so
+ * it never disagrees with the block files; gitignored repos (the common case)
+ * have no tree entry and get `null`. `nextBlocks` is the post-commit view of
+ * the blocks dir; `memo` is the blob memo a compare-and-swap retry loop
+ * threads through, so a retry never re-reads a blob it already resolved.
+ */
+export async function regenerateGenArtifact(params: {
+  client: RepoContentClient;
+  tree: TreeEntry[];
+  packagePath: string | null;
+  branch: string;
+  nextBlocks: Iterable<BlockSource>;
+  memo: Map<string, string>;
+}): Promise<FileChange | null> {
+  const { client, tree, packagePath, branch } = params;
+  const genPath = genArtifactPath(packagePath);
+  if (!tree.some((e) => e.type === "blob" && e.path === genPath)) return null;
+  const files = await resolveBlockContents(
+    client,
+    params.nextBlocks,
+    params.memo,
+  );
+  const { decofile, skipped } = mergeBlocks(files);
+  if (skipped.length > 0) {
+    console.warn("decofile gen: dropped blocks that were not valid JSON", {
+      repo: repoIdentityKey(client.repo),
+      branch,
+      packagePath,
+      blocks: skipped.map((s) => s.key),
+    });
+  }
+  return { path: genPath, content: decofile };
+}
+
+/** The commit message of a decofile write: what changed, plus the co-author. */
+export function decofileCommitMessage(
+  setKeys: string[],
+  deleteKeys: string[],
+  coAuthor: CoAuthorIdentity | null | undefined,
+): string {
+  const summarize = (keys: string[]): string => {
+    const shown = keys.slice(0, 3).join(", ");
+    return keys.length > 3 ? `${shown} (+${keys.length - 3} more)` : shown;
+  };
+  const parts: string[] = [];
+  if (setKeys.length > 0) parts.push(`update ${summarize(setKeys)}`);
+  if (deleteKeys.length > 0) parts.push(`delete ${summarize(deleteKeys)}`);
+  return appendCoAuthorTrailer(
+    `chore(decofile): ${parts.join("; ")}`,
+    coAuthor,
+  );
+}