app/engine/changeset.ts

 // Composing and committing a real code change directly from protocol

 // data -- no working-tree file, no `write_file` tool. The content of

 // every changed file lives entirely in the Ask/Answer payload that

 // proposed it (the same way a Rung carries its own full content); this

 // is the one place that content actually becomes a real git commit,

 // using isomorphic-git's plumbing (writeBlob/writeTree/writeCommit/

 // writeRef) rather than a working-tree checkout. That also makes this

 // directly portable to the Cloudflare move: a Worker has no persistent

 // working tree either, so building a commit from in-memory content is

 // the only shape that was ever going to survive that move.

 //

 // Flat paths only (single path segment, no subdirectories) -- writeTree

 // writes one tree level per call, so a nested path would need manual

 // subtree construction. Not needed yet; add it if a real changeset

 // actually requires nested directories.

 import * as git from "isomorphic-git";

 import fs from "node:fs";

 export interface ChangesetFile {

  path: string;

  content: string;

 }

 export interface CommitAuthor {

  name: string;

  email: string;

 }

 export async function commitChangeset(repoDir: string, input: { files: ChangesetFile[]; message: string; author: CommitAuthor }): Promise<string> {

  for (const f of input.files) {

  if (f.path.includes("/")) throw new Error(`commitChangeset: "${f.path}" has a subdirectory; only flat, single-segment paths are supported right now.`);

  }

  let parentOid: string | undefined;

  try {

  parentOid = await git.resolveRef({ fs, dir: repoDir, ref: "HEAD" });

  } catch {

  parentOid = undefined; // the repo's first commit

  }

  const entries: git.TreeEntry[] = parentOid ? (await git.readTree({ fs, dir: repoDir, oid: parentOid })).tree : [];

  for (const f of input.files) {

  const oid = await git.writeBlob({ fs, dir: repoDir, blob: new TextEncoder().encode(f.content) });

  const entry: git.TreeEntry = { mode: "100644", path: f.path, oid, type: "blob" };

  const i = entries.findIndex((e) => e.path === f.path);

  if (i >= 0) entries[i] = entry;

  else entries.push(entry);

  }

  const treeOid = await git.writeTree({ fs, dir: repoDir, tree: entries });

  const timestamp = Math.floor(Date.now() / 1000);

  const person = { ...input.author, timestamp, timezoneOffset: 0 };

  const commitOid = await git.writeCommit({

  fs,

  dir: repoDir,

  commit: { message: input.message, tree: treeOid, parent: parentOid ? [parentOid] : [], author: person, committer: person },

  });

  const branch = (await git.currentBranch({ fs, dir: repoDir })) ?? "main";

  await git.writeRef({ fs, dir: repoDir, ref: `refs/heads/${branch}`, value: commitOid, force: true });

  return commitOid;

 }