chore: initialize POM 2 repo (docs guards green; release gates recorded NOT RUN pending install)

src/git.ts

@@ -0,0 +1,43 @@
+import { execFile } from "node:child_process";
+import { promisify } from "node:util";
+import { join } from "node:path";
+import type { PomConfig, PomState } from "./domain";
+import { stage } from "./domain";
+import { pathExists } from "./persistence";
+
+const execFileAsync = promisify(execFile);
+
+async function git(root: string, args: string[]): Promise<string> {
+  const result = await execFileAsync("git", ["-C", root, ...args], { maxBuffer: 4 * 1024 * 1024 });
+  return result.stdout.trim();
+}
+
+export async function ensureGit(state: PomState, config: PomConfig): Promise<void> {
+  if (config.gitMode === "off") return;
+  if (!(await pathExists(join(state.projectRoot, ".git")))) {
+    await git(state.projectRoot, ["init"]);
+    await git(state.projectRoot, ["config", "user.name", "POM Production Kernel"]);
+    await git(state.projectRoot, ["config", "user.email", "pom@local.invalid"]);
+  }
+}
+
+export async function enterStageBranch(state: PomState, config: PomConfig): Promise<string | undefined> {
+  if (config.gitMode !== "branch-per-stage") return undefined;
+  await ensureGit(state, config);
+  const spec = stage(state.currentStage);
+  const branch = `pom/stage-${spec.id}-${spec.slug}`;
+  const branches = await git(state.projectRoot, ["branch", "--format=%(refname:short)"]);
+  if (branches.split("\n").includes(branch)) await git(state.projectRoot, ["switch", branch]);
+  else await git(state.projectRoot, ["switch", "-c", branch]);
+  return branch;
+}
+
+export async function checkpointStage(state: PomState, config: PomConfig, label: string): Promise<string | undefined> {
+  if (config.gitMode === "off") return undefined;
+  await ensureGit(state, config);
+  await git(state.projectRoot, ["add", "-A"]);
+  const status = await git(state.projectRoot, ["status", "--porcelain"]);
+  if (!status) return undefined;
+  await git(state.projectRoot, ["commit", "-m", label]);
+  return git(state.projectRoot, ["rev-parse", "--short", "HEAD"]);
+}