chore: import upstream snapshot with attribution

lib/bin-context.ts

@@ -0,0 +1,28 @@
+/**
+ * bin-context — tiny shared helpers for non-interactive gstack bins that need the
+ * project slug, current branch, and argv flags. Extracted from the decision bins
+ * (gstack-decision-log / gstack-decision-search) so the slug/branch/flag plumbing
+ * lives in one audited place instead of being copy-pasted per bin.
+ */
+
+import { spawnSync } from "child_process";
+
+/** Resolve the project slug via the `gstack-slug` helper (parses `SLUG=...`). */
+export function resolveSlug(slugBinPath: string): string {
+  const r = spawnSync(slugBinPath, { encoding: "utf-8" });
+  const m = (r.stdout || "").match(/^SLUG=(.+)$/m);
+  return m ? m[1].trim() : "unknown";
+}
+
+/** Current git branch, or undefined on detached HEAD / outside a repo. */
+export function gitBranch(): string | undefined {
+  const r = spawnSync("git", ["rev-parse", "--abbrev-ref", "HEAD"], { encoding: "utf-8" });
+  const b = (r.stdout || "").trim();
+  return b && b !== "HEAD" ? b : undefined;
+}
+
+/** The value following `--flag` in argv, or undefined if absent. */
+export function flagValue(args: string[], name: string): string | undefined {
+  const i = args.indexOf(name);
+  return i >= 0 ? args[i + 1] : undefined;
+}