home back: rollback via home-manager switch --rollback — homeBack parses home generations (newest-first), takes gen[0]=current and gen[1]=target, confirms, runs 'home-manager switch --rollback'; <2 generations prints 'already at the oldest generation' instead of failing; build+tests green

@@ -944,7 +944,30 @@944944         return;945945     }946946 947+    if (std.mem.eql(u8, ctx.sub, "back")) return homeBack(ctx);948+947949     return output.subcommandHelp("home", &home_help, null);950+}951+952+fn homeBack(ctx: Ctx) !void {953+    const out = try exec.homeGenerations(ctx.gpa, ctx.io, &ctx.machine);954+    defer ctx.gpa.free(out);955+    const gens = try parseHomeGenerations(ctx.gpa, out);956+    defer freeHomeGens(ctx.gpa, gens);957+958+    // Newest-first: [0] is current, [1] is the generation to roll back to.959+    if (gens.len < 2) {960+        output.alreadyOldest();961+        return;962+    }963+    const current = gens[0].number;964+    const prev = gens[1].number;965+966+    output.homeBackStart(ctx.machine.name, current, prev);967+    if (ctx.cfg.confirm and !output.confirm("")) return;968+    const code = try exec.homeManagerRollback(ctx.io, &ctx.machine, ctx.gpa);969+    if (code != 0) return error.BuildFailed;970+    output.homeBackDone(prev);948971 }949972 950973 fn homeApply(ctx: Ctx, mode: exec.HomeManagerMode) !void {