fix(lint): use Fmt.failwith and err_* helpers (E215/E340)

Replace failwith (Fmt.str ...) with Fmt.failwith, and introduce err_*
helper functions for Error (Fmt.str ...) patterns across pid1, precommit,
qemu (qmp_protocol, vm), and requests (tls_config, websocket).

bin/main.ml

···
     let width = int_of_string (String.trim (input_line ic)) in
     ignore (Unix.close_process_in ic);
     width
-  with _ -> 80
+  with Failure _ | End_of_file | Unix.Unix_error _ -> 80
 
 let truncate_subject max_len s =
   if String.length s <= max_len then s else String.sub s 0 (max_len - 1) ^ "…"

lib/precommit.ml

···
 
 module Log = (val Logs.src_log log_src : Logs.LOG)
 
+let err_no_dune_project dir =
+  Error (Fmt.str "%s: No dune-project found (use --force to override)" dir)
+
+let err_no_git_dir dir = Error (Fmt.str "%s: No .git directory found" dir)
+
 type ctx = { cwd : Eio.Fs.dir_ty Eio.Path.t; fs : Eio.Fs.dir_ty Eio.Path.t }
 
 let ctx ~cwd ~fs =
···
 let read_file ~fs path = Eio.Path.load Eio.Path.(fs / path)
 
 let write_file ~fs ~dry_run path content =
-  if dry_run then Printf.printf "Would create %s\n" path
+  if dry_run then Fmt.pr "Would create %s@." path
   else Eio.Path.save ~create:(`Or_truncate 0o644) Eio.Path.(fs / path) content
 
 let chmod_exec ~dry_run path =
-  if dry_run then Printf.printf "Would chmod +x %s\n" path
-  else Unix.chmod path 0o755
+  if dry_run then Fmt.pr "Would chmod +x %s@." path else Unix.chmod path 0o755
 
 let mkdir_p ~fs ~dry_run path =
-  if dry_run then Printf.printf "Would create %s/\n" path
+  if dry_run then Fmt.pr "Would create %s/@." path
   else Eio.Path.mkdirs ~exists_ok:true ~perm:0o755 Eio.Path.(fs / path)
 
 let check_formatting_disabled ~fs path =
···
   let dune_project = Filename.concat dir "dune-project" in
   let ocamlformat_path = Filename.concat dir ".ocamlformat" in
   if (not force) && not (file_exists ~fs:ctx.cwd dune_project) then
-    Error (Fmt.str "%s: No dune-project found (use --force to override)" dir)
+    err_no_dune_project dir
   else
     match git_root ~cwd:ctx.cwd ~fs:ctx.fs dir with
-    | None -> Error (Fmt.str "%s: No .git directory found" dir)
+    | None -> err_no_git_dir dir
     | Some git_root ->
         let git_dir_path = Filename.concat git_root ".git" in
         let git_dir = resolve_git_dir ~fs:ctx.fs git_dir_path in
···
   else abs_path
 
 let rec git_projects ctx dir =
-  let entries = try Eio.Path.read_dir Eio.Path.(ctx.cwd / dir) with _ -> [] in
+  let entries =
+    try Eio.Path.read_dir Eio.Path.(ctx.cwd / dir) with Eio.Io _ -> []
+  in
   let child_path name = if dir = "." then name else Filename.concat dir name in
   (* If dir has .git, include it *)
   let self_has_git = List.mem ".git" entries in
···
           let content = Eio.Path.load Eio.Path.(fs / global_config_path) in
           let config = Git.Config.of_string content in
           (Git.Config.user config).email
-        with _ -> None)
+        with Eio.Io _ | Failure _ -> None)
 
 (* Check if commit was made by the current user *)
 let is_my_commit ~user_email commit =
···
 
 let backup_branch ctx dir =
   match git_root ~cwd:ctx.cwd ~fs:ctx.fs dir with
-  | None -> failwith (Fmt.str "%s: No .git directory found" dir)
+  | None -> Fmt.failwith "%s: No .git directory found" dir
   | Some git_root ->
       let repo = Git.Repository.open_repo ~fs:ctx.fs (Fpath.v git_root) in
       let branch =
···
 
 let rewrite_ai_attribution ctx dir =
   match git_root ~cwd:ctx.cwd ~fs:ctx.fs dir with
-  | None -> Error (Fmt.str "%s: No .git directory found" dir)
+  | None -> err_no_git_dir dir
   | Some git_root -> (
       let repo = Git.Repository.open_repo ~fs:ctx.fs (Fpath.v git_root) in
       let user_email = user_email ~fs:ctx.fs repo in