ipc, worker: dial and bind through netaddr (V-484)

Five hardcoded transports, three in internal/ipc and two in
internal/worker, all now go through the seam address. The unix perms
logic moved into netaddr, so the two copies of parentDir and the umask
dance are gone.

peerCaller already returned ok=false for a non-unix conn, so the
SO_PEERCRED path degrades correctly on tcp with no change.

internal/ipc/server.go

@@ -8,11 +8,11 @@ import (
 	"fmt"
 	"log"
 	"net"
-	"os"
 	"sync"
 	"sync/atomic"
 	"time"
 
+	"github.com/kami/maven/internal/netaddr"
 	"github.com/kami/maven/internal/store"
 	"golang.org/x/sys/unix"
 )
@@ -446,6 +446,7 @@ func mapErr(err error) error {
 type Server struct {
 	api  atomic.Value // stores CoreAPI
 	path string
+	addr netaddr.Addr
 
 	ln     net.Listener
 	wg     sync.WaitGroup
@@ -610,31 +611,29 @@ type CheckFunc func(ctx context.Context, m Method, params json.RawMessage) error
 // MethodAssertStepUp dispatch calls this instead of going through CoreAPI.
 type StepUpFunc func(ctx context.Context) error
 
-// Listen creates a Server bound to path. path's parent dir must exist and be
-// 0700 (we chmod it if we own it); the socket file itself is created 0600 so
-// only the same unix user can connect — the current "auth floor", same radius
-// as wg at the network boundary. Removing a stale socket at path first lets
-// the daemon restart cleanly.
+// Listen creates a Server bound to path.
+//
+// A bare path is a unix socket, unchanged: its parent dir is 0700 and the
+// socket file itself is 0600, so only the same unix user can connect — the
+// current "auth floor", same radius as wg at the network boundary. A stale
+// socket is removed first so the daemon restarts cleanly.
+//
+// A "tcp://host:port?token=..." address binds a network listener instead, for
+// a module that lives on another host. There is no filesystem there to be the
+// auth floor, so netaddr checks the shared token before this package sees the
+// connection and a token is mandatory. See internal/netaddr.
 func Listen(path string, api CoreAPI) (*Server, error) {
-	_ = os.Remove(path) // stale socket from a crashed daemon; ignore missing
-	if err := os.MkdirAll(parentDir(path), 0o700); err != nil {
-		return nil, fmt.Errorf("ipc: mkdir socket dir: %w", err)
-	}
-	// umask could widen the perms on socket creation; tighten then chmod to
-	// be explicit. 0600 ⇒ read+write by owner only.
-	oldMask := unix.Umask(0o077)
-	ln, err := net.Listen("unix", path)
-	unix.Umask(oldMask)
+	addr, err := netaddr.Parse(path)
 	if err != nil {
-		return nil, fmt.Errorf("ipc: listen %s: %w", path, err)
+		return nil, err
 	}
-	if err := os.Chmod(path, 0o600); err != nil {
-		_ = ln.Close()
-		_ = os.Remove(path)
-		return nil, fmt.Errorf("ipc: chmod socket: %w", err)
+	ln, err := netaddr.Listen(addr)
+	if err != nil {
+		return nil, err
 	}
 	s := &Server{
 		path: path,
+		addr: addr,
 		ln:   ln,
 		done: make(chan struct{}),
 	}
@@ -1268,7 +1267,7 @@ func (s *Server) Close() error {
 		// missing the seal costs every write since the last clean shutdown.
 		log.Printf("ipc: %d connection(s) still busy after %s, closing anyway", s.liveConns(), closeGrace)
 	}
-	_ = os.Remove(s.path)
+	netaddr.Cleanup(s.addr)
 	return err
 }
 
@@ -1338,25 +1337,6 @@ func (s *Server) Path() string { return s.path }
 // while the server is serving (dispatch loads api once per request via atomic).
 func (s *Server) SetAPI(api CoreAPI) { s.api.Store(api) }
 
-func parentDir(p string) string {
-	if i := lastIndexByte(p, '/'); i >= 0 {
-		if i == 0 {
-			return "/"
-		}
-		return p[:i]
-	}
-	return "."
-}
-
-func lastIndexByte(s string, b byte) int {
-	for i := len(s) - 1; i >= 0; i-- {
-		if s[i] == b {
-			return i
-		}
-	}
-	return -1
-}
-
 // peerCaller — read SO_PEERCRED off a unix conn to identify the connecting
 // process. Returns ok=false on a non-unix conn or a platform without
 // SO_PEERCRED; the caller then proceeds without a Caller (the socket perms