pbhw: --one-wire never reached the suite's own sessions

The flag was plumbed through pbrig.Deployment to the host-tool subprocess
calls and nowhere else, so identity() and scan() opened a raw port and drove
a shared line as though it were two wires. On real one-wire hardware the
adapter's echo answers the knock before the device does, so the suite would
have died at its very first check — "the loader never answered; nothing below
can be trusted" — for the one deployment the flag exists to test, and every
result after it is gated on that check passing.

Both now open through pbrig.Rig.open_port(), which applies the deployment's
link mode. The gap underneath was that only the subprocess path could reach
those facts at all; anything driving the protocol in-process had to restate
them, and did not.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tools/pbhw.py

@@ -53,7 +53,7 @@ class Suite:
         """The info block, which every later check takes its bounds from."""
         module = pbrig.load_pureboot(self.rig.d.pureboot)
         self.rig.reset()
-        port = module.Port(self.rig.d.port, self.rig.d.baud)
+        port = self.rig.open_port()  # wrapped for the echo where the line is shared
         try:
             loader = module.Loader(port)
             if self.rig.d.autobaud:
@@ -87,7 +87,10 @@ class Suite:
                 rate = module.scan_rate(self.rig.d.baud, pct)
                 self.rig.reset()
                 try:
-                    port = module.Port(self.rig.d.port, rate)
+                    # Same wrap as identity(): on a shared line an undiscarded
+                    # echo answers every rate a scan probes, so the walk would
+                    # report the first one it tried.
+                    port = self.rig.open_port(rate)
                 except module.Error as error:
                     self.check("scan opens every probe rate", False, f"{rate} Bd: {error}")
                     return

tools/pbrig.py

@@ -281,6 +281,22 @@ class Rig:
             return 99, f"TIMEOUT after {timeout}s\n{expired.stdout or ''}{expired.stderr or ''}"
         return result.returncode, (result.stdout or "") + (result.stderr or "")
 
+    def open_port(self, baud: int | None = None):
+        """A port opened the way this deployment says to speak to the board.
+
+        Everything the rig runs as a *subprocess* gets its flags from
+        `pureboot()` above; anything that drives the protocol in-process has
+        to reach the same facts, and until this existed only the subprocess
+        path could. A shared line is the one where that gap is fatal rather
+        than untidy: the host reads back every byte it writes, so an
+        undiscarded echo answers the knock before the device does. Open
+        through here and a one-wire deployment cannot be silently driven as
+        a two-wire one.
+        """
+        module = load_pureboot(self.d.pureboot)
+        port = module.Port(self.d.port, self.d.baud if baud is None else baud)
+        return module.OneWirePort(port) if self.d.one_wire else port
+
     def capture(self, seconds: float = 2.0, baud: int | None = None) -> bytes:
         """Listen to whatever the board is saying, at an arbitrary rate.