test: move the handshake regression in beside the rest

It was written next to the loader source; the harness lives at the repo root.
Not registered with ctest yet — it belongs beside pureboot.planner, which is
the other test of the host tool's pure logic.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

pureboot/test/test_handshake.py

@@ -1,104 +0,0 @@
-#!/usr/bin/env python3
-"""Host-tool activation handshake: it must not hang on a flooding target.
-
-`_handshake` drains the line after it sees a prompt, to absorb a real loader's
-trailing bytes before it asks for the identity. That drain must be bounded: a
-target that never falls quiet — a board stuck in a reset loop presents exactly
-this, ~60 reboots/s of UART-reset garbage in which a stray 0x2b reads as a
-prompt — otherwise spins the tool forever. Regression for that hang, plus a
-control that a well-behaved loader still connects.
-
-Stdlib only; run with `python test/test_handshake.py`.
-"""
-import importlib.util
-import pathlib
-import threading
-import time
-
-PB = pathlib.Path(__file__).resolve().parents[1] / "pureboot.py"
-_spec = importlib.util.spec_from_file_location("pureboot", PB)
-pb = importlib.util.module_from_spec(_spec)
-_spec.loader.exec_module(pb)
-
-P = F = 0
-
-
-def check(name, ok):
-    global P, F
-    P, F = P + (1 if ok else 0), F + (0 if ok else 1)
-    print(f"  [{'PASS' if ok else 'FAIL'}] {name}")
-
-
-class FloodPort:
-    """A line that never falls quiet: read_available always returns bytes, and
-    they contain a prompt. No identity ever completes."""
-
-    def flush_input(self):
-        pass
-
-    def write(self, data):
-        pass
-
-    def read_available(self, wait):
-        time.sleep(0.01)  # a real read waits; keep the busy loop off a core
-        return b"+\x00\xff"
-
-    def read_exact(self, count, timeout):
-        raise pb.Error("no identity")
-
-
-class LoaderPort:
-    """A well-behaved pureboot 5: one prompt to the knock, then quiet, then the
-    slim identity (version 5 + m328p signature) and a closing prompt."""
-
-    def __init__(self):
-        self.reads = self.exacts = 0
-
-    def flush_input(self):
-        pass
-
-    def write(self, data):
-        pass
-
-    def read_available(self, wait):
-        self.reads += 1
-        return b"+" if self.reads == 1 else b""  # prompt once, then settle quiet
-
-    def read_exact(self, count, timeout):
-        self.exacts += 1
-        return b"\x05\x1e\x95\x0f" if self.exacts == 1 else b"+"  # identity, then prompt
-
-
-def terminates(port, wait, budget):
-    """Run connect_autobaud in a thread; True if it returns/raises within
-    `budget` seconds rather than hanging."""
-    done = threading.Event()
-
-    def run():
-        try:
-            pb.Loader(port).connect_autobaud(wait)
-        except Exception:
-            pass
-        finally:
-            done.set()
-
-    threading.Thread(target=run, daemon=True).start()
-    return done.wait(budget)
-
-
-def main():
-    # the hang: a flooding target must not spin the drain forever. With wait=0.5
-    # the whole handshake has to give up well inside a few seconds.
-    check("flooding target: handshake terminates, drain is bounded",
-          terminates(FloodPort(), wait=0.5, budget=4.0))
-
-    # the control: a real loader still connects and reads identity.
-    info = pb.Loader(LoaderPort()).connect_autobaud(2.0)
-    check("well-behaved loader still connects (version 5)", info.version == 5)
-
-    print(f"\n  {P} passed, {F} failed")
-    return 1 if F else 0
-
-
-if __name__ == "__main__":
-    raise SystemExit(main())