refactor(node): platform abstraction for Windows portability (W1-W2-W5-W6-W7)

Platform directories, signal handling, chmod guards, ffmpeg discovery,
and platform-conditional CLI messages — all testable on Linux.

See docs/WINDOWS-PORT.md §5 for the plan these implement.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

1 files changed, 5 insertions, 3 deletions

diff --git a/packages/meshbay-node/src/meshbay_node/transport/quic_server.py b/packages/meshbay-node/src/meshbay_node/transport/quic_server.py
index 6dde3ff..95fccf1 100644
--- a/packages/meshbay-node/src/meshbay_node/transport/quic_server.py
+++ b/packages/meshbay-node/src/meshbay_node/transport/quic_server.py
@@ -53,6 +53,7 @@ from meshbay_common.groupbox import PURPOSE_ACK, seal
 from meshbay_common.protocol import MNP, file_chunk_wire
 from meshbay_node.indexer import GroupIndex
 from meshbay_node.transport.wire import index_sync_message
+from meshbay_node import platform
 
 log = logging.getLogger(__name__)
 
@@ -545,7 +546,7 @@ def _extract_segment(file_path: Path, start_time: float, duration: float) -> byt
     """Extract one HLS segment via ffmpeg. Returns MPEG-TS bytes or None on failure."""
     try:
         result = subprocess.run(
-            ["ffmpeg", "-hide_banner", "-loglevel", "error",
+            [platform.ffmpeg_cmd(), "-hide_banner", "-loglevel", "error",
              "-ss", str(start_time),
              "-i", str(file_path),
              "-t", str(duration),
@@ -596,8 +597,9 @@ class QuicChunkServer:
         # Peer sets are per group now — see _MNPServerProtocol._peer_registry().
         self._host      = host
         self._port      = port
-        self._cert_path = cert_path or Path.home() / ".config/meshbay/node_tls.crt"
-        self._key_path  = key_path  or Path.home() / ".config/meshbay/node_tls.key"
+        from meshbay_node.platform import config_dir
+        self._cert_path = cert_path or config_dir() / "node_tls.crt"
+        self._key_path  = key_path  or config_dir() / "node_tls.key"
         self._server    = None
         self._task      = None
         self._session_tickets: dict[bytes, Any] = {}