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, 4 insertions, 4 deletions

diff --git a/packages/meshbay-node/src/meshbay_node/transport/webrtc_server.py b/packages/meshbay-node/src/meshbay_node/transport/webrtc_server.py
index 0154319..e333ae8 100644
--- a/packages/meshbay-node/src/meshbay_node/transport/webrtc_server.py
+++ b/packages/meshbay-node/src/meshbay_node/transport/webrtc_server.py
@@ -100,7 +100,7 @@ from meshbay_common.protocol import MNP, chunk_ciphertext, file_chunk_wire
 from meshbay_node.transport.wire import index_sync_message
 from meshbay_node.indexer import GroupIndex
 from meshbay_node.indexer.indexer import DirectoryIndexer
-from meshbay_node import linkpreview, ops
+from meshbay_node import linkpreview, ops, platform
 # Re-imported under its original name: every call site and existing test in
 # this module still refers to it as `_probe_video`. The implementation lives
 # in media_probe.py so the indexer package (imported just above) can call it
@@ -3441,7 +3441,7 @@ class WebRTCPeerSession:
         try:
             async with sem:
                 proc = await asyncio.create_subprocess_exec(
-                    "ffmpeg", "-hide_banner", "-loglevel", "error",
+                    platform.ffmpeg_cmd(), "-hide_banner", "-loglevel", "error",
                     "-ss", str(segment_index * segment_duration),
                     "-i", str(file_path),
                     "-t", str(segment_duration),
@@ -4360,7 +4360,7 @@ class WebRTCPeerSession:
             # forced out of its MediaSource with no further explanation.
             codec_args += ["-c:a", "aac", "-ac", "2", "-b:a", "192k"]
         proc = await asyncio.create_subprocess_exec(
-            "ffmpeg", "-hide_banner", "-loglevel", "error",
+            platform.ffmpeg_cmd(), "-hide_banner", "-loglevel", "error",
             *seek_args,
             "-i", str(file_path),
             *map_args,
@@ -4556,7 +4556,7 @@ async def _transcode_audio_to_aac(file_path: Path) -> bytes:
     tmp_path = Path(tmp_name)
     try:
         proc = await asyncio.create_subprocess_exec(
-            "ffmpeg", "-hide_banner", "-loglevel", "error", "-y",
+            platform.ffmpeg_cmd(), "-hide_banner", "-loglevel", "error", "-y",
             "-i", str(file_path),
             "-vn", "-c:a", "aac", "-ac", "2", "-b:a", "192k",
             "-f", "ipod", str(tmp_path),