Freeze the dormant sync IPC bridge (#161)

Author: myobie

CHANGELOG.md

@@ -8,6 +8,12 @@ EXPERIMENTAL, so on-disk formats and the CLI may change without notice.
 
 ### Changed
 
+- **The dormant `fabric/sync-ipc/1` local bridge now has a frozen contract.**
+  Versioned, bounded control frames negotiate peer resolution, raw sync streams,
+  status, shutdown, and structured errors. The socket is owner-only, verifies
+  the local user and daemon-instance nonce, and applies no extra framing after
+  a stream is ready. Production still uses the embedded sync engine.
+
 - **`fabric doctor` now gives uncertainty a distinct exit code.** Code 0 means
   verified healthy, code 1 means a problem or setup remains, and code 3 means
   one or more checks are unknown with no known problem. Clap keeps code 2 for

README.md

@@ -972,6 +972,11 @@ The sync engine receives explicit config and state paths instead of the daemon
 home. It holds `<home>/sync/owner.lock` for its lifetime, so a second engine
 fails before it reads or changes the same state.
 
+The library also defines a dormant `fabric/sync-ipc/1` Unix bridge for the
+planned companion process. Its owner-only socket uses bounded, versioned control
+messages, then carries raw `fabric/sync/1` bytes. No production request selects
+this bridge yet; the daemon remains the embedded sync owner.
+
 Entries live in an authoritative, hand-editable `syncs.toml` next to `peers.toml`
 (`~/.config/fabric/syncs.toml` for the default home, `<home>/syncs.toml` with
 `--home` or `FABRIC_HOME`):