feat(record): add raw ZED body MCAP capture

docs/caveats.md

@@ -86,6 +86,10 @@ If you need audio transport, muxing, or A/V sync, that is outside the current re
 
 MCAP recording stores one `foxglove.CompressedVideo` message per encoded access unit. Replay depends on encoded keyframes carrying decoder configuration; this is handled by the current writer on keyframes.
 
+### MCAP Body Recording Is Raw Packet Capture
+
+When the producer exposes ZED body tracking, MCAP recording stores one raw `cvmmap.body_tracking.v1` message per body PUB packet on `/camera/body` by default. These payload bytes are not normalized by `cvmmap-streamer`; downstream consumers should parse them with the cv-mmap body-tracking v1 contract.
+
 ## External Server Caveats
 
 ### Local SRS Defaults Can Hit `ulimit`

docs/compat_matrix.md

@@ -45,6 +45,7 @@ MCAP support is validated separately with:
 
 - `./build/mcap_reader_tester`
 - `./build/mcap_replay_tester`
+- `./build/mcap_body_record_tester`
 - `./scripts/replay_mcap.sh`
 
 Current recording scope:
@@ -53,6 +54,7 @@ Current recording scope:
 |--------|-------|-------|
 | MCAP `foxglove.CompressedVideo` | H.264 | Stored as Annex B access units |
 | MCAP `foxglove.CompressedVideo` | H.265 | Stored as Annex B access units |
+| MCAP raw body packets | `cvmmap.body_tracking.v1` | Payload bytes are identical to the cv-mmap ZED body PUB packet |
 
 ## Current Defaults
 

docs/mcap_body_tracking.md

@@ -0,0 +1,44 @@
+# MCAP ZED Body Tracking Contract
+
+`cvmmap-streamer` records native cv-mmap ZED body-tracking packets into MCAP as a raw binary channel.
+
+## Channel
+
+- default topic: `/camera/body`
+- `messageEncoding`: `cvmmap.body_tracking.v1`
+- schema: none (`schemaId = 0`)
+- channel metadata:
+  - `packet_layout = cvmmap_body_tracking_v1`
+  - `payload_format = raw`
+  - `source_transport = cv-mmap-body-pub`
+
+The channel is created lazily on the first valid body packet, so non-body inputs do not produce an empty `/camera/body` channel.
+
+## Payload
+
+Each MCAP message payload is byte-for-byte identical to the cv-mmap ZED body PUB packet:
+
+- 64-byte `body_tracking_message_header_t`
+- followed by `body_count` packed `body_tracking_body_t` records
+
+The intended parser contract is the existing cv-mmap body-tracking v1 layout:
+
+- `cvmmap::parse_body_tracking_message(...)`
+- `cv-mmap/docs/cvmmap_body_tracking_v1.ksy`
+
+This recording path does not remap joints, filter fields, or convert the packet into protobuf/JSON.
+
+## Timing And Alignment
+
+- `logTime` and `publishTime` use `header.timestamp_ns`
+- if `header.timestamp_ns == 0`, they fall back to `header.sdk_timestamp_ns`
+- cross-topic alignment should use body `frame_count` and timestamps, not MCAP file order
+
+## Configuration
+
+MCAP body capture follows the normal MCAP recording switch:
+
+- enable MCAP with `--mcap` or `record.mcap.enabled = true`
+- override the body topic with `--mcap-body-topic` or `record.mcap.body_topic`
+
+There is no separate body-enable flag. If the input never emits body packets, no body channel is written.