No, I don’t need `SPEC.md` or `SOURCES.md` for this first report. I used the checked-out LXMF source directly. I did not edit `SPEC.md` or any other file.

**LXMessage Serialized Structure**

Source inspected: LXMF commit `fab12ad9bf9f997797034950f289fe41a79dcf5a`

Core `lxmf_bytes` layout:

```text
destination_hash || source_hash || signature || msgpack_payload
```

Where `msgpack_payload` is:

```text
[
  timestamp,
  title,
  content,
  fields,
  optional_stamp
]
```

The fifth element is only present when a normal message stamp is generated and appended.

| Field | Serialized position | Type / size | Source origin | Test vector confirmed |
|---|---:|---|---|---|
| `destination_hash` | bytes `0..15` | 16 bytes | [LXMessage.py](/usr/local/src/reticulum/LXMF/LXMF/LXMessage.py:383), length from [LXMessage.py](/usr/local/src/reticulum/LXMF/LXMF/LXMessage.py:40) and RNS 128-bit truncated hashes in [Reticulum.py](/usr/local/src/reticulum/Reticulum/RNS/Reticulum.py:146) | No |
| `source_hash` | bytes `16..31` | 16 bytes | [LXMessage.py](/usr/local/src/reticulum/LXMF/LXMF/LXMessage.py:384) | No |
| `signature` | bytes `32..95` | 64 bytes | [LXMessage.py](/usr/local/src/reticulum/LXMF/LXMF/LXMessage.py:378), [LXMessage.py](/usr/local/src/reticulum/LXMF/LXMF/LXMessage.py:385); RNS signature length from [Identity.py](/usr/local/src/reticulum/Reticulum/RNS/Identity.py:59) and [Identity.py](/usr/local/src/reticulum/Reticulum/RNS/Identity.py:80) | No |
| `msgpack_payload` | bytes `96..end` | msgpack list | [LXMessage.py](/usr/local/src/reticulum/LXMF/LXMF/LXMessage.py:362), packed at [LXMessage.py](/usr/local/src/reticulum/LXMF/LXMF/LXMessage.py:381) | No |
| `timestamp` | payload index `0` | Python float, normally msgpack float64 on this RNS umsgpack | [LXMessage.py](/usr/local/src/reticulum/LXMF/LXMF/LXMessage.py:357), [LXMessage.py](/usr/local/src/reticulum/LXMF/LXMF/LXMessage.py:362); float64 behavior from [umsgpack.py](/usr/local/src/reticulum/Reticulum/RNS/vendor/umsgpack.py:1177) and [umsgpack.py](/usr/local/src/reticulum/Reticulum/RNS/vendor/umsgpack.py:325) | No |
| `title` | payload index `1` | bytes | [LXMessage.py](/usr/local/src/reticulum/LXMF/LXMF/LXMessage.py:130), [LXMessage.py](/usr/local/src/reticulum/LXMF/LXMF/LXMessage.py:193), [LXMessage.py](/usr/local/src/reticulum/LXMF/LXMF/LXMessage.py:362) | No |
| `content` | payload index `2` | bytes | [LXMessage.py](/usr/local/src/reticulum/LXMF/LXMF/LXMessage.py:135), [LXMessage.py](/usr/local/src/reticulum/LXMF/LXMF/LXMessage.py:202), [LXMessage.py](/usr/local/src/reticulum/LXMF/LXMF/LXMessage.py:362) | No |
| `fields` | payload index `3` | dict, default `{}` | [LXMessage.py](/usr/local/src/reticulum/LXMF/LXMF/LXMessage.py:215), [LXMessage.py](/usr/local/src/reticulum/LXMF/LXMF/LXMessage.py:362) | No |
| `stamp` | payload index `4`, optional | bytes, only if generated | [LXMessage.py](/usr/local/src/reticulum/LXMF/LXMF/LXMessage.py:371), [LXMessage.py](/usr/local/src/reticulum/LXMF/LXMF/LXMessage.py:373); extracted on unpack at [LXMessage.py](/usr/local/src/reticulum/LXMF/LXMF/LXMessage.py:754) | No |

**Hash And Signature**

`message_id` / `hash` is:

```text
SHA256(destination_hash || source_hash || msgpack([timestamp, title, content, fields]))
```

Source: [LXMessage.py](/usr/local/src/reticulum/LXMF/LXMF/LXMessage.py:364), [LXMessage.py](/usr/local/src/reticulum/LXMF/LXMF/LXMessage.py:368), RNS SHA-256 at [Identity.py](/usr/local/src/reticulum/Reticulum/RNS/Identity.py:238).

The signature is over:

```text
destination_hash || source_hash || msgpack([timestamp, title, content, fields]) || message_id
```

Source: [LXMessage.py](/usr/local/src/reticulum/LXMF/LXMF/LXMessage.py:375), [LXMessage.py](/usr/local/src/reticulum/LXMF/LXMF/LXMessage.py:378), RNS signing at [Identity.py](/usr/local/src/reticulum/Reticulum/RNS/Identity.py:767).

Important: the optional normal `stamp` is excluded from both `message_id` and signature. Unpack removes payload index `4` before recomputing hash/signature material: [LXMessage.py](/usr/local/src/reticulum/LXMF/LXMF/LXMessage.py:754).

**Outer Representations**

Direct/link/resource delivery uses full `self.packed` unchanged: [LXMessage.py](/usr/local/src/reticulum/LXMF/LXMF/LXMessage.py:636), [LXMessage.py](/usr/local/src/reticulum/LXMF/LXMF/LXMessage.py:654).

Opportunistic packet delivery omits the destination hash from the packet payload because the RNS packet destination already implies it:

```text
source_hash || signature || msgpack_payload
```

Source: [LXMessage.py](/usr/local/src/reticulum/LXMF/LXMF/LXMessage.py:633).

Propagated and paper messages wrap/encrypt everything after the destination hash:

```text
destination_hash || encrypted(source_hash || signature || msgpack_payload)
```

Source: propagated [LXMessage.py](/usr/local/src/reticulum/LXMF/LXMF/LXMessage.py:429), paper [LXMessage.py](/usr/local/src/reticulum/LXMF/LXMF/LXMessage.py:449). Propagation transit additionally msgpacks `[time.time(), [lxmf_data]]`: [LXMessage.py](/usr/local/src/reticulum/LXMF/LXMF/LXMessage.py:436).

**Notes**

The README is not authoritative here: it describes payload order as timestamp, content, title, fields, but current code serializes timestamp, title, content, fields.

No test vector confirmation exists in this checkout. There is no `tools/` directory and no tracked `SPEC.md` or `SOURCES.md`, so every “Test vector confirmed” entry above is marked `No`.