release: v0.1.0

First cut release. Snapshots ./src/ as ./versions/v0.1.0/ via
`just cut-version v0.1.0` (22 files: 21 chapter MDs + SUMMARY.md).
Deployed alongside `latest` at:

  https://swaits.github.io/meshcore-spec/v0.1.0/

Also:

- CHANGELOG.md adopts Keep a Changelog-style version sections.
  Future entries land under [Unreleased] and graduate to a version
  heading when cut. The existing date-stamped pass entries stay
  put as a historical record of the work captured in v0.1.0.
- README.md fixes a stale "per vX.Y.Z tag" mention left over from
  the tag-based versioning model, and links the current release
  explicitly.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

versions/v0.1.0/20-bridge-protocol.md

@@ -0,0 +1,69 @@
+# MeshCore Protocol Specification
+
+## Section 20: Bridge Protocol
+
+### Overview
+
+The bridge protocol enables MeshCore packet forwarding over non-LoRa transports
+such as RS232 serial links and ESP-NOW WiFi. It adds a simple framing layer
+with a magic number and checksum around the raw MeshCore packet.
+
+### Frame Format
+
+```
+┌──────────────┬──────────────┬──────────────┬──────────────┐
+│  Magic (2B)  │   Payload    │ Checksum (2B)│              │
+│   0xC03E     │  (variable)  │ Fletcher-16  │              │
+└──────────────┴──────────────┴──────────────┴──────────────┘
+```
+
+### Fields
+
+| Field | Size | Type | Description |
+|-------|------|------|-------------|
+| Magic | 2 bytes | uint16 | `0xC03E` — identifies the frame as a MeshCore bridge packet |
+| Payload | variable | raw | Raw MeshCore packet (as produced by `Packet::writeTo()`) |
+| Checksum | 2 bytes | Fletcher-16 | Fletcher-16 checksum over the payload |
+
+### RS232 Variant
+
+The RS232 variant adds a length field between the magic and payload:
+
+```
+┌──────────────┬──────────────┬──────────────┬──────────────┐
+│  Magic (2B)  │  Length (2B) │   Payload    │ Checksum (2B)│
+│   0xC03E     │  uint16_le   │  (variable)  │ Fletcher-16  │
+└──────────────┴──────────────┴──────────────┴──────────────┘
+```
+
+| Field | Size | Type | Description |
+|-------|------|------|-------------|
+| Length | 2 bytes | uint16_le | Length of the payload in bytes |
+
+### Fletcher-16 Checksum
+
+The Fletcher-16 checksum is computed over the payload bytes:
+
+```
+function fletcher16(data):
+    sum1 = 0
+    sum2 = 0
+    for byte in data:
+        sum1 = (sum1 + byte) mod 255
+        sum2 = (sum2 + sum1) mod 255
+    return (sum2 << 8) | sum1
+```
+
+### ESP-NOW Variant
+
+For ESP-NOW transport, the frame format is the same as the basic format (magic +
+payload + checksum) without the length field, since ESP-NOW provides its own
+length framing.
+
+### Cross-References
+
+- [Section 1: Wire Format](01-wire-format.md) — Packet format within payload
+
+### Reference Implementation
+
+- Bridge handling in MeshCore firmware (board-specific implementations)