Design documentation illustration pass and FLP→FMP rename

Rename FIPS Link Protocol (FLP) to FIPS Mesh Protocol (FMP)

  The "Link Protocol" name understated the layer's scope — spanning tree
  construction, bloom filter routing, greedy forwarding, and mesh-wide
  coordination go well beyond link-level concerns. Rename fips-link-layer.md
  to fips-mesh-layer.md, update FLP→FMP throughout docs and source code
  (FLP_VERSION→FMP_VERSION, wire.rs, rx_loop.rs, spanning_tree.rs).

New SVG illustrations

  - Protocol stack: color-coded layer diagram replacing ASCII art
  - OSI mapping: side-by-side comparison with traditional networking layers
  - Bloom filter propagation: 6-node tree with sender-colored filter boxes
    showing split-horizon computation per link
  - Routing decision flowchart: 5-step priority chain with candidate ranking
    by tree distance and link performance
  - Coordinate discovery: sequence diagram showing LookupRequest propagation,
    response caching, and SessionSetup cache warming

Redesigned existing SVGs

  - Architecture overview: uniform node layout, U-shaped encrypted link
    connectors, separate end-to-end session line
  - Node architecture: split Router Core into FSP and FMP layers, reorganize
    transports into Overlay/Shared Medium/Point-to-Point categories
  - Identity derivation: wider boxes, visible encode arrow, dashed npub line

fips-intro.md revisions

  - Add inline references to prior work: Yggdrasil/Ironwood for coordinate
    routing, Noise Protocol Framework for IK handshakes, WireGuard for
    index-based session dispatch, Wikipedia for bloom filters, split-horizon,
    and greedy embedding
  - Add explanatory paragraphs after bloom filter diagram describing
    split-horizon filter computation and candidate selection behavior
  - Simplify transport abstraction language, remove I2P/LoRa references
  - Fix LookupRequest wording ("propagates" not "floods"), note intermediate
    node coordinate caching on lookup responses
  - Rewrite architecture overview prose to match redesigned diagrams

src/node/wire.rs

@@ -1,6 +1,6 @@
 //! Wire Format Parsing and Serialization
 //!
-//! Defines the FIPS link-layer wire format (FLP) for packet dispatch.
+//! Defines the FIPS mesh-layer wire format (FMP) for packet dispatch.
 //! All packets begin with a 4-byte common prefix followed by phase-specific fields.
 //!
 //! ## Common Prefix (4 bytes)
@@ -24,8 +24,8 @@ use crate::noise::{HANDSHAKE_MSG1_SIZE, HANDSHAKE_MSG2_SIZE, TAG_SIZE};
 // Constants
 // ============================================================================
 
-/// FLP protocol version (4 high bits of byte 0).
-pub const FLP_VERSION: u8 = 0;
+/// FMP protocol version (4 high bits of byte 0).
+pub const FMP_VERSION: u8 = 0;
 
 /// Phase value for established (encrypted) frames.
 pub const PHASE_ESTABLISHED: u8 = 0x0;
@@ -70,7 +70,7 @@ pub const FLAG_SP: u8 = 0x04;
 // Common Prefix
 // ============================================================================
 
-/// Parsed common packet prefix (first 4 bytes of every FLP packet).
+/// Parsed common packet prefix (first 4 bytes of every FMP packet).
 ///
 /// Wire format:
 /// ```text
@@ -156,7 +156,7 @@ impl EncryptedHeader {
         let version = data[0] >> 4;
         let phase = data[0] & 0x0F;
 
-        if version != FLP_VERSION || phase != PHASE_ESTABLISHED {
+        if version != FMP_VERSION || phase != PHASE_ESTABLISHED {
             return None;
         }
 
@@ -222,7 +222,7 @@ impl Msg1Header {
         let version = data[0] >> 4;
         let phase = data[0] & 0x0F;
 
-        if version != FLP_VERSION || phase != PHASE_MSG1 {
+        if version != FMP_VERSION || phase != PHASE_MSG1 {
             return None;
         }
 
@@ -278,7 +278,7 @@ impl Msg2Header {
         let version = data[0] >> 4;
         let phase = data[0] & 0x0F;
 
-        if version != FLP_VERSION || phase != PHASE_MSG2 {
+        if version != FMP_VERSION || phase != PHASE_MSG2 {
             return None;
         }
 
@@ -317,7 +317,7 @@ pub fn build_msg1(sender_idx: SessionIndex, noise_msg1: &[u8]) -> Vec<u8> {
     let payload_len = (4 + noise_msg1.len()) as u16; // sender_idx + noise_msg1
 
     let mut packet = Vec::with_capacity(MSG1_WIRE_SIZE);
-    packet.push(CommonPrefix::ver_phase_byte(FLP_VERSION, PHASE_MSG1));
+    packet.push(CommonPrefix::ver_phase_byte(FMP_VERSION, PHASE_MSG1));
     packet.push(0x00); // flags must be zero
     packet.extend_from_slice(&payload_len.to_le_bytes());
     packet.extend_from_slice(&sender_idx.to_le_bytes());
@@ -334,7 +334,7 @@ pub fn build_msg2(sender_idx: SessionIndex, receiver_idx: SessionIndex, noise_ms
     let payload_len = (4 + 4 + noise_msg2.len()) as u16; // sender + receiver + noise
 
     let mut packet = Vec::with_capacity(MSG2_WIRE_SIZE);
-    packet.push(CommonPrefix::ver_phase_byte(FLP_VERSION, PHASE_MSG2));
+    packet.push(CommonPrefix::ver_phase_byte(FMP_VERSION, PHASE_MSG2));
     packet.push(0x00); // flags must be zero
     packet.extend_from_slice(&payload_len.to_le_bytes());
     packet.extend_from_slice(&sender_idx.to_le_bytes());
@@ -353,7 +353,7 @@ pub fn build_established_header(
     payload_len: u16,
 ) -> [u8; ESTABLISHED_HEADER_SIZE] {
     let mut header = [0u8; ESTABLISHED_HEADER_SIZE];
-    header[0] = CommonPrefix::ver_phase_byte(FLP_VERSION, PHASE_ESTABLISHED);
+    header[0] = CommonPrefix::ver_phase_byte(FMP_VERSION, PHASE_ESTABLISHED);
     header[1] = flags;
     header[2..4].copy_from_slice(&payload_len.to_le_bytes());
     header[4..8].copy_from_slice(&receiver_idx.to_le_bytes());