codec: replace codec! with a Codec derive (SFT-8112)

The derive is meant for keyos IPC, so by default it prefixes structs and
enum variants with their length, which lets old and new versions of a
type decode each other. QuantumLink's own wire types use it frozen,
which keeps the codec! layout byte for byte.

Decode no longer abstracts over the byte container. The borrowed form
points into a &[u8] instead, and the frame parser slices stream payloads
out of the record's Bytes itself.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: badicsalex

Cargo.lock

@@ -3,6 +3,7 @@ resolver = "2"
 members = [
   "btp",
   "codec",
+  "codec/macro",
   "common",
   "keyos",
   "router",
@@ -21,7 +22,8 @@ license = "MIT OR Apache-2.0"
 bytes = "1.11.1"
 
 # workspace crates
-ql-codec = { path = "codec" }
+ql-codec = { path = "codec", features = ["derive"] }
+ql-codec-macro = { path = "codec/macro" }
 ql-common = { path = "common" }
 ql-fsm = { path = "fsm" }
 ql-keyos = { path = "keyos" }

Cargo.toml

@@ -37,11 +37,10 @@ pub fn packet_version(data: &[u8]) -> Option<Version> {
     }
 }
 
-ql_codec::codec! {
-    #[derive(Debug, Clone, Copy, PartialEq, Eq)]
-    struct Header {
-        sequence: u16,
-        index: u16,
-        tagged_record_len: u32,
-    }
+#[derive(Debug, Clone, Copy, PartialEq, Eq, ql_codec::Codec)]
+#[codec(frozen)]
+struct Header {
+    sequence: u16,
+    index: u16,
+    tagged_record_len: u32,
 }

btp/src/lib.rs

@@ -7,3 +7,7 @@ license.workspace = true
 
 [dependencies]
 bytes = { workspace = true }
+ql-codec-macro = { workspace = true, optional = true }
+
+[features]
+derive = ["dep:ql-codec-macro"]

codec/Cargo.toml

@@ -0,0 +1,23 @@
+[package]
+name = "ql-codec-macro"
+version = "0.1.0"
+edition = "2021"
+description = "QuantumLink codec derive"
+license.workspace = true
+
+[lib]
+proc-macro = true
+
+[dependencies]
+proc-macro2 = "1.0.101"
+quote = "1.0.40"
+syn = { version = "2.0.106", default-features = false, features = [
+  "clone-impls",
+  "derive",
+  "parsing",
+  "printing",
+  "proc-macro",
+] }
+
+[dev-dependencies]
+ql-codec = { workspace = true, features = ["derive"] }