refactor: drop alktype dependency; add BAST doc for chunk header

- Remove alktype from Cargo.toml (its only usage was a thin wrapper
  over jsonschema::options().build())
- Replace alktype::validation::build_validator with direct jsonschema
  in dispatch.rs
- Add docs/architecture/chunk-header.bast.json — the chunk header's
  BAST (Binary Abstract Syntax Tree) machine-readable wire spec
- Embed as channels::wire::CHUNK_HEADER_BAST via include_str! so
  downstream Rust crates can consume it without a file lookup
- Add test asserting the embedded BAST doc is valid JSON and matches
  the wire format
- Update AGENTS.md §10 and implementation-specialist.md: BAST docs
  are the contract; trivial/hot-path formats stay hand-rolled,
  complex formats use the alktype engine or codegen

Verification:
- cargo test: 543 passed, 0 failed
- cargo clippy --all-targets -- -D warnings: clean
- cargo fmt --check: clean
- cargo doc --no-deps: clean
- BAST doc compiles + round-trips against alktype v0.2.0 engine

.opencode/agents/implementation-specialist.md

@@ -241,9 +241,16 @@ Read `AGENTS.md` at project root for full details. Key rules:
    `AuthToken`, `Capabilities`, `OwnershipProvider`, `HandlerError`,
    `StreamError` live in this crate. Do not add a separate `alkcore` dependency.
    Keep them lean (no TLS, no transport coupling, no endpoint/accept-loop).
-10. **`alktype` dependency** — use `alktype` for binary layout (channels chunk
+10. **BAST documents for wire formats** — every binary wire format carries a
-    header, future binary payload schemas) and JSON payload schema validation
+    BAST (Binary Abstract Syntax Tree) document as its machine-readable spec
-    (`OperationSpec`'s `input_schema`/`output_schema`). Do not roll your own.
+    (e.g. the channels chunk header's `docs/architecture/chunk-header.bast.json`,
+    embedded as `CHUNK_HEADER_BAST`). BAST is plain JSON — no dependency
+    required to author or consume it. The `alktype` crate compiles BAST into
+    readers/writers/validators; future codegen derives language-specific
+    implementations. Trivial or hot-path formats (chunk header, tty framing)
+    stay hand-rolled with the BAST doc as the contract; complex formats (sftp)
+    use the alktype engine or codegen. Do not roll your own offset map or
+    validator for complex formats.
 11. **Feature flags** — transports may be feature-gated if the need arises. The
     base crate should compile lean (no `quinn`, no `iroh` unless the feature is
     on). Verify both `cargo test` (default) and `cargo test --all-features` pass

AGENTS.md

@@ -136,11 +136,18 @@ session, not just spawned implementation agents.
    dial and the TLS config are concerns of the consumer, not of this
    crate. See ADR-007, ADR-008, ADR-009.
 
-10. **`alktype` dependency** — use `alktype` for binary layout (the
+10. **BAST documents for wire formats** — every binary wire format in
-    channels chunk header, future binary payload schemas) and JSON
+    this crate carries a BAST (Binary Abstract Syntax Tree) document as
-    payload schema validation (`OperationSpec`'s `input_schema`/
+    its machine-readable spec (e.g. the channels chunk header's
-    `output_schema`). Do not roll your own offset map or validator. See
+    `docs/architecture/chunk-header.bast.json`, embedded as
-    the alktype crate at `/workspace/@alkdev/alktype`.
+    `CHUNK_HEADER_BAST`). BAST is plain JSON — no dependency required
+    to author or consume it. The `alktype` crate compiles BAST into
+    readers/writers/validators; future codegen derives
+    language-specific implementations. Trivial or hot-path formats
+    (chunk header, tty framing) stay hand-rolled with the BAST doc as
+    the contract; complex formats (sftp) use the alktype engine or
+    codegen. Do not roll your own offset map or validator for complex
+    formats. See the alktype crate at `/workspace/@alkdev/alktype`.
 
 11. **Feature flags** — transports may be feature-gated if the need
     arises. The base crate should compile lean (no `quinn`, no `iroh`

Cargo.lock

@@ -29,7 +29,6 @@ dependencies = [
 name = "alkcall"
 version = "0.1.1"
 dependencies = [
- "alktype",
  "async-trait",
  "bytes",
  "futures",
@@ -44,16 +43,6 @@ dependencies = [
  "zeroize",
 ]
 
-[[package]]
-name = "alktype"
-version = "0.1.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a102e5ec20cc0209b7c72d4abaa2c9b4f44b72a4cee2706be98d19125c2318dc"
-dependencies = [
- "jsonschema",
- "serde_json",
-]
-
 [[package]]
 name = "allocator-api2"
 version = "0.2.21"
@@ -332,12 +321,6 @@ dependencies = [
  "foldhash",
 ]
 
-[[package]]
-name = "hashbrown"
-version = "0.17.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ed5909b6e89a2db4456e54cd5f673791d7eca6732202bbf2a9cc504fe2f9b84a"
-
 [[package]]
 name = "icu_collections"
 version = "2.2.0"
@@ -441,16 +424,6 @@ dependencies = [
  "icu_properties",
 ]
 
-[[package]]
-name = "indexmap"
-version = "2.14.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d466e9454f08e4a911e14806c24e16fba1b4c121d1ea474396f396069cf949d9"
-dependencies = [
- "equivalent",
- "hashbrown 0.17.1",
-]
-
 [[package]]
 name = "itoa"
 version = "1.0.18"
@@ -756,7 +729,7 @@ dependencies = [
  "ahash",
  "fluent-uri",
  "getrandom 0.3.4",
- "hashbrown 0.16.1",
+ "hashbrown",
  "itoa",
  "micromap",
  "parking_lot",
@@ -841,7 +814,6 @@ version = "1.0.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "c841b55ecdae098c80dcae9cf767f6f8a0c2cdb3416bbef72181df4d0fe73f14"
 dependencies = [
- "indexmap",
  "itoa",
  "memchr",
  "serde",

Cargo.toml

@@ -18,7 +18,6 @@ name = "alkcall"
 default = []
 
 [dependencies]
-alktype = "0.1.0"
 jsonschema = { version = "0.46", default-features = false }
 tokio = { version = "1", features = ["full"] }
 serde = { version = "1", features = ["derive"] }

docs/architecture/README.md

@@ -272,8 +272,8 @@ feature flags) or in the downstream alknet crate.
 - `@alkdev/alknet: docs/architecture/` — the source architecture docs
   these were ported from (renumbered from alknet ADR-001..094 to alkcall
   ADR-001..045)
-- `@alkdev/alktype` — the binary struct engine, used for channels chunk
+- `@alkdev/alktype` — the binary struct engine; compiles BAST documents
-  header layout and JSON payload schema validation
+  (e.g. `chunk-header.bast.json`) into readers/writers/validators
 - `@alkdev/pubsub` — the TypeScript EventEnvelope prior art the call
   wire format was derived from
 

docs/architecture/channels-wire.md

@@ -21,6 +21,14 @@ multiplexing on the `BiStream` the channels layer gives it.
 
 8 bytes of header, followed by `length` bytes of opaque payload.
 
+The machine-readable spec is the BAST document
+[`chunk-header.bast.json`](chunk-header.bast.json) (embedded in the
+crate as `channels::wire::CHUNK_HEADER_BAST`). BAST is plain JSON —
+any language can consume it; the `alktype` crate compiles it into
+readers/writers/validators, and future codegen derives
+language-specific implementations. The Rust implementation is
+hand-rolled (the hot path); the BAST document is the contract.
+
 | field | offset | width | meaning |
 |-------|--------|-------|---------|
 | `channel_id` | 0 | 4 (BE) | The logical channel this chunk belongs to. Channel 0 is pre-negotiated as `alk/call` (ADR-036). Channels 1..N are opened dynamically via `channel/open` (ADR-037). |

docs/architecture/chunk-header.bast.json

@@ -0,0 +1,12 @@
+{
+  "$defs": {
+    "ChunkHeader": {
+      "kind": "struct",
+      "endian": "big",
+      "fields": [
+        { "name": "channel_id", "kind": "uint32" },
+        { "name": "length", "kind": "uint32" }
+      ]
+    }
+  }
+}

docs/reviews/003-alpn-prefix-rename.md

@@ -355,7 +355,11 @@ These were checked and are correct — the rename does not affect them:
 - **No logic changes:** the rename is purely mechanical. No function
   signatures, trait bounds, or control flow change. ✓
 - **No new dependencies, no feature flag changes.** ✓
-- **`alktype` dependency unaffected.** ✓
+- **`alktype` dependency:** dropped in a follow-up commit (the only
+  usage, `alktype::validation::build_validator`, was a thin wrapper
+  over `jsonschema`; the chunk header BAST document
+  `docs/architecture/chunk-header.bast.json` carries the wire-format
+  spec without the dependency). ✓
 - **483 tests pass before the rename; they should all pass after.** ✓
 - **The `alknet/` prefix in `derive_alpn_from_op_name` is the only
   non-mechanical change** — the function's logic stays the same, only

src/channels/wire.rs

@@ -34,6 +34,17 @@ pub const MAX_CHUNK_LEN: u32 = 16 * 1024 * 1024;
 /// without an explicit open op exchange.
 pub const CHANNEL_ID_ZERO: u32 = 0;
 
+/// The chunk header's BAST (Binary Abstract Syntax Tree) document —
+/// the machine-readable wire-format spec. The canonical copy is
+/// `docs/architecture/chunk-header.bast.json`; this const embeds it so
+/// downstream Rust crates can consume it without a file lookup. BAST is
+/// plain JSON consumable by any language; the `alktype` crate compiles
+/// it into readers/writers/validators, and future codegen derives
+/// language-specific implementations from it. The hand-rolled
+/// [`parse_header`]/[`write_header`] functions are the hot path; the
+/// BAST document is the contract.
+pub const CHUNK_HEADER_BAST: &str = include_str!("../../docs/architecture/chunk-header.bast.json");
+
 /// The parsed 8-byte chunk header.
 ///
 /// `length = 0` is the EOF sentinel — the reassembled stream interprets
@@ -251,6 +262,39 @@ mod tests {
         }
     }
 
+    #[test]
+    fn chunk_header_bast_is_valid_json_and_describes_the_wire_format() {
+        let doc: serde_json::Value =
+            serde_json::from_str(CHUNK_HEADER_BAST).expect("BAST doc is valid JSON");
+        let def = doc
+            .get("$defs")
+            .and_then(|d| d.get("ChunkHeader"))
+            .expect("ChunkHeader def present");
+        assert_eq!(def.get("kind").and_then(|v| v.as_str()), Some("struct"));
+        assert_eq!(def.get("endian").and_then(|v| v.as_str()), Some("big"));
+        let fields = def
+            .get("fields")
+            .and_then(|v| v.as_array())
+            .expect("fields");
+        assert_eq!(fields.len(), 2);
+        assert_eq!(
+            fields[0].get("name").and_then(|v| v.as_str()),
+            Some("channel_id")
+        );
+        assert_eq!(
+            fields[0].get("kind").and_then(|v| v.as_str()),
+            Some("uint32")
+        );
+        assert_eq!(
+            fields[1].get("name").and_then(|v| v.as_str()),
+            Some("length")
+        );
+        assert_eq!(
+            fields[1].get("kind").and_then(|v| v.as_str()),
+            Some("uint32")
+        );
+    }
+
     #[tokio::test]
     async fn read_header_round_trips_through_duplex() {
         let (mut reader, mut writer) = tokio::io::duplex(64);

src/protocol/dispatch.rs

@@ -353,7 +353,7 @@ impl Dispatcher {
                     .registry
                     .registration(&operation_name)
                     .and_then(|r| r.spec.publish_schema.as_ref())
-                    .and_then(|schema| match alktype::validation::build_validator(schema) {
+                    .and_then(|schema| match jsonschema::options().build(schema) {
                         Ok(v) => Some(v),
                         Err(e) => {
                             warn!(