Draft builder API (ADR-009) and generalized validation validate_bytes (ADR-010) for v0.1.0

- ADR-009: fluent Rust builder producing serde_json::Value, covers
  AlkType kinds + standard JSON Schema; resolves OQ-003 (alkcall is the
  unblocking consumer)
- ADR-010: AlkTypeEngine::validate_bytes(&[u8]) as the single-call
  binary-buffer validation entry point; materialize Value from bytes,
  then validate; two methods on one struct, not a trait
- builder.md: full builder API spec (Schema, Definitions, Discriminator)
  with four usage examples (channels chunk header, call input schema,
  SFTP Packet union, OperationSpec error schemas)
- validation.md: new validate_bytes subsection + entry-point comparison
  table; AlkTypeEngine impl block updated; design decisions table updated
- overview.md: builder.md added to component pointers; 'Not a schema
  builder' scope boundary retired; ADR-009/010 added to decisions table;
  OQ-003 marked resolved; Consumers table adds alkcall as first consumer
- open-questions.md + questions/003: OQ-003 moved from deferred(scope)
  to resolved (ADR-009)
- README.md: builder doc + ADR-009/010 added; OQ-003 marked resolved;
  two new Key Design Principles (9, 10) for v0.1.0 additions

Doc-only change; 346 tests pass, clippy clean.

docs/architecture/README.md

@@ -1,6 +1,6 @@
 ---
 status: draft
-last_updated: 2026-07-22
+last_updated: 2026-08-11
 ---
 
 # alktype
@@ -18,7 +18,8 @@ format definition; the engine is generic.
 | [schema-layer.md](schema-layer.md) | draft | The 19 `AlkType:*` kinds, jsonschema custom keyword integration, TypeBox interop, schema annotations |
 | [layout-engine.md](layout-engine.md) | draft | Offset computation, the two layout modes (packed sequential vs aligned static), alignment, endianness, variable-length handling |
 | [data-access.md](data-access.md) | draft | Read/write functions, TUnion dispatch, field paths, zero-copy access, length-prefix reading |
-| [validation.md](validation.md) | draft | Custom keyword validators for all 19 `AlkType:*` kinds, `AlkTypeError`, load-time vs access-time validation, `AlkTypeEngine` |
+| [validation.md](validation.md) | draft | Custom keyword validators for all 19 `AlkType:*` kinds, `AlkTypeError`, load-time vs access-time validation, `AlkTypeEngine`; `validate_bytes` for binary buffers (ADR-010) |
+| [builder.md](builder.md) | draft | Fluent Rust API for constructing alktype JSON Schemas at runtime, producing `serde_json::Value`; covers AlkType kinds + standard JSON Schema (ADR-009) |
 
 ## Applicable ADRs
 
@@ -32,6 +33,8 @@ format definition; the engine is generic.
 | [006](decisions/006-reject-non-final-inline-length-prefixed-in-aligned-mode.md) | Reject Non-Final Inline Length-Prefixed Variable Fields in Aligned Mode | Prevents silent data corruption (inline variable data clobbering subsequent fields) |
 | [007](decisions/007-packed-mode-read-factory.md) | Packed-Mode Read API — Engine as SequentialReader Factory | `engine.sequential_reader()` returns an owned reader, not a reference |
 | [008](decisions/008-reject-tunion-in-aligned-mode.md) | Reject TUnion in Aligned Mode for v1 | Unions are the protocol pattern; aligned-mode union semantics were broken |
+| [009](decisions/009-builder-api.md) | Builder API for Schema Construction | Fluent Rust API producing `serde_json::Value`; covers AlkType kinds + standard JSON Schema; resolves OQ-003 |
+| [010](decisions/010-generalized-validation-validate-bytes.md) | Generalized Validation — `validate_bytes` on `AlkTypeEngine` | Single-call binary-buffer validation; materialize `Value` from bytes, then validate; two methods on one struct, not a trait |
 
 ## Relevant Open Questions
 
@@ -39,7 +42,7 @@ format definition; the engine is generic.
 |----|-------|--------|-----------|
 | OQ-001 | Arrays of variable-length-element structs | deferred(scope) | Requires lazy walking logic; blocked on a concrete consumer that needs it |
 | OQ-002 | `no_std` + `alloc` support | deferred(scope) | Target `std` for v1; blocked on an embedded use case |
-| OQ-003 | Builder API for schema construction | deferred(scope) | Schemas are authored in TypeBox or hand-written JSON for v1; blocked on a concrete need |
+| OQ-003 | Builder API for schema construction | resolved (ADR-009) | Resolved in v0.1.0; alkcall is the concrete consumer; see [builder.md](builder.md) |
 
 ## Key Design Principles
 
@@ -95,6 +98,21 @@ format definition; the engine is generic.
    with a known schema, use alktype. See [overview.md](overview.md) and
    [ADR-001](decisions/001-alktype-purpose-scope-jsonschema-engine.md).
 
+9. **Schemas can be built at runtime from Rust (v0.1.0).** A fluent
+   builder API produces `serde_json::Value` for both AlkType-kind
+   schemas and standard JSON Schema, covering alkcall's two roles
+   (binary layout + JSON payloads) from one module. The builder is
+   additive — consumers with static schemas continue to load JSON.
+   See [builder.md](builder.md) and [ADR-009](decisions/009-builder-api.md).
+
+10. **Two validation entry points, one engine (v0.1.0).**
+    `validate_json(&Value)` for already-parsed JSON (call's payloads);
+    `validate_bytes(&[u8])` for binary buffers (channels' chunk header).
+    Same underlying `jsonschema` validator; the bytes path materializes
+    a `Value` tree via the layout engine, then validates. See
+    [validation.md](validation.md) and
+    [ADR-010](decisions/010-generalized-validation-validate-bytes.md).
+
 ## References
 
 - `@alkdev/alknet: docs/research/alknet-typedef/findings.md` — POC results