Mizan-Rust backend adapter: server-side substrate + three-way parity

Adds first-class Rust-backed Mizan to sit alongside mizan-django and
mizan-fastapi. A Rust dev writes:

    #[derive(Mizan, Serialize, Deserialize)]
    pub struct ProfileOutput { pub user_id: i64, pub name: String }

    #[mizan::context("user")]
    pub struct UserCtx;

    #[mizan::client(context = UserCtx)]
    pub async fn user_profile(_req: &RequestHandle<'_>, user_id: i64) -> ProfileOutput { ... }

…and gets byte-identical KDL to the Python emitters, served over the
same wire protocol the React / Rust / Vue / Svelte kernels speak.

New crates:
- cores/mizan-rust/         (Cargo: mizan-core)     — IR types, KDL emitter, traits, registry,
                                                       runtime (compute_invalidation / compute_merges
                                                       ported from mizan-fastapi), graph_check with
                                                       structural type-matching
- cores/mizan-rust-macros/  (Cargo: mizan-macros)   — #[derive(Mizan)], #[mizan::context],
                                                       #[mizan::client] proc macros
- backends/mizan-rust-axum/ (Cargo: mizan-axum)     — axum HTTP adapter: /session/, /call/, /ctx/:name/
- tests/afi/rust_app/                                — AFI fixture port + server / export-ir binaries

Substrate-shape moves required by cross-language equivalence:
- IR canonicalization: functions / contexts / context-members / shared-by
  now sort alphabetically in both Python and Rust emitters. The IR is a
  contract; linkme doesn't preserve declaration order, so canonical sort
  is the only stable mapping. afi_ir.kdl + per-target baselines regenerated.
- MizanType::TYPE_NAME is a const (with a default type_name() reader) so
  it's usable in linkme TypeEntry static initializers.
- Tree-shaken type registry: #[derive(Mizan)] only emits the trait impl;
  the #[mizan::client] macro registers canonical-named entries from
  fn signatures, including Vec<T> element types for ref resolution.
- Merge resolution is structural (NamedType shape comparison) rather than
  by name — matches the Python types_match_for_merge semantics.

Three-way forcing functions:
- tests/afi/test_codegen_parity.py — Django ≡ FastAPI ≡ Rust on KDL bytes (3 pass)
- tests/rust/run_wire_parity.py    — 12/12 probes against FastAPI + Rust (EXIT=0)

Incidental fixes surfaced by the new tests:
- Stale `from .registry import validate_registry` import removed from
  mizan-django/setup/discovery.py (referenced a function that no longer
  exists; was masking codegen-parity).
- BASE_DIR added to tests/afi/django_app/project/settings.py.
- /session/ endpoint added to mizan-fastapi for protocol-shaped readiness
  probe parity (wire-parity harness now polls /api/mizan/session/ on both
  backends rather than FastAPI's /openapi.json).
- Root .gitignore picks up Rust target/ across the tree so new crates
  don't need per-crate gitignore.

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

cores/mizan-rust/tests/afi_parity.rs

@@ -0,0 +1,129 @@
+//! Byte-equivalence: the Rust KDL emitter (driven by the proc macros)
+//! against `protocol/mizan-codegen/tests/fixtures/afi_ir.kdl` (canonical
+//! Python-emitted reference).
+//!
+//! This is the Phase-2 verifier — the AFI fixture is authored against the
+//! real consumer surface (`#[derive(Mizan)] / #[mizan::context] /
+//! #[mizan::client]`), not hand-built static specs.
+
+use mizan_core as mizan;
+use mizan_core::prelude::*;
+use mizan_core::RequestHandle;
+use serde::{Deserialize, Serialize};
+use std::path::PathBuf;
+
+// ─── Output / shared types ──────────────────────────────────────────────────
+
+#[derive(Mizan, Serialize, Deserialize, Debug, Clone)]
+pub struct EchoOutput {
+    pub message: String,
+}
+
+#[derive(Mizan, Serialize, Deserialize, Debug, Clone)]
+pub struct WhoamiOutput {
+    pub email: String,
+    pub authenticated: bool,
+}
+
+#[derive(Mizan, Serialize, Deserialize, Debug, Clone)]
+pub struct ProfileOutput {
+    pub user_id: i64,
+    pub name: String,
+}
+
+#[derive(Mizan, Serialize, Deserialize, Debug, Clone)]
+pub struct OrderOutput {
+    pub id: i64,
+    pub user_id: i64,
+    pub total: i64,
+}
+
+#[derive(Mizan, Serialize, Deserialize, Debug, Clone)]
+pub struct StatusOutput {
+    pub ok: bool,
+}
+
+#[mizan::context("user")]
+pub struct UserCtx;
+
+// ─── Fixture functions (mirroring tests/afi/fixture.py) ────────────────────
+
+#[mizan::client]
+pub async fn echo(_req: &RequestHandle<'_>, text: String) -> EchoOutput {
+    EchoOutput {
+        message: format!("echo: {text}"),
+    }
+}
+
+#[mizan::client]
+pub async fn whoami(_req: &RequestHandle<'_>) -> WhoamiOutput {
+    WhoamiOutput {
+        email: "anon@example.com".into(),
+        authenticated: false,
+    }
+}
+
+#[mizan::client(context = UserCtx)]
+pub async fn user_profile(_req: &RequestHandle<'_>, user_id: i64) -> ProfileOutput {
+    ProfileOutput {
+        user_id,
+        name: "placeholder".into(),
+    }
+}
+
+#[mizan::client(context = UserCtx)]
+pub async fn user_orders(_req: &RequestHandle<'_>, _user_id: i64) -> Vec<OrderOutput> {
+    vec![]
+}
+
+#[mizan::client(affects = UserCtx)]
+pub async fn update_profile(
+    _req: &RequestHandle<'_>,
+    _user_id: i64,
+    _name: String,
+) -> StatusOutput {
+    StatusOutput { ok: true }
+}
+
+#[mizan::client]
+pub async fn find_user(_req: &RequestHandle<'_>, _user_id: i64) -> Option<ProfileOutput> {
+    None
+}
+
+#[mizan::client(merge = UserCtx)]
+pub async fn rename_user(
+    _req: &RequestHandle<'_>,
+    user_id: i64,
+    name: String,
+) -> ProfileOutput {
+    ProfileOutput { user_id, name }
+}
+
+// ─── The byte-equivalence test ──────────────────────────────────────────────
+
+fn canonical_kdl_path() -> PathBuf {
+    PathBuf::from(env!("CARGO_MANIFEST_DIR"))
+        .join("../../protocol/mizan-codegen/tests/fixtures/afi_ir.kdl")
+}
+
+#[test]
+fn build_ir_matches_canonical_afi_kdl() {
+    let expected = std::fs::read_to_string(canonical_kdl_path()).expect("read canonical KDL");
+    let actual = mizan_core::build_ir();
+
+    if actual != expected {
+        for (lineno, (a, b)) in actual.lines().zip(expected.lines()).enumerate() {
+            if a != b {
+                panic!(
+                    "KDL diverges at line {}:\n  expected: {b:?}\n  actual:   {a:?}",
+                    lineno + 1,
+                );
+            }
+        }
+        panic!(
+            "KDL diverges in length: actual_len={} expected_len={}",
+            actual.len(),
+            expected.len(),
+        );
+    }
+}