mizan-tauri + Pydantic-aware codegen: Tauri-as-Mizan-backend substrate

Tauri now joins FastAPI/Django/axum as a first-class Mizan backend. The
React frontend calls Mizan-registered functions through Tauri's IPC
with the same {result, invalidate, merge} envelope the HTTP path uses;
the schema flows Pydantic → decoru → Rust → KDL → TS in one
mizan-generate invocation.

New packages:
* backends/mizan-tauri — Tauri plugin exposing a single `mizan_invoke`
  command that routes through mizan-core's FUNCTIONS / CONTEXTS
  registries. No per-function tauri::command; the linkme slice IS the
  dispatch table.
* frontends/mizan-tauri-transport — TS package exporting
  tauriTransport() that wraps invoke('plugin:mizan|mizan_invoke', ...)
  and re-shapes errors into MizanError. Pairs with mizan-tauri.

@mizan/base — pluggable transport:
* Adds MizanTransport interface + transport config field.
* Existing fetch-based body factored into httpTransport() (default).
* mizanCall/mizanFetch delegate to config.transport; merge/invalidate
  side-effects stay in the kernel (transport-agnostic).
* Consumers swap via configure({ transport: tauriTransport() }).

mizan-codegen — Rust source + Pydantic pre-step:
* [source.rust] runs a Cargo bin (cargo run --bin <name>) and parses
  KDL from stdout. The bin uses mizan_core::build_ir() after
  force-linking the consumer's #[derive(Mizan)] / #[mizan::client]
  registrations.
* [source.rust.pydantic] is an optional pre-step that pipes an
  embedded Python bridge (scripts/run_decoru.py) to python and writes
  decoru-emitted Rust types into the consumer crate. The bridge
  auto-discovers BaseModel subclasses AND Enum subclasses
  (last-variant-is-default convention so decoru's impl Default keeps
  compiling against enum-typed fields without explicit Pydantic
  defaults).
* Pure-Rust usage stays intact — omit pydantic block and write Rust
  types by hand.

mizan-macros:
* #[mizan::client] now supports Result<T, MizanError> returns. The
  dispatch wrapper `?`-unwraps the user fn so server-side errors
  surface as the protocol's standard {code, message, details?}
  envelope; T-returning functions stay unchanged.
* #[derive(Mizan)] strips the r# raw-identifier prefix and honors
  field-level #[serde(rename = "...")] when emitting IR field names.
  Matches serde's wire shape — fixes IR-vs-JSON drift for Rust-keyword
  fields (e.g. `r#type` → `type`).

react.tsx template:
* Conditionally emits context-related imports / useContextSubscription
  helper based on has_global || !named_contexts.is_empty(). Consumers
  without contexts (mutation/RPC-only apps like claude-manage) no
  longer get dead imports that trip noUnusedLocals.

Verified end-to-end: cargo build clean across mizan-tauri,
mizan-codegen, AFI rust_app; AFI three-way KDL parity tests pass;
claude-manage migration drives the full stack (Pydantic schema →
generated TS api → Tauri-IPC transport → mizan-core dispatch).

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

backends/mizan-tauri/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "mizan-tauri"
+version = "0.1.0"
+edition = "2021"
+description = "Tauri backend adapter for Mizan — typed RPC dispatch over Tauri's IPC. Single `mizan_invoke` command routes through mizan-core's compile-time function registry."
+license = "MIT"
+
+[dependencies]
+mizan-core = { path = "../../cores/mizan-rust" }
+tauri = { version = "2", features = [] }
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"

backends/mizan-tauri/src/lib.rs

@@ -0,0 +1,220 @@
+//! Mizan Tauri adapter — typed RPC dispatch over Tauri's IPC.
+//!
+//! Ships as a Tauri plugin. The consumer installs it with one line:
+//!
+//! ```ignore
+//! tauri::Builder::default()
+//!     .plugin(mizan_tauri::init())
+//!     .run(tauri::generate_context!())
+//!     .expect("error while running tauri application");
+//! ```
+//!
+//! The plugin exposes a single command `mizan_invoke` (full Tauri name
+//! `plugin:mizan|mizan_invoke`). The JS-side `@mizan/tauri-transport`
+//! sends call/fetch envelopes to it; the dispatch routes through
+//! `mizan-core`'s FUNCTIONS / CONTEXTS registries — the same
+//! linkme-backed distributed slices the HTTP adapter (mizan-rust-axum)
+//! consumes. There is no per-function tauri::command; the registry IS
+//! the dispatch table.
+//!
+//! Wire envelope:
+//!
+//! ```json
+//! { "op": "call",  "fn": "list_sessions", "args": {} }
+//! { "op": "fetch", "context": "session",  "params": {} }
+//! ```
+//!
+//! Response shapes mirror POST /call/ and GET /ctx/.../ from
+//! mizan-rust-axum:
+//!
+//! * `call`  → `{ result, invalidate, merge? }`
+//! * `fetch` → `{ <fnName>: <result>, ... }` (a flat bundle)
+//!
+//! Error responses come back as the `Err` variant of the Tauri command's
+//! `Result`, which Tauri serializes into the JS-side `Promise.reject`.
+//! The TS-side transport re-wraps it into a `MizanError` so consumers
+//! see one error surface regardless of transport.
+
+use mizan_core::{
+    compute_invalidation, compute_merges, lookup_context, lookup_function,
+    FunctionSpec, InvalidationTarget, MergeEntry, MizanError, RequestHandle, FUNCTIONS,
+};
+use serde::{Deserialize, Serialize};
+use serde_json::{json, Map, Value};
+use tauri::{
+    plugin::{Builder, TauriPlugin},
+    Runtime,
+};
+
+/// Build the Mizan Tauri plugin. Install with `.plugin(mizan_tauri::init())`
+/// on the `tauri::Builder`. The plugin name is `mizan`; the dispatch
+/// command is reachable from JS as `plugin:mizan|mizan_invoke`.
+pub fn init<R: Runtime>() -> TauriPlugin<R> {
+    Builder::<R>::new("mizan")
+        .invoke_handler(tauri::generate_handler![mizan_invoke])
+        .build()
+}
+
+// === Wire envelope ===
+
+/// One Mizan request. The JS-side transport sends `{ envelope: ... }`;
+/// Tauri's serde deserializer pulls this struct out of the `envelope`
+/// field of the invoke payload.
+#[derive(Debug, Deserialize)]
+#[serde(tag = "op")]
+pub enum Envelope {
+    #[serde(rename = "call")]
+    Call {
+        /// Wire-level function name — registered name on the Rust side.
+        #[serde(rename = "fn")]
+        function_name: String,
+        #[serde(default)]
+        args: Map<String, Value>,
+    },
+    #[serde(rename = "fetch")]
+    Fetch {
+        context: String,
+        #[serde(default)]
+        params: Map<String, Value>,
+    },
+}
+
+/// Error payload returned to the frontend. Mirrors the HTTP adapter's
+/// `{"code", "message", "details?"}` shape; the TS-side transport reads
+/// this and constructs a `MizanError`.
+#[derive(Debug, Serialize)]
+pub struct ErrorPayload {
+    pub code: &'static str,
+    pub message: String,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub details: Option<Value>,
+}
+
+impl From<MizanError> for ErrorPayload {
+    fn from(e: MizanError) -> Self {
+        let details = if let MizanError::ValidationFailed { details, .. } = &e {
+            Some(details.clone())
+        } else {
+            None
+        };
+        Self {
+            code: e.code(),
+            message: e.message().to_string(),
+            details,
+        }
+    }
+}
+
+// === Dispatch ===
+
+/// The single Mizan dispatch command. Registered on the plugin's invoke
+/// handler — the consumer never wires it directly.
+///
+/// `app: AppHandle` is auto-injected by Tauri; the function body borrows
+/// it into a `RequestHandle` so `#[mizan::client]` functions can
+/// `req.downcast::<tauri::AppHandle>()` for app-managed state or event
+/// emission. Stateless functions ignore the handle.
+#[tauri::command]
+async fn mizan_invoke<R: Runtime>(
+    app: tauri::AppHandle<R>,
+    envelope: Envelope,
+) -> Result<Value, ErrorPayload> {
+    match envelope {
+        Envelope::Call {
+            function_name,
+            args,
+        } => handle_call(&app, &function_name, args).await,
+        Envelope::Fetch { context, params } => handle_fetch(&app, &context, params).await,
+    }
+}
+
+async fn handle_call<R: Runtime>(
+    app: &tauri::AppHandle<R>,
+    fn_name: &str,
+    args: Map<String, Value>,
+) -> Result<Value, ErrorPayload> {
+    let fn_spec = lookup_function(fn_name).ok_or_else(|| {
+        ErrorPayload::from(MizanError::NotFound(format!(
+            "function {fn_name:?} not registered"
+        )))
+    })?;
+
+    let req = RequestHandle::new(app);
+    let result = fn_spec
+        .dispatch(req, Value::Object(args.clone()))
+        .await
+        .map_err(ErrorPayload::from)?;
+
+    let invalidate: Vec<Value> = compute_invalidation(fn_spec, &args)
+        .iter()
+        .map(InvalidationTarget::to_json)
+        .collect();
+    let merges = compute_merges(fn_spec, &args, &result);
+    let merge_payload: Option<Vec<Value>> = if merges.is_empty() {
+        None
+    } else {
+        Some(merges.iter().map(MergeEntry::to_json).collect())
+    };
+
+    let mut payload = json!({
+        "result": result,
+        "invalidate": invalidate,
+    });
+    if let Some(merge) = merge_payload {
+        payload
+            .as_object_mut()
+            .expect("payload is a JSON object")
+            .insert("merge".into(), Value::Array(merge));
+    }
+    Ok(payload)
+}
+
+async fn handle_fetch<R: Runtime>(
+    app: &tauri::AppHandle<R>,
+    context_name: &str,
+    params: Map<String, Value>,
+) -> Result<Value, ErrorPayload> {
+    if lookup_context(context_name).is_none() {
+        return Err(ErrorPayload::from(MizanError::NotFound(format!(
+            "context {context_name:?} not registered"
+        ))));
+    }
+
+    let members: Vec<&dyn FunctionSpec> = FUNCTIONS
+        .iter()
+        .copied()
+        .filter(|f| f.context() == Some(context_name))
+        .collect();
+    if members.is_empty() {
+        return Err(ErrorPayload::from(MizanError::NotFound(format!(
+            "context {context_name:?} has no registered members"
+        ))));
+    }
+
+    let mut bundled = Map::new();
+    for fn_spec in &members {
+        let args = filter_args(*fn_spec, &params);
+        let req = RequestHandle::new(app);
+        let result = fn_spec
+            .dispatch(req, Value::Object(args))
+            .await
+            .map_err(ErrorPayload::from)?;
+        bundled.insert(fn_spec.name().to_string(), result);
+    }
+
+    Ok(Value::Object(bundled))
+}
+
+/// Filter the envelope's params down to keys this function declares as
+/// input. The HTTP/axum adapter coerces string-typed query params to
+/// JSON primitives in the equivalent step; the Tauri arg channel already
+/// carries typed JSON, so the filter is sufficient on its own.
+fn filter_args(fn_spec: &dyn FunctionSpec, params: &Map<String, Value>) -> Map<String, Value> {
+    let mut out = Map::new();
+    for ip in fn_spec.input_params() {
+        if let Some(v) = params.get(ip.name) {
+            out.insert(ip.name.into(), v.clone());
+        }
+    }
+    out
+}

cores/mizan-rust-macros/src/derive.rs

@@ -142,7 +142,14 @@ fn emit_struct(s: &DataStruct) -> TokenStream {
             .ident
             .as_ref()
             .expect("named field always has an ident");
-        let name = ident.to_string();
+        // Field-level `#[serde(rename = "...")]` wins; otherwise strip
+        // the raw-identifier prefix that Rust uses to escape keywords
+        // (`r#type` → `type`). Serde itself strips the prefix when
+        // computing the default field name; the IR has to match the
+        // wire form, not the Rust source form.
+        let raw_ident = ident.to_string();
+        let stripped = raw_ident.strip_prefix("r#").unwrap_or(&raw_ident);
+        let name = serde_rename(&field.attrs).unwrap_or_else(|| stripped.to_string());
         let shape = type_shape_expr(&field.ty);
 
         // A field is `required` iff its type is not `Option<...>`. Defaults

cores/mizan-rust-macros/src/function.rs

@@ -353,7 +353,13 @@ pub fn expand(args: FunctionArgs, item: ItemFn) -> TokenStream {
     let output_nullable = analysis.nullable;
     let private = args.private;
 
-    let dispatch_body = build_dispatch(&item, &input_args, has_input, &input_type_ident);
+    let dispatch_body = build_dispatch(
+        &item,
+        &input_args,
+        has_input,
+        &input_type_ident,
+        analysis.returns_result,
+    );
 
     quote! {
         // Keep the user's original fn intact — the macro never rewrites the
@@ -454,8 +460,18 @@ fn build_dispatch(
     input_args: &[InputArg],
     has_input: bool,
     input_type_ident: &syn::Ident,
+    returns_result: bool,
 ) -> TokenStream {
     let inner = &item.sig.ident;
+    // When the user returns `Result<T, MizanError>`, lift Err out into the
+    // dispatch wrapper's outer Result so the HTTP/IPC adapter can surface
+    // it as the standard error envelope. When the user returns `T`,
+    // serialize directly — the substrate has no error path for them.
+    let unwrap_user_result = if returns_result {
+        quote! { ? }
+    } else {
+        TokenStream::new()
+    };
     if has_input {
         let arg_names: Vec<_> = input_args.iter().map(|a| &a.ident).collect();
         quote! {
@@ -467,7 +483,7 @@ fn build_dispatch(
             let result = #inner(
                 &req,
                 #( validated.#arg_names ),*
-            ).await;
+            ).await #unwrap_user_result;
             ::mizan_core::__priv::serde_json::to_value(&result)
                 .map_err(|e| ::mizan_core::MizanError::InternalError(
                     format!("output serialization failed: {e}"),
@@ -476,7 +492,7 @@ fn build_dispatch(
     } else {
         quote! {
             let _ = args;
-            let result = #inner(&req).await;
+            let result = #inner(&req).await #unwrap_user_result;
             ::mizan_core::__priv::serde_json::to_value(&result)
                 .map_err(|e| ::mizan_core::MizanError::InternalError(
                     format!("output serialization failed: {e}"),

cores/mizan-rust-macros/src/shape.rs

@@ -16,20 +16,32 @@ pub struct ReturnAnalysis {
     pub is_vec: bool,
     /// When `is_vec`, this is the element type `T`.
     pub vec_inner: Option<Type>,
+    /// True when the user's return type is `Result<T, MizanError>` — the
+    /// dispatch wrapper emits `?` so user-side errors bubble out as
+    /// `MizanError` instead of being serialized into the success payload.
+    /// The IR sees only the `T` side; the error variant is the substrate's
+    /// invariant, not part of the output shape.
+    pub returns_result: bool,
 }
 
 pub fn analyze_return(ty: &Type) -> ReturnAnalysis {
-    let (inner, nullable) = if let Some(t) = unwrap_option(ty) {
-        (t, true)
+    let (effective, returns_result) = if let Some(ok) = unwrap_result_ok(ty) {
+        (ok, true)
     } else {
         (ty.clone(), false)
     };
+    let (inner, nullable) = if let Some(t) = unwrap_option(&effective) {
+        (t, true)
+    } else {
+        (effective, false)
+    };
     if let Some(elem) = unwrap_vec(&inner) {
         ReturnAnalysis {
             inner: inner.clone(),
             nullable,
             is_vec: true,
             vec_inner: Some(elem),
+            returns_result,
         }
     } else {
         ReturnAnalysis {
@@ -37,10 +49,27 @@ pub fn analyze_return(ty: &Type) -> ReturnAnalysis {
             nullable,
             is_vec: false,
             vec_inner: None,
+            returns_result,
         }
     }
 }
 
+/// If `ty` is `Result<T, E>`, return `T`. Otherwise None. The substrate
+/// only honors `Result<T, MizanError>`; the macro doesn't try to verify
+/// `E` here — it lets rustc raise the type-mismatch at the `?` site if
+/// the consumer used a non-MizanError variant.
+pub fn unwrap_result_ok(ty: &Type) -> Option<Type> {
+    let path = match ty {
+        Type::Path(TypePath { qself: None, path }) => path,
+        _ => return None,
+    };
+    let last = path.segments.last()?;
+    if last.ident != "Result" {
+        return None;
+    }
+    extract_single_generic(&last.arguments)
+}
+
 /// Emit a `TypeShape` const-expression for `ty`. Used inside `#[derive(Mizan)]`
 /// when constructing the struct field shapes.
 pub fn type_shape_expr(ty: &Type) -> TokenStream {

frontends/mizan-base/src/index.ts

@@ -30,6 +30,39 @@ export class MizanError extends Error {
     }
 }
 
+// === Transport ===
+
+/**
+ * Wire surface the kernel uses to reach a Mizan backend. The default
+ * implementation is `httpTransport()` (POST /call/, GET /ctx/). Tauri
+ * apps swap in `tauriTransport()` from `@mizan/tauri-transport`. Any
+ * future transport — workers, edge runtimes, channels — implements this
+ * interface and replaces the default via `configure({ transport })`.
+ */
+export interface MizanTransport {
+    /** RPC dispatch — invokes a Mizan-registered function. */
+    call(
+        fnName: string,
+        args: Record<string, any>,
+    ): Promise<MizanCallResponse>
+    /** Context-bundle fetch — invokes a Mizan-registered context. */
+    fetch(
+        contextName: string,
+        params?: Record<string, any>,
+    ): Promise<any>
+}
+
+/**
+ * Raw envelope a transport returns from `call()`. The kernel uses the
+ * `merge` and `invalidate` arrays to drive client-side cache updates;
+ * `result` is the function's typed return value.
+ */
+export interface MizanCallResponse {
+    result: any
+    invalidate?: Array<string | { context: string; params?: Record<string, any> } | { function: string }>
+    merge?: Array<{ context: string; slot: string; value: unknown; params?: Record<string, any> }>
+}
+
 // === Configuration ===
 
 interface MizanConfig {
@@ -45,6 +78,13 @@ interface MizanConfig {
      * this onto the schema-advertised capability surface.
      */
     session: boolean
+    /**
+     * Wire transport. Defaults to `httpTransport()` (fetch-based,
+     * compatible with FastAPI / Django backends). Swap with a custom
+     * transport (e.g. `tauriTransport()`) at app entry to route
+     * Mizan calls through a different channel.
+     */
+    transport: MizanTransport
 }
 
 const config: MizanConfig = {
@@ -53,6 +93,8 @@ const config: MizanConfig = {
     csrfCookieName: 'csrftoken',
     csrfHeaderName: 'X-CSRFToken',
     session: true,
+    // Initialized below once httpTransport is defined.
+    transport: null as unknown as MizanTransport,
 }
 
 export function configure(opts: Partial<MizanConfig>): void {
@@ -344,42 +386,68 @@ async function resolveHeaders(): Promise<Record<string, string>> {
     }
 }
 
+/**
+ * Default Mizan transport — POST `${baseUrl}/call/` and GET
+ * `${baseUrl}/ctx/${name}/`. Compatible with `mizan-fastapi`,
+ * `mizan-django`, and `mizan-rust-axum`. Swap with a different
+ * transport via `configure({ transport })` when running in a
+ * non-HTTP host (e.g. Tauri).
+ */
+export function httpTransport(): MizanTransport {
+    return {
+        async call(functionName, args) {
+            const headers = await resolveHeaders()
+            headers['Content-Type'] = 'application/json'
+
+            const res = await fetch(`${config.baseUrl}/call/`, {
+                method: 'POST',
+                headers,
+                credentials: 'same-origin',
+                body: JSON.stringify({ fn: functionName, args }),
+            })
+            if (!res.ok) throw new MizanError(res.status, await res.text())
+            return res.json()
+        },
+        async fetch(contextName, params) {
+            const url = new URL(
+                `${config.baseUrl}/ctx/${contextName}/`,
+                typeof globalThis.location !== 'undefined'
+                    ? globalThis.location.origin
+                    : 'http://localhost',
+            )
+            if (params) {
+                for (const [k, v] of Object.entries(params)) {
+                    url.searchParams.set(k, String(v))
+                }
+            }
+            const headers = await resolveHeaders()
+            const res = await fetchWithRetry(url.toString(), {
+                headers,
+                credentials: 'same-origin',
+            })
+            if (!res.ok) throw new MizanError(res.status, await res.text())
+            return res.json()
+        },
+    }
+}
+
+// Install the default transport now that httpTransport is in scope. The
+// config object was constructed earlier with a placeholder so the type
+// stayed honest; this line is the actual binding.
+config.transport = httpTransport()
+
 export async function mizanFetch(
     contextName: string,
     params?: Record<string, any>,
 ): Promise<any> {
-    const url = new URL(
-        `${config.baseUrl}/ctx/${contextName}/`,
-        typeof globalThis.location !== 'undefined' ? globalThis.location.origin : 'http://localhost',
-    )
-    if (params) {
-        for (const [k, v] of Object.entries(params)) {
-            url.searchParams.set(k, String(v))
-        }
-    }
-
-    const headers = await resolveHeaders()
-    const res = await fetchWithRetry(url.toString(), { headers, credentials: 'same-origin' })
-    if (!res.ok) throw new MizanError(res.status, await res.text())
-    return res.json()
+    return config.transport.fetch(contextName, params)
 }
 
 export async function mizanCall(
     functionName: string,
     args: Record<string, any>,
 ): Promise<any> {
-    const headers = await resolveHeaders()
-    headers['Content-Type'] = 'application/json'
-
-    const res = await fetch(`${config.baseUrl}/call/`, {
-        method: 'POST',
-        headers,
-        credentials: 'same-origin',
-        body: JSON.stringify({ fn: functionName, args }),
-    })
-    if (!res.ok) throw new MizanError(res.status, await res.text())
-
-    const data = await res.json()
+    const data = await config.transport.call(functionName, args)
 
     // Server-driven merges run before invalidations so a context that is
     // both merged-into and invalidated ends in the invalidation state — the
@@ -395,9 +463,12 @@ export async function mizanCall(
         for (const entry of data.invalidate) {
             if (typeof entry === 'string') {
                 invalidate(entry)
-            } else {
+            } else if ('context' in entry) {
                 invalidate(entry.context, entry.params)
             }
+            // {function: name} entries route through the kernel's
+            // function-output cache layer, which lives in the framework
+            // adapter; mizan-base treats them as a no-op here.
         }
     }
 

frontends/mizan-tauri-transport/package.json

@@ -0,0 +1,15 @@
+{
+  "name": "@mizan/tauri-transport",
+  "version": "0.1.0",
+  "description": "Mizan transport adapter routing calls through Tauri's IPC instead of HTTP. Paired with the `mizan-tauri` Rust plugin.",
+  "type": "module",
+  "main": "src/index.ts",
+  "exports": {
+    ".": "./src/index.ts"
+  },
+  "peerDependencies": {
+    "@mizan/base": "*",
+    "@tauri-apps/api": "^2"
+  },
+  "license": "MIT"
+}

frontends/mizan-tauri-transport/src/index.ts

@@ -0,0 +1,81 @@
+/**
+ * @mizan/tauri-transport — routes Mizan calls through Tauri's IPC
+ * instead of HTTP fetch. Paired with the `mizan-tauri` Rust plugin
+ * (which exposes a single `mizan_invoke` command).
+ *
+ * Usage:
+ *
+ *   import { configure } from '@mizan/base'
+ *   import { tauriTransport } from '@mizan/tauri-transport'
+ *
+ *   configure({ transport: tauriTransport() })
+ *
+ * The transport keeps the same protocol surface as the HTTP transport
+ * (call/fetch envelopes, {result, invalidate, merge} response shape),
+ * so the codegen output and React adapter are unchanged — only the
+ * wire channel differs.
+ */
+
+import { invoke } from '@tauri-apps/api/core'
+import { MizanError, type MizanCallResponse, type MizanTransport } from '@mizan/base'
+
+/** Plugin-prefixed Tauri command — `init()` on the Rust side installs
+ * the plugin under the name `mizan`, so the dispatch command is
+ * reachable from JS as `plugin:mizan|mizan_invoke`. */
+const COMMAND = 'plugin:mizan|mizan_invoke'
+
+type TauriError = {
+    code?: string
+    message?: string
+    details?: unknown
+}
+
+/**
+ * Wrap a `mizan-tauri` error payload into a `MizanError` so consumers
+ * see one error surface regardless of transport. Tauri's invoke()
+ * rejects with the raw `Err` payload from the Rust command; we re-shape
+ * it to the same `{error: {code, message, details}}` envelope the HTTP
+ * transport surfaces.
+ */
+function wrapError(raw: unknown): MizanError {
+    if (raw && typeof raw === 'object') {
+        const err = raw as TauriError
+        const body = JSON.stringify({ error: { code: err.code, message: err.message, details: err.details } })
+        // 0 means "no HTTP status" — the IPC transport bypassed the
+        // protocol's HTTP layer. The error envelope still carries
+        // .code/.message/.details so consumers don't have to special-case.
+        return new MizanError(0, body)
+    }
+    return new MizanError(0, JSON.stringify({ error: { message: String(raw) } }))
+}
+
+/**
+ * Build a Mizan transport that routes through Tauri's IPC. Install via:
+ *
+ *   import { configure } from '@mizan/base'
+ *   import { tauriTransport } from '@mizan/tauri-transport'
+ *   configure({ transport: tauriTransport() })
+ */
+export function tauriTransport(): MizanTransport {
+    return {
+        async call(fnName, args): Promise<MizanCallResponse> {
+            try {
+                const data = await invoke<MizanCallResponse>(COMMAND, {
+                    envelope: { op: 'call', fn: fnName, args },
+                })
+                return data
+            } catch (e) {
+                throw wrapError(e)
+            }
+        },
+        async fetch(contextName, params) {
+            try {
+                return await invoke(COMMAND, {
+                    envelope: { op: 'fetch', context: contextName, params: params ?? {} },
+                })
+            } catch (e) {
+                throw wrapError(e)
+            }
+        },
+    }
+}

protocol/mizan-codegen/scripts/run_decoru.py

@@ -0,0 +1,136 @@
+#!/usr/bin/env python3
+"""Pydantic → Rust codegen helper invoked by mizan-codegen's
+`[source.rust.pydantic]` step.
+
+Reads a JSON payload from argv[1] with keys:
+  - module:  Python module to import (e.g. "claude_manage.schema")
+  - output:  Path to write the generated Rust file
+  - derives: List of derive identifiers to apply to every emitted item
+  - header:  Optional file prefix (e.g. an AUTO-GENERATED warning)
+
+Discovers every BaseModel subclass declared in the module (handled by
+decoru) AND every Enum subclass declared there (handled inline — decoru
+itself is scoped to BaseModel). Writes one Rust file containing both.
+
+Bundled with the mizan-codegen binary (include_str!) and piped to
+`python -` at codegen time — no install step beyond decoru being
+importable in the python environment.
+"""
+
+import importlib
+import inspect
+import json
+import sys
+import textwrap
+from enum import Enum
+from pathlib import Path
+
+from pydantic import BaseModel  # type: ignore[import-untyped]
+
+from decoru import emit_rust_struct, walk_pydantic_model  # type: ignore[import-untyped]
+
+
+def _declared_in(module, obj) -> bool:
+    return getattr(obj, "__module__", None) == module.__name__
+
+
+def discover_models(module) -> list[type[BaseModel]]:
+    """BaseModel subclasses declared in this module. Imported helpers are
+    skipped — only own-module declarations qualify."""
+    return [
+        obj
+        for _, obj in inspect.getmembers(module, inspect.isclass)
+        if issubclass(obj, BaseModel)
+        and obj is not BaseModel
+        and _declared_in(module, obj)
+    ]
+
+
+def discover_enums(module) -> list[type[Enum]]:
+    """Enum subclasses declared in this module. Filters out the
+    framework's own Enum class and anything imported from elsewhere."""
+    return [
+        obj
+        for _, obj in inspect.getmembers(module, inspect.isclass)
+        if issubclass(obj, Enum) and obj is not Enum and _declared_in(module, obj)
+    ]
+
+
+def _pascal_case(s: str) -> str:
+    return "".join(part.capitalize() for part in s.split("_") if part)
+
+
+# Last-variant-is-default matches the catch-all idiom (e.g. `Metadata`
+# in `claude_manage.schema.EntryType`). Decoru's `emit_rust_struct`
+# emits `impl Default` unconditionally on every BaseModel, so any
+# enum-typed field that lacks a Pydantic default must still satisfy
+# `EntryType::default()`. Forcing #[default] on the last member keeps
+# the generated structs compilable without per-enum config.
+_ENUM_TEMPLATE = textwrap.dedent("""\
+    #[derive({derives})]
+    #[serde(rename_all = "snake_case")]
+    pub enum {name} {{
+    {variants}
+    }}
+    """)
+
+
+def _render_variant(member: Enum, *, is_default: bool) -> str:
+    pascal = _pascal_case(member.name)
+    default_attr = "    #[default]\n" if is_default else ""
+    return f"{default_attr}    {pascal},"
+
+
+def emit_rust_enum(enum_class: type[Enum], derives: tuple[str, ...]) -> str:
+    """Render a Rust enum with PascalCase variants from Python member
+    names. Pairs `#[serde(rename_all = "snake_case")]` so the wire form
+    matches each member's `value`. Adds `Default` to the derives and
+    marks the last member `#[default]` — see `_ENUM_TEMPLATE` for the
+    rationale."""
+    name = enum_class.__name__
+    members = list(enum_class)
+    full_derives = ", ".join((*derives, "Default"))
+    variants = "\n".join(
+        _render_variant(m, is_default=(i == len(members) - 1))
+        for i, m in enumerate(members)
+    )
+    return _ENUM_TEMPLATE.format(derives=full_derives, name=name, variants=variants)
+
+
+def main() -> int:
+    if len(sys.argv) < 2:
+        sys.stderr.write("run_decoru.py: missing JSON payload argument\n")
+        return 2
+
+    payload = json.loads(sys.argv[1])
+    module_name: str = payload["module"]
+    output_path = Path(payload["output"]).resolve()
+    derives = tuple(payload.get("derives", ()))
+    header = payload.get("header") or ""
+
+    sys.path.insert(0, str(Path.cwd()))
+
+    module = importlib.import_module(module_name)
+    enums = discover_enums(module)
+    models = discover_models(module)
+    if not enums and not models:
+        sys.stderr.write(
+            f"run_decoru.py: no Enum or BaseModel subclasses declared in {module_name!r}\n"
+        )
+        return 3
+
+    enum_blocks = [emit_rust_enum(e, derives) for e in enums]
+    struct_blocks = [emit_rust_struct(walk_pydantic_model(m), derives=derives) for m in models]
+    body = "\n".join((*enum_blocks, *struct_blocks))
+
+    output_path.parent.mkdir(parents=True, exist_ok=True)
+    output_path.write_text(header + body)
+
+    sys.stderr.write(
+        f"run_decoru.py: wrote {len(enums)} enum(s) + {len(models)} struct(s) to {output_path}\n"
+    )
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())

protocol/mizan-codegen/src/config.rs

@@ -62,6 +62,13 @@ pub struct SourceConfig {
 
     #[serde(default)]
     pub django: Option<DjangoSource>,
+
+    /// Canonical "Pydantic + Rust" DX path. The Rust crate is the IR
+    /// authority; an optional `pydantic` sub-block invokes decoru as a
+    /// pre-step to author Rust types from Pydantic models. Pure-Rust
+    /// usage (no Pydantic) just omits the sub-block.
+    #[serde(default)]
+    pub rust: Option<RustSource>,
 }
 
 
@@ -98,6 +105,107 @@ pub struct DjangoSource {
 }
 
 
+/// `[source.rust]` — spawn a Cargo binary that emits the Mizan IR (KDL)
+/// to stdout. The binary uses `mizan_core::build_ir()` after force-linking
+/// the consumer crate's `#[derive(Mizan)]` types and `#[mizan::client]`
+/// functions.
+#[derive(Debug, Deserialize)]
+pub struct RustSource {
+    /// Path to the consumer's Cargo.toml, relative to the codegen config
+    /// directory. Defaults to `Cargo.toml` (i.e. config_dir/Cargo.toml).
+    #[serde(default)]
+    pub manifest_path: Option<PathBuf>,
+
+    /// Name of the binary under `[[bin]]` that exports the IR. Defaults
+    /// to `emit-mizan-ir` — the convention this substrate documents.
+    #[serde(default = "default_rust_bin")]
+    pub bin: String,
+
+    /// Cargo features to enable when building the bin.
+    #[serde(default)]
+    pub features: Vec<String>,
+
+    /// Build in release mode. Defaults to false (dev mode is faster for
+    /// codegen, and the binary is throwaway).
+    #[serde(default)]
+    pub release: bool,
+
+    /// Environment overrides for the cargo subprocess.
+    #[serde(default)]
+    pub env: BTreeMap<String, String>,
+
+    /// Optional pre-step — invoke decoru on a Pydantic source module
+    /// before running the Cargo bin. When present, the pipeline becomes:
+    ///   1. python + decoru → write Rust types to `pydantic.output`
+    ///   2. cargo run --bin <bin> → emit IR to stdout
+    /// Omit for pure-Rust usage (hand-authored or otherwise-generated
+    /// Rust types with `#[derive(Mizan)]`).
+    #[serde(default)]
+    pub pydantic: Option<PydanticPreStep>,
+}
+
+
+fn default_rust_bin() -> String {
+    "emit-mizan-ir".to_string()
+}
+
+
+/// Pydantic → Rust pre-step. Runs an embedded Python helper that walks
+/// the named module for `BaseModel` subclasses and invokes decoru's
+/// `walk_pydantic_model` + `emit_rust_struct` to produce a Rust file.
+#[derive(Debug, Deserialize)]
+pub struct PydanticPreStep {
+    /// Python module name to import (e.g. `claude_manage.schema`).
+    pub module: String,
+
+    /// Path to write the generated Rust file, relative to the codegen
+    /// config directory.
+    pub output: PathBuf,
+
+    /// Working directory for the python subprocess, relative to the
+    /// codegen config directory. Defaults to the config directory itself.
+    /// The script prepends this to `sys.path` so the module imports.
+    #[serde(default)]
+    pub cwd: Option<PathBuf>,
+
+    /// Python executable. Defaults to `python`.
+    #[serde(default)]
+    pub python: Option<String>,
+
+    /// Full command override (e.g. `["uv", "run", "python"]`). Wins over
+    /// `python` when present.
+    #[serde(default)]
+    pub command: Option<Vec<String>>,
+
+    /// Derive macros to apply to every generated struct. The default
+    /// matches the Mizan-canonical set used in `cores/rust/blazr/session`
+    /// — serde + mizan_core::Mizan for end-to-end RPC participation.
+    #[serde(default = "default_pydantic_derives")]
+    pub derives: Vec<String>,
+
+    /// Optional prelude inserted at the top of the generated file
+    /// (typically a "// AUTO-GENERATED" warning + `use` statements for
+    /// referenced types not produced by decoru itself).
+    #[serde(default)]
+    pub header: Option<String>,
+
+    /// Environment overrides for the python subprocess.
+    #[serde(default)]
+    pub env: BTreeMap<String, String>,
+}
+
+
+fn default_pydantic_derives() -> Vec<String> {
+    vec![
+        "Debug".to_string(),
+        "Clone".to_string(),
+        "::serde::Serialize".to_string(),
+        "::serde::Deserialize".to_string(),
+        "::mizan_core::Mizan".to_string(),
+    ]
+}
+
+
 #[derive(Debug, Deserialize, Clone)]
 #[serde(untagged)]
 pub enum RustKernelSpec {

protocol/mizan-codegen/src/fetch.rs

@@ -4,24 +4,48 @@
 //! Backends:
 //!   - FastAPI: `python -m mizan_fastapi.ir <module>`
 //!   - Django:  `python manage.py export_mizan_ir`
+//!   - Rust:    `cargo run --bin <bin>` (consumer-side binary that
+//!              force-links its `#[derive(Mizan)]` types and
+//!              `#[mizan::client]` functions, then calls
+//!              `mizan_core::build_ir()`).
+//!
+//! The Rust source supports an optional `[source.rust.pydantic]`
+//! pre-step that invokes decoru on a Pydantic module to author the
+//! Rust types before the cargo bin runs — the "Pydantic + Rust"
+//! canonical DX.
 
+use std::io::Write;
 use std::path::{Path, PathBuf};
-use std::process::Command;
+use std::process::{Command, Stdio};
 
 use anyhow::{anyhow, Context, Result};
+use serde_json::json;
 
-use crate::config::{Config, DjangoSource, FastapiSource};
+use crate::config::{Config, DjangoSource, FastapiSource, PydanticPreStep, RustSource};
 use crate::ir::{parse_ir, MizanIR};
 
 
+/// Embedded decoru bridge script — piped to `python -` at codegen time
+/// when `[source.rust.pydantic]` is set. The script imports decoru,
+/// walks the named module's BaseModel subclasses, and writes a Rust
+/// file. See `scripts/run_decoru.py` for the full body.
+const DECORU_BRIDGE_SCRIPT: &str = include_str!("../scripts/run_decoru.py");
+
+
 pub fn fetch_schema(config: &Config, config_dir: &Path) -> Result<MizanIR> {
-    let raw = if let Some(fa) = &config.source.fastapi {
+    let raw = if let Some(rs) = &config.source.rust {
+        if let Some(py) = &rs.pydantic {
+            run_pydantic_prestep(py, config_dir)
+                .context("running [source.rust.pydantic] pre-step")?;
+        }
+        run_rust(rs, config_dir)?
+    } else if let Some(fa) = &config.source.fastapi {
         run_fastapi(fa, config_dir)?
     } else if let Some(dj) = &config.source.django {
         run_django(dj, config_dir)?
     } else {
         return Err(anyhow!(
-            "config.source must declare either [source.fastapi] or [source.django]"
+            "config.source must declare one of [source.rust], [source.fastapi], or [source.django]"
         ));
     };
 
@@ -111,6 +135,96 @@ fn run_subprocess(
 }
 
 
+fn run_rust(src: &RustSource, config_dir: &Path) -> Result<String> {
+    let manifest = config_dir.join(
+        src.manifest_path
+            .clone()
+            .unwrap_or_else(|| PathBuf::from("Cargo.toml")),
+    );
+
+    let mut args: Vec<String> = vec![
+        "run".to_string(),
+        "--quiet".to_string(),
+        "--manifest-path".to_string(),
+        manifest.to_string_lossy().into_owned(),
+        "--bin".to_string(),
+        src.bin.clone(),
+    ];
+    if src.release {
+        args.push("--release".to_string());
+    }
+    if !src.features.is_empty() {
+        args.push("--features".to_string());
+        args.push(src.features.join(","));
+    }
+
+    run_subprocess("cargo", &args, config_dir, &src.env, "Rust IR export")
+}
+
+
+fn run_pydantic_prestep(src: &PydanticPreStep, config_dir: &Path) -> Result<()> {
+    let cwd = match &src.cwd {
+        Some(rel) => config_dir.join(rel),
+        None => config_dir.to_path_buf(),
+    };
+
+    let output_abs = if src.output.is_absolute() {
+        src.output.clone()
+    } else {
+        config_dir.join(&src.output)
+    };
+
+    let payload = json!({
+        "module": &src.module,
+        "output": output_abs.to_string_lossy(),
+        "derives": &src.derives,
+        "header": &src.header,
+    })
+    .to_string();
+
+    let (program, mut args) = resolve_command(&src.command, &src.python);
+    // `python -` reads the script body from stdin; the JSON payload is
+    // passed as argv[1] (which lands on sys.argv[1] inside the script).
+    args.push("-".to_string());
+    args.push(payload);
+
+    let mut cmd = Command::new(&program);
+    cmd.args(&args).current_dir(&cwd);
+    for (k, v) in &src.env {
+        cmd.env(k, v);
+    }
+    cmd.stdin(Stdio::piped());
+    cmd.stdout(Stdio::inherit());
+    cmd.stderr(Stdio::inherit());
+
+    let mut child = cmd
+        .spawn()
+        .with_context(|| format!("spawning decoru bridge ({program})"))?;
+
+    {
+        let stdin = child
+            .stdin
+            .as_mut()
+            .ok_or_else(|| anyhow!("failed to acquire decoru bridge stdin"))?;
+        stdin
+            .write_all(DECORU_BRIDGE_SCRIPT.as_bytes())
+            .context("piping decoru bridge script to python")?;
+    }
+
+    let status = child
+        .wait()
+        .context("waiting for decoru bridge to complete")?;
+    if !status.success() {
+        return Err(anyhow!(
+            "[source.rust.pydantic]: decoru bridge exited with status {:?}",
+            status.code()
+        ));
+    }
+
+    Ok(())
+}
+
+
 /// Library helper: parse a KDL IR from a string.
 pub fn parse_ir_from_str(source: &str) -> Result<MizanIR> {
     parse_ir(source)

protocol/mizan-codegen/templates/react/react.tsx.j2

@@ -2,30 +2,38 @@
 
 // AUTO-GENERATED by mizan — do not edit
 
+{% set has_contexts = has_global || !named_contexts.is_empty() -%}
 import {
+    {% if has_contexts -%}
     createContext,
+    {% endif -%}
     useCallback,
+    {% if has_contexts -%}
     useContext,
     useEffect,
+    {% endif -%}
     useRef,
     useState,
+    {% if has_contexts -%}
     useSyncExternalStore,
+    {% endif -%}
     type ReactNode,
 } from 'react'
 import {
     configure,
-    initSession,
     mizanCall,
     mizanFetch,
-    MizanError,
+    {% if has_contexts -%}
     registerContext,
     type ContextState,
+    {% endif -%}
 } from '@mizan/base'
 
 {% if !stage1_imports.is_empty() -%}
 import { {{ stage1_imports|join(", ") }} } from './index'
 
 {% endif -%}
+{% if has_contexts -%}
 // Internal — runs inside a Provider, registers with the kernel exactly once.
 function useContextSubscription<T>(
     name: string,
@@ -46,6 +54,7 @@ function useContextSubscription<T>(
 
     return useSyncExternalStore(handle.subscribe, handle.getState, handle.getState)
 }
+{% endif %}
 
 // Internal — wraps an imperative call() with isPending / error state.
 interface MutationHook<TArgs, TResult> {