feat: v0.1.0 — Studio Plugin SDK

First release of the SDK that Studio plugins depend on.

What v0.1 ships:

- WIT contract under wit/ (studio-plugin.wit +
  deps/platform/world.wit, both verbatim from
  fai/platform/wit/).
- wit-bindgen 0.36 generate! call with pub_export_macro
  enabled so the emitted __export_studio_plugin_impl! macro
  is reachable from downstream plugin crates.
- export_plugin!(MyType) convenience macro that wraps the
  bindgen-generated impl macro.
- README documenting usage + v0.1 limits (single-world ->
  all-three-hooks-required, no proc-macro yet, edition
  2021 pinned by wit-bindgen output).

What v0.1 doesn't yet do:

- Plugins still declare all three Guest impls (theme,
  translate, output-view). v0.2 splits the WIT into one
  world per hook.
- No #[plugin(...)] proc-macro. v0.2 wraps generate! +
  Guest impl generation into a single attribute.
- Host-side: the hub doesn't yet load studio-plugin-world
  components or expose InvokePlugin RPC — that's the next
  push.

Validated against the in-tree studio-theme-solarized
plugin: 22 KiB stripped .wasm artefact, valid Component
Model, passes wasm-tools component wit inspection.

Signed-off-by: flemming-it <sf@flemming.it>

wit/deps/platform/world.wit

@@ -0,0 +1,99 @@
+// =============================================================
+// FROZEN. Wire contract between hub and modules.
+// =============================================================
+//
+// This file is the stable wire contract between the F∆I Hub
+// and any module compiled against it. It is **frozen at v1.0**.
+//
+// Frozen means:
+//
+//   - No removal, rename, or signature change of any existing
+//     interface, function, type, field, or variant case.
+//   - Additive changes (new types, new variant cases at the end,
+//     new fields with stable defaults) require a minor bump
+//     (1.0 -> 1.1) and a coordinated review.
+//   - Any breaking change requires a major bump (1.0 -> 2.0)
+//     and a parallel-world transition plan.
+//
+// The fai_runtime crate ships a snapshot test that fails if
+// this file changes without an intentional, reviewed update.
+// See `crates/fai_runtime/tests/wit_freeze.rs`.
+//
+// Module authors do NOT depend on this file directly. They
+// use `fai-module-sdk`, which wraps these bindings behind a
+// stable, ergonomic surface. That is what protects modules
+// from any future evolution of this contract.
+
+package fai:platform@1.0.0;
+
+/// Types that flow between the host (hub) and modules.
+interface types {
+  /// A typed value passed between the host and a module.
+  variant payload {
+    /// Plain UTF-8 text.
+    text(string),
+    /// Arbitrary JSON encoded as a string.
+    json(string),
+    /// Raw bytes with a MIME type.
+    bytes(bytes-value),
+    /// A reference to a file, by URI.
+    file-ref(file-ref),
+  }
+
+  /// Inline byte content.
+  record bytes-value {
+    mime-type: string,
+    data: list<u8>,
+  }
+
+  /// File reference by URI.
+  record file-ref {
+    uri: string,
+    mime-type: string,
+    size-bytes: u64,
+    sha256: string,
+  }
+
+  /// Context passed with every invocation.
+  record invocation-context {
+    invocation-id: string,
+    capability-namespace: string,
+    capability-name: string,
+    deadline-ms: u64,
+  }
+
+  /// Structured error type returned by modules.
+  variant invocation-error {
+    invalid-input(string),
+    permission-denied(string),
+    resource-exhausted(string),
+    deadline-exceeded,
+    internal(string),
+  }
+}
+
+/// The host-provided interface that modules can import to talk back.
+interface host {
+  /// Log a structured message. Level is "trace", "debug", "info", "warn", "error".
+  log: func(level: string, message: string);
+}
+
+/// The core interface every module exports.
+interface invoke {
+  use types.{payload, invocation-context, invocation-error};
+
+  /// Invoke the module with inputs, receive outputs or an error.
+  invoke: func(
+    ctx: invocation-context,
+    inputs: list<tuple<string, payload>>,
+  ) -> result<list<tuple<string, payload>>, invocation-error>;
+}
+
+/// The world a module component targets.
+///
+/// Modules `export` the invoke interface to be callable by the hub.
+/// Modules `import` the host interface to emit logs.
+world module {
+  import host;
+  export invoke;
+}