Implementing WASM runtime

wit/tool.wit

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+// WASM Tool Sandbox Interface
+//
+// Defines the contract between sandboxed tools and the host runtime.
+// Tools export the `tool` interface; the host provides the `host` interface.
+
+package near:agent;
+
+/// Host-provided capabilities for sandboxed tools.
+///
+/// These are the only ways a sandboxed tool can interact with the outside world.
+/// The set is intentionally minimal to reduce attack surface.
+interface host {
+    /// Log levels for structured logging.
+    enum log-level {
+        trace,
+        debug,
+        info,
+        warn,
+        error,
+    }
+
+    /// Emit a log message.
+    ///
+    /// Messages are collected and emitted after execution completes.
+    /// Rate-limited to 1000 entries per execution, 4KB per message.
+    log: func(level: log-level, message: string);
+
+    /// Get the current timestamp in milliseconds since Unix epoch.
+    now-millis: func() -> u64;
+
+    /// Read a file from the workspace (if capability granted).
+    ///
+    /// Path must be relative (no leading /) and cannot contain "..".
+    /// Returns None if the file doesn't exist or capability not granted.
+    workspace-read: func(path: string) -> option<string>;
+}
+
+/// Tool interface that sandboxed tools must implement.
+interface tool {
+    /// Request payload for tool execution.
+    record request {
+        /// JSON-encoded parameters matching the tool's schema.
+        params: string,
+        /// Optional JSON-encoded job context for stateful operations.
+        context: option<string>,
+    }
+
+    /// Response from tool execution.
+    record response {
+        /// JSON-encoded result on success.
+        result: option<string>,
+        /// Error message on failure.
+        error: option<string>,
+    }
+
+    /// Execute the tool with the given request.
+    ///
+    /// This is the main entry point. The tool should:
+    /// 1. Parse params as JSON according to its schema
+    /// 2. Perform the operation
+    /// 3. Return a response with either result or error set
+    execute: func(req: request) -> response;
+
+    /// Get the JSON Schema for this tool's parameters.
+    ///
+    /// Must return a valid JSON Schema object describing the expected
+    /// structure of the `params` field in requests.
+    schema: func() -> string;
+
+    /// Get a human-readable description of what this tool does.
+    ///
+    /// Used by the LLM to understand when to invoke the tool.
+    description: func() -> string;
+}
+
+/// World definition for sandboxed tools.
+///
+/// Tools import host capabilities and export the tool interface.
+world sandboxed-tool {
+    import host;
+    export tool;
+}