fix(cli): support stdin via dash convention in import command

Fixes bounty issue #1574

The import command now recognizes the standard Unix convention of using
"-" (dash) as a filename to read from stdin. Previously, using
"cortex import -" would attempt to read from a file literally named
"-" which would fail. Now it properly reads JSON content from stdin.

Author: factorydroid

cortex-cli/src/import_cmd.rs

@@ -18,7 +18,7 @@ use crate::export_cmd::{ExportMessage, SessionExport};
 /// Import a session from JSON format.
 #[derive(Debug, Parser)]
 pub struct ImportCommand {
-    /// Path to the JSON file to import, or URL to fetch
+    /// Path to the JSON file to import, URL to fetch, or "-" to read from stdin
     #[arg(value_name = "FILE_OR_URL")]
     pub source: String,
 
@@ -39,16 +39,23 @@ impl ImportCommand {
             .ok_or_else(|| anyhow::anyhow!("Could not determine home directory"))?;
 
         // Read the export data
-        let json_content =
-            if self.source.starts_with("http://") || self.source.starts_with("https://") {
-                // Fetch from URL
-                fetch_url(&self.source).await?
-            } else {
-                // Read from local file
-                let path = PathBuf::from(&self.source);
-                std::fs::read_to_string(&path)
-                    .with_context(|| format!("Failed to read file: {}", path.display()))?
-            };
+        let json_content = if self.source == "-" {
+            // Read from stdin (standard Unix convention)
+            use std::io::Read;
+            let mut buffer = String::new();
+            std::io::stdin()
+                .read_to_string(&mut buffer)
+                .with_context(|| "Failed to read from stdin")?;
+            buffer
+        } else if self.source.starts_with("http://") || self.source.starts_with("https://") {
+            // Fetch from URL
+            fetch_url(&self.source).await?
+        } else {
+            // Read from local file
+            let path = PathBuf::from(&self.source);
+            std::fs::read_to_string(&path)
+                .with_context(|| format!("Failed to read file: {}", path.display()))?
+        };
 
         // Parse the export
         let export: SessionExport = serde_json::from_str(&json_content)