Dynamically refresh skill instructions each turn (#9217)

Signed-off-by: Douwe Osinga <douwe@squareup.com>
Co-authored-by: Douwe Osinga <douwe@squareup.com>

crates/goose/src/agents/extension_manager.rs

@@ -106,9 +106,7 @@ impl Extension {
     }
 
     fn get_instructions(&self) -> Option<String> {
-        self.server_info
-            .as_ref()
-            .and_then(|info| info.instructions.clone())
+        self.client.get_instructions()
     }
 
     fn get_client(&self) -> McpClientBox {

crates/goose/src/agents/mcp_client.rs

@@ -84,6 +84,13 @@ pub trait McpClientTrait: Send + Sync {
 
     fn get_info(&self) -> Option<&InitializeResult>;
 
+    /// Return the extension's current instructions. The default reads from
+    /// `get_info()`, but platform extensions can override this to provide
+    /// dynamically computed instructions (e.g. freshly discovered skills).
+    fn get_instructions(&self) -> Option<String> {
+        self.get_info().and_then(|info| info.instructions.clone())
+    }
+
     async fn list_resources(
         &self,
         _session_id: &str,

crates/goose/src/agents/prompt_manager.rs

@@ -441,11 +441,9 @@ mod tests {
             .values()
             .map(|def| {
                 let client = (def.client_factory)(context.clone());
-                let info = client.get_info();
-                let instructions = info
-                    .and_then(|i| i.instructions.clone())
-                    .unwrap_or_default();
-                let has_resources = info
+                let instructions = client.get_instructions().unwrap_or_default();
+                let has_resources = client
+                    .get_info()
                     .and_then(|i| i.capabilities.resources.as_ref())
                     .is_some();
                 ExtensionInfo::new(def.name, &instructions, has_resources)