fix: use less strict timestamp in system prompt (#2434)

crates/goose/src/agents/prompt_manager.rs

@@ -9,6 +9,7 @@ use crate::{config::Config, prompt_template};
 pub struct PromptManager {
     system_prompt_override: Option<String>,
     system_prompt_extras: Vec<String>,
+    current_date_timestamp: String,
 }
 
 impl Default for PromptManager {
@@ -22,6 +23,8 @@ impl PromptManager {
         PromptManager {
             system_prompt_override: None,
             system_prompt_extras: Vec::new(),
+            // Use the fixed current date time so that prompt cache can be used.
+            current_date_timestamp: Utc::now().format("%Y-%m-%d %H:%M:%S").to_string(),
         }
     }
 
@@ -79,8 +82,10 @@ impl PromptManager {
 
         context.insert("extensions", serde_json::to_value(extensions_info).unwrap());
 
-        let current_date_time = Utc::now().format("%Y-%m-%d %H:%M:%S").to_string();
+        context.insert(
-        context.insert("current_date_time", Value::String(current_date_time));
+            "current_date_time",
+            Value::String(self.current_date_timestamp.clone()),
+        );
 
         // Add the suggestion about disabling extensions if flag is true
         context.insert(