loopd: [compact] threshold, summary_chars and summarise

Co-Authored-By: ornith-1.5-35b-a3b <agent@wntrmute.dev>

crates/loopd/src/config.rs

@@ -175,6 +175,8 @@ pub struct Config {
     pub broker: Broker,
     #[serde(default)]
     pub memory: Memory,
+    #[serde(default)]
+    pub compact: Compact,
 }
 
 /// `[memory]`: `memoryd`'s socket for `loopd` (M5a spec, section 9). An empty path means the
@@ -185,6 +187,26 @@ pub struct Memory {
     pub socket: std::path::PathBuf,
 }
 
+/// `[compact]`: when a session starts a new epoch, and how long a summary may be (M5d spec,
+/// section 5). `summarise` is stored here and unused until M5d-2.
+#[derive(Debug, Clone, PartialEq, Deserialize)]
+#[serde(deny_unknown_fields, default)]
+pub struct Compact {
+    pub threshold: f64,
+    pub summary_chars: usize,
+    pub summarise: Vec<String>,
+}
+
+impl Default for Compact {
+    fn default() -> Self {
+        Self {
+            threshold: 0.85,
+            summary_chars: 4_000,
+            summarise: vec!["http_fetch".to_string()],
+        }
+    }
+}
+
 #[derive(Debug)]
 pub enum ConfigError {
     Read(std::path::PathBuf, std::io::Error),
@@ -232,4 +254,9 @@ impl Config {
             self.channel.socket.clone()
         }
     }
+
+    /// `compact.md` beside the system prompt: the summary call's last user message.
+    pub fn compact_prompt(&self) -> std::path::PathBuf {
+        self.baseline.system.with_file_name("compact.md")
+    }
 }