Finish long-running agent parity

src/engine.rs

@@ -364,7 +364,7 @@ pub(crate) struct GenerationOutput {
 #[cfg(target_os = "macos")]
 pub(crate) struct CompactionOutput {
     pub(crate) summary: String,
-    pub(crate) tail: Vec<ChatTurn>,
+    pub(crate) tail_start: usize,
     pub(crate) context_tokens: u32,
     pub(crate) checkpoint: PathBuf,
 }
@@ -530,19 +530,23 @@ impl Generator {
         Ok(output)
     }
 
+    #[allow(clippy::too_many_arguments)]
     pub(crate) fn compact(
         &mut self,
         messages: &[ChatTurn],
         settings: &TurnSettings,
+        rebuild_system_prompt: &str,
         reason: &str,
         checkpoint: &Path,
         cancelled: &AtomicBool,
         mut progress: impl FnMut(u32, u32, Option<f32>),
+        mut phase: impl FnMut(&'static str),
     ) -> Result<CompactionOutput, String> {
         let _ = std::fs::remove_file(checkpoint);
         self.executor.reset()?;
         self.checkpoint = None;
         let result = (|| {
+            phase("Compacting durable task state…");
             let mut private_messages = messages.to_vec();
             private_messages.push(ChatTurn {
                 user: true,
@@ -555,15 +559,24 @@ impl Generator {
             });
             let mut private_settings = settings.clone();
             private_settings.reasoning_mode = ReasoningMode::Direct;
-            private_settings.max_generated_tokens = crate::compaction::SUMMARY_MAX_TOKENS;
+            let private_prompt = self.executor.model().render_conversation(
+                &private_settings.system_prompt,
+                &private_messages,
+                private_settings.reasoning_mode,
+            );
+            private_settings.max_generated_tokens = crate::compaction::summary_budget(
+                private_prompt.len().min(u32::MAX as usize) as u32,
+                self.executor.context(),
+            )
+            .ok_or_else(|| "not enough context left to request compaction summary".to_owned())?;
             private_settings.temperature = 0.0;
-            private_settings.stops.extend([
+            private_settings.stops = vec![
                 "<｜DSML｜".into(),
                 "<DSML｜".into(),
                 "<tool_call>".into(),
                 "<think>".into(),
                 "</think>".into(),
-            ]);
+            ];
             let (output, prompt_complete) = self.generate_inner(
                 &private_messages,
                 &private_settings,
@@ -580,6 +593,7 @@ impl Generator {
             }
 
             // The private request must never become the rebuilt session prefix.
+            phase("Rebuilding compacted context…");
             self.executor.reset()?;
             self.checkpoint = None;
 
@@ -609,7 +623,7 @@ impl Generator {
             );
             let tail = messages[start..].to_vec();
             let rebuilt_system =
-                crate::compaction::summary_system_prompt(&settings.system_prompt, Some(&summary));
+                crate::compaction::summary_system_prompt(rebuild_system_prompt, Some(&summary));
             let history_tokens = self.executor.model().render_history(
                 &rebuilt_system,
                 &tail,
@@ -627,10 +641,11 @@ impl Generator {
                 return Err("context compaction interrupted during rebuild".into());
             }
             let tag = conversation_tag(&rebuilt_system, settings.reasoning_mode, &tail);
+            phase("Saving compacted context…");
             self.save_checkpoint(checkpoint, tag)?;
             Ok(CompactionOutput {
                 summary,
-                tail,
+                tail_start: start,
                 context_tokens: history_tokens.len() as u32,
                 checkpoint: checkpoint.to_owned(),
             })
@@ -645,6 +660,20 @@ impl Generator {
         result
     }
 
+    pub(crate) fn rendered_history_tokens(
+        &self,
+        messages: &[ChatTurn],
+        settings: &TurnSettings,
+    ) -> Result<u32, String> {
+        u32::try_from(
+            self.executor
+                .model()
+                .render_history(&settings.system_prompt, messages, settings.reasoning_mode)
+                .len(),
+        )
+        .map_err(|_| "rendered conversation is too large".to_owned())
+    }
+
     fn select_checkpoint(
         &mut self,
         checkpoint: &Path,