loopd: write the next epoch from a compaction summary

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

crates/loopd/src/compact.rs

@@ -2,12 +2,14 @@
 //! (M5d spec, section 3). Task 07 writes the next files; task 08 calls this after a turn.
 
 use bxcore::sanitize::neutralise;
-use bxcore::{LogRecord, Usage};
+use bxcore::{Epoch, LogRecord, Timestamp, Usage};
 
-use crate::baseline::messages_with_carry;
+use crate::baseline::{Baseline, messages_with_carry};
 use crate::config::Config;
 use crate::llama::{ChatMessage, ChatRequest, Client};
+use crate::memory::MemorySource;
 use crate::session::Session;
+use crate::tools::Registry;
 use crate::turn::is_context_full;
 
 /// Why a summary call or a next-epoch write failed. Every variant's `Display` ends with the
@@ -90,3 +92,44 @@ pub fn summarise(cfg: &Config, client: &Client, session: &Session) -> Result<Str
         }),
     }
 }
+
+/// Append `EpochEnd` (unless it is already last), rebuild the baseline from `memory`, and
+/// switch `session` onto the next epoch. When the current log already ends with `EpochEnd`,
+/// that record's summary is the carry and the argument is ignored.
+pub fn commit(
+    session: &mut Session,
+    cfg: &Config,
+    registry: &Registry,
+    memory: &dyn MemorySource,
+    summary: String,
+) -> Result<(), CompactError> {
+    let (next, summary) = match session.records().last() {
+        Some(LogRecord::EpochEnd { next, summary, .. }) => (*next, summary.clone()),
+        _ => {
+            let next = Epoch(session.epoch().0.saturating_add(1));
+            session
+                .append(LogRecord::EpochEnd {
+                    time: Timestamp::now(),
+                    next,
+                    summary: summary.clone(),
+                })
+                .map_err(|e| CompactError::Failed {
+                    detail: e.to_string(),
+                })?;
+            (next, summary)
+        }
+    };
+    let block = memory
+        .block()
+        .map_err(|e| CompactError::Failed { detail: e })?;
+    let baseline =
+        Baseline::assemble_with(cfg, registry, &block).map_err(|e| CompactError::Failed {
+            detail: e.to_string(),
+        })?;
+    session
+        .begin_epoch(next, baseline, summary)
+        .map_err(|e| CompactError::Failed {
+            detail: e.to_string(),
+        })?;
+    Ok(())
+}