Separate returns from longer statement blocks

[onechat] / memory.go

diff --git a/memory.go b/memory.go
index 0be2fde9f025ef2732f56f8c9c8786d00a262e5e..bcc10951921751aad707a32f7180799e023e9a18 100644 (file)
--- a/memory.go
+++ b/memory.go
@@ -5,43 +5,46 @@ import (
        "encoding/json"
        "errors"
        "fmt"
        "encoding/json"
        "errors"
        "fmt"

+       "log"

        "os"
        "path/filepath"
        "os"
        "path/filepath"

+       "strings"

        "sync"
        "time"
 )
 
        "sync"
        "time"
 )
 

-// errNoView tells that a chat has messages but no saved view.
-var errNoView = errors.New("the chat has messages but no saved view")
+var (
+       // errMemoryNoView tells that a chat has messages but no saved view.
+       errMemoryNoView = errors.New("the chat has messages but no saved view")

 
 

-// Memory is the memory of one chat: the message log, the summary tree, and the
-// view. It saves the view to view.json after each change and loads it at start.
-// It never builds the view again from the log, because a new view differs from
-// the live one and so loses the prompt cache.
-type Memory struct {
-       mutex sync.Mutex
-       root  string
-       log   *Log
-       tree  *Tree
-       chat  *View
-}
-
-// viewFile is the content of view.json.
-type viewFile struct {
-       Chat viewState `json:"chat"`
-}
+       // errMemoryUnsettled tells that a line of the view stays pending,
+       // because its build failed.
+       errMemoryUnsettled = errors.New("a summary of the view failed, and it is tried again at the next message")
+)

 
 

-// openMemory opens the chat in root. The clock gives the dates of new messages
-// and the days of new nodes.
-func openMemory(ctx context.Context, root string, clock func() time.Time) (*Memory, error) {
+// openMemory opens the chat in root and starts the builds that are ready. The
+// clock gives the dates of new messages and the days of new nodes. logger gets
+// one line for each failed build. The builds stop when ctx ends or at Close.
+func openMemory(ctx context.Context, root string, clock func() time.Time, summarizer Summarizer, logger *log.Logger) (*Memory, error) {

        log, err := openLog(ctx, root, clock)
        if err != nil {
                return nil, err
        }
 
        m := &Memory{
        log, err := openLog(ctx, root, clock)
        if err != nil {
                return nil, err
        }
 
        m := &Memory{

-               root: root,
-               log:  log,
+               root:       root,
+               log:        log,
+               queue:      newBuildQueue(),
+               summarizer: summarizer,
+               logger:     logger,
+               changed:    make(chan struct{}),
+       }
+
+       m.ctx, m.cancel = context.WithCancel(ctx)
+
+       m.syncer, err = openSyncer(root)
+       if err != nil {
+               return nil, errors.Join(err, m.Close())

        }
 
        m.tree, err = openTree(ctx, root, log.Len(), clock)
        }
 
        m.tree, err = openTree(ctx, root, log.Len(), clock)


@@ -54,141 +57,407 @@ func openMemory(ctx context.Context, root string, clock func() time.Time) (*Memo
                return nil, errors.Join(fmt.Errorf("load view: %w", err), m.Close())
        }
 
                return nil, errors.Join(fmt.Errorf("load view: %w", err), m.Close())
        }
 

+       err = m.restoreQueue()
+       if err != nil {
+               return nil, errors.Join(fmt.Errorf("restore build queue: %w", err), m.Close())
+       }
+
+       err = m.catchUp()
+       if err != nil {
+               return nil, errors.Join(err, m.Close())
+       }
+
+       m.mutex.Lock()
+       m.syncer.Written()
+       m.dispatch()
+       m.mutex.Unlock()
+

        return m, nil
 }
 
        return m, nil
 }
 

-// load reads the saved view. A crash can stop an append after the log write and
-// before the view save, so load continues the view with the messages that it
-// does not cover yet.
-func (m *Memory) load() error {
-       data, err := os.ReadFile(m.viewPath())
-       if errors.Is(err, os.ErrNotExist) && m.log.Len() == 0 {
-               m.chat = newView(chatHigh, chatLow)
-               return nil
+// Summarizer builds the text of one node with a model.
+type Summarizer interface {
+       Summarize(ctx context.Context, task Task) (string, error)
+}
+
+// Memory is the memory of one chat: the message log, the summary tree, the chat
+// view, the compaction view, and the queue of the builds. The compaction view
+// is the chat view merged further, at the limits of 16 to 32 KB. It takes the
+// same new lines, and it merges again in one batch when it is too large or when
+// the chat view merges. So the compactions share its prefix in the prompt
+// cache. It saves the views to view.json after each change and loads them at
+// start. It never builds the views again from the log, because a new view
+// differs from the live one and so loses the prompt cache.
+//
+// Each write goes to the operating system at once, and a syncer makes the
+// writes durable by group commit in the background. Flush waits until the
+// writes so far are durable.
+//
+// The summarizer builds the nodes in the queue in the background. The start
+// reads the indexes once to fill the queue again. After that, only a new
+// message or a new node adds work. Memory keeps the nodes of the views and the
+// tasks of the running builds. It reads all other messages and nodes from their
+// day files through the indexes.
+type Memory struct {
+       mutex      sync.Mutex
+       root       string
+       log        *Log
+       syncer     *Syncer
+       tree       *Tree
+       chat       *View
+       cview      *View
+       queue      *BuildQueue
+       summarizer Summarizer
+       logger     *log.Logger
+       ctx        context.Context
+       cancel     context.CancelFunc
+       workers    sync.WaitGroup
+       changed    chan struct{}
+}
+
+// Close stops the builds, waits for them, makes the writes durable, closes the
+// files of the chat, and releases its lock.
+func (m *Memory) Close() error {
+       m.cancel()
+       m.workers.Wait()
+
+       m.mutex.Lock()
+       defer m.mutex.Unlock()
+
+       var err error
+       if m.syncer != nil {
+               err = m.syncer.Close()

        }
 
        }
 

-       if errors.Is(err, os.ErrNotExist) {
-               return errNoView
+       if m.tree != nil {
+               err = errors.Join(err, m.tree.Close())

        }
 
        }
 

+       return errors.Join(err, m.log.Close())
+}
+
+// Append logs a new message, adds it to the tree and the views, and starts the
+// builds that are ready, also the failed ones.
+func (m *Memory) Append(kind, text string) (Message, error) {
+       return m.AppendDated(kind, text, "")
+}
+
+// AppendDated appends a message with its RFC 3339 date and builds its nodes. An
+// empty date uses the clock, as Append does.
+func (m *Memory) AppendDated(kind, text, date string) (Message, error) {
+       m.mutex.Lock()
+       defer m.mutex.Unlock()
+
+       message, err := m.log.AppendDated(kind, text, date)

        if err != nil {
        if err != nil {

-               return fmt.Errorf("read view: %w", err)
+               return Message{}, fmt.Errorf("append dated log message: %w", err)

        }
 
        }
 

-       var file viewFile
-       err = json.Unmarshal(data, &file)
+       defer m.syncer.Written()
+
+       err = m.addMessage(message)

        if err != nil {
        if err != nil {

-               return fmt.Errorf("decode view: %w", err)
+               return Message{}, fmt.Errorf("add dated message to memory: %w", err)

        }
 
        }
 

-       m.chat, err = restoreView(file.Chat, chatHigh, chatLow, m.tree)
+       err = m.save()

        if err != nil {
        if err != nil {

-               return err
+               return Message{}, fmt.Errorf("save dated message view: %w", err)

        }
 
        }
 

-       if m.chat.end > m.log.Len() {
-               return fmt.Errorf("view covers %d messages, but the log has %d", m.chat.end, m.log.Len())
+       m.queue.Retry()
+       m.dispatch()
+
+       return message, nil
+}
+
+// children reads the two children of the node key.
+func (m *Memory) children(key NodeKey) (Node, Node, error) {
+       var children [2]Node
+       for n := range children {
+               child, built, err := m.tree.Node(key.level-1, 2*key.index+n)
+               if err != nil {
+                       return Node{}, Node{}, err
+               }
+
+               if !built {
+                       return Node{}, Node{}, fmt.Errorf("node (%d, %d) is not built", key.level-1, 2*key.index+n)
+               }
+
+               children[n] = child

        }
 
        }
 

-       if m.chat.end == m.log.Len() {
-               return nil
+       return children[0], children[1], nil
+}
+
+// Wait returns when no build runs. The failed builds wait for the next message.
+func (m *Memory) Wait(ctx context.Context) error {
+       for {
+               m.mutex.Lock()
+               running := m.queue.Running()
+               changed := m.changed
+               m.mutex.Unlock()
+
+               if running == 0 {
+                       return nil
+               }
+
+               select {
+               case <-changed:
+               case <-ctx.Done():
+                       return ctx.Err()
+               }

        }
        }

+}

 
 

-       for m.chat.end < m.log.Len() {
-               err = m.addMessage(m.log.Message(m.chat.end))
-               if err != nil {
-                       return err
+// Settle returns when the chat view has no pending line, so that every message
+// so far is summarized. A pending line with no build that runs belongs to a
+// failed build, which waits for the next message, so Settle returns
+// errMemoryUnsettled in place of a wait that never ends.
+func (m *Memory) Settle(ctx context.Context) error {
+       for {
+               m.mutex.Lock()
+               pending := m.chat.Pending()
+               running := m.queue.Running()
+               changed := m.changed
+               m.mutex.Unlock()
+
+               if !pending {
+                       return nil
+               }
+
+               if running == 0 {
+                       return errMemoryUnsettled
+               }
+
+               select {
+               case <-changed:
+               case <-ctx.Done():
+                       return ctx.Err()

                }
        }
                }
        }

+}

 
 

-       return m.save()
+// Flush returns when every write before the call is durable.
+func (m *Memory) Flush(ctx context.Context) error {
+       return m.syncer.Flush(ctx)

 }
 
 }
 

-// Close closes the files of the chat and releases its lock.
-func (m *Memory) Close() error {
+// ViewLines returns the lines of the chat view, each with its newline, without
+// the leaf lines of the messages in skip.
+func (m *Memory) ViewLines(skip map[int]bool) []string {

        m.mutex.Lock()
        defer m.mutex.Unlock()
 
        m.mutex.Lock()
        defer m.mutex.Unlock()
 

-       var err error
-       if m.tree != nil {
-               err = m.tree.Close()
-       }
+       return m.chat.LinesWithout(skip)
+}

 
 

-       return errors.Join(err, m.log.Close())
+// Len returns the number of messages in the log.
+func (m *Memory) Len() int {
+       m.mutex.Lock()
+       defer m.mutex.Unlock()
+
+       return m.log.Len()

 }
 
 }
 

-// Append logs a new message and adds it to the tree and the view.
-func (m *Memory) Append(kind, text string) (Message, error) {
+// Message reads the message with the given ID.
+func (m *Memory) Message(id int) (Message, error) {
+       m.mutex.Lock()
+       defer m.mutex.Unlock()
+
+       return m.log.Message(id)
+}
+
+// Node reads the node (l, i) if it is built.
+func (m *Memory) Node(level, index int) (Node, bool, error) {

        m.mutex.Lock()
        defer m.mutex.Unlock()
 
        m.mutex.Lock()
        defer m.mutex.Unlock()
 

-       message, err := m.log.Append(kind, text)
+       return m.tree.Node(level, index)
+}
+
+// load reads the saved views.
+func (m *Memory) load() error {
+       data, err := os.ReadFile(m.viewPath())
+       if errors.Is(err, os.ErrNotExist) && m.log.Len() == 0 {
+               m.chat = newView(viewChatHigh, viewChatLow)
+               m.cview = newView(viewCompactionHigh, viewCompactionLow)
+
+               return nil
+       }
+
+       if errors.Is(err, os.ErrNotExist) {
+               return errMemoryNoView
+       }
+

        if err != nil {
        if err != nil {

-               return Message{}, err
+               return fmt.Errorf("read view: %w", err)

        }
 
        }
 

-       err = m.addMessage(message)
+       var file MemoryViewFile
+       err = json.Unmarshal(data, &file)

        if err != nil {
        if err != nil {

-               return Message{}, err
+               return fmt.Errorf("decode view: %w", err)

        }
 
        }
 

-       err = m.save()
+       m.chat, err = restoreView(file.Chat, viewChatHigh, viewChatLow, m.tree)

        if err != nil {
        if err != nil {

-               return Message{}, err
+               return fmt.Errorf("chat view: %w", err)

        }
 
        }
 

-       return message, nil
+       m.cview, err = restoreView(file.Compaction, viewCompactionHigh, viewCompactionLow, m.tree)
+       if err != nil {
+               return fmt.Errorf("compaction view: %w", err)
+       }
+
+       if m.cview.end != m.chat.end {
+               return fmt.Errorf("compaction view covers %d messages, but the chat view %d", m.cview.end, m.chat.end)
+       }
+
+       if m.chat.end > m.log.Len() {
+               return fmt.Errorf("view covers %d messages, but the log has %d", m.chat.end, m.log.Len())
+       }
+
+       return nil

 }
 
 }
 

-// addMessage builds the leaf of message when it needs no model call and appends
-// it to the view.
-func (m *Memory) addMessage(message Message) error {
-       _, built := m.tree.Node(0, message.ID)
-       leaf, free := freeLeaf(message)
-       if free && !built {
-               err := m.build(leaf)
+// restoreQueue adds the work of the messages in the view to the queue. It
+// builds each node that needs no model call and that a crash left out.
+func (m *Memory) restoreQueue() error {
+       for id := range m.chat.end {
+               built, err := m.tree.Built(0, id)
+               if err != nil {
+                       return err
+               }
+
+               if built {
+                       continue
+               }
+
+               message, err := m.log.Message(id)
+               if err != nil {
+                       return err
+               }
+
+               leaf, free := freeLeaf(message)
+               if !free {
+                       m.queue.AddLeaf(id)
+                       continue
+               }
+
+               err = m.build(leaf)

                if err != nil {
                        return err
                }
        }
 
                if err != nil {
                        return err
                }
        }
 

-       m.chat.Append(m.tree)
+       keys, err := m.tree.Keys()
+       if err != nil {
+               return err
+       }
+
+       for _, key := range keys {
+               if key.index%2 != 0 {
+                       continue
+               }
+
+               err = m.settle(key)
+               if err != nil {
+                       return err
+               }
+       }

 
        return nil
 }
 
 
        return nil
 }
 

-// build adds node to the tree, and then each parent above it that needs no
-// model call.
-func (m *Memory) build(node Node) error {
-       for {
-               err := m.tree.Add(node)
+// catchUp adds the messages that the view does not cover yet. A crash can stop
+// an append after the log write and before the view save.
+func (m *Memory) catchUp() error {
+       if m.chat.end == m.log.Len() {
+               return nil
+       }
+
+       for m.chat.end < m.log.Len() {
+               message, err := m.log.Message(m.chat.end)

                if err != nil {
                        return err
                }
 
                if err != nil {
                        return err
                }
 

-               sibling, built := m.tree.Node(node.Level, node.Index^1)
-               if !built {
-                       return nil
+               err = m.addMessage(message)
+               if err != nil {
+                       return err

                }
                }

+       }
+
+       return m.save()
+}

 
 

-               left, right := node, sibling
-               if node.Index%2 != 0 {
-                       left, right = sibling, node
+// dispatch starts the builds that are ready, up to the limit. A build whose
+// input cannot be read fails and waits for the next message.
+func (m *Memory) dispatch() {
+       for m.ctx.Err() == nil {
+               key, ready := m.queue.Next()
+               if !ready {
+                       return

                }
 
                }
 

-               parent, free := freeMerge(left, right)
-               if !free {
-                       return nil
+               task, err := m.task(key)
+               if err != nil {
+                       m.failed(key, fmt.Errorf("read its input: %w", err))
+                       m.queue.Fail(key)
+
+                       continue

                }
 
                }
 

-               node = parent
+               m.workers.Add(1)
+               go m.run(key, task)

        }
 }
 
        }
 }
 

+// addMessage builds the leaf of message when it needs no model call, or else
+// adds the leaf to the queue. Then it appends the leaf to the views. A crash can
+// stop an append after the leaf build and before the view save, so a leaf that
+// is built already stays as it is, and restoreQueue settles its parent.
+func (m *Memory) addMessage(message Message) error {
+       built, err := m.tree.Built(0, message.ID)
+       if err != nil {
+               return err
+       }
+
+       leaf, free := freeLeaf(message)
+       switch {
+       case built:
+       case free:
+               err = m.build(leaf)
+               if err != nil {
+                       return err
+               }
+       default:
+               m.queue.AddLeaf(message.ID)
+       }
+
+       merged, err := m.chat.Append(m.tree)
+       if err != nil {
+               return fmt.Errorf("append to chat view: %w", err)
+       }
+
+       _, err = m.cview.Append(m.tree)
+       if err == nil && merged {
+               err = m.cview.Coarsen(m.chat, m.tree)
+       }
+
+       if err != nil {
+               return fmt.Errorf("append to compaction view: %w", err)
+       }
+
+       return nil
+}
+

 // save writes the views to view.json.
 func (m *Memory) save() error {
 // save writes the views to view.json.
 func (m *Memory) save() error {

-       data, err := json.Marshal(viewFile{
-               Chat: m.chat.State(),
+       data, err := json.Marshal(MemoryViewFile{
+               Chat:       m.chat.State(),
+               Compaction: m.cview.State(),

        })
        if err != nil {
                return fmt.Errorf("encode view: %w", err)
        })
        if err != nil {
                return fmt.Errorf("encode view: %w", err)


@@ -206,55 +475,249 @@ func (m *Memory) viewPath() string {
        return filepath.Join(m.root, "view.json")
 }
 
        return filepath.Join(m.root, "view.json")
 }
 

-// View returns the chat view as the model reads it.
-func (m *Memory) View() string {
-       m.mutex.Lock()
-       defer m.mutex.Unlock()
+// build adds node to the tree, keeps it in the views when it is a pending line,
+// and settles its parent.
+func (m *Memory) build(node Node) error {
+       err := m.tree.Add(node)
+       if err != nil {
+               return err
+       }

 
 

-       return m.chat.Render(m.tree)
+       m.chat.Refresh(node)
+       m.cview.Refresh(node)
+
+       return m.settle(NodeKey{node.Level, node.Index})

 }
 
 }
 

-// writeFileAtomic replaces the file at path with data. A reader or a crash sees
-// the old file or the new file, never a part of one.
-func writeFileAtomic(path string, data []byte) error {
-       dir := filepath.Dir(path)
-       file, err := os.CreateTemp(dir, "."+filepath.Base(path)+".*")
+// settle looks at the parent of the built node key when both children are
+// built. It builds each parent that needs no model call, up the tree, and adds
+// the first other parent to the queue.
+func (m *Memory) settle(key NodeKey) error {
+       for {
+               parent := NodeKey{key.level + 1, key.index / 2}
+               ready, err := m.ready(parent)
+               if err != nil || !ready {
+                       return err
+               }
+
+               left, right, err := m.children(parent)
+               if err != nil {
+                       return err
+               }
+
+               node, free := freeMerge(left, right)
+               if !free {
+                       m.queue.AddMerge(parent)
+                       return nil
+               }
+
+               err = m.tree.Add(node)
+               if err != nil {
+                       return err
+               }
+
+               key = parent
+       }
+}
+
+// task returns the build task of the node key, with its input read from the log
+// or the tree.
+func (m *Memory) task(key NodeKey) (Task, error) {
+       task := Task{
+               Level:   key.level,
+               Index:   key.index,
+               Context: m.context(key.level, key.index),
+       }
+
+       if key.level == 0 {
+               message, err := m.log.Message(key.index)
+               if err != nil {
+                       return Task{}, err
+               }
+
+               task.Input = []string{leafSource(message)}
+
+               return task, nil
+       }
+
+       left, right, err := m.children(key)

        if err != nil {
        if err != nil {

-               return fmt.Errorf("create temporary file: %w", err)
+               return Task{}, err

        }
 
        }
 

-       _, err = file.Write(data)
-       if err == nil {
-               err = file.Sync()
+       for _, child := range []Node{left, right} {
+               task.Input = append(task.Input, strings.ReplaceAll(child.Text, "\n", " "))

        }
 
        }
 

-       err = errors.Join(err, file.Close())
+       return task, nil
+}
+
+// run builds one node with the summarizer. A failed build stays in the queue
+// until the next message.
+func (m *Memory) run(key NodeKey, task Task) {
+       defer m.workers.Done()
+
+       text, err := m.summarizer.Summarize(m.ctx, task)
+
+       m.mutex.Lock()
+       defer m.mutex.Unlock()
+

        if err == nil {
        if err == nil {

-               err = os.Rename(file.Name(), path)
+               err = m.build(Node{
+                       Level: key.level,
+                       Index: key.index,
+                       Text:  text,
+                       Size:  len(text),
+               })
+               m.syncer.Written()
+       }
+
+       if err != nil && m.ctx.Err() == nil {
+               m.failed(key, err)

        }
 
        if err != nil {
        }
 
        if err != nil {

-               return errors.Join(fmt.Errorf("replace file: %w", err), os.Remove(file.Name()))
+               m.queue.Fail(key)
+       } else {
+               m.queue.Done(key)
+       }
+
+       close(m.changed)
+       m.changed = make(chan struct{})
+       m.dispatch()
+}
+
+// failed logs the failed build of the node key with its cause err.
+func (m *Memory) failed(key NodeKey, err error) {
+       m.logger.Printf("summary failed, retry at next message: node (%d, %d): %v", key.level, key.index, err)
+}
+
+// ready tells if both children of the node key are built and the node is not.
+func (m *Memory) ready(key NodeKey) (bool, error) {
+       for _, index := range []int{2 * key.index, 2*key.index + 1} {
+               built, err := m.tree.Built(key.level-1, index)
+               if err != nil || !built {
+                       return false, err
+               }
+       }
+
+       built, err := m.tree.Built(key.level, key.index)
+
+       return !built, err
+}
+
+func (m *Memory) context(level, index int) string {
+       end := index
+       if level > 0 {
+               end = nodeEnd(level, index)

        }
 
        }
 

-       return syncDir(dir)
+       return m.cview.Context(end)

 }
 
 }
 

-// syncDir flushes the entries of dir to the disk.
-func syncDir(dir string) (err error) {
-       handle, err := os.Open(dir)
+// View returns the chat view as the model reads it.
+func (m *Memory) View() string {
+       m.mutex.Lock()
+       defer m.mutex.Unlock()
+
+       return m.chat.Render()
+}
+
+// Context returns the compaction view for the build of node (l, i). It ends
+// before the message of a leaf, or after the last message of a merge, and it
+// stops at the first line that is not built.
+func (m *Memory) Context(level, index int) string {
+       m.mutex.Lock()
+       defer m.mutex.Unlock()
+
+       return m.context(level, index)
+}
+
+// rebuildComplete checks the whole tree, not only the visible view. A compactor
+// can fail without an HTTP error, for example with an empty line. Such a failed
+// merge can be absent from the view and must prevent a swap.
+func (m *Memory) rebuildComplete() error {
+       m.mutex.Lock()
+       defer m.mutex.Unlock()
+
+       if len(m.queue.leaves) != 0 || len(m.queue.queued) != 0 {
+               return errors.New("rebuild failed: summary tree has unfinished nodes")
+       }
+
+       return nil
+}
+
+// buildModelLines returns the sizes of the nodes that the model wrote, in tree
+// order. A node that fits its source with no model call is not one of them.
+func (m *Memory) buildModelLines() ([]int, error) {
+       m.mutex.Lock()
+       defer m.mutex.Unlock()
+
+       keys, err := m.tree.Keys()

        if err != nil {
        if err != nil {

-               return fmt.Errorf("open directory: %w", err)
+               return nil, fmt.Errorf("list built nodes: %w", err)

        }
 
        }
 

-       defer func() {
-               err = errors.Join(err, handle.Close())
-       }()
+       var sizes []int
+       for _, key := range keys {
+               var node Node

 
 

-       err = handle.Sync()
+               node, _, err = m.tree.Node(key.level, key.index)
+               if err != nil {
+                       return nil, fmt.Errorf("read built node: %w", err)
+               }
+
+               var model bool
+
+               model, err = m.buildBuiltByModel(key)
+               if err != nil {
+                       return nil, fmt.Errorf("check model source: %w", err)
+               }
+
+               if model {
+                       sizes = append(sizes, node.Size)
+               }
+       }
+
+       return sizes, nil
+}
+
+// buildBuiltByModel tells if the node key needed a model call: a leaf whose
+// source is over nodeBytes, or a merge whose children do not fit in one node.
+func (m *Memory) buildBuiltByModel(key NodeKey) (bool, error) {
+       if key.level == 0 {
+               message, err := m.log.Message(key.index)
+               if err != nil {
+                       return false, fmt.Errorf("read leaf source: %w", err)
+               }
+
+               _, free := freeLeaf(message)
+
+               return !free, nil
+       }
+
+       left, right, err := m.children(key)

        if err != nil {
        if err != nil {

-               return fmt.Errorf("flush directory: %w", err)
+               return false, fmt.Errorf("read merge sources: %w", err)

        }
 
        }
 

-       return nil
+       _, free := freeMerge(left, right)
+
+       return !free, nil
+}
+
+// Task is the build of the node (Level, Index). Context is the compaction view
+// for the build. Input holds the source "kind: text" of a leaf, or the two
+// child lines of a merge with their newlines as spaces.
+type Task struct {
+       Level   int
+       Index   int
+       Context string
+       Input   []string
+}
+
+// MemoryViewFile is the content of view.json.
+type MemoryViewFile struct {
+       Chat       ViewState `json:"chat"`
+       Compaction ViewState `json:"compaction"`

 }
 }