X-Git-Url: https://git.giacomolli.uk/onechat/blobdiff_plain/f2d227db9c3b556c7b0e1cfe735ccc54311850e5..2124c559da8f164a43a3da987b399b6ac6125035:/memory.go?ds=sidebyside

diff --git a/memory.go b/memory.go
index 792fe21..a240b6c 100644
--- a/memory.go
+++ b/memory.go
@@ -5,6 +5,7 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"log/slog"
 	"os"
 	"path/filepath"
 	"strings"
@@ -12,24 +13,73 @@ import (
 	"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")
+
+	// 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 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 *slog.Logger) (*Memory, error) {
+	log, err := openLog(ctx, root, clock)
+	if err != nil {
+		return nil, err
+	}
+
+	m := &Memory{
+		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)
+	if err != nil {
+		return nil, errors.Join(err, m.Close())
+	}
+
+	err = m.load()
+	if err != nil {
+		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
+}
 
 // Summarizer builds the text of one node with a model.
 type Summarizer interface {
 	Summarize(ctx context.Context, task Task) (string, error)
 }
 
-// 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
-}
-
 // 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
@@ -52,106 +102,278 @@ type Memory struct {
 	mutex      sync.Mutex
 	root       string
 	log        *Log
-	syncer     *syncer
+	syncer     *Syncer
 	tree       *Tree
 	chat       *View
 	cview      *View
-	queue      *queue
+	queue      *BuildQueue
 	summarizer Summarizer
+	logger     *slog.Logger
 	ctx        context.Context
 	cancel     context.CancelFunc
 	workers    sync.WaitGroup
 	changed    chan struct{}
 }
 
-// viewFile is the content of view.json.
-type viewFile struct {
-	Chat       viewState `json:"chat"`
-	Compaction viewState `json:"compaction"`
+// 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 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, "")
 }
 
-// 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. The builds
-// stop when ctx ends or at Close.
-func openMemory(ctx context.Context, root string, clock func() time.Time, summarizer Summarizer) (*Memory, error) {
-	log, err := openLog(ctx, root, clock)
+// 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()
+
+	return m.appendDated(kind, text, date)
+}
+
+// appendDated appends under the memory lock and updates the views and builds.
+func (m *Memory) appendDated(kind, text, date string) (Message, error) {
+	message, err := m.log.AppendDated(kind, text, date)
 	if err != nil {
-		return nil, err
+		return Message{}, fmt.Errorf("append dated log message: %w", err)
 	}
 
-	m := &Memory{
-		root:       root,
-		log:        log,
-		queue:      newQueue(),
-		summarizer: summarizer,
-		changed:    make(chan struct{}),
-	}
+	defer m.syncer.Written()
 
-	m.ctx, m.cancel = context.WithCancel(ctx)
+	err = m.addMessage(message)
+	if err != nil {
+		return Message{}, fmt.Errorf("add dated message to memory: %w", err)
+	}
 
-	m.syncer, err = openSyncer(root)
+	err = m.save()
 	if err != nil {
-		return nil, errors.Join(err, m.Close())
+		return Message{}, fmt.Errorf("save dated message view: %w", err)
 	}
 
-	m.tree, err = openTree(ctx, root, log.Len(), clock)
+	m.queue.Retry()
+	m.dispatch()
+
+	return message, nil
+}
+
+// AppendOnce appends a queued message. prepare saves its log ID before the
+// append, under the memory lock. A saved ID permits recovery after a stop
+// between that save and the append, without a second log entry. prepare must
+// not call Memory. The caller stops delivery after a failed append.
+func (m *Memory) AppendOnce(kind, text string, id *int, prepare func(int) error) (Message, error) {
+	m.mutex.Lock()
+	defer m.mutex.Unlock()
+
+	if id != nil && *id < m.log.Len() {
+		message, err := m.log.Message(*id)
+		if err != nil {
+			return Message{}, fmt.Errorf("read queued message: %w", err)
+		}
+
+		if message.Kind != kind || message.Text != text {
+			return Message{}, errors.New("queued message does not match its log entry")
+		}
+
+		return message, nil
+	}
+
+	if id != nil && *id != m.log.Len() {
+		return Message{}, errors.New("queued message is beyond the log")
+	}
+
+	err := prepare(m.log.Len())
 	if err != nil {
-		return nil, errors.Join(err, m.Close())
+		return Message{}, fmt.Errorf("prepare queued message: %w", err)
 	}
 
-	err = m.load()
+	message, err := m.appendDated(kind, text, "")
 	if err != nil {
-		return nil, errors.Join(fmt.Errorf("load view: %w", err), m.Close())
+		return Message{}, fmt.Errorf("append queued message: %w", err)
 	}
 
-	err = m.restoreQueue()
+	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
+	}
+
+	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()
+		}
+	}
+}
+
+// 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()
+		}
+	}
+}
+
+// Flush returns when every write before the call is durable.
+func (m *Memory) Flush(ctx context.Context) error {
+	return m.syncer.Flush(ctx)
+}
+
+// Snapshot flushes all memory writes and runs snapshot while no append or
+// summary write can change the log, indexes, tree, or views. snapshot must not
+// call Memory.
+func (m *Memory) Snapshot(ctx context.Context, snapshot func() error) error {
+	m.mutex.Lock()
+	defer m.mutex.Unlock()
+
+	err := m.Flush(ctx)
 	if err != nil {
-		return nil, errors.Join(fmt.Errorf("restore build queue: %w", err), m.Close())
+		return fmt.Errorf("flush memory snapshot: %w", err)
 	}
 
-	err = m.catchUp()
+	err = snapshot()
 	if err != nil {
-		return nil, errors.Join(err, m.Close())
+		return fmt.Errorf("copy memory snapshot: %w", err)
 	}
 
+	return nil
+}
+
+// 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()
-	m.syncer.Written()
-	m.dispatch()
-	m.mutex.Unlock()
+	defer m.mutex.Unlock()
 
-	return m, nil
+	return m.chat.LinesWithout(skip)
+}
+
+// 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()
+}
+
+// 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()
+
+	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(chatHigh, chatLow)
-		m.cview = newView(compactionHigh, compactionLow)
+		m.chat = newView(viewChatHigh, viewChatLow)
+		m.cview = newView(viewCompactionHigh, viewCompactionLow)
 
 		return nil
 	}
 
 	if errors.Is(err, os.ErrNotExist) {
-		return errNoView
+		return errMemoryNoView
 	}
 
 	if err != nil {
 		return fmt.Errorf("read view: %w", err)
 	}
 
-	var file viewFile
+	var file MemoryViewFile
+
 	err = json.Unmarshal(data, &file)
 	if err != nil {
 		return fmt.Errorf("decode view: %w", err)
 	}
 
-	m.chat, err = restoreView(file.Chat, chatHigh, chatLow, m.tree)
+	m.chat, err = restoreView(file.Chat, viewChatHigh, viewChatLow, m.tree)
 	if err != nil {
 		return fmt.Errorf("chat view: %w", err)
 	}
 
-	m.cview, err = restoreView(file.Compaction, compactionHigh, compactionLow, m.tree)
+	m.cview, err = restoreView(file.Compaction, viewCompactionHigh, viewCompactionLow, m.tree)
 	if err != nil {
 		return fmt.Errorf("compaction view: %w", err)
 	}
@@ -188,6 +410,7 @@ func (m *Memory) restoreQueue() error {
 		leaf, free := freeLeaf(message)
 		if !free {
 			m.queue.AddLeaf(id)
+
 			continue
 		}
 
@@ -238,54 +461,27 @@ func (m *Memory) catchUp() error {
 	return m.save()
 }
 
-// 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 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) {
-	m.mutex.Lock()
-	defer m.mutex.Unlock()
+// 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
+		}
 
-	message, err := m.log.Append(kind, text)
-	if err != nil {
-		return Message{}, err
-	}
+		task, err := m.task(key)
+		if err != nil {
+			m.failed(key, fmt.Errorf("read its input: %w", err))
+			m.queue.Fail(key)
 
-	defer m.syncer.Written()
+			continue
+		}
 
-	err = m.addMessage(message)
-	if err != nil {
-		return Message{}, err
-	}
+		m.workers.Add(1)
 
-	err = m.save()
-	if err != nil {
-		return Message{}, err
+		go m.run(key, task)
 	}
-
-	m.queue.Retry()
-	m.dispatch()
-
-	return message, nil
 }
 
 // addMessage builds the leaf of message when it needs no model call, or else
@@ -327,6 +523,28 @@ func (m *Memory) addMessage(message Message) error {
 	return nil
 }
 
+// save writes the views to view.json.
+func (m *Memory) save() error {
+	data, err := json.Marshal(MemoryViewFile{
+		Chat:       m.chat.State(),
+		Compaction: m.cview.State(),
+	})
+	if err != nil {
+		return fmt.Errorf("encode view: %w", err)
+	}
+
+	err = writeFileAtomic(m.viewPath(), append(data, '\n'))
+	if err != nil {
+		return fmt.Errorf("save view: %w", err)
+	}
+
+	return nil
+}
+
+func (m *Memory) viewPath() string {
+	return filepath.Join(m.root, "view.json")
+}
+
 // 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 {
@@ -338,15 +556,15 @@ func (m *Memory) build(node Node) error {
 	m.chat.Refresh(node)
 	m.cview.Refresh(node)
 
-	return m.settle(nodeKey{node.Level, node.Index})
+	return m.settle(NodeKey{node.Level, node.Index})
 }
 
 // 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 {
+func (m *Memory) settle(key NodeKey) error {
 	for {
-		parent := nodeKey{key.level + 1, key.index / 2}
+		parent := NodeKey{key.level + 1, key.index / 2}
 		ready, err := m.ready(parent)
 		if err != nil || !ready {
 			return err
@@ -360,6 +578,7 @@ func (m *Memory) settle(key nodeKey) error {
 		node, free := freeMerge(left, right)
 		if !free {
 			m.queue.AddMerge(parent)
+
 			return nil
 		}
 
@@ -372,62 +591,9 @@ func (m *Memory) settle(key nodeKey) error {
 	}
 }
 
-// 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
-}
-
-// 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
-	}
-
-	return children[0], children[1], nil
-}
-
-// 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
-		}
-
-		task, err := m.task(key)
-		if err != nil {
-			m.queue.Fail(key)
-			continue
-		}
-
-		m.workers.Add(1)
-		go m.run(key, task)
-	}
-}
-
 // 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) {
+func (m *Memory) task(key NodeKey) (Task, error) {
 	task := Task{
 		Level:   key.level,
 		Index:   key.index,
@@ -459,7 +625,7 @@ func (m *Memory) task(key nodeKey) (Task, error) {
 
 // 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) {
+func (m *Memory) run(key NodeKey, task Task) {
 	defer m.workers.Done()
 
 	text, err := m.summarizer.Summarize(m.ctx, task)
@@ -477,6 +643,10 @@ func (m *Memory) run(key nodeKey, task Task) {
 		m.syncer.Written()
 	}
 
+	if err != nil && m.ctx.Err() == nil {
+		m.failed(key, err)
+	}
+
 	if err != nil {
 		m.queue.Fail(key)
 	} else {
@@ -484,55 +654,37 @@ func (m *Memory) run(key nodeKey, task Task) {
 	}
 
 	close(m.changed)
+
 	m.changed = make(chan struct{})
 	m.dispatch()
 }
 
-// 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
-		}
+// failed logs the failed build of the node key with its cause err.
+func (m *Memory) failed(key NodeKey, err error) {
+	m.logger.Warn("summary failed", "level", key.level, "index", key.index, "err", err)
+}
 
-		select {
-		case <-changed:
-		case <-ctx.Done():
-			return ctx.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
 		}
 	}
-}
 
-// Flush returns when every write before the call is durable.
-func (m *Memory) Flush(ctx context.Context) error {
-	return m.syncer.Flush(ctx)
-}
+	built, err := m.tree.Built(key.level, key.index)
 
-// save writes the views to view.json.
-func (m *Memory) save() error {
-	data, err := json.Marshal(viewFile{
-		Chat:       m.chat.State(),
-		Compaction: m.cview.State(),
-	})
-	if err != nil {
-		return fmt.Errorf("encode view: %w", err)
-	}
+	return !built, err
+}
 
-	err = writeFileAtomic(m.viewPath(), append(data, '\n'))
-	if err != nil {
-		return fmt.Errorf("save view: %w", err)
+func (m *Memory) context(level, index int) string {
+	end := index
+	if level > 0 {
+		end = nodeEnd(level, index)
 	}
 
-	return nil
-}
-
-func (m *Memory) viewPath() string {
-	return filepath.Join(m.root, "view.json")
+	return m.cview.Context(end)
 }
 
 // View returns the chat view as the model reads it.
@@ -543,45 +695,102 @@ func (m *Memory) View() string {
 	return m.chat.Render()
 }
 
-// Len returns the number of messages in the log.
-func (m *Memory) Len() int {
+// 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.log.Len()
+	return m.context(level, index)
 }
 
-// Message reads the message with the given ID.
-func (m *Memory) Message(id int) (Message, error) {
+// 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()
 
-	return m.log.Message(id)
+	if len(m.queue.leaves) != 0 || len(m.queue.queued) != 0 {
+		return errors.New("rebuild failed: summary tree has unfinished nodes")
+	}
+
+	return nil
 }
 
-// Node reads the node (l, i) if it is built.
-func (m *Memory) Node(level, index int) (Node, bool, error) {
+// 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()
 
-	return m.tree.Node(level, index)
-}
+	keys, err := m.tree.Keys()
+	if err != nil {
+		return nil, fmt.Errorf("list built nodes: %w", err)
+	}
 
-// 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()
+	var sizes []int
 
-	return m.context(level, index)
+	for _, key := range keys {
+		var node Node
+
+		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
 }
 
-func (m *Memory) context(level, index int) string {
-	end := index
-	if level > 0 {
-		end = nodeEnd(level, index)
+// 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
 	}
 
-	return m.cview.Context(end)
+	left, right, err := m.children(key)
+	if err != nil {
+		return false, fmt.Errorf("read merge sources: %w", err)
+	}
+
+	_, 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"`
 }