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6 changes: 3 additions & 3 deletions agent/compaction/doc.go
Original file line number Diff line number Diff line change
@@ -1,7 +1,7 @@
// Copyright (c) Microsoft. All rights reserved.

// Package compaction reduces conversation history to fit a model's context
// window. It provides a context provider and composable strategies — sliding
// window, truncation, summarization, tool-result eviction, and context-window
// sizing — selected by triggers evaluated over a message index.
// window. It provides history and context providers plus composable strategies
// — sliding window, truncation, summarization, tool-result eviction, and
// context-window sizing — selected by triggers evaluated over a message index.
package compaction
240 changes: 240 additions & 0 deletions agent/compaction/historyprovider.go
Original file line number Diff line number Diff line change
@@ -0,0 +1,240 @@
// Copyright (c) Microsoft. All rights reserved.

package compaction

import (
"cmp"
"context"
"log/slog"
"runtime"
"slices"
"sync"
"weak"

"github.com/microsoft/agent-framework-go/agent"
"github.com/microsoft/agent-framework-go/message"
"github.com/microsoft/agent-framework-go/message/messagefilter"
)

const defaultHistoryProviderSourceID = "CompactionHistoryProvider"

// HistoryProviderConfig configures the provider created by [NewHistoryProvider].
type HistoryProviderConfig struct {
// Strategy is the compaction strategy applied to persisted history.
Strategy Strategy

// SourceID identifies messages loaded from this provider.
// When empty, a default compaction history provider source ID is used.
SourceID string

// StateKey identifies where provider state is stored in the session.
// When empty, SourceID is used.
StateKey string

// StateInitializer returns initial messages on first use.
// When nil, no initial messages are used.
StateInitializer func(*agent.Session) []*message.Message

// Optional filter applied to messages loaded from storage before they are included.
// Defaults to passing all loaded messages through.
ProvideOutputMessageFilter messagefilter.Filter

// Optional filter applied to request messages before storing them.
// Defaults to messages that did not come from a history provider.
StoreInputRequestMessageFilter messagefilter.Filter

// Optional filter applied to response messages before storing them.
// Defaults to passing all response messages through.
StoreInputResponseMessageFilter messagefilter.Filter

// TokenCounter computes token counts for message groups.
// When nil, token counts are estimated from UTF-8 byte counts.
TokenCounter TokenCounter

// Logger emits provider diagnostics when set.
Logger *slog.Logger
}

type historyProviderState struct {
Messages []*message.Message `json:"messages,omitempty"`
}

type historyProviderSessionLocks struct {
locks sync.Map // map[weak.Pointer[agent.Session]]*sync.Mutex
nullSessionLock sync.Mutex
}

type historyProvider struct {
config HistoryProviderConfig
locks *historyProviderSessionLocks
}

func (l *historyProviderSessionLocks) forOptions(options []agent.Option) *sync.Mutex {
session, _ := agent.GetOption(options, agent.WithSession)
if session == nil {
return &l.nullSessionLock
}
key := weak.Make(session)
if existing, ok := l.locks.Load(key); ok {
return existing.(*sync.Mutex)
}
actual, loaded := l.locks.LoadOrStore(key, &sync.Mutex{})
if !loaded {
runtime.AddCleanup(session, func(k weak.Pointer[agent.Session]) {
l.locks.Delete(k)
}, key)
}
return actual.(*sync.Mutex)
}

// NewHistoryProvider creates a session-backed history provider that compacts stored history.
//
// The provider stores conversation history in the session like [agent.NewInMemoryHistoryProvider],
// but it automatically applies Strategy whenever history is loaded or updated. This gives history
// providers first-class reducer-trigger behavior without requiring a separate context provider.
func NewHistoryProvider(cfg HistoryProviderConfig) agent.HistoryProvider {
if cfg.Strategy == nil {
panic("Strategy is required")
}
cfg.SourceID = cmp.Or(cfg.SourceID, defaultHistoryProviderSourceID)
cfg.StateKey = cmp.Or(cfg.StateKey, cfg.SourceID)
return &historyProvider{config: cfg, locks: new(historyProviderSessionLocks)}
}

func (p *historyProvider) Invoking(ctx context.Context, invoking agent.InvokingContext) ([]*message.Message, error) {
mu := p.locks.forOptions(invoking.Options)
mu.Lock()
defer mu.Unlock()

session, _ := agent.GetOption(invoking.Options, agent.WithSession)
if session == nil {
return invoking.Messages, nil
}
state, err := getHistoryProviderState(session, p.config.StateKey, p.config.StateInitializer)
if err != nil {
return nil, err
}

history := slices.Clone(state.Messages)
if p.config.ProvideOutputMessageFilter != nil {
history, err = p.config.ProvideOutputMessageFilter(ctx, history)
if err != nil {
return nil, err
}
}

source := message.Source{Type: agent.SourceTypeHistoryProvider, ID: p.config.SourceID}
messages := make([]*message.Message, 0, len(history)+len(invoking.Messages))
for _, msg := range history {
if msg == nil {
messages = append(messages, nil)
} else {
messages = append(messages, msg.WithSource(source))
}
}
messages = append(messages, invoking.Messages...)

compacted, err := compactHistory(ctx, p.config.Strategy, messages, p.config.TokenCounter, p.config.Logger)
if err != nil {
return nil, err
}
inputMessages := make(map[*message.Message]struct{}, len(invoking.Messages))
for _, msg := range invoking.Messages {
inputMessages[msg] = struct{}{}
}
for i, msg := range compacted {
if msg == nil || msg.Source == source {
continue
}
if _, ok := inputMessages[msg]; !ok {
compacted[i] = msg.WithSource(source)
}
}
return compacted, nil
}

func (p *historyProvider) Invoked(ctx context.Context, invoked agent.InvokedContext) error {
if invoked.Err != nil {
return nil
}

requestFilter := p.config.StoreInputRequestMessageFilter
if requestFilter == nil {
requestFilter = messagefilter.NotSourceTypes(agent.SourceTypeHistoryProvider)
}
filteredRequest, err := requestFilter(ctx, slices.Clone(invoked.RequestMessages))
if err != nil {
return err
}
filteredResponse := invoked.ResponseMessages
if p.config.StoreInputResponseMessageFilter != nil {
filteredResponse, err = p.config.StoreInputResponseMessageFilter(ctx, slices.Clone(invoked.ResponseMessages))
if err != nil {
return err
}
}

mu := p.locks.forOptions(invoked.Options)
mu.Lock()
defer mu.Unlock()

session, _ := agent.GetOption(invoked.Options, agent.WithSession)
if session == nil {
return nil
}
state, err := getHistoryProviderState(session, p.config.StateKey, p.config.StateInitializer)
if err != nil {
return err
}

messages := slices.Clone(state.Messages)
if p.config.ProvideOutputMessageFilter != nil {
messages, err = p.config.ProvideOutputMessageFilter(ctx, messages)
if err != nil {
return err
}
}
messages = append(messages, filteredRequest...)
messages = append(messages, filteredResponse...)

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NewHistoryProvider applies Strategy.Compact in both Invoking (line ~137, transient history returned to the model) and Invoked (line ~199, persisted session state), i.e. twice per turn with no way to select a single trigger point.

Upstream InMemoryChatHistoryProviderOptions.ReducerTriggerEvent (dotnet/src/Microsoft.Agents.AI.Abstractions/InMemoryChatHistoryProviderOptions.cs) only ever fires the reducer at one configurable point — BeforeMessagesRetrieval (default) or AfterMessageAdded — precisely to avoid redundant reducer invocations. InMemoryChatHistoryProvider.cs (ProvideChatHistoryAsync/StoreChatHistoryAsync) shows the reducer is gated by if (this.ReducerTriggerEvent is ... ) at each site, never both.

For SummarizationStrategy (LLM-backed), this divergence causes an extra summarizer call every turn versus the .NET pattern. Consider adding a trigger-point option (defaulting to pre-retrieval only, matching .NET) or applying the strategy at just one of the two lifecycle points, unless the double application to keep persisted state always-compacted is an intentional, documented divergence.

compacted, err := compactHistory(ctx, p.config.Strategy, messages, p.config.TokenCounter, p.config.Logger)
if err != nil {
return err
}
state.Messages = slices.Clone(compacted)
session.Set(p.config.StateKey, state)
return nil
}

func getHistoryProviderState(session *agent.Session, stateKey string, initializer func(*agent.Session) []*message.Message) (historyProviderState, error) {
var state historyProviderState
if ok, err := session.Get(stateKey, &state); err != nil {
return state, err
} else if ok {
return state, nil
}
if initializer != nil {
state.Messages = slices.Clone(initializer(session))
}
session.Set(stateKey, state)
return state, nil
}

func compactHistory(ctx context.Context, strategy Strategy, messages []*message.Message, tokenCounter TokenCounter, logger *slog.Logger) ([]*message.Message, error) {
if len(messages) == 0 {
return nil, nil
}
index := CreateMessageIndex(messages, tokenCounter)
beforeMessages := index.IncludedMessageCount()
if logger != nil {
logger.DebugContext(ctx, "applying history compaction", slog.Int("messages", beforeMessages))
}
if _, err := strategy.Compact(ctx, index); err != nil {
return nil, err
}
afterMessages := index.IncludedMessageCount()
if logger != nil && afterMessages < beforeMessages {
logger.DebugContext(ctx, "history compaction applied", slog.Int("before_messages", beforeMessages), slog.Int("after_messages", afterMessages))
}
return index.IncludedMessages(), nil
}
143 changes: 143 additions & 0 deletions agent/compaction/historyprovider_test.go
Original file line number Diff line number Diff line change
@@ -0,0 +1,143 @@
// Copyright (c) Microsoft. All rights reserved.

package compaction_test

import (
"context"
"encoding/json"
"slices"
"testing"

"github.com/microsoft/agent-framework-go/agent"
"github.com/microsoft/agent-framework-go/agent/compaction"
"github.com/microsoft/agent-framework-go/internal/agenttest"
"github.com/microsoft/agent-framework-go/message"
"github.com/microsoft/agent-framework-go/message/messagefilter"
)

func invokeHistoryProvider(provider agent.HistoryProvider, ctx context.Context, messages []*message.Message, options ...agent.Option) ([]*message.Message, error) {
return provider.Invoking(ctx, agent.InvokingContext{Messages: messages, Options: options})
}

func invokeHistoryProviderInvoked(provider agent.HistoryProvider, ctx context.Context, requestMessages, responseMessages []*message.Message, options ...agent.Option) error {
return provider.Invoked(ctx, agent.InvokedContext{RequestMessages: requestMessages, ResponseMessages: responseMessages, Options: options})
}

func TestNewHistoryProvider_CompactsPersistedHistory(t *testing.T) {
session := agenttest.CreateSession()
minimumPreservedGroups := 2
provider := compaction.NewHistoryProvider(compaction.HistoryProviderConfig{
SourceID: "compaction-history",
Strategy: &compaction.TruncationStrategy{
Trigger: compaction.GroupsExceed(2),
MinimumPreservedGroups: &minimumPreservedGroups,
},
})

if err := invokeHistoryProviderInvoked(provider, t.Context(), []*message.Message{textMessage(message.RoleUser, "u1")}, []*message.Message{textMessage(message.RoleAssistant, "a1")}, agent.WithSession(session)); err != nil {
t.Fatalf("store turn 1: %v", err)
}
if err := invokeHistoryProviderInvoked(provider, t.Context(), []*message.Message{textMessage(message.RoleUser, "u2")}, []*message.Message{textMessage(message.RoleAssistant, "a2")}, agent.WithSession(session)); err != nil {
t.Fatalf("store turn 2: %v", err)
}

loaded, err := invokeHistoryProvider(provider, t.Context(), []*message.Message{textMessage(message.RoleUser, "u3")}, agent.WithSession(session))
if err != nil {
t.Fatalf("load history: %v", err)
}
if got, want := messageTexts(loaded), []string{"a2", "u3"}; !slices.Equal(got, want) {
t.Fatalf("loaded history = %v, want %v", got, want)
}

if got, want := loaded[0].Source, (message.Source{Type: agent.SourceTypeHistoryProvider, ID: "compaction-history"}); got != want {
t.Fatalf("history source = %#v, want %#v", got, want)
}

data, err := json.Marshal(session)
if err != nil {
t.Fatalf("marshal session: %v", err)
}
restored := agenttest.CreateSession()
if err := json.Unmarshal(data, restored); err != nil {
t.Fatalf("unmarshal session: %v", err)
}

var state struct {
Messages []*message.Message `json:"messages,omitempty"`
}
if ok, err := restored.Get("compaction-history", &state); err != nil || !ok {
t.Fatalf("expected persisted state, ok=%v err=%v", ok, err)
}
if got, want := messageTexts(state.Messages), []string{"u2", "a2"}; !slices.Equal(got, want) {
t.Fatalf("persisted history = %v, want %v", got, want)
}
}

func TestNewHistoryProvider_FiltersHistoryBeforeSummarization(t *testing.T) {
session := agenttest.CreateSession()
minimumPreservedGroups := 2
secret := textMessage(message.RoleUser, "secret")
secret.Source = message.Source{Type: agent.SourceTypeContextProvider, ID: "private"}
var summarized []*message.Message
provider := compaction.NewHistoryProvider(compaction.HistoryProviderConfig{
SourceID: "compaction-history",
StateInitializer: func(*agent.Session) []*message.Message {
return []*message.Message{
secret,
textMessage(message.RoleAssistant, "visible 1"),
textMessage(message.RoleUser, "visible 2"),
}
},
ProvideOutputMessageFilter: messagefilter.ExternalOnly,
Strategy: &compaction.SummarizationStrategy{
Trigger: compaction.GroupsExceed(2),
Summarizer: compaction.SummarizerFunc(func(_ context.Context, messages []*message.Message) (string, error) {
summarized = slices.Clone(messages)
return "visible context", nil
}),
MinimumPreservedGroups: &minimumPreservedGroups,
},
})

loaded, err := invokeHistoryProvider(provider, t.Context(), []*message.Message{textMessage(message.RoleUser, "current")}, agent.WithSession(session))
if err != nil {
t.Fatalf("load history: %v", err)
}
if got, want := messageTexts(loaded), []string{"[Summary]\nvisible context", "visible 2", "current"}; !slices.Equal(got, want) {
t.Fatalf("loaded history = %v, want %v", got, want)
}
if slices.Contains(messageTexts(summarized), "secret") {
t.Fatalf("filtered message was summarized: %v", messageTexts(summarized))
}
}

func TestNewHistoryProvider_LoadsCompactedSummaryAsHistory(t *testing.T) {
session := agenttest.CreateSession()
minimumPreservedGroups := 2
provider := compaction.NewHistoryProvider(compaction.HistoryProviderConfig{
SourceID: "compaction-history",
Strategy: &compaction.SummarizationStrategy{
Trigger: compaction.GroupsExceed(2),
Summarizer: compaction.SummarizerFunc(func(context.Context, []*message.Message) (string, error) { return "older context", nil }),
MinimumPreservedGroups: &minimumPreservedGroups,
},
})

if err := invokeHistoryProviderInvoked(provider, t.Context(), []*message.Message{textMessage(message.RoleUser, "u1")}, []*message.Message{textMessage(message.RoleAssistant, "a1")}, agent.WithSession(session)); err != nil {
t.Fatalf("store turn 1: %v", err)
}
if err := invokeHistoryProviderInvoked(provider, t.Context(), []*message.Message{textMessage(message.RoleUser, "u2")}, []*message.Message{textMessage(message.RoleAssistant, "a2")}, agent.WithSession(session)); err != nil {
t.Fatalf("store turn 2: %v", err)
}

loaded, err := invokeHistoryProvider(provider, t.Context(), []*message.Message{textMessage(message.RoleUser, "u3")}, agent.WithSession(session))
if err != nil {
t.Fatalf("load history: %v", err)
}
if got, want := messageTexts(loaded), []string{"[Summary]\nolder context", "a2", "u3"}; !slices.Equal(got, want) {
t.Fatalf("loaded history = %v, want %v", got, want)
}
if got, want := loaded[0].Source, (message.Source{Type: agent.SourceTypeHistoryProvider, ID: "compaction-history"}); got != want {
t.Fatalf("summary source = %#v, want %#v", got, want)
}
}
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