feat(agent): split harness compaction and session modules

This commit is contained in:
Mario Zechner
2026-05-03 03:13:45 +02:00
parent a5b27367d3
commit 83599e789d
13 changed files with 1910 additions and 939 deletions

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/**
* Branch summarization for tree navigation.
*
* When navigating to a different point in the session tree, this generates
* a summary of the branch being left so context isn't lost.
*/
import type { Model } from "@mariozechner/pi-ai";
import { completeSimple } from "@mariozechner/pi-ai";
import type { AgentMessage } from "../../types.js";
import {
convertToLlm,
createBranchSummaryMessage,
createCompactionSummaryMessage,
createCustomMessage,
} from "../messages.js";
import type { SessionTree, SessionTreeEntry } from "../types.js";
import { estimateTokens } from "./compaction.js";
import {
computeFileLists,
createFileOps,
extractFileOpsFromMessage,
type FileOperations,
formatFileOperations,
SUMMARIZATION_SYSTEM_PROMPT,
serializeConversation,
} from "./utils.js";
// ============================================================================
// Types
// ============================================================================
export interface BranchSummaryResult {
summary?: string;
readFiles?: string[];
modifiedFiles?: string[];
aborted?: boolean;
error?: string;
}
/** Details stored in BranchSummaryEntry.details for file tracking */
export interface BranchSummaryDetails {
readFiles: string[];
modifiedFiles: string[];
}
export type { FileOperations } from "./utils.js";
export interface BranchPreparation {
/** Messages extracted for summarization, in chronological order */
messages: AgentMessage[];
/** File operations extracted from tool calls */
fileOps: FileOperations;
/** Total estimated tokens in messages */
totalTokens: number;
}
export interface CollectEntriesResult {
/** Entries to summarize, in chronological order */
entries: SessionTreeEntry[];
/** Common ancestor between old and new position, if any */
commonAncestorId: string | null;
}
export interface GenerateBranchSummaryOptions {
/** Model to use for summarization */
model: Model<any>;
/** API key for the model */
apiKey: string;
/** Request headers for the model */
headers?: Record<string, string>;
/** Abort signal for cancellation */
signal: AbortSignal;
/** Optional custom instructions for summarization */
customInstructions?: string;
/** If true, customInstructions replaces the default prompt instead of being appended */
replaceInstructions?: boolean;
/** Tokens reserved for prompt + LLM response (default 16384) */
reserveTokens?: number;
}
// ============================================================================
// Entry Collection
// ============================================================================
/**
* Collect entries that should be summarized when navigating from one position to another.
*
* Walks from oldLeafId back to the common ancestor with targetId, collecting entries
* along the way. Does NOT stop at compaction boundaries - those are included and their
* summaries become context.
*
* @param session - Session manager (read-only access)
* @param oldLeafId - Current position (where we're navigating from)
* @param targetId - Target position (where we're navigating to)
* @returns Entries to summarize and the common ancestor
*/
export async function collectEntriesForBranchSummary(
session: SessionTree,
oldLeafId: string | null,
targetId: string,
): Promise<CollectEntriesResult> {
// If no old position, nothing to summarize
if (!oldLeafId) {
return { entries: [], commonAncestorId: null };
}
// Find common ancestor (deepest node that's on both paths)
const oldPath = new Set((await session.getBranch(oldLeafId)).map((e) => e.id));
const targetPath = await session.getBranch(targetId);
// targetPath is root-first, so iterate backwards to find deepest common ancestor
let commonAncestorId: string | null = null;
for (let i = targetPath.length - 1; i >= 0; i--) {
if (oldPath.has(targetPath[i].id)) {
commonAncestorId = targetPath[i].id;
break;
}
}
// Collect entries from old leaf back to common ancestor
const entries: SessionTreeEntry[] = [];
let current: string | null = oldLeafId;
while (current && current !== commonAncestorId) {
const entry = await session.getEntry(current);
if (!entry) break;
entries.push(entry);
current = entry.parentId;
}
// Reverse to get chronological order
entries.reverse();
return { entries, commonAncestorId };
}
// ============================================================================
// Entry to Message Conversion
// ============================================================================
/**
* Extract AgentMessage from a session entry.
* Similar to getMessageFromEntry in compaction.ts but also handles compaction entries.
*/
function getMessageFromEntry(entry: SessionTreeEntry): AgentMessage | undefined {
switch (entry.type) {
case "message":
// Skip tool results - context is in assistant's tool call
if (entry.message.role === "toolResult") return undefined;
return entry.message;
case "custom_message":
return createCustomMessage(entry.customType, entry.content, entry.display, entry.details, entry.timestamp);
case "branch_summary":
return createBranchSummaryMessage(entry.summary, entry.fromId, entry.timestamp);
case "compaction":
return createCompactionSummaryMessage(entry.summary, entry.tokensBefore, entry.timestamp);
// These don't contribute to conversation content
case "thinking_level_change":
case "model_change":
case "custom":
case "label":
case "session_info":
return undefined;
}
}
/**
* Prepare entries for summarization with token budget.
*
* Walks entries from NEWEST to OLDEST, adding messages until we hit the token budget.
* This ensures we keep the most recent context when the branch is too long.
*
* Also collects file operations from:
* - Tool calls in assistant messages
* - Existing branch_summary entries' details (for cumulative tracking)
*
* @param entries - Entries in chronological order
* @param tokenBudget - Maximum tokens to include (0 = no limit)
*/
export function prepareBranchEntries(entries: SessionTreeEntry[], tokenBudget: number = 0): BranchPreparation {
const messages: AgentMessage[] = [];
const fileOps = createFileOps();
let totalTokens = 0;
// First pass: collect file ops from ALL entries (even if they don't fit in token budget)
// This ensures we capture cumulative file tracking from nested branch summaries
// Only extract from pi-generated summaries (fromHook !== true), not extension-generated ones
for (const entry of entries) {
if (entry.type === "branch_summary" && !entry.fromHook && entry.details) {
const details = entry.details as BranchSummaryDetails;
if (Array.isArray(details.readFiles)) {
for (const f of details.readFiles) fileOps.read.add(f);
}
if (Array.isArray(details.modifiedFiles)) {
// Modified files go into both edited and written for proper deduplication
for (const f of details.modifiedFiles) {
fileOps.edited.add(f);
}
}
}
}
// Second pass: walk from newest to oldest, adding messages until token budget
for (let i = entries.length - 1; i >= 0; i--) {
const entry = entries[i];
const message = getMessageFromEntry(entry);
if (!message) continue;
// Extract file ops from assistant messages (tool calls)
extractFileOpsFromMessage(message, fileOps);
const tokens = estimateTokens(message);
// Check budget before adding
if (tokenBudget > 0 && totalTokens + tokens > tokenBudget) {
// If this is a summary entry, try to fit it anyway as it's important context
if (entry.type === "compaction" || entry.type === "branch_summary") {
if (totalTokens < tokenBudget * 0.9) {
messages.unshift(message);
totalTokens += tokens;
}
}
// Stop - we've hit the budget
break;
}
messages.unshift(message);
totalTokens += tokens;
}
return { messages, fileOps, totalTokens };
}
// ============================================================================
// Summary Generation
// ============================================================================
const BRANCH_SUMMARY_PREAMBLE = `The user explored a different conversation branch before returning here.
Summary of that exploration:
`;
const BRANCH_SUMMARY_PROMPT = `Create a structured summary of this conversation branch for context when returning later.
Use this EXACT format:
## Goal
[What was the user trying to accomplish in this branch?]
## Constraints & Preferences
- [Any constraints, preferences, or requirements mentioned]
- [Or "(none)" if none were mentioned]
## Progress
### Done
- [x] [Completed tasks/changes]
### In Progress
- [ ] [Work that was started but not finished]
### Blocked
- [Issues preventing progress, if any]
## Key Decisions
- **[Decision]**: [Brief rationale]
## Next Steps
1. [What should happen next to continue this work]
Keep each section concise. Preserve exact file paths, function names, and error messages.`;
/**
* Generate a summary of abandoned branch entries.
*
* @param entries - Session entries to summarize (chronological order)
* @param options - Generation options
*/
export async function generateBranchSummary(
entries: SessionTreeEntry[],
options: GenerateBranchSummaryOptions,
): Promise<BranchSummaryResult> {
const { model, apiKey, headers, signal, customInstructions, replaceInstructions, reserveTokens = 16384 } = options;
// Token budget = context window minus reserved space for prompt + response
const contextWindow = model.contextWindow || 128000;
const tokenBudget = contextWindow - reserveTokens;
const { messages, fileOps } = prepareBranchEntries(entries, tokenBudget);
if (messages.length === 0) {
return { summary: "No content to summarize" };
}
// Transform to LLM-compatible messages, then serialize to text
// Serialization prevents the model from treating it as a conversation to continue
const llmMessages = convertToLlm(messages);
const conversationText = serializeConversation(llmMessages);
// Build prompt
let instructions: string;
if (replaceInstructions && customInstructions) {
instructions = customInstructions;
} else if (customInstructions) {
instructions = `${BRANCH_SUMMARY_PROMPT}\n\nAdditional focus: ${customInstructions}`;
} else {
instructions = BRANCH_SUMMARY_PROMPT;
}
const promptText = `<conversation>\n${conversationText}\n</conversation>\n\n${instructions}`;
const summarizationMessages = [
{
role: "user" as const,
content: [{ type: "text" as const, text: promptText }],
timestamp: Date.now(),
},
];
// Call LLM for summarization
const response = await completeSimple(
model,
{ systemPrompt: SUMMARIZATION_SYSTEM_PROMPT, messages: summarizationMessages },
{ apiKey, headers, signal, maxTokens: 2048 },
);
// Check if aborted or errored
if (response.stopReason === "aborted") {
return { aborted: true };
}
if (response.stopReason === "error") {
return { error: response.errorMessage || "Summarization failed" };
}
let summary = response.content
.filter((c): c is { type: "text"; text: string } => c.type === "text")
.map((c) => c.text)
.join("\n");
// Prepend preamble to provide context about the branch summary
summary = BRANCH_SUMMARY_PREAMBLE + summary;
// Compute file lists and append to summary
const { readFiles, modifiedFiles } = computeFileLists(fileOps);
summary += formatFileOperations(readFiles, modifiedFiles);
return {
summary: summary || "No summary generated",
readFiles,
modifiedFiles,
};
}

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/**
* Context compaction for long sessions.
*
* Pure functions for compaction logic. The session manager handles I/O,
* and after compaction the session is reloaded.
*/
import type { AssistantMessage, Model, Usage } from "@mariozechner/pi-ai";
import { completeSimple } from "@mariozechner/pi-ai";
import type { AgentMessage, ThinkingLevel } from "../../types.js";
import {
convertToLlm,
createBranchSummaryMessage,
createCompactionSummaryMessage,
createCustomMessage,
} from "../messages.js";
import { buildSessionContext } from "../session/session-tree.js";
import type { CompactionEntry, SessionTreeEntry } from "../types.js";
import {
computeFileLists,
createFileOps,
extractFileOpsFromMessage,
type FileOperations,
formatFileOperations,
SUMMARIZATION_SYSTEM_PROMPT,
serializeConversation,
} from "./utils.js";
// ============================================================================
// File Operation Tracking
// ============================================================================
/** Details stored in CompactionEntry.details for file tracking */
export interface CompactionDetails {
readFiles: string[];
modifiedFiles: string[];
}
/**
* Extract file operations from messages and previous compaction entries.
*/
function extractFileOperations(
messages: AgentMessage[],
entries: SessionTreeEntry[],
prevCompactionIndex: number,
): FileOperations {
const fileOps = createFileOps();
// Collect from previous compaction's details (if pi-generated)
if (prevCompactionIndex >= 0) {
const prevCompaction = entries[prevCompactionIndex] as CompactionEntry;
if (!prevCompaction.fromHook && prevCompaction.details) {
// fromHook field kept for session file compatibility
const details = prevCompaction.details as CompactionDetails;
if (Array.isArray(details.readFiles)) {
for (const f of details.readFiles) fileOps.read.add(f);
}
if (Array.isArray(details.modifiedFiles)) {
for (const f of details.modifiedFiles) fileOps.edited.add(f);
}
}
}
// Extract from tool calls in messages
for (const msg of messages) {
extractFileOpsFromMessage(msg, fileOps);
}
return fileOps;
}
// ============================================================================
// Message Extraction
// ============================================================================
/**
* Extract AgentMessage from an entry if it produces one.
* Returns undefined for entries that don't contribute to LLM context.
*/
function getMessageFromEntry(entry: SessionTreeEntry): AgentMessage | undefined {
if (entry.type === "message") {
return entry.message;
}
if (entry.type === "custom_message") {
return createCustomMessage(entry.customType, entry.content, entry.display, entry.details, entry.timestamp);
}
if (entry.type === "branch_summary") {
return createBranchSummaryMessage(entry.summary, entry.fromId, entry.timestamp);
}
if (entry.type === "compaction") {
return createCompactionSummaryMessage(entry.summary, entry.tokensBefore, entry.timestamp);
}
return undefined;
}
function getMessageFromEntryForCompaction(entry: SessionTreeEntry): AgentMessage | undefined {
if (entry.type === "compaction") {
return undefined;
}
return getMessageFromEntry(entry);
}
/** Result from compact() - SessionManager adds uuid/parentUuid when saving */
export interface CompactionResult<T = unknown> {
summary: string;
firstKeptEntryId: string;
tokensBefore: number;
/** Extension-specific data (e.g., ArtifactIndex, version markers for structured compaction) */
details?: T;
}
// ============================================================================
// Types
// ============================================================================
export interface CompactionSettings {
enabled: boolean;
reserveTokens: number;
keepRecentTokens: number;
}
export const DEFAULT_COMPACTION_SETTINGS: CompactionSettings = {
enabled: true,
reserveTokens: 16384,
keepRecentTokens: 20000,
};
// ============================================================================
// Token calculation
// ============================================================================
/**
* Calculate total context tokens from usage.
* Uses the native totalTokens field when available, falls back to computing from components.
*/
export function calculateContextTokens(usage: Usage): number {
return usage.totalTokens || usage.input + usage.output + usage.cacheRead + usage.cacheWrite;
}
/**
* Get usage from an assistant message if available.
* Skips aborted and error messages as they don't have valid usage data.
*/
function getAssistantUsage(msg: AgentMessage): Usage | undefined {
if (msg.role === "assistant" && "usage" in msg) {
const assistantMsg = msg as AssistantMessage;
if (assistantMsg.stopReason !== "aborted" && assistantMsg.stopReason !== "error" && assistantMsg.usage) {
return assistantMsg.usage;
}
}
return undefined;
}
/**
* Find the last non-aborted assistant message usage from session entries.
*/
export function getLastAssistantUsage(entries: SessionTreeEntry[]): Usage | undefined {
for (let i = entries.length - 1; i >= 0; i--) {
const entry = entries[i];
if (entry.type === "message") {
const usage = getAssistantUsage(entry.message);
if (usage) return usage;
}
}
return undefined;
}
export interface ContextUsageEstimate {
tokens: number;
usageTokens: number;
trailingTokens: number;
lastUsageIndex: number | null;
}
function getLastAssistantUsageInfo(messages: AgentMessage[]): { usage: Usage; index: number } | undefined {
for (let i = messages.length - 1; i >= 0; i--) {
const usage = getAssistantUsage(messages[i]);
if (usage) return { usage, index: i };
}
return undefined;
}
/**
* Estimate context tokens from messages, using the last assistant usage when available.
* If there are messages after the last usage, estimate their tokens with estimateTokens.
*/
export function estimateContextTokens(messages: AgentMessage[]): ContextUsageEstimate {
const usageInfo = getLastAssistantUsageInfo(messages);
if (!usageInfo) {
let estimated = 0;
for (const message of messages) {
estimated += estimateTokens(message);
}
return {
tokens: estimated,
usageTokens: 0,
trailingTokens: estimated,
lastUsageIndex: null,
};
}
const usageTokens = calculateContextTokens(usageInfo.usage);
let trailingTokens = 0;
for (let i = usageInfo.index + 1; i < messages.length; i++) {
trailingTokens += estimateTokens(messages[i]);
}
return {
tokens: usageTokens + trailingTokens,
usageTokens,
trailingTokens,
lastUsageIndex: usageInfo.index,
};
}
/**
* Check if compaction should trigger based on context usage.
*/
export function shouldCompact(contextTokens: number, contextWindow: number, settings: CompactionSettings): boolean {
if (!settings.enabled) return false;
return contextTokens > contextWindow - settings.reserveTokens;
}
// ============================================================================
// Cut point detection
// ============================================================================
/**
* Estimate token count for a message using chars/4 heuristic.
* This is conservative (overestimates tokens).
*/
export function estimateTokens(message: AgentMessage): number {
let chars = 0;
switch (message.role) {
case "user": {
const content = (message as { content: string | Array<{ type: string; text?: string }> }).content;
if (typeof content === "string") {
chars = content.length;
} else if (Array.isArray(content)) {
for (const block of content) {
if (block.type === "text" && block.text) {
chars += block.text.length;
}
}
}
return Math.ceil(chars / 4);
}
case "assistant": {
const assistant = message as AssistantMessage;
for (const block of assistant.content) {
if (block.type === "text") {
chars += block.text.length;
} else if (block.type === "thinking") {
chars += block.thinking.length;
} else if (block.type === "toolCall") {
chars += block.name.length + JSON.stringify(block.arguments).length;
}
}
return Math.ceil(chars / 4);
}
case "custom":
case "toolResult": {
if (typeof message.content === "string") {
chars = message.content.length;
} else {
for (const block of message.content) {
if (block.type === "text" && block.text) {
chars += block.text.length;
}
if (block.type === "image") {
chars += 4800; // Estimate images as 4000 chars, or 1200 tokens
}
}
}
return Math.ceil(chars / 4);
}
case "bashExecution": {
chars = message.command.length + message.output.length;
return Math.ceil(chars / 4);
}
case "branchSummary":
case "compactionSummary": {
chars = message.summary.length;
return Math.ceil(chars / 4);
}
}
return 0;
}
/**
* Find valid cut points: indices of user, assistant, custom, or bashExecution messages.
* Never cut at tool results (they must follow their tool call).
* When we cut at an assistant message with tool calls, its tool results follow it
* and will be kept.
* BashExecutionMessage is treated like a user message (user-initiated context).
*/
function findValidCutPoints(entries: SessionTreeEntry[], startIndex: number, endIndex: number): number[] {
const cutPoints: number[] = [];
for (let i = startIndex; i < endIndex; i++) {
const entry = entries[i];
switch (entry.type) {
case "message": {
const role = entry.message.role;
switch (role) {
case "bashExecution":
case "custom":
case "branchSummary":
case "compactionSummary":
case "user":
case "assistant":
cutPoints.push(i);
break;
case "toolResult":
break;
}
break;
}
case "thinking_level_change":
case "model_change":
case "compaction":
case "branch_summary":
case "custom":
case "custom_message":
case "label":
case "session_info":
break;
}
// branch_summary and custom_message are user-role messages, valid cut points
if (entry.type === "branch_summary" || entry.type === "custom_message") {
cutPoints.push(i);
}
}
return cutPoints;
}
/**
* Find the user message (or bashExecution) that starts the turn containing the given entry index.
* Returns -1 if no turn start found before the index.
* BashExecutionMessage is treated like a user message for turn boundaries.
*/
export function findTurnStartIndex(entries: SessionTreeEntry[], entryIndex: number, startIndex: number): number {
for (let i = entryIndex; i >= startIndex; i--) {
const entry = entries[i];
// branch_summary and custom_message are user-role messages, can start a turn
if (entry.type === "branch_summary" || entry.type === "custom_message") {
return i;
}
if (entry.type === "message") {
const role = entry.message.role;
if (role === "user" || role === "bashExecution") {
return i;
}
}
}
return -1;
}
export interface CutPointResult {
/** Index of first entry to keep */
firstKeptEntryIndex: number;
/** Index of user message that starts the turn being split, or -1 if not splitting */
turnStartIndex: number;
/** Whether this cut splits a turn (cut point is not a user message) */
isSplitTurn: boolean;
}
/**
* Find the cut point in session entries that keeps approximately `keepRecentTokens`.
*
* Algorithm: Walk backwards from newest, accumulating estimated message sizes.
* Stop when we've accumulated >= keepRecentTokens. Cut at that point.
*
* Can cut at user OR assistant messages (never tool results). When cutting at an
* assistant message with tool calls, its tool results come after and will be kept.
*
* Returns CutPointResult with:
* - firstKeptEntryIndex: the entry index to start keeping from
* - turnStartIndex: if cutting mid-turn, the user message that started that turn
* - isSplitTurn: whether we're cutting in the middle of a turn
*
* Only considers entries between `startIndex` and `endIndex` (exclusive).
*/
export function findCutPoint(
entries: SessionTreeEntry[],
startIndex: number,
endIndex: number,
keepRecentTokens: number,
): CutPointResult {
const cutPoints = findValidCutPoints(entries, startIndex, endIndex);
if (cutPoints.length === 0) {
return { firstKeptEntryIndex: startIndex, turnStartIndex: -1, isSplitTurn: false };
}
// Walk backwards from newest, accumulating estimated message sizes
let accumulatedTokens = 0;
let cutIndex = cutPoints[0]; // Default: keep from first message (not header)
for (let i = endIndex - 1; i >= startIndex; i--) {
const entry = entries[i];
if (entry.type !== "message") continue;
// Estimate this message's size
const messageTokens = estimateTokens(entry.message);
accumulatedTokens += messageTokens;
// Check if we've exceeded the budget
if (accumulatedTokens >= keepRecentTokens) {
// Find the closest valid cut point at or after this entry
for (let c = 0; c < cutPoints.length; c++) {
if (cutPoints[c] >= i) {
cutIndex = cutPoints[c];
break;
}
}
break;
}
}
// Scan backwards from cutIndex to include any non-message entries (bash, settings, etc.)
while (cutIndex > startIndex) {
const prevEntry = entries[cutIndex - 1];
// Stop at session header or compaction boundaries
if (prevEntry.type === "compaction") {
break;
}
if (prevEntry.type === "message") {
// Stop if we hit any message
break;
}
// Include this non-message entry (bash, settings change, etc.)
cutIndex--;
}
// Determine if this is a split turn
const cutEntry = entries[cutIndex];
const isUserMessage = cutEntry.type === "message" && cutEntry.message.role === "user";
const turnStartIndex = isUserMessage ? -1 : findTurnStartIndex(entries, cutIndex, startIndex);
return {
firstKeptEntryIndex: cutIndex,
turnStartIndex,
isSplitTurn: !isUserMessage && turnStartIndex !== -1,
};
}
// ============================================================================
// Summarization
// ============================================================================
const SUMMARIZATION_PROMPT = `The messages above are a conversation to summarize. Create a structured context checkpoint summary that another LLM will use to continue the work.
Use this EXACT format:
## Goal
[What is the user trying to accomplish? Can be multiple items if the session covers different tasks.]
## Constraints & Preferences
- [Any constraints, preferences, or requirements mentioned by user]
- [Or "(none)" if none were mentioned]
## Progress
### Done
- [x] [Completed tasks/changes]
### In Progress
- [ ] [Current work]
### Blocked
- [Issues preventing progress, if any]
## Key Decisions
- **[Decision]**: [Brief rationale]
## Next Steps
1. [Ordered list of what should happen next]
## Critical Context
- [Any data, examples, or references needed to continue]
- [Or "(none)" if not applicable]
Keep each section concise. Preserve exact file paths, function names, and error messages.`;
const UPDATE_SUMMARIZATION_PROMPT = `The messages above are NEW conversation messages to incorporate into the existing summary provided in <previous-summary> tags.
Update the existing structured summary with new information. RULES:
- PRESERVE all existing information from the previous summary
- ADD new progress, decisions, and context from the new messages
- UPDATE the Progress section: move items from "In Progress" to "Done" when completed
- UPDATE "Next Steps" based on what was accomplished
- PRESERVE exact file paths, function names, and error messages
- If something is no longer relevant, you may remove it
Use this EXACT format:
## Goal
[Preserve existing goals, add new ones if the task expanded]
## Constraints & Preferences
- [Preserve existing, add new ones discovered]
## Progress
### Done
- [x] [Include previously done items AND newly completed items]
### In Progress
- [ ] [Current work - update based on progress]
### Blocked
- [Current blockers - remove if resolved]
## Key Decisions
- **[Decision]**: [Brief rationale] (preserve all previous, add new)
## Next Steps
1. [Update based on current state]
## Critical Context
- [Preserve important context, add new if needed]
Keep each section concise. Preserve exact file paths, function names, and error messages.`;
/**
* Generate a summary of the conversation using the LLM.
* If previousSummary is provided, uses the update prompt to merge.
*/
export async function generateSummary(
currentMessages: AgentMessage[],
model: Model<any>,
reserveTokens: number,
apiKey: string,
headers?: Record<string, string>,
signal?: AbortSignal,
customInstructions?: string,
previousSummary?: string,
thinkingLevel?: ThinkingLevel,
): Promise<string> {
const maxTokens = Math.floor(0.8 * reserveTokens);
// Use update prompt if we have a previous summary, otherwise initial prompt
let basePrompt = previousSummary ? UPDATE_SUMMARIZATION_PROMPT : SUMMARIZATION_PROMPT;
if (customInstructions) {
basePrompt = `${basePrompt}\n\nAdditional focus: ${customInstructions}`;
}
// Serialize conversation to text so model doesn't try to continue it
// Convert to LLM messages first (handles custom types like bashExecution, custom, etc.)
const llmMessages = convertToLlm(currentMessages);
const conversationText = serializeConversation(llmMessages);
// Build the prompt with conversation wrapped in tags
let promptText = `<conversation>\n${conversationText}\n</conversation>\n\n`;
if (previousSummary) {
promptText += `<previous-summary>\n${previousSummary}\n</previous-summary>\n\n`;
}
promptText += basePrompt;
const summarizationMessages = [
{
role: "user" as const,
content: [{ type: "text" as const, text: promptText }],
timestamp: Date.now(),
},
];
const completionOptions =
model.reasoning && thinkingLevel && thinkingLevel !== "off"
? { maxTokens, signal, apiKey, headers, reasoning: thinkingLevel }
: { maxTokens, signal, apiKey, headers };
const response = await completeSimple(
model,
{ systemPrompt: SUMMARIZATION_SYSTEM_PROMPT, messages: summarizationMessages },
completionOptions,
);
if (response.stopReason === "error") {
throw new Error(`Summarization failed: ${response.errorMessage || "Unknown error"}`);
}
const textContent = response.content
.filter((c): c is { type: "text"; text: string } => c.type === "text")
.map((c) => c.text)
.join("\n");
return textContent;
}
// ============================================================================
// Compaction Preparation (for extensions)
// ============================================================================
export interface CompactionPreparation {
/** UUID of first entry to keep */
firstKeptEntryId: string;
/** Messages that will be summarized and discarded */
messagesToSummarize: AgentMessage[];
/** Messages that will be turned into turn prefix summary (if splitting) */
turnPrefixMessages: AgentMessage[];
/** Whether this is a split turn (cut point in middle of turn) */
isSplitTurn: boolean;
tokensBefore: number;
/** Summary from previous compaction, for iterative update */
previousSummary?: string;
/** File operations extracted from messagesToSummarize */
fileOps: FileOperations;
/** Compaction settions from settings.jsonl */
settings: CompactionSettings;
}
export function prepareCompaction(
pathEntries: SessionTreeEntry[],
settings: CompactionSettings,
): CompactionPreparation | undefined {
if (pathEntries.length > 0 && pathEntries[pathEntries.length - 1].type === "compaction") {
return undefined;
}
let prevCompactionIndex = -1;
for (let i = pathEntries.length - 1; i >= 0; i--) {
if (pathEntries[i].type === "compaction") {
prevCompactionIndex = i;
break;
}
}
let previousSummary: string | undefined;
let boundaryStart = 0;
if (prevCompactionIndex >= 0) {
const prevCompaction = pathEntries[prevCompactionIndex] as CompactionEntry;
previousSummary = prevCompaction.summary;
const firstKeptEntryIndex = pathEntries.findIndex((entry) => entry.id === prevCompaction.firstKeptEntryId);
boundaryStart = firstKeptEntryIndex >= 0 ? firstKeptEntryIndex : prevCompactionIndex + 1;
}
const boundaryEnd = pathEntries.length;
const tokensBefore = estimateContextTokens(buildSessionContext(pathEntries).messages).tokens;
const cutPoint = findCutPoint(pathEntries, boundaryStart, boundaryEnd, settings.keepRecentTokens);
// Get UUID of first kept entry
const firstKeptEntry = pathEntries[cutPoint.firstKeptEntryIndex];
if (!firstKeptEntry?.id) {
return undefined; // Session needs migration
}
const firstKeptEntryId = firstKeptEntry.id;
const historyEnd = cutPoint.isSplitTurn ? cutPoint.turnStartIndex : cutPoint.firstKeptEntryIndex;
// Messages to summarize (will be discarded after summary)
const messagesToSummarize: AgentMessage[] = [];
for (let i = boundaryStart; i < historyEnd; i++) {
const msg = getMessageFromEntryForCompaction(pathEntries[i]);
if (msg) messagesToSummarize.push(msg);
}
// Messages for turn prefix summary (if splitting a turn)
const turnPrefixMessages: AgentMessage[] = [];
if (cutPoint.isSplitTurn) {
for (let i = cutPoint.turnStartIndex; i < cutPoint.firstKeptEntryIndex; i++) {
const msg = getMessageFromEntryForCompaction(pathEntries[i]);
if (msg) turnPrefixMessages.push(msg);
}
}
// Extract file operations from messages and previous compaction
const fileOps = extractFileOperations(messagesToSummarize, pathEntries, prevCompactionIndex);
// Also extract file ops from turn prefix if splitting
if (cutPoint.isSplitTurn) {
for (const msg of turnPrefixMessages) {
extractFileOpsFromMessage(msg, fileOps);
}
}
return {
firstKeptEntryId,
messagesToSummarize,
turnPrefixMessages,
isSplitTurn: cutPoint.isSplitTurn,
tokensBefore,
previousSummary,
fileOps,
settings,
};
}
// ============================================================================
// Main compaction function
// ============================================================================
const TURN_PREFIX_SUMMARIZATION_PROMPT = `This is the PREFIX of a turn that was too large to keep. The SUFFIX (recent work) is retained.
Summarize the prefix to provide context for the retained suffix:
## Original Request
[What did the user ask for in this turn?]
## Early Progress
- [Key decisions and work done in the prefix]
## Context for Suffix
- [Information needed to understand the retained recent work]
Be concise. Focus on what's needed to understand the kept suffix.`;
/**
* Generate summaries for compaction using prepared data.
* Returns CompactionResult - SessionManager adds uuid/parentUuid when saving.
*
* @param preparation - Pre-calculated preparation from prepareCompaction()
* @param customInstructions - Optional custom focus for the summary
*/
export { serializeConversation } from "./utils.js";
export async function compact(
preparation: CompactionPreparation,
model: Model<any>,
apiKey: string,
headers?: Record<string, string>,
customInstructions?: string,
signal?: AbortSignal,
thinkingLevel?: ThinkingLevel,
): Promise<CompactionResult> {
const {
firstKeptEntryId,
messagesToSummarize,
turnPrefixMessages,
isSplitTurn,
tokensBefore,
previousSummary,
fileOps,
settings,
} = preparation;
// Generate summaries (can be parallel if both needed) and merge into one
let summary: string;
if (isSplitTurn && turnPrefixMessages.length > 0) {
// Generate both summaries in parallel
const [historyResult, turnPrefixResult] = await Promise.all([
messagesToSummarize.length > 0
? generateSummary(
messagesToSummarize,
model,
settings.reserveTokens,
apiKey,
headers,
signal,
customInstructions,
previousSummary,
thinkingLevel,
)
: Promise.resolve("No prior history."),
generateTurnPrefixSummary(
turnPrefixMessages,
model,
settings.reserveTokens,
apiKey,
headers,
signal,
thinkingLevel,
),
]);
// Merge into single summary
summary = `${historyResult}\n\n---\n\n**Turn Context (split turn):**\n\n${turnPrefixResult}`;
} else {
// Just generate history summary
summary = await generateSummary(
messagesToSummarize,
model,
settings.reserveTokens,
apiKey,
headers,
signal,
customInstructions,
previousSummary,
thinkingLevel,
);
}
// Compute file lists and append to summary
const { readFiles, modifiedFiles } = computeFileLists(fileOps);
summary += formatFileOperations(readFiles, modifiedFiles);
if (!firstKeptEntryId) {
throw new Error("First kept entry has no UUID - session may need migration");
}
return {
summary,
firstKeptEntryId,
tokensBefore,
details: { readFiles, modifiedFiles } as CompactionDetails,
};
}
/**
* Generate a summary for a turn prefix (when splitting a turn).
*/
async function generateTurnPrefixSummary(
messages: AgentMessage[],
model: Model<any>,
reserveTokens: number,
apiKey: string,
headers?: Record<string, string>,
signal?: AbortSignal,
thinkingLevel?: ThinkingLevel,
): Promise<string> {
const maxTokens = Math.floor(0.5 * reserveTokens); // Smaller budget for turn prefix
const llmMessages = convertToLlm(messages);
const conversationText = serializeConversation(llmMessages);
const promptText = `<conversation>\n${conversationText}\n</conversation>\n\n${TURN_PREFIX_SUMMARIZATION_PROMPT}`;
const summarizationMessages = [
{
role: "user" as const,
content: [{ type: "text" as const, text: promptText }],
timestamp: Date.now(),
},
];
const response = await completeSimple(
model,
{ systemPrompt: SUMMARIZATION_SYSTEM_PROMPT, messages: summarizationMessages },
model.reasoning && thinkingLevel && thinkingLevel !== "off"
? { maxTokens, signal, apiKey, headers, reasoning: thinkingLevel }
: { maxTokens, signal, apiKey, headers },
);
if (response.stopReason === "error") {
throw new Error(`Turn prefix summarization failed: ${response.errorMessage || "Unknown error"}`);
}
return response.content
.filter((c): c is { type: "text"; text: string } => c.type === "text")
.map((c) => c.text)
.join("\n");
}

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/**
* Shared utilities for compaction and branch summarization.
*/
import type { Message } from "@mariozechner/pi-ai";
import type { AgentMessage } from "../../types.js";
// ============================================================================
// File Operation Tracking
// ============================================================================
export interface FileOperations {
read: Set<string>;
written: Set<string>;
edited: Set<string>;
}
export function createFileOps(): FileOperations {
return {
read: new Set(),
written: new Set(),
edited: new Set(),
};
}
/**
* Extract file operations from tool calls in an assistant message.
*/
export function extractFileOpsFromMessage(message: AgentMessage, fileOps: FileOperations): void {
if (message.role !== "assistant") return;
if (!("content" in message) || !Array.isArray(message.content)) return;
for (const block of message.content) {
if (typeof block !== "object" || block === null) continue;
if (!("type" in block) || block.type !== "toolCall") continue;
if (!("arguments" in block) || !("name" in block)) continue;
const args = block.arguments as Record<string, unknown> | undefined;
if (!args) continue;
const path = typeof args.path === "string" ? args.path : undefined;
if (!path) continue;
switch (block.name) {
case "read":
fileOps.read.add(path);
break;
case "write":
fileOps.written.add(path);
break;
case "edit":
fileOps.edited.add(path);
break;
}
}
}
/**
* Compute final file lists from file operations.
* Returns readFiles (files only read, not modified) and modifiedFiles.
*/
export function computeFileLists(fileOps: FileOperations): { readFiles: string[]; modifiedFiles: string[] } {
const modified = new Set([...fileOps.edited, ...fileOps.written]);
const readOnly = [...fileOps.read].filter((f) => !modified.has(f)).sort();
const modifiedFiles = [...modified].sort();
return { readFiles: readOnly, modifiedFiles };
}
/**
* Format file operations as XML tags for summary.
*/
export function formatFileOperations(readFiles: string[], modifiedFiles: string[]): string {
const sections: string[] = [];
if (readFiles.length > 0) {
sections.push(`<read-files>\n${readFiles.join("\n")}\n</read-files>`);
}
if (modifiedFiles.length > 0) {
sections.push(`<modified-files>\n${modifiedFiles.join("\n")}\n</modified-files>`);
}
if (sections.length === 0) return "";
return `\n\n${sections.join("\n\n")}`;
}
// ============================================================================
// Message Serialization
// ============================================================================
/** Maximum characters for a tool result in serialized summaries. */
const TOOL_RESULT_MAX_CHARS = 2000;
/**
* Truncate text to a maximum character length for summarization.
* Keeps the beginning and appends a truncation marker.
*/
function truncateForSummary(text: string, maxChars: number): string {
if (text.length <= maxChars) return text;
const truncatedChars = text.length - maxChars;
return `${text.slice(0, maxChars)}\n\n[... ${truncatedChars} more characters truncated]`;
}
/**
* Serialize LLM messages to text for summarization.
* This prevents the model from treating it as a conversation to continue.
* Call convertToLlm() first to handle custom message types.
*
* Tool results are truncated to keep the summarization request within
* reasonable token budgets. Full content is not needed for summarization.
*/
export function serializeConversation(messages: Message[]): string {
const parts: string[] = [];
for (const msg of messages) {
if (msg.role === "user") {
const content =
typeof msg.content === "string"
? msg.content
: msg.content
.filter((c): c is { type: "text"; text: string } => c.type === "text")
.map((c) => c.text)
.join("");
if (content) parts.push(`[User]: ${content}`);
} else if (msg.role === "assistant") {
const textParts: string[] = [];
const thinkingParts: string[] = [];
const toolCalls: string[] = [];
for (const block of msg.content) {
if (block.type === "text") {
textParts.push(block.text);
} else if (block.type === "thinking") {
thinkingParts.push(block.thinking);
} else if (block.type === "toolCall") {
const args = block.arguments as Record<string, unknown>;
const argsStr = Object.entries(args)
.map(([k, v]) => `${k}=${JSON.stringify(v)}`)
.join(", ");
toolCalls.push(`${block.name}(${argsStr})`);
}
}
if (thinkingParts.length > 0) {
parts.push(`[Assistant thinking]: ${thinkingParts.join("\n")}`);
}
if (textParts.length > 0) {
parts.push(`[Assistant]: ${textParts.join("\n")}`);
}
if (toolCalls.length > 0) {
parts.push(`[Assistant tool calls]: ${toolCalls.join("; ")}`);
}
} else if (msg.role === "toolResult") {
const content = msg.content
.filter((c): c is { type: "text"; text: string } => c.type === "text")
.map((c) => c.text)
.join("");
if (content) {
parts.push(`[Tool result]: ${truncateForSummary(content, TOOL_RESULT_MAX_CHARS)}`);
}
}
}
return parts.join("\n\n");
}
// ============================================================================
// Summarization System Prompt
// ============================================================================
export const SUMMARIZATION_SYSTEM_PROMPT = `You are a context summarization assistant. Your task is to read a conversation between a user and an AI coding assistant, then produce a structured summary following the exact format specified.
Do NOT continue the conversation. Do NOT respond to any questions in the conversation. ONLY output the structured summary.`;