feat(agent): split harness compaction and session modules
This commit is contained in:
Mario Zechner
355
packages/agent/src/harness/compaction/branch-summarization.ts
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355
packages/agent/src/harness/compaction/branch-summarization.ts
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/**
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* Branch summarization for tree navigation.
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*
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* When navigating to a different point in the session tree, this generates
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* a summary of the branch being left so context isn't lost.
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*/
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import type { Model } from "@mariozechner/pi-ai";
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import { completeSimple } from "@mariozechner/pi-ai";
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import type { AgentMessage } from "../../types.js";
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import {
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convertToLlm,
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createBranchSummaryMessage,
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createCompactionSummaryMessage,
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createCustomMessage,
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} from "../messages.js";
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import type { SessionTree, SessionTreeEntry } from "../types.js";
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import { estimateTokens } from "./compaction.js";
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import {
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computeFileLists,
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createFileOps,
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extractFileOpsFromMessage,
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type FileOperations,
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formatFileOperations,
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SUMMARIZATION_SYSTEM_PROMPT,
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serializeConversation,
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} from "./utils.js";
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// ============================================================================
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// Types
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// ============================================================================
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export interface BranchSummaryResult {
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summary?: string;
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readFiles?: string[];
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modifiedFiles?: string[];
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aborted?: boolean;
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error?: string;
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}
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/** Details stored in BranchSummaryEntry.details for file tracking */
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export interface BranchSummaryDetails {
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readFiles: string[];
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modifiedFiles: string[];
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}
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export type { FileOperations } from "./utils.js";
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export interface BranchPreparation {
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/** Messages extracted for summarization, in chronological order */
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messages: AgentMessage[];
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/** File operations extracted from tool calls */
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fileOps: FileOperations;
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/** Total estimated tokens in messages */
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totalTokens: number;
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}
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export interface CollectEntriesResult {
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/** Entries to summarize, in chronological order */
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entries: SessionTreeEntry[];
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/** Common ancestor between old and new position, if any */
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commonAncestorId: string | null;
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}
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export interface GenerateBranchSummaryOptions {
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/** Model to use for summarization */
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model: Model<any>;
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/** API key for the model */
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apiKey: string;
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/** Request headers for the model */
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headers?: Record<string, string>;
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/** Abort signal for cancellation */
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signal: AbortSignal;
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/** Optional custom instructions for summarization */
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customInstructions?: string;
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/** If true, customInstructions replaces the default prompt instead of being appended */
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replaceInstructions?: boolean;
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/** Tokens reserved for prompt + LLM response (default 16384) */
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reserveTokens?: number;
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}
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// ============================================================================
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// Entry Collection
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// ============================================================================
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/**
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* Collect entries that should be summarized when navigating from one position to another.
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*
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* Walks from oldLeafId back to the common ancestor with targetId, collecting entries
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* along the way. Does NOT stop at compaction boundaries - those are included and their
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* summaries become context.
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*
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* @param session - Session manager (read-only access)
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* @param oldLeafId - Current position (where we're navigating from)
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* @param targetId - Target position (where we're navigating to)
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* @returns Entries to summarize and the common ancestor
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*/
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export async function collectEntriesForBranchSummary(
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session: SessionTree,
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oldLeafId: string | null,
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targetId: string,
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): Promise<CollectEntriesResult> {
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// If no old position, nothing to summarize
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if (!oldLeafId) {
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return { entries: [], commonAncestorId: null };
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}
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// Find common ancestor (deepest node that's on both paths)
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const oldPath = new Set((await session.getBranch(oldLeafId)).map((e) => e.id));
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const targetPath = await session.getBranch(targetId);
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// targetPath is root-first, so iterate backwards to find deepest common ancestor
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let commonAncestorId: string | null = null;
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for (let i = targetPath.length - 1; i >= 0; i--) {
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if (oldPath.has(targetPath[i].id)) {
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commonAncestorId = targetPath[i].id;
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break;
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}
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}
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// Collect entries from old leaf back to common ancestor
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const entries: SessionTreeEntry[] = [];
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let current: string | null = oldLeafId;
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while (current && current !== commonAncestorId) {
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const entry = await session.getEntry(current);
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if (!entry) break;
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entries.push(entry);
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current = entry.parentId;
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}
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// Reverse to get chronological order
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entries.reverse();
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return { entries, commonAncestorId };
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}
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// ============================================================================
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// Entry to Message Conversion
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// ============================================================================
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/**
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* Extract AgentMessage from a session entry.
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* Similar to getMessageFromEntry in compaction.ts but also handles compaction entries.
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*/
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function getMessageFromEntry(entry: SessionTreeEntry): AgentMessage | undefined {
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switch (entry.type) {
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case "message":
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// Skip tool results - context is in assistant's tool call
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if (entry.message.role === "toolResult") return undefined;
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return entry.message;
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case "custom_message":
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return createCustomMessage(entry.customType, entry.content, entry.display, entry.details, entry.timestamp);
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case "branch_summary":
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return createBranchSummaryMessage(entry.summary, entry.fromId, entry.timestamp);
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case "compaction":
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return createCompactionSummaryMessage(entry.summary, entry.tokensBefore, entry.timestamp);
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// These don't contribute to conversation content
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case "thinking_level_change":
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case "model_change":
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case "custom":
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case "label":
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case "session_info":
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return undefined;
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}
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}
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/**
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* Prepare entries for summarization with token budget.
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*
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* Walks entries from NEWEST to OLDEST, adding messages until we hit the token budget.
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* This ensures we keep the most recent context when the branch is too long.
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*
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* Also collects file operations from:
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* - Tool calls in assistant messages
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* - Existing branch_summary entries' details (for cumulative tracking)
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*
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* @param entries - Entries in chronological order
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* @param tokenBudget - Maximum tokens to include (0 = no limit)
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*/
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export function prepareBranchEntries(entries: SessionTreeEntry[], tokenBudget: number = 0): BranchPreparation {
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const messages: AgentMessage[] = [];
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const fileOps = createFileOps();
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let totalTokens = 0;
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// First pass: collect file ops from ALL entries (even if they don't fit in token budget)
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// This ensures we capture cumulative file tracking from nested branch summaries
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// Only extract from pi-generated summaries (fromHook !== true), not extension-generated ones
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for (const entry of entries) {
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if (entry.type === "branch_summary" && !entry.fromHook && entry.details) {
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const details = entry.details as BranchSummaryDetails;
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if (Array.isArray(details.readFiles)) {
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for (const f of details.readFiles) fileOps.read.add(f);
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}
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if (Array.isArray(details.modifiedFiles)) {
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// Modified files go into both edited and written for proper deduplication
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for (const f of details.modifiedFiles) {
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fileOps.edited.add(f);
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}
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}
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}
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}
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// Second pass: walk from newest to oldest, adding messages until token budget
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for (let i = entries.length - 1; i >= 0; i--) {
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const entry = entries[i];
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const message = getMessageFromEntry(entry);
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if (!message) continue;
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// Extract file ops from assistant messages (tool calls)
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extractFileOpsFromMessage(message, fileOps);
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const tokens = estimateTokens(message);
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// Check budget before adding
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if (tokenBudget > 0 && totalTokens + tokens > tokenBudget) {
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// If this is a summary entry, try to fit it anyway as it's important context
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if (entry.type === "compaction" || entry.type === "branch_summary") {
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if (totalTokens < tokenBudget * 0.9) {
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messages.unshift(message);
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totalTokens += tokens;
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}
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}
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// Stop - we've hit the budget
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break;
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}
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messages.unshift(message);
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totalTokens += tokens;
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}
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return { messages, fileOps, totalTokens };
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}
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// ============================================================================
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// Summary Generation
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// ============================================================================
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const BRANCH_SUMMARY_PREAMBLE = `The user explored a different conversation branch before returning here.
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Summary of that exploration:
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`;
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const BRANCH_SUMMARY_PROMPT = `Create a structured summary of this conversation branch for context when returning later.
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Use this EXACT format:
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## Goal
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[What was the user trying to accomplish in this branch?]
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## Constraints & Preferences
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- [Any constraints, preferences, or requirements mentioned]
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- [Or "(none)" if none were mentioned]
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## Progress
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### Done
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- [x] [Completed tasks/changes]
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### In Progress
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- [ ] [Work that was started but not finished]
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### Blocked
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- [Issues preventing progress, if any]
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## Key Decisions
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- **[Decision]**: [Brief rationale]
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## Next Steps
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1. [What should happen next to continue this work]
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Keep each section concise. Preserve exact file paths, function names, and error messages.`;
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/**
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* Generate a summary of abandoned branch entries.
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*
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* @param entries - Session entries to summarize (chronological order)
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* @param options - Generation options
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*/
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export async function generateBranchSummary(
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entries: SessionTreeEntry[],
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options: GenerateBranchSummaryOptions,
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): Promise<BranchSummaryResult> {
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const { model, apiKey, headers, signal, customInstructions, replaceInstructions, reserveTokens = 16384 } = options;
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// Token budget = context window minus reserved space for prompt + response
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const contextWindow = model.contextWindow || 128000;
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const tokenBudget = contextWindow - reserveTokens;
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const { messages, fileOps } = prepareBranchEntries(entries, tokenBudget);
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if (messages.length === 0) {
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return { summary: "No content to summarize" };
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}
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// Transform to LLM-compatible messages, then serialize to text
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// Serialization prevents the model from treating it as a conversation to continue
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const llmMessages = convertToLlm(messages);
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const conversationText = serializeConversation(llmMessages);
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// Build prompt
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let instructions: string;
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if (replaceInstructions && customInstructions) {
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instructions = customInstructions;
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} else if (customInstructions) {
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instructions = `${BRANCH_SUMMARY_PROMPT}\n\nAdditional focus: ${customInstructions}`;
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} else {
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instructions = BRANCH_SUMMARY_PROMPT;
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}
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const promptText = `<conversation>\n${conversationText}\n</conversation>\n\n${instructions}`;
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const summarizationMessages = [
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{
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role: "user" as const,
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content: [{ type: "text" as const, text: promptText }],
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timestamp: Date.now(),
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},
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];
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// Call LLM for summarization
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const response = await completeSimple(
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model,
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{ systemPrompt: SUMMARIZATION_SYSTEM_PROMPT, messages: summarizationMessages },
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{ apiKey, headers, signal, maxTokens: 2048 },
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);
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// Check if aborted or errored
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if (response.stopReason === "aborted") {
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return { aborted: true };
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}
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if (response.stopReason === "error") {
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return { error: response.errorMessage || "Summarization failed" };
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}
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let summary = response.content
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.filter((c): c is { type: "text"; text: string } => c.type === "text")
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.map((c) => c.text)
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.join("\n");
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// Prepend preamble to provide context about the branch summary
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summary = BRANCH_SUMMARY_PREAMBLE + summary;
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// Compute file lists and append to summary
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const { readFiles, modifiedFiles } = computeFileLists(fileOps);
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summary += formatFileOperations(readFiles, modifiedFiles);
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return {
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summary: summary || "No summary generated",
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readFiles,
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modifiedFiles,
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};
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}
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