Merge feature/context-injection into main

- Add node_versions table with migrations for tracking history
- Add version tracking to addNode/updateNode in store
- Add getNodeHistory, getNodeAtTime, diffVersions, restoreVersion
- Add NodeVersion, HistoricalNode, NodeDiff types
- Add summary generation with caching for memory_summary

src/cli/commands/config.ts

@@ -0,0 +1,81 @@
+import { Command } from 'commander';
+import chalk from 'chalk';
+import { getConfig, setConfig, listConfig, resetConfig, CortexConfig } from '../../core/config';
+
+export const configCommand = new Command('config')
+  .description('Manage Cortex configuration');
+
+configCommand
+  .command('get <key>')
+  .description('Get a config value')
+  .action((key: string) => {
+    try {
+      const value = getConfig(key as keyof CortexConfig);
+      console.log(value);
+    } catch (err) {
+      console.error(chalk.red(`Unknown config key: ${key}`));
+      process.exit(1);
+    }
+  });
+
+configCommand
+  .command('set <key> <value>')
+  .description('Set a config value')
+  .action((key: string, value: string) => {
+    // Validate key exists
+    const validKeys = [
+      'context.maxTokens',
+      'context.maxNodes',
+      'context.includeRecent',
+      'context.includeProject',
+      'context.includeTasks',
+      'context.includeDecisions',
+    ];
+
+    if (!validKeys.includes(key)) {
+      console.error(chalk.red(`Unknown config key: ${key}`));
+      console.error(chalk.dim(`Valid keys: ${validKeys.join(', ')}`));
+      process.exit(1);
+    }
+
+    // Parse value based on key type
+    let parsed: string | number | boolean = value;
+    if (key.startsWith('context.max')) {
+      parsed = parseInt(value, 10);
+      if (isNaN(parsed)) {
+        console.error(chalk.red(`Invalid number: ${value}`));
+        process.exit(1);
+      }
+    } else if (key.startsWith('context.include')) {
+      if (value !== 'true' && value !== 'false') {
+        console.error(chalk.red(`Invalid boolean: ${value} (use true or false)`));
+        process.exit(1);
+      }
+      parsed = value === 'true';
+    }
+
+    setConfig(key as keyof CortexConfig, parsed as any);
+    console.log(chalk.green(`Set ${key} = ${parsed}`));
+  });
+
+configCommand
+  .command('list')
+  .description('List all config values')
+  .action(() => {
+    const configs = listConfig();
+    console.log(chalk.bold('Configuration:'));
+    console.log();
+
+    for (const { key, value, isDefault } of configs) {
+      const displayValue = isDefault ? chalk.dim(`${value} (default)`) : chalk.cyan(value);
+      console.log(`  ${chalk.yellow(key)}: ${displayValue}`);
+    }
+  });
+
+configCommand
+  .command('reset <key>')
+  .description('Reset a config key to default')
+  .action((key: string) => {
+    resetConfig(key as keyof CortexConfig);
+    console.log(chalk.green(`Reset ${key} to default`));
+  });

src/cli/commands/context.ts

@@ -0,0 +1,85 @@
+import { Command } from 'commander';
+import chalk from 'chalk';
+import * as path from 'path';
+import { gatherContext, DEFAULT_CONTEXT_CONFIG } from '../../core/context';
+
+export const contextCommand = new Command('context')
+  .description('Preview or inject context for a Claude session')
+  .option('-p, --project <name>', 'Project name (defaults to current directory name)')
+  .option('-q, --query <text>', 'Additional semantic search query')
+  .option('--max-tokens <n>', 'Maximum tokens', String(DEFAULT_CONTEXT_CONFIG.maxTokens))
+  .option('--max-nodes <n>', 'Maximum nodes', String(DEFAULT_CONTEXT_CONFIG.maxNodes))
+  .option('--format <fmt>', 'Output format: markdown or json', 'markdown')
+  .option('--no-recent', 'Exclude recent activity')
+  .option('--no-tasks', 'Exclude open tasks')
+  .option('--no-decisions', 'Exclude decisions')
+  .action(async (opts) => {
+    const project = opts.project ?? path.basename(process.cwd());
+
+    const result = await gatherContext({
+      project,
+      semanticQuery: opts.query,
+      config: {
+        maxTokens: parseInt(opts.maxTokens),
+        maxNodes: parseInt(opts.maxNodes),
+        includeRecent: opts.recent !== false,
+        includeTasks: opts.tasks !== false,
+        includeDecisions: opts.decisions !== false,
+      },
+    });
+
+    if (opts.format === 'json') {
+      console.log(JSON.stringify({
+        project,
+        nodeCount: result.nodes.length,
+        nodes: result.nodes.map(r => ({
+          id: r.node.id,
+          kind: r.node.kind,
+          title: r.node.title,
+          score: r.score,
+          reason: r.reason,
+        })),
+      }, null, 2));
+      return;
+    }
+
+    // Markdown output
+    if (result.nodes.length === 0) {
+      console.log(chalk.yellow('No relevant context found.'));
+      return;
+    }
+
+    console.log(chalk.cyan(`# Context for ${project}`));
+    console.log(chalk.dim(`(${result.nodes.length} nodes)`));
+    console.log();
+    console.log(result.formatted);
+  });
+
+/**
+ * Hook command for Claude Code integration
+ * Outputs context to stdout for injection
+ */
+export const contextHookCommand = new Command('context-hook')
+  .description('Hook handler for Claude Code session start (outputs context to stdout)')
+  .option('-p, --project <name>', 'Project name (defaults to current directory name)')
+  .option('--max-tokens <n>', 'Maximum tokens', String(DEFAULT_CONTEXT_CONFIG.maxTokens))
+  .action(async (opts) => {
+    const project = opts.project ?? path.basename(process.cwd());
+
+    const result = await gatherContext({
+      project,
+      config: {
+        maxTokens: parseInt(opts.maxTokens),
+      },
+    });
+
+    if (result.nodes.length === 0) {
+      // Output nothing if no context
+      return;
+    }
+
+    // Output markdown directly to stdout for Claude to consume
+    console.log(`<cortex-context project="${project}">`);
+    console.log(result.formatted);
+    console.log('</cortex-context>');
+  });

src/cli/commands/diff.ts

@@ -0,0 +1,90 @@
+import { Command } from 'commander';
+import chalk from 'chalk';
+import { findNodeByPrefix, diffVersions, getNodeAtTime, getNodeHistory } from '../../core/store';
+
+export const diffCommand = new Command('diff')
+  .argument('<id>', 'Node ID (or prefix)')
+  .option('--v1 <n>', 'First version number')
+  .option('--v2 <n>', 'Second version number')
+  .option('--from <date>', 'Start date (ISO format or timestamp)')
+  .option('--to <date>', 'End date (ISO format or timestamp)')
+  .option('--format <fmt>', 'Output format: text or json', 'text')
+  .description('Compare two versions of a node')
+  .action(async (idRaw: string, opts) => {
+    const node = findNodeByPrefix(idRaw);
+    if (!node) {
+      console.error(chalk.red(`Node not found: ${idRaw}`));
+      process.exit(1);
+    }
+
+    let v1: number;
+    let v2: number;
+
+    if (opts.v1 && opts.v2) {
+      v1 = parseInt(opts.v1);
+      v2 = parseInt(opts.v2);
+    } else if (opts.from && opts.to) {
+      // Parse dates
+      const fromTs = Date.parse(opts.from);
+      const toTs = Date.parse(opts.to);
+
+      if (isNaN(fromTs) || isNaN(toTs)) {
+        console.error(chalk.red('Invalid date format. Use ISO format (e.g., 2024-01-01) or timestamp.'));
+        process.exit(1);
+      }
+
+      const fromNode = getNodeAtTime(node.id, fromTs);
+      const toNode = getNodeAtTime(node.id, toTs);
+
+      if (!fromNode || !toNode) {
+        console.error(chalk.red('Could not find versions for the specified dates.'));
+        process.exit(1);
+      }
+
+      v1 = fromNode.version;
+      v2 = toNode.version;
+    } else {
+      // Default: compare latest two versions
+      const history = getNodeHistory(node.id);
+      if (history.length < 2) {
+        console.log(chalk.yellow('Not enough versions to compare.'));
+        return;
+      }
+      v1 = history[1].version; // Second latest
+      v2 = history[0].version; // Latest
+    }
+
+    const diff = diffVersions(node.id, v1, v2);
+    if (!diff) {
+      console.error(chalk.red('One or both versions not found.'));
+      process.exit(1);
+    }
+
+    if (opts.format === 'json') {
+      console.log(JSON.stringify(diff, null, 2));
+      return;
+    }
+
+    console.log(chalk.bold.cyan(`[${node.kind}] ${node.title}`));
+    console.log(`ID: ${node.id}`);
+    console.log(`Comparing: ${chalk.cyan(`v${v1}`)} -> ${chalk.cyan(`v${v2}`)}`);
+    console.log('');
+
+    if (diff.changes.length === 0) {
+      console.log(chalk.green('No changes between versions.'));
+      return;
+    }
+
+    for (const change of diff.changes) {
+      console.log(chalk.bold(`${change.field}:`));
+
+      const oldStr = typeof change.old === 'string' ? change.old : JSON.stringify(change.old);
+      const newStr = typeof change.new === 'string' ? change.new : JSON.stringify(change.new);
+
+      console.log(chalk.red(`  - ${oldStr}`));
+      console.log(chalk.green(`  + ${newStr}`));
+      console.log('');
+    }
+
+    console.log(chalk.dim(`${diff.changes.length} field(s) changed`));
+  });

src/cli/commands/history.ts

@@ -0,0 +1,48 @@
+import { Command } from 'commander';
+import chalk from 'chalk';
+import { findNodeByPrefix, getNodeHistory } from '../../core/store';
+
+export const historyCommand = new Command('history')
+  .argument('<id>', 'Node ID (or prefix)')
+  .option('--format <fmt>', 'Output format: text or json', 'text')
+  .description('Show version history for a node')
+  .action(async (idRaw: string, opts) => {
+    const node = findNodeByPrefix(idRaw);
+    if (!node) {
+      console.error(chalk.red(`Node not found: ${idRaw}`));
+      process.exit(1);
+    }
+
+    const history = getNodeHistory(node.id);
+
+    if (history.length === 0) {
+      console.log(chalk.yellow('No version history found.'));
+      return;
+    }
+
+    if (opts.format === 'json') {
+      console.log(JSON.stringify({ nodeId: node.id, title: node.title, versions: history }, null, 2));
+      return;
+    }
+
+    console.log(chalk.bold.cyan(`[${node.kind}] ${node.title}`));
+    console.log(`ID: ${node.id}`);
+    console.log(chalk.bold('\nVersion History:'));
+    console.log('');
+
+    for (const v of history) {
+      const validFrom = new Date(v.validFrom).toLocaleString();
+      const validUntil = v.validUntil ? new Date(v.validUntil).toLocaleString() : chalk.green('current');
+      const createdBy = chalk.dim(`(${v.createdBy})`);
+
+      console.log(`  ${chalk.cyan(`v${v.version}`)} ${createdBy}`);
+      console.log(`    ${chalk.dim('From:')} ${validFrom}`);
+      console.log(`    ${chalk.dim('Until:')} ${validUntil}`);
+      console.log(`    ${chalk.dim('Title:')} ${v.title}`);
+      if (v.status) console.log(`    ${chalk.dim('Status:')} ${v.status}`);
+      if (v.tags.length) console.log(`    ${chalk.dim('Tags:')} ${v.tags.join(', ')}`);
+      console.log('');
+    }
+
+    console.log(chalk.dim(`${history.length} version(s)`));
+  });

src/cli/commands/restore.ts

@@ -0,0 +1,65 @@
+import { Command } from 'commander';
+import chalk from 'chalk';
+import { findNodeByPrefix, restoreVersion, getNodeHistory, getCurrentVersion } from '../../core/store';
+
+export const restoreCommand = new Command('restore')
+  .argument('<id>', 'Node ID (or prefix)')
+  .option('-v, --to-version <n>', 'Version number to restore')
+  .option('--format <fmt>', 'Output format: text or json', 'text')
+  .description('Restore a node to a previous version (creates new version)')
+  .action(async (idRaw: string, opts) => {
+    const node = findNodeByPrefix(idRaw);
+    if (!node) {
+      console.error(chalk.red(`Node not found: ${idRaw}`));
+      process.exit(1);
+    }
+
+    if (!opts.toVersion) {
+      // Show available versions and ask user to specify
+      const history = getNodeHistory(node.id);
+      console.log(chalk.bold.cyan(`[${node.kind}] ${node.title}`));
+      console.log(`ID: ${node.id}`);
+      console.log(`Current version: ${chalk.cyan(`v${getCurrentVersion(node.id)}`)}`);
+      console.log('');
+      console.log(chalk.bold('Available versions:'));
+      for (const v of history) {
+        const validFrom = new Date(v.validFrom).toLocaleString();
+        const current = v.validUntil === null ? chalk.green(' (current)') : '';
+        console.log(`  ${chalk.cyan(`v${v.version}`)} - ${validFrom} - ${v.title}${current}`);
+      }
+      console.log('');
+      console.log(chalk.yellow('Use --to-version <n> or -v <n> to restore to a specific version.'));
+      return;
+    }
+
+    const targetVersion = parseInt(opts.toVersion);
+    const currentVersion = getCurrentVersion(node.id);
+
+    if (targetVersion === currentVersion) {
+      console.log(chalk.yellow('Cannot restore to the current version.'));
+      return;
+    }
+
+    const restored = await restoreVersion(node.id, targetVersion, 'restore');
+    if (!restored) {
+      console.error(chalk.red(`Version ${targetVersion} not found.`));
+      process.exit(1);
+    }
+
+    if (opts.format === 'json') {
+      console.log(JSON.stringify({ message: `Restored to version ${targetVersion}`, node: { ...restored, embedding: undefined } }, null, 2));
+      return;
+    }
+
+    console.log(chalk.green(`Restored node to version ${targetVersion}`));
+    console.log(`New version: ${chalk.cyan(`v${getCurrentVersion(node.id)}`)}`);
+    console.log('');
+    console.log(chalk.bold.cyan(`[${restored.kind}] ${restored.title}`));
+    console.log(`ID:      ${restored.id}`);
+    if (restored.status) console.log(`Status:  ${restored.status}`);
+    if (restored.tags.length) console.log(`Tags:    ${restored.tags.join(', ')}`);
+    if (restored.content) {
+      console.log('');
+      console.log(restored.content);
+    }
+  });

src/cli/commands/show.ts

@@ -1,11 +1,12 @@
 import { Command } from 'commander';
 import chalk from 'chalk';
-import { findNodeByPrefix } from '../../core/store';
+import { findNodeByPrefix, getNodeAtTime, getCurrentVersion } from '../../core/store';
 import { getConnections } from '../../core/graph';
 
 export const showCommand = new Command('show')
   .argument('<id>', 'Node ID (or prefix)')
   .option('--format <fmt>', 'Output format: text or json', 'text')
+  .option('--at <timestamp>', 'Show node at a specific point in time (ISO date or timestamp)')
   .description('Show a node and its connections')
   .action(async (idRaw: string, opts) => {
     const node = findNodeByPrefix(idRaw);
@@ -14,15 +15,56 @@ export const showCommand = new Command('show')
       process.exit(1);
     }
 
+    // If --at is specified, show historical state
+    if (opts.at) {
+      const ts = isNaN(Number(opts.at)) ? Date.parse(opts.at) : Number(opts.at);
+      if (isNaN(ts)) {
+        console.error(chalk.red('Invalid timestamp format. Use ISO date (e.g., 2024-01-01) or Unix timestamp.'));
+        process.exit(1);
+      }
+
+      const historical = getNodeAtTime(node.id, ts);
+      if (!historical) {
+        console.error(chalk.red('No version found for the specified time.'));
+        process.exit(1);
+      }
+
+      if (opts.format === 'json') {
+        console.log(JSON.stringify(historical, null, 2));
+        return;
+      }
+
+      console.log(chalk.dim(`Viewing historical state at: ${new Date(ts).toLocaleString()}`));
+      console.log('');
+      console.log(chalk.bold.cyan(`[${historical.kind}] ${historical.title}`));
+      console.log(`ID:      ${historical.id}`);
+      console.log(`Version: v${historical.version}`);
+      if (historical.status) console.log(`Status:  ${historical.status}`);
+      if (historical.tags.length) console.log(`Tags:    ${historical.tags.join(', ')}`);
+      console.log(`Valid:   ${new Date(historical.validFrom).toLocaleString()} - ${historical.validUntil ? new Date(historical.validUntil).toLocaleString() : 'current'}`);
+      if (historical.content) console.log(`\n${historical.content}`);
+
+      // Render structured sections
+      if (historical.metadata?.sections && Array.isArray(historical.metadata.sections)) {
+        for (const sec of historical.metadata.sections) {
+          console.log(`\n${chalk.bold(`-- ${sec.label} --`)}`);
+          if (sec.body) console.log(sec.body);
+        }
+      }
+      return;
+    }
+
     const conns = getConnections(node.id);
+    const version = getCurrentVersion(node.id);
 
     if (opts.format === 'json') {
-      console.log(JSON.stringify({ ...node, embedding: undefined, connections: conns }, null, 2));
+      console.log(JSON.stringify({ ...node, embedding: undefined, version, connections: conns }, null, 2));
       return;
     }
 
     console.log(chalk.bold.cyan(`[${node.kind}] ${node.title}`));
     console.log(`ID:      ${node.id}`);
+    console.log(`Version: v${version}`);
     if (node.status) console.log(`Status:  ${node.status}`);
     if (node.tags.length) console.log(`Tags:    ${node.tags.join(', ')}`);
     console.log(`Created: ${new Date(node.createdAt).toLocaleString()}`);

src/cli/index.ts

@@ -11,7 +11,11 @@ import { graphCommand } from './commands/graph';
 import { serveCommand } from './commands/serve';
 import { decayCommand } from './commands/decay';
 import { childrenCommand } from './commands/children';
+import { historyCommand } from './commands/history';
+import { diffCommand } from './commands/diff';
+import { restoreCommand } from './commands/restore';
 import { captureCommand, captureHookCommand, configCommand } from './commands/capture';
+import { contextCommand, contextHookCommand } from './commands/context';
 import { closeDb } from '../core/db';
 
 const program = new Command();
@@ -32,8 +36,13 @@ program.addCommand(graphCommand);
 program.addCommand(serveCommand);
 program.addCommand(decayCommand);
 program.addCommand(childrenCommand);
+program.addCommand(historyCommand);
+program.addCommand(diffCommand);
+program.addCommand(restoreCommand);
 program.addCommand(captureCommand);
 program.addCommand(captureHookCommand);
+program.addCommand(contextCommand);
+program.addCommand(contextHookCommand);
 program.addCommand(configCommand);
 
 program.hook('postAction', () => {

src/core/config.ts

@@ -0,0 +1,119 @@
+import { getDb } from './db';
+
+export interface CortexConfig {
+  // Context injection settings
+  'context.maxTokens': number;
+  'context.maxNodes': number;
+  'context.includeRecent': boolean;
+  'context.includeProject': boolean;
+  'context.includeTasks': boolean;
+  'context.includeDecisions': boolean;
+}
+
+const DEFAULTS: CortexConfig = {
+  'context.maxTokens': 4000,
+  'context.maxNodes': 20,
+  'context.includeRecent': true,
+  'context.includeProject': true,
+  'context.includeTasks': true,
+  'context.includeDecisions': true,
+};
+
+/**
+ * Ensure the config table exists
+ */
+function ensureConfigTable(): void {
+  const db = getDb();
+  db.exec(`
+    CREATE TABLE IF NOT EXISTS config (
+      key TEXT PRIMARY KEY,
+      value TEXT NOT NULL,
+      updated_at INTEGER NOT NULL
+    )
+  `);
+}
+
+/**
+ * Get a config value
+ */
+export function getConfig<K extends keyof CortexConfig>(key: K): CortexConfig[K] {
+  ensureConfigTable();
+  const db = getDb();
+  const row = db.prepare('SELECT value FROM config WHERE key = ?').get(key) as { value: string } | undefined;
+
+  if (!row) {
+    return DEFAULTS[key];
+  }
+
+  // Parse based on expected type
+  const defaultValue = DEFAULTS[key];
+  if (typeof defaultValue === 'boolean') {
+    return (row.value === 'true') as unknown as CortexConfig[K];
+  }
+  if (typeof defaultValue === 'number') {
+    return parseInt(row.value, 10) as unknown as CortexConfig[K];
+  }
+  return row.value as unknown as CortexConfig[K];
+}
+
+/**
+ * Set a config value
+ */
+export function setConfig<K extends keyof CortexConfig>(key: K, value: CortexConfig[K]): void {
+  ensureConfigTable();
+  const db = getDb();
+  const now = Date.now();
+  const strValue = String(value);
+
+  db.prepare(`
+    INSERT INTO config (key, value, updated_at)
+    VALUES (?, ?, ?)
+    ON CONFLICT(key) DO UPDATE SET value = ?, updated_at = ?
+  `).run(key, strValue, now, strValue, now);
+}
+
+/**
+ * List all config values
+ */
+export function listConfig(): Array<{ key: string; value: string; isDefault: boolean }> {
+  ensureConfigTable();
+  const db = getDb();
+  const rows = db.prepare('SELECT key, value FROM config').all() as Array<{ key: string; value: string }>;
+  const stored = new Map(rows.map(r => [r.key, r.value]));
+
+  const result: Array<{ key: string; value: string; isDefault: boolean }> = [];
+
+  for (const [key, defaultValue] of Object.entries(DEFAULTS)) {
+    const storedValue = stored.get(key);
+    if (storedValue !== undefined) {
+      result.push({ key, value: storedValue, isDefault: false });
+    } else {
+      result.push({ key, value: String(defaultValue), isDefault: true });
+    }
+  }
+
+  return result;
+}
+
+/**
+ * Reset a config key to default
+ */
+export function resetConfig(key: keyof CortexConfig): void {
+  ensureConfigTable();
+  const db = getDb();
+  db.prepare('DELETE FROM config WHERE key = ?').run(key);
+}
+
+/**
+ * Get context config as a structured object
+ */
+export function getContextConfig() {
+  return {
+    maxTokens: getConfig('context.maxTokens'),
+    maxNodes: getConfig('context.maxNodes'),
+    includeRecent: getConfig('context.includeRecent'),
+    includeProject: getConfig('context.includeProject'),
+    includeTasks: getConfig('context.includeTasks'),
+    includeDecisions: getConfig('context.includeDecisions'),
+  };
+}

src/core/context.ts

@@ -0,0 +1,291 @@
+import { getDb } from './db';
+import { query, listNodes } from './store';
+import { Node, NodeKind } from '../types';
+import { getContextConfig } from './config';
+
+export interface RankedNode {
+  node: Node;
+  score: number;
+  reason: 'recent' | 'project' | 'task' | 'decision' | 'semantic';
+}
+
+export interface ContextConfig {
+  maxTokens: number;
+  maxNodes: number;
+  includeRecent: boolean;
+  includeProject: boolean;
+  includeTasks: boolean;
+  includeDecisions: boolean;
+}
+
+export const DEFAULT_CONTEXT_CONFIG: ContextConfig = {
+  maxTokens: 4000,
+  maxNodes: 20,
+  includeRecent: true,
+  includeProject: true,
+  includeTasks: true,
+  includeDecisions: true,
+};
+
+/**
+ * Get nodes accessed within the last N hours
+ */
+export function getRecentNodes(hours: number = 48, limit: number = 10): Node[] {
+  const db = getDb();
+  const cutoff = Date.now() - hours * 60 * 60 * 1000;
+
+  const rows = db.prepare(`
+    SELECT * FROM nodes
+    WHERE is_stale = 0 AND last_accessed_at > ?
+    ORDER BY last_accessed_at DESC
+    LIMIT ?
+  `).all(cutoff, limit) as any[];
+
+  return rows.map(rowToNode);
+}
+
+/**
+ * Get nodes tagged with a specific project name
+ */
+export function getProjectNodes(projectName: string, limit: number = 10): Node[] {
+  return listNodes({ tags: [projectName.toLowerCase()], limit });
+}
+
+/**
+ * Get open tasks (status: todo, in_progress, or active)
+ */
+export function getOpenTasks(limit: number = 10): Node[] {
+  const db = getDb();
+
+  const rows = db.prepare(`
+    SELECT * FROM nodes
+    WHERE is_stale = 0
+      AND kind = 'task'
+      AND (status = 'todo' OR status = 'in_progress' OR status = 'active' OR status IS NULL)
+    ORDER BY updated_at DESC
+    LIMIT ?
+  `).all(limit) as any[];
+
+  return rows.map(rowToNode);
+}
+
+/**
+ * Get recent decisions
+ */
+export function getRecentDecisions(limit: number = 5): Node[] {
+  return listNodes({ kind: 'decision', limit });
+}
+
+/**
+ * Get semantic matches for a query
+ */
+export async function getSemanticMatches(queryText: string, limit: number = 10): Promise<RankedNode[]> {
+  const results = await query(queryText, { limit });
+  return results.map(r => ({
+    node: r.node,
+    score: r.score,
+    reason: 'semantic' as const,
+  }));
+}
+
+/**
+ * Estimate token count for a node (rough approximation)
+ */
+function estimateTokens(node: Node): number {
+  const text = `${node.title} ${node.content || ''} ${node.tags.join(' ')}`;
+  // Rough estimate: 1 token ≈ 4 characters
+  return Math.ceil(text.length / 4);
+}
+
+/**
+ * Deduplicate and rank nodes, keeping highest score per node
+ */
+function dedupeAndRank(candidates: RankedNode[]): RankedNode[] {
+  const byId = new Map<string, RankedNode>();
+
+  for (const c of candidates) {
+    const existing = byId.get(c.node.id);
+    if (!existing || c.score > existing.score) {
+      byId.set(c.node.id, c);
+    }
+  }
+
+  return Array.from(byId.values()).sort((a, b) => b.score - a.score);
+}
+
+/**
+ * Select nodes within token budget
+ */
+function selectWithinBudget(candidates: RankedNode[], maxTokens: number, maxNodes: number): RankedNode[] {
+  const selected: RankedNode[] = [];
+  let totalTokens = 0;
+
+  for (const c of candidates) {
+    if (selected.length >= maxNodes) break;
+
+    const tokens = estimateTokens(c.node);
+    if (totalTokens + tokens > maxTokens) continue;
+
+    selected.push(c);
+    totalTokens += tokens;
+  }
+
+  return selected;
+}
+
+/**
+ * Group nodes by their reason
+ */
+function groupByReason(nodes: RankedNode[]): Record<string, RankedNode[]> {
+  const groups: Record<string, RankedNode[]> = {};
+
+  for (const n of nodes) {
+    if (!groups[n.reason]) groups[n.reason] = [];
+    groups[n.reason].push(n);
+  }
+
+  return groups;
+}
+
+/**
+ * Format a single node for context output
+ */
+function formatNode(ranked: RankedNode): string {
+  const n = ranked.node;
+  const lines: string[] = [];
+
+  lines.push(`### ${n.title}`);
+  if (n.content) {
+    // Truncate long content
+    const content = n.content.length > 500 ? n.content.slice(0, 500) + '...' : n.content;
+    lines.push(content);
+  }
+  if (n.tags.length) {
+    lines.push(`*Tags: ${n.tags.join(', ')}*`);
+  }
+
+  return lines.join('\n');
+}
+
+/**
+ * Format context as markdown
+ */
+export function formatContext(nodes: RankedNode[]): string {
+  if (nodes.length === 0) {
+    return '*No relevant context found.*';
+  }
+
+  const groups = groupByReason(nodes);
+  const sections: string[] = [];
+
+  // Order: project > decisions > tasks > recent > semantic
+  const order: Array<{ key: string; title: string }> = [
+    { key: 'project', title: 'Project Context' },
+    { key: 'decision', title: 'Key Decisions' },
+    { key: 'task', title: 'Open Tasks' },
+    { key: 'recent', title: 'Recent Activity' },
+    { key: 'semantic', title: 'Related Memories' },
+  ];
+
+  for (const { key, title } of order) {
+    const group = groups[key];
+    if (group?.length) {
+      sections.push(`## ${title}\n\n${group.map(formatNode).join('\n\n')}`);
+    }
+  }
+
+  return sections.join('\n\n---\n\n');
+}
+
+/**
+ * Main context gathering function
+ */
+export async function gatherContext(
+  options: {
+    project?: string;
+    semanticQuery?: string;
+    config?: Partial<ContextConfig>;
+  } = {}
+): Promise<{ nodes: RankedNode[]; formatted: string }> {
+  // Load stored config, then override with any passed options
+  const storedConfig = getContextConfig();
+  const config = { ...storedConfig, ...options.config };
+  const candidates: RankedNode[] = [];
+
+  // 1. Project-specific nodes (highest priority)
+  if (config.includeProject && options.project) {
+    const projectNodes = getProjectNodes(options.project, 10);
+    candidates.push(...projectNodes.map(node => ({
+      node,
+      score: 0.95,
+      reason: 'project' as const,
+    })));
+  }
+
+  // 2. Recent decisions
+  if (config.includeDecisions) {
+    const decisions = getRecentDecisions(5);
+    candidates.push(...decisions.map(node => ({
+      node,
+      score: 0.85,
+      reason: 'decision' as const,
+    })));
+  }
+
+  // 3. Open tasks
+  if (config.includeTasks) {
+    const tasks = getOpenTasks(5);
+    candidates.push(...tasks.map(node => ({
+      node,
+      score: 0.80,
+      reason: 'task' as const,
+    })));
+  }
+
+  // 4. Recent activity
+  if (config.includeRecent) {
+    const recent = getRecentNodes(48, 10);
+    candidates.push(...recent.map(node => ({
+      node,
+      score: 0.70,
+      reason: 'recent' as const,
+    })));
+  }
+
+  // 5. Semantic search on project context
+  if (options.semanticQuery) {
+    const semantic = await getSemanticMatches(options.semanticQuery, 10);
+    // Scale semantic scores to fit our priority scheme
+    candidates.push(...semantic.map(r => ({
+      ...r,
+      score: r.score * 0.6, // Max 0.6 for semantic matches
+    })));
+  }
+
+  // Dedupe, rank, and select within budget
+  const ranked = dedupeAndRank(candidates);
+  const selected = selectWithinBudget(ranked, config.maxTokens, config.maxNodes);
+
+  return {
+    nodes: selected,
+    formatted: formatContext(selected),
+  };
+}
+
+// Helper to convert DB row to Node (duplicated from store.ts to avoid circular deps)
+function rowToNode(row: any): Node {
+  return {
+    id: row.id,
+    kind: row.kind,
+    title: row.title,
+    content: row.content,
+    status: row.status ?? undefined,
+    tags: JSON.parse(row.tags || '[]'),
+    metadata: JSON.parse(row.metadata || '{}'),
+    embedding: null, // Don't load embeddings for context
+    createdAt: row.created_at,
+    updatedAt: row.updated_at,
+    lastAccessedAt: row.last_accessed_at ?? row.updated_at,
+    isStale: !!row.is_stale,
+  };
+}

src/core/db.ts

@@ -32,6 +32,21 @@ CREATE TABLE IF NOT EXISTS node_tags (
   PRIMARY KEY (node_id, tag)
 );
 
+CREATE TABLE IF NOT EXISTS node_versions (
+  id TEXT PRIMARY KEY,
+  node_id TEXT NOT NULL,
+  version INTEGER NOT NULL,
+  title TEXT NOT NULL,
+  content TEXT NOT NULL DEFAULT '',
+  status TEXT,
+  tags TEXT DEFAULT '[]',
+  metadata TEXT DEFAULT '{}',
+  valid_from INTEGER NOT NULL,
+  valid_until INTEGER,
+  created_by TEXT DEFAULT 'user',
+  FOREIGN KEY (node_id) REFERENCES nodes(id) ON DELETE CASCADE
+);
+
 CREATE INDEX IF NOT EXISTS idx_nodes_kind ON nodes(kind);
 CREATE INDEX IF NOT EXISTS idx_nodes_status ON nodes(status);
 CREATE INDEX IF NOT EXISTS idx_nodes_created ON nodes(created_at DESC);
@@ -40,6 +55,9 @@ CREATE INDEX IF NOT EXISTS idx_edges_from ON edges(from_id);
 CREATE INDEX IF NOT EXISTS idx_edges_to ON edges(to_id);
 CREATE INDEX IF NOT EXISTS idx_edges_type ON edges(type);
 CREATE INDEX IF NOT EXISTS idx_tags_tag ON node_tags(tag);
+CREATE INDEX IF NOT EXISTS idx_versions_node ON node_versions(node_id, version);
+CREATE INDEX IF NOT EXISTS idx_versions_time ON node_versions(valid_from, valid_until);
+CREATE UNIQUE INDEX IF NOT EXISTS idx_versions_node_version ON node_versions(node_id, version);
 `;
 
 let _db: Database.Database | null = null;
@@ -68,6 +86,41 @@ export function getDb(): Database.Database {
     _db.exec('UPDATE nodes SET last_accessed_at = updated_at WHERE last_accessed_at IS NULL');
   }
 
+  // Migration: add version column to nodes table
+  if (!cols.some((c: any) => c.name === 'version')) {
+    _db.exec('ALTER TABLE nodes ADD COLUMN version INTEGER DEFAULT 1');
+    _db.exec('UPDATE nodes SET version = 1 WHERE version IS NULL');
+  }
+
+  // Migration: backfill node_versions for existing nodes without versions
+  const existingWithoutVersion = _db.prepare(`
+    SELECT * FROM nodes WHERE id NOT IN (SELECT DISTINCT node_id FROM node_versions)
+  `).all() as any[];
+
+  if (existingWithoutVersion.length > 0) {
+    const insertVersion = _db.prepare(`
+      INSERT INTO node_versions (id, node_id, version, title, content, status, tags, metadata, valid_from, valid_until, created_by)
+      VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
+    `);
+
+    for (const node of existingWithoutVersion) {
+      const versionId = require('crypto').randomUUID();
+      insertVersion.run(
+        versionId,
+        node.id,
+        1,
+        node.title,
+        node.content,
+        node.status,
+        node.tags,
+        node.metadata,
+        node.created_at,
+        null,
+        'migration'
+      );
+    }
+  }
+
   return _db;
 }
 

src/core/store.ts

@@ -1,6 +1,6 @@
 import { randomUUID as uuid } from 'crypto';
 import { getDb } from './db';
-import { Node, Edge, AddNodeInput, UpdateNodeInput, ListOptions, QueryOptions, SearchResult, EdgeType } from '../types';
+import { Node, Edge, AddNodeInput, UpdateNodeInput, ListOptions, QueryOptions, SearchResult, EdgeType, NodeVersion, HistoricalNode, NodeDiff } from '../types';
 import { hybridSearch, deserializeEmbedding } from './search/index';
 import { getEmbedding } from './search/ollama';
 
@@ -43,21 +43,44 @@ export async function addNode(input: AddNodeInput): Promise<Node> {
   // Try to get embedding
   const embedding = await getEmbedding(`${input.title} ${content}`);
 
-  db.prepare(`
-    INSERT INTO nodes (id, kind, title, content, status, tags, metadata, embedding, created_at, updated_at, last_accessed_at)
-    VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
-  `).run(
-    id, input.kind, input.title, content, input.status ?? null,
-    JSON.stringify(tags), JSON.stringify(metadata),
-    embedding ? serializeEmbedding(embedding) : null,
-    now, now, now
-  );
+  const transaction = db.transaction(() => {
+    db.prepare(`
+      INSERT INTO nodes (id, kind, title, content, status, tags, metadata, embedding, created_at, updated_at, last_accessed_at, version)
+      VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
+    `).run(
+      id, input.kind, input.title, content, input.status ?? null,
+      JSON.stringify(tags), JSON.stringify(metadata),
+      embedding ? serializeEmbedding(embedding) : null,
+      now, now, now, 1
+    );
 
-  // Insert tags
-  const insertTag = db.prepare('INSERT OR IGNORE INTO node_tags (node_id, tag) VALUES (?, ?)');
-  for (const tag of tags) {
-    insertTag.run(id, tag);
-  }
+    // Insert tags
+    const insertTag = db.prepare('INSERT OR IGNORE INTO node_tags (node_id, tag) VALUES (?, ?)');
+    for (const tag of tags) {
+      insertTag.run(id, tag);
+    }
+
+    // Create initial version record
+    const versionId = uuid();
+    db.prepare(`
+      INSERT INTO node_versions (id, node_id, version, title, content, status, tags, metadata, valid_from, valid_until, created_by)
+      VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
+    `).run(
+      versionId,
+      id,
+      1,
+      input.title,
+      content,
+      input.status ?? null,
+      JSON.stringify(tags),
+      JSON.stringify(metadata),
+      now,
+      null,
+      'user'
+    );
+  });
+
+  transaction();
 
   notifyDirty();
   return {
@@ -114,46 +137,88 @@ export function listNodes(options: ListOptions = {}): Node[] {
   return nodes;
 }
 
-export async function updateNode(id: string, input: UpdateNodeInput): Promise<Node | null> {
+export async function updateNode(id: string, input: UpdateNodeInput, createdBy: string = 'user'): Promise<Node | null> {
   const db = getDb();
-  const existing = getNode(id);
-  if (!existing) return null;
+  // Get existing node without updating last_accessed_at
+  const existingRow = db.prepare('SELECT * FROM nodes WHERE id = ?').get(id) as any;
+  if (!existingRow) return null;
+  const existing = rowToNode(existingRow);
 
   const now = Date.now();
-  const sets: string[] = ['updated_at = ?'];
-  const params: any[] = [now];
 
-  if (input.title !== undefined) { sets.push('title = ?'); params.push(input.title); }
-  if (input.content !== undefined) { sets.push('content = ?'); params.push(input.content); }
-  if (input.status !== undefined) { sets.push('status = ?'); params.push(input.status); }
-  if (input.isStale !== undefined) { sets.push('is_stale = ?'); params.push(input.isStale ? 1 : 0); }
-  if (input.tags !== undefined) { sets.push('tags = ?'); params.push(JSON.stringify(input.tags)); }
-  if (input.metadata !== undefined) {
-    const merged = { ...existing.metadata, ...input.metadata };
-    sets.push('metadata = ?');
-    params.push(JSON.stringify(merged));
-  }
+  // Get current version number
+  const currentVersion = existingRow.version ?? 1;
+  const newVersion = currentVersion + 1;
 
-  // Re-embed if title or content changed
+  // Create version snapshot in a transaction
+  const transaction = db.transaction(() => {
+    // Close out the current version by setting valid_until
+    db.prepare(`
+      UPDATE node_versions SET valid_until = ? WHERE node_id = ? AND valid_until IS NULL
+    `).run(now, id);
+
+    // Insert new version record with the NEW state (after update)
+    const versionId = uuid();
+    const newTitle = input.title ?? existing.title;
+    const newContent = input.content ?? existing.content;
+    const newStatus = input.status !== undefined ? input.status : existing.status;
+    const newTags = input.tags ?? existing.tags;
+    const newMetadata = input.metadata !== undefined ? { ...existing.metadata, ...input.metadata } : existing.metadata;
+
+    db.prepare(`
+      INSERT INTO node_versions (id, node_id, version, title, content, status, tags, metadata, valid_from, valid_until, created_by)
+      VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
+    `).run(
+      versionId,
+      id,
+      newVersion,
+      newTitle,
+      newContent,
+      newStatus ?? null,
+      JSON.stringify(newTags),
+      JSON.stringify(newMetadata),
+      now,
+      null,
+      createdBy
+    );
+
+    // Build the update query
+    const sets: string[] = ['updated_at = ?', 'version = ?'];
+    const params: any[] = [now, newVersion];
+
+    if (input.title !== undefined) { sets.push('title = ?'); params.push(input.title); }
+    if (input.content !== undefined) { sets.push('content = ?'); params.push(input.content); }
+    if (input.status !== undefined) { sets.push('status = ?'); params.push(input.status); }
+    if (input.isStale !== undefined) { sets.push('is_stale = ?'); params.push(input.isStale ? 1 : 0); }
+    if (input.tags !== undefined) { sets.push('tags = ?'); params.push(JSON.stringify(input.tags)); }
+    if (input.metadata !== undefined) {
+      const merged = { ...existing.metadata, ...input.metadata };
+      sets.push('metadata = ?');
+      params.push(JSON.stringify(merged));
+    }
+
+    params.push(id);
+    db.prepare(`UPDATE nodes SET ${sets.join(', ')} WHERE id = ?`).run(...params);
+
+    // Update tags if changed
+    if (input.tags !== undefined) {
+      db.prepare('DELETE FROM node_tags WHERE node_id = ?').run(id);
+      const insertTag = db.prepare('INSERT OR IGNORE INTO node_tags (node_id, tag) VALUES (?, ?)');
+      for (const tag of input.tags) {
+        insertTag.run(id, tag);
+      }
+    }
+  });
+
+  transaction();
+
+  // Re-embed if title or content changed (outside transaction since it's async)
   if (input.title !== undefined || input.content !== undefined) {
     const newTitle = input.title ?? existing.title;
     const newContent = input.content ?? existing.content;
     const embedding = await getEmbedding(`${newTitle} ${newContent}`);
     if (embedding) {
-      sets.push('embedding = ?');
-      params.push(serializeEmbedding(embedding));
-    }
-  }
-
-  params.push(id);
-  db.prepare(`UPDATE nodes SET ${sets.join(', ')} WHERE id = ?`).run(...params);
-
-  // Update tags if changed
-  if (input.tags !== undefined) {
-    db.prepare('DELETE FROM node_tags WHERE node_id = ?').run(id);
-    const insertTag = db.prepare('INSERT OR IGNORE INTO node_tags (node_id, tag) VALUES (?, ?)');
-    for (const tag of input.tags) {
-      insertTag.run(id, tag);
+      db.prepare('UPDATE nodes SET embedding = ? WHERE id = ?').run(serializeEmbedding(embedding), id);
     }
   }
 
@@ -195,3 +260,114 @@ export async function query(text: string, options: QueryOptions = {}): Promise<S
   const nodes = listNodes({ kind: options.kind, tags: options.tags, includeStale: options.includeStale });
   return hybridSearch(nodes, text, options);
 }
+
+// Version tracking functions
+
+function rowToNodeVersion(row: any): NodeVersion {
+  return {
+    id: row.id,
+    nodeId: row.node_id,
+    version: row.version,
+    title: row.title,
+    content: row.content,
+    status: row.status ?? undefined,
+    tags: JSON.parse(row.tags || '[]'),
+    metadata: JSON.parse(row.metadata || '{}'),
+    validFrom: row.valid_from,
+    validUntil: row.valid_until ?? null,
+    createdBy: row.created_by,
+  };
+}
+
+function rowToHistoricalNode(row: any, nodeRow: any): HistoricalNode {
+  return {
+    id: nodeRow.id,
+    kind: nodeRow.kind,
+    title: row.title,
+    content: row.content,
+    status: row.status ?? undefined,
+    tags: JSON.parse(row.tags || '[]'),
+    metadata: JSON.parse(row.metadata || '{}'),
+    version: row.version,
+    validFrom: row.valid_from,
+    validUntil: row.valid_until ?? null,
+  };
+}
+
+export function getNodeHistory(id: string): NodeVersion[] {
+  const db = getDb();
+  const rows = db.prepare(`
+    SELECT * FROM node_versions WHERE node_id = ? ORDER BY version DESC
+  `).all(id) as any[];
+  return rows.map(rowToNodeVersion);
+}
+
+export function getNodeAtTime(id: string, timestamp: number): HistoricalNode | null {
+  const db = getDb();
+  const nodeRow = db.prepare('SELECT * FROM nodes WHERE id = ?').get(id) as any;
+  if (!nodeRow) return null;
+
+  const versionRow = db.prepare(`
+    SELECT * FROM node_versions
+    WHERE node_id = ? AND valid_from <= ? AND (valid_until IS NULL OR valid_until > ?)
+    ORDER BY version DESC LIMIT 1
+  `).get(id, timestamp, timestamp) as any;
+
+  if (!versionRow) return null;
+  return rowToHistoricalNode(versionRow, nodeRow);
+}
+
+export function getNodeVersion(id: string, version: number): HistoricalNode | null {
+  const db = getDb();
+  const nodeRow = db.prepare('SELECT * FROM nodes WHERE id = ?').get(id) as any;
+  if (!nodeRow) return null;
+
+  const versionRow = db.prepare(`
+    SELECT * FROM node_versions WHERE node_id = ? AND version = ?
+  `).get(id, version) as any;
+
+  if (!versionRow) return null;
+  return rowToHistoricalNode(versionRow, nodeRow);
+}
+
+export function diffVersions(id: string, v1: number, v2: number): NodeDiff | null {
+  const version1 = getNodeVersion(id, v1);
+  const version2 = getNodeVersion(id, v2);
+
+  if (!version1 || !version2) return null;
+
+  const changes: NodeDiff['changes'] = [];
+  const fieldsToCompare: (keyof HistoricalNode)[] = ['title', 'content', 'status', 'tags', 'metadata'];
+
+  for (const field of fieldsToCompare) {
+    const oldVal = version1[field];
+    const newVal = version2[field];
+    const oldStr = JSON.stringify(oldVal);
+    const newStr = JSON.stringify(newVal);
+    if (oldStr !== newStr) {
+      changes.push({ field, old: oldVal, new: newVal });
+    }
+  }
+
+  return { nodeId: id, v1, v2, changes };
+}
+
+export async function restoreVersion(id: string, version: number, createdBy: string = 'restore'): Promise<Node | null> {
+  const historical = getNodeVersion(id, version);
+  if (!historical) return null;
+
+  // updateNode will handle creating a new version
+  return updateNode(id, {
+    title: historical.title,
+    content: historical.content,
+    status: historical.status,
+    tags: historical.tags,
+    metadata: historical.metadata,
+  }, createdBy);
+}
+
+export function getCurrentVersion(id: string): number {
+  const db = getDb();
+  const row = db.prepare('SELECT version FROM nodes WHERE id = ?').get(id) as any;
+  return row?.version ?? 1;
+}

src/mcp/index.ts

@@ -1,7 +1,7 @@
 import { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js';
 import { StdioServerTransport } from '@modelcontextprotocol/sdk/server/stdio.js';
 import { z } from 'zod/v3';
-import { query, listNodes, getNode, findNodeByPrefix, addNode, addEdge, removeNode, removeEdge, updateNode } from '../core/store';
+import { query, listNodes, getNode, findNodeByPrefix, addNode, addEdge, removeNode, removeEdge, updateNode, getNodeHistory, getNodeAtTime, getNodeVersion, diffVersions, restoreVersion } from '../core/store';
 import { getConnections, getEdgesByNode } from '../core/graph';
 import { cosineSimilarity } from '../core/search/vector';
 import { getDb } from '../core/db';
@@ -367,6 +367,37 @@ server.tool(
   }
 );
 
+// --- memory_context ---
+import { gatherContext, DEFAULT_CONTEXT_CONFIG } from '../core/context';
+
+server.tool(
+  'memory_context',
+  'Get relevant context for a Claude session. Gathers recent activity, project-specific nodes, open tasks, and decisions. Use at session start.',
+  {
+    project: z.string().optional().describe('Project name to filter by (e.g. "cortex")'),
+    query: z.string().optional().describe('Optional semantic search query'),
+    maxTokens: z.number().optional().describe(`Max tokens in output (default ${DEFAULT_CONTEXT_CONFIG.maxTokens})`),
+    maxNodes: z.number().optional().describe(`Max nodes to include (default ${DEFAULT_CONTEXT_CONFIG.maxNodes})`),
+  },
+  async ({ project, query: semanticQuery, maxTokens, maxNodes }) => {
+    const result = await gatherContext({
+      project,
+      semanticQuery,
+      config: {
+        maxTokens: maxTokens ?? DEFAULT_CONTEXT_CONFIG.maxTokens,
+        maxNodes: maxNodes ?? DEFAULT_CONTEXT_CONFIG.maxNodes,
+      },
+    });
+
+    return {
+      content: [{
+        type: 'text' as const,
+        text: result.formatted,
+      }],
+    };
+  }
+);
+
 // --- memory_summary ---
 import { getCachedSummary, generateSummary } from '../core/summary';
 
@@ -463,6 +494,102 @@ server.tool(
   }
 );
 
+// --- memory_history ---
+server.tool(
+  'memory_history',
+  'Get version history for a node',
+  {
+    id: z.string().describe('Node ID or prefix'),
+  },
+  async ({ id }) => {
+    const node = getNode(id) ?? findNodeByPrefix(id);
+    if (!node) {
+      return { content: [{ type: 'text' as const, text: serialize({ error: 'Node not found' }) }], isError: true };
+    }
+    const history = getNodeHistory(node.id);
+    return { content: [{ type: 'text' as const, text: serialize({ nodeId: node.id, title: node.title, versions: history }) }] };
+  }
+);
+
+// --- memory_show_at ---
+server.tool(
+  'memory_show_at',
+  'Show node at a specific point in time',
+  {
+    id: z.string().describe('Node ID or prefix'),
+    timestamp: z.union([z.number(), z.string()]).describe('Unix ms or ISO date string'),
+  },
+  async ({ id, timestamp }) => {
+    const node = getNode(id) ?? findNodeByPrefix(id);
+    if (!node) {
+      return { content: [{ type: 'text' as const, text: serialize({ error: 'Node not found' }) }], isError: true };
+    }
+
+    // Parse timestamp
+    let ts: number;
+    if (typeof timestamp === 'number') {
+      ts = timestamp;
+    } else {
+      const parsed = Date.parse(timestamp);
+      if (isNaN(parsed)) {
+        return { content: [{ type: 'text' as const, text: serialize({ error: 'Invalid timestamp format' }) }], isError: true };
+      }
+      ts = parsed;
+    }
+
+    const historical = getNodeAtTime(node.id, ts);
+    if (!historical) {
+      return { content: [{ type: 'text' as const, text: serialize({ error: 'No version found for the specified time' }) }], isError: true };
+    }
+    return { content: [{ type: 'text' as const, text: serialize(historical) }] };
+  }
+);
+
+// --- memory_diff ---
+server.tool(
+  'memory_diff',
+  'Compare two versions of a node',
+  {
+    id: z.string().describe('Node ID or prefix'),
+    v1: z.number().describe('First version number'),
+    v2: z.number().describe('Second version number'),
+  },
+  async ({ id, v1, v2 }) => {
+    const node = getNode(id) ?? findNodeByPrefix(id);
+    if (!node) {
+      return { content: [{ type: 'text' as const, text: serialize({ error: 'Node not found' }) }], isError: true };
+    }
+
+    const diff = diffVersions(node.id, v1, v2);
+    if (!diff) {
+      return { content: [{ type: 'text' as const, text: serialize({ error: 'One or both versions not found' }) }], isError: true };
+    }
+    return { content: [{ type: 'text' as const, text: serialize(diff) }] };
+  }
+);
+
+// --- memory_restore ---
+server.tool(
+  'memory_restore',
+  'Restore a node to a previous version (creates new version)',
+  {
+    id: z.string().describe('Node ID or prefix'),
+    version: z.number().describe('Version number to restore'),
+  },
+  async ({ id, version }) => {
+    const node = getNode(id) ?? findNodeByPrefix(id);
+    if (!node) {
+      return { content: [{ type: 'text' as const, text: serialize({ error: 'Node not found' }) }], isError: true };
+    }
+
+    const restored = await restoreVersion(node.id, version);
+    if (!restored) {
+      return { content: [{ type: 'text' as const, text: serialize({ error: 'Version not found' }) }], isError: true };
+    }
+    return { content: [{ type: 'text' as const, text: serialize({ message: `Restored to version ${version}`, node: restored }) }] };
+  }
+);
+
 async function main() {
   const transport = new StdioServerTransport();
   await server.connect(transport);

src/server/routes.ts

@@ -4,6 +4,8 @@ import { getConnections, buildTree } from '../core/graph';
 import { getDb } from '../core/db';
 import { determineGroupingStrategy, groupResults } from './queryOrganizer';
 import { getLastReport, markDirty, runMaintenance } from './heartbeat';
+import { getCachedSummary, generateSummary } from '../core/summary';
+import { gatherContext } from '../core/context';
 
 const router = Router();
 
@@ -149,6 +151,20 @@ router.post('/query/organize', async (req: Request, res: Response) => {
   }
 });
 
+// Summary — hierarchical pre-computed graph summary
+router.get('/summary', async (req: Request, res: Response) => {
+  try {
+    const refresh = req.query.refresh === 'true';
+    let summary = refresh ? null : getCachedSummary();
+    if (!summary) {
+      summary = await generateSummary();
+    }
+    res.json(summary);
+  } catch (err: any) {
+    res.status(500).json({ error: err.message });
+  }
+});
+
 // Maintenance status
 router.get('/maintenance/status', (_req: Request, res: Response) => {
   const report = getLastReport();
@@ -166,6 +182,42 @@ router.post('/maintenance/run', async (_req: Request, res: Response) => {
   }
 });
 
+// Context — get session context for Claude
+router.get('/context', async (req: Request, res: Response) => {
+  try {
+    const project = req.query.project as string | undefined;
+    const semanticQuery = req.query.query as string | undefined;
+    const maxTokens = req.query.maxTokens ? parseInt(req.query.maxTokens as string) : undefined;
+    const maxNodes = req.query.maxNodes ? parseInt(req.query.maxNodes as string) : undefined;
+    const format = req.query.format as string || 'markdown';
+
+    const result = await gatherContext({
+      project,
+      semanticQuery,
+      config: { maxTokens, maxNodes } as any,
+    });
+
+    if (format === 'json') {
+      res.json({
+        project,
+        nodeCount: result.nodes.length,
+        nodes: result.nodes.map(r => ({
+          id: r.node.id,
+          kind: r.node.kind,
+          title: r.node.title,
+          score: r.score,
+          reason: r.reason,
+        })),
+        formatted: result.formatted,
+      });
+    } else {
+      res.type('text/markdown').send(result.formatted);
+    }
+  } catch (err: any) {
+    res.status(500).json({ error: err.message });
+  }
+});
+
 // Prompt — AI-driven natural language instruction
 router.post('/prompt', async (req: Request, res: Response) => {
   try {

src/types.ts

@@ -71,3 +71,42 @@ export interface ListOptions {
   limit?: number;
   includeStale?: boolean;
 }
+
+// Version tracking types
+export interface NodeVersion {
+  id: string;
+  nodeId: string;
+  version: number;
+  title: string;
+  content: string;
+  status?: string;
+  tags: string[];
+  metadata: Record<string, any>;
+  validFrom: number;
+  validUntil: number | null;
+  createdBy: string;
+}
+
+export interface HistoricalNode {
+  id: string;
+  kind: NodeKind;
+  title: string;
+  content: string;
+  status?: string;
+  tags: string[];
+  metadata: Record<string, any>;
+  version: number;
+  validFrom: number;
+  validUntil: number | null;
+}
+
+export interface NodeDiff {
+  nodeId: string;
+  v1: number;
+  v2: number;
+  changes: {
+    field: string;
+    old: any;
+    new: any;
+  }[];
+}