Add persistent disk cache for parsed session data

Cache normalized turns/calls to ~/.cache/codeburn/session-cache.json so
the CLI skips re-parsing unchanged JSONL files on subsequent runs.
File reconciliation uses dev+ino+mtime+size fingerprinting; cost,
classification, and summaries are recomputed at query time. Atomic
writes via temp+fsync+rename, deep structural validation on load,
per-provider env fingerprinting, and best-effort save so cache failures
never break the CLI. ~6x speedup on warm cache.

src/fs-utils.ts

@@ -71,6 +71,8 @@ export type SessionLine = string | Buffer
 type ReadSessionLinesOptions = {
   largeLineAsBuffer?: boolean
   largeLineThresholdBytes?: number
+  startByteOffset?: number
+  byteOffsetTracker?: { lastCompleteLineOffset: number }
 }
 
 export function readSessionLines(
@@ -102,9 +104,10 @@ export async function* readSessionLines(
     return
   }
 
-  // Raw Buffers — no encoding. This avoids readline's ConsString trees
-  // which OOM on V8 when regex-flattening 100 MB+ lines.
-  const stream = createReadStream(filePath)
+  const stream = createReadStream(
+    filePath,
+    options.startByteOffset !== undefined ? { start: options.startByteOffset } : undefined,
+  )
   const SKIP_HEAD = 2048
   const largeLineThreshold = options.largeLineThresholdBytes ?? LARGE_STREAM_LINE_BYTES
   const formatLine = (buf: Buffer, lineLen: number, head?: string): SessionLine => {
@@ -115,6 +118,8 @@ export async function* readSessionLines(
   let len = 0
   let skipping = false
   let headChecked = false
+  let chunkBase = options.startByteOffset ?? 0
+  const tracker = options.byteOffsetTracker
 
   try {
     for await (const raw of stream) {
@@ -128,6 +133,7 @@ export async function* readSessionLines(
           if (nl === -1) {
             pos = chunk.length
           } else {
+            if (tracker) tracker.lastCompleteLineOffset = chunkBase + nl + 1
             skipping = false
             pos = nl + 1
           }
@@ -140,6 +146,7 @@ export async function* readSessionLines(
             len += nl - pos
           }
           pos = nl + 1
+          if (tracker) tracker.lastCompleteLineOffset = chunkBase + pos
 
           if (len === 0) {
             parts = []
@@ -183,6 +190,7 @@ export async function* readSessionLines(
           }
         }
       }
+      chunkBase += chunk.length
     }
 
     if (!skipping && len > 0) {

src/parser.ts

@@ -6,6 +6,19 @@ import { discoverAllSessions, getProvider } from './providers/index.js'
 import { flushCodexCache } from './codex-cache.js'
 import { flushAntigravityCache } from './providers/antigravity.js'
 import { isSqliteBusyError } from './sqlite.js'
+import {
+  type CachedCall,
+  type CachedFile,
+  type CachedTurn,
+  type ProviderSection,
+  type SessionCache,
+  cleanupOrphanedTempFiles,
+  computeEnvFingerprint,
+  fingerprintFile,
+  loadCache,
+  reconcileFile,
+  saveCache,
+} from './session-cache.js'
 import type { ParsedProviderCall } from './providers/types.js'
 import type {
   AssistantMessageContent,
@@ -995,6 +1008,7 @@ function parseApiCall(entry: JournalEntry): ParsedApiCall | null {
     timestamp: entry.timestamp ?? '',
     bashCommands: bashCmds,
     deduplicationKey: msg.id ?? `claude:${entry.timestamp}`,
+    cacheCreationOneHourTokens: cacheCreation.oneHourTokens || undefined,
   }
 }
 
@@ -1321,31 +1335,115 @@ async function collectJsonlFiles(dirPath: string): Promise<string[]> {
   return jsonlFiles
 }
 
-async function scanProjectDirs(dirs: Array<{ path: string; name: string }>, seenMsgIds: Set<string>, dateRange?: DateRange): Promise<ProjectSummary[]> {
-  const projectMap = new Map<string, { project: string; projectPath: string; sessions: SessionSummary[] }>()
+async function scanProjectDirs(
+  dirs: Array<{ path: string; name: string }>,
+  seenMsgIds: Set<string>,
+  diskCache: SessionCache,
+  dateRange?: DateRange,
+): Promise<ProjectSummary[]> {
+  const section = getOrCreateProviderSection(diskCache, 'claude')
+  const allDiscoveredFiles = new Set<string>()
+
+  type FileInfo = { dirName: string; fp: NonNullable<Awaited<ReturnType<typeof fingerprintFile>>> }
+  const unchangedFiles: Array<{ filePath: string; dirName: string; cached: CachedFile }> = []
+  const changedFiles: Array<{ filePath: string; info: FileInfo }> = []
 
   for (const { path: dirPath, name: dirName } of dirs) {
     const jsonlFiles = await collectJsonlFiles(dirPath)
-
     for (const filePath of jsonlFiles) {
-      const parsed = await parseSessionFile(filePath, dirName, seenMsgIds, dateRange)
-      if (parsed && parsed.session.apiCalls > 0) {
-        const projectPath = parsed.canonicalCwd ?? unsanitizePath(dirName)
-        const projectKey = parsed.canonicalCwd ? normalizeProjectPathKey(parsed.canonicalCwd) : `slug:${dirName}`
-        const existing = projectMap.get(projectKey)
-        if (existing) {
-          existing.sessions.push(parsed.session)
-        } else {
-          projectMap.set(projectKey, { project: dirName, projectPath, sessions: [parsed.session] })
-        }
+      allDiscoveredFiles.add(filePath)
+      const fp = await fingerprintFile(filePath)
+      if (!fp) continue
+
+      const action = reconcileFile(fp, section.files[filePath])
+      if (action.action === 'unchanged') {
+        unchangedFiles.push({ filePath, dirName, cached: section.files[filePath]! })
+      } else {
+        changedFiles.push({ filePath, info: { dirName, fp } })
       }
     }
   }
 
-  // If a slug has both cwd-keyed and slug-keyed entries (mixed sessions where
-  // some carry a canonical cwd and some don't), fold the slug-keyed sessions
-  // into the cwd-keyed entry so the canonical projectPath is preserved
-  // regardless of file iteration order.
+  // Pre-seed dedup set from cached (unchanged) files
+  for (const { cached } of unchangedFiles) {
+    for (const turn of cached.turns) {
+      for (const call of turn.calls) {
+        seenMsgIds.add(call.deduplicationKey)
+      }
+    }
+  }
+
+  // Parse changed files, update cache
+  for (const { filePath, info } of changedFiles) {
+    // Clear stale entry before parse — if parse fails, file is excluded
+    delete section.files[filePath]
+
+    const tracker = { lastCompleteLineOffset: 0 }
+    const entries = await parseClaudeEntries(filePath, tracker)
+    if (!entries) continue
+
+    const turns = groupIntoTurns(dedupeStreamingMessageIds(entries), seenMsgIds)
+    section.files[filePath] = {
+      fingerprint: info.fp,
+      lastCompleteLineOffset: tracker.lastCompleteLineOffset,
+      canonicalCwd: extractCanonicalCwd(entries),
+      mcpInventory: extractMcpInventory(entries),
+      turns: turns.map(parsedTurnToCachedTurn),
+    }
+  }
+
+  // Remove deleted files from cache
+  for (const cachedPath of Object.keys(section.files)) {
+    if (!allDiscoveredFiles.has(cachedPath)) {
+      delete section.files[cachedPath]
+    }
+  }
+
+  // Query-time: derive ProjectSummary[] from all cached turns
+  const projectMap = new Map<string, { project: string; projectPath: string; sessions: SessionSummary[] }>()
+
+  const allFiles = [
+    ...unchangedFiles.map(f => ({ filePath: f.filePath, dirName: f.dirName })),
+    ...changedFiles.map(f => ({ filePath: f.filePath, dirName: f.info.dirName })),
+  ]
+
+  for (const { filePath, dirName } of allFiles) {
+    const cachedFile = section.files[filePath]
+    if (!cachedFile || cachedFile.turns.length === 0) continue
+
+    let classifiedTurns = cachedFile.turns.map(cachedTurnToClassified)
+
+    if (dateRange) {
+      classifiedTurns = classifiedTurns.filter(turn => {
+        if (turn.assistantCalls.length === 0) return false
+        const firstCallTs = turn.assistantCalls[0]!.timestamp
+        if (!firstCallTs) return false
+        const ts = new Date(firstCallTs)
+        return ts >= dateRange.start && ts <= dateRange.end
+      })
+    }
+
+    if (classifiedTurns.length === 0) continue
+
+    const sessionId = basename(filePath, '.jsonl')
+    const projectPath = cachedFile.canonicalCwd ?? unsanitizePath(dirName)
+    const mcpInv = cachedFile.mcpInventory.length > 0 ? cachedFile.mcpInventory : undefined
+    const session = buildSessionSummary(sessionId, dirName, classifiedTurns, mcpInv)
+
+    if (session.apiCalls > 0) {
+      const projectKey = cachedFile.canonicalCwd
+        ? normalizeProjectPathKey(cachedFile.canonicalCwd)
+        : `slug:${dirName}`
+      const existing = projectMap.get(projectKey)
+      if (existing) {
+        existing.sessions.push(session)
+      } else {
+        projectMap.set(projectKey, { project: dirName, projectPath, sessions: [session] })
+      }
+    }
+  }
+
+  // Fold slug-keyed entries into cwd-keyed entries
   const cwdKeyByDirName = new Map<string, string>()
   for (const [key, entry] of projectMap) {
     if (!key.startsWith('slug:') && !cwdKeyByDirName.has(entry.project)) {
@@ -1411,6 +1509,136 @@ function providerCallToTurn(call: ParsedProviderCall): ParsedTurn {
   }
 }
 
+// ── Cache Conversion ───────────────────────────────────────────────────
+
+function apiCallToCachedCall(call: ParsedApiCall): CachedCall {
+  return {
+    provider: call.provider,
+    model: call.model,
+    usage: { ...call.usage, cacheCreationOneHourTokens: call.cacheCreationOneHourTokens ?? 0 },
+    speed: call.speed,
+    timestamp: call.timestamp,
+    tools: call.tools,
+    bashCommands: call.bashCommands,
+    skills: call.skills,
+    deduplicationKey: call.deduplicationKey,
+  }
+}
+
+function parsedTurnToCachedTurn(turn: ParsedTurn): CachedTurn {
+  return {
+    timestamp: turn.timestamp,
+    sessionId: turn.sessionId,
+    userMessage: turn.userMessage.slice(0, 2000),
+    calls: turn.assistantCalls.map(apiCallToCachedCall),
+  }
+}
+
+function providerCallToCachedTurn(call: ParsedProviderCall): CachedTurn {
+  return {
+    timestamp: call.timestamp,
+    sessionId: call.sessionId,
+    userMessage: call.userMessage.slice(0, 2000),
+    calls: [{
+      provider: call.provider,
+      model: call.model,
+      usage: {
+        inputTokens: call.inputTokens,
+        outputTokens: call.outputTokens,
+        cacheCreationInputTokens: call.cacheCreationInputTokens,
+        cacheReadInputTokens: call.cacheReadInputTokens,
+        cachedInputTokens: call.cachedInputTokens,
+        reasoningTokens: call.reasoningTokens,
+        webSearchRequests: call.webSearchRequests,
+        cacheCreationOneHourTokens: 0,
+      },
+      speed: call.speed,
+      timestamp: call.timestamp,
+      tools: call.tools,
+      bashCommands: call.bashCommands,
+      skills: [],
+      deduplicationKey: call.deduplicationKey,
+      project: call.project,
+      projectPath: call.projectPath,
+    }],
+  }
+}
+
+function cachedCallToApiCall(call: CachedCall): ParsedApiCall {
+  const u = call.usage
+  const outputForCost = call.provider === 'claude'
+    ? u.outputTokens
+    : u.outputTokens + u.reasoningTokens
+  const costUSD = calculateCost(
+    call.model, u.inputTokens, outputForCost,
+    u.cacheCreationInputTokens, u.cacheReadInputTokens,
+    u.webSearchRequests, call.speed, u.cacheCreationOneHourTokens,
+  )
+  return {
+    provider: call.provider,
+    model: call.model,
+    usage: {
+      inputTokens: u.inputTokens,
+      outputTokens: u.outputTokens,
+      cacheCreationInputTokens: u.cacheCreationInputTokens,
+      cacheReadInputTokens: u.cacheReadInputTokens,
+      cachedInputTokens: u.cachedInputTokens,
+      reasoningTokens: u.reasoningTokens,
+      webSearchRequests: u.webSearchRequests,
+    },
+    costUSD,
+    tools: call.tools,
+    mcpTools: extractMcpTools(call.tools),
+    skills: call.skills,
+    hasAgentSpawn: call.tools.includes('Agent'),
+    hasPlanMode: call.tools.includes('EnterPlanMode'),
+    speed: call.speed,
+    timestamp: call.timestamp,
+    bashCommands: call.bashCommands,
+    deduplicationKey: call.deduplicationKey,
+    cacheCreationOneHourTokens: u.cacheCreationOneHourTokens || undefined,
+  }
+}
+
+function cachedTurnToClassified(turn: CachedTurn): ClassifiedTurn {
+  const parsed: ParsedTurn = {
+    userMessage: turn.userMessage,
+    assistantCalls: turn.calls.map(cachedCallToApiCall),
+    timestamp: turn.timestamp,
+    sessionId: turn.sessionId,
+  }
+  return classifyTurn(parsed)
+}
+
+// ── Cache-Aware Parsing Helpers ────────────────────────────────────────
+
+async function parseClaudeEntries(
+  filePath: string,
+  tracker: { lastCompleteLineOffset: number },
+): Promise<JournalEntry[] | null> {
+  const entries: JournalEntry[] = []
+  let hasLines = false
+  for await (const line of readSessionLines(filePath, undefined, {
+    largeLineAsBuffer: true,
+    byteOffsetTracker: tracker,
+  })) {
+    hasLines = true
+    const entry = parseJsonlLine(line)
+    if (entry) entries.push(compactEntry(entry))
+  }
+  if (!hasLines || entries.length === 0) return null
+  return entries
+}
+
+function getOrCreateProviderSection(cache: SessionCache, provider: string): ProviderSection {
+  const envFp = computeEnvFingerprint(provider)
+  const existing = cache.providers[provider]
+  if (existing && existing.envFingerprint === envFp) return existing
+  const section = { envFingerprint: envFp, files: {} }
+  cache.providers[provider] = section
+  return section
+}
+
 const warnedProviderReadFailures = new Set<string>()
 
 function warnProviderReadFailureOnce(providerName: string, err: unknown): void {
@@ -1428,47 +1656,66 @@ async function parseProviderSources(
   providerName: string,
   sources: Array<{ path: string; project: string }>,
   seenKeys: Set<string>,
+  diskCache: SessionCache,
   dateRange?: DateRange,
 ): Promise<ProjectSummary[]> {
   const provider = await getProvider(providerName)
   if (!provider) return []
 
-  const sessionMap = new Map<string, { project: string; projectPath?: string; turns: ClassifiedTurn[] }>()
+  const section = getOrCreateProviderSection(diskCache, providerName)
+  const allDiscoveredFiles = new Set<string>()
 
-  try {
-    for (const source of sources) {
-      if (dateRange) {
-        try {
-          const s = await stat(source.path)
-          if (s.mtimeMs < dateRange.start.getTime()) continue
-        } catch { /* fall through; treat unknown stat as "may contain data" */ }
+  type SourceInfo = { source: { path: string; project: string }; fp: NonNullable<Awaited<ReturnType<typeof fingerprintFile>>> }
+  const unchangedSources: Array<{ source: { path: string; project: string }; cached: CachedFile }> = []
+  const changedSources: SourceInfo[] = []
+
+  for (const source of sources) {
+    allDiscoveredFiles.add(source.path)
+    const fp = await fingerprintFile(source.path)
+    if (!fp) continue
+
+    const action = reconcileFile(fp, section.files[source.path])
+    if (action.action === 'unchanged') {
+      unchangedSources.push({ source, cached: section.files[source.path]! })
+    } else {
+      changedSources.push({ source, fp })
+    }
+  }
+
+  // Parser dedup: cross-provider keys + cached file keys.
+  // Separate from seenKeys so parsing doesn't suppress query-time output.
+  const parserDedup = new Set(seenKeys)
+  for (const { cached } of unchangedSources) {
+    for (const turn of cached.turns) {
+      for (const call of turn.calls) {
+        parserDedup.add(call.deduplicationKey)
       }
+    }
+  }
+
+  // Parse changed files, update cache
+  let didParse = false
+  try {
+    for (const { source, fp } of changedSources) {
+      if (dateRange) {
+        if (fp.mtimeMs < dateRange.start.getTime()) continue
+      }
+
+      // Clear stale entry before parse — if parse fails, file is excluded
+      delete section.files[source.path]
+
       const parser = provider.createSessionParser(
         { path: source.path, project: source.project, provider: providerName },
-        seenKeys,
+        parserDedup,
       )
 
       try {
+        const turns: CachedTurn[] = []
         for await (const call of parser.parse()) {
-          if (dateRange) {
-            if (!call.timestamp) continue
-            const ts = new Date(call.timestamp)
-            if (ts < dateRange.start || ts > dateRange.end) continue
-          }
-
-          const turn = providerCallToTurn(call)
-          const classified = classifyTurn(turn)
-          const project = call.project ?? source.project
-          const key = `${providerName}:${call.sessionId}:${project}`
-
-          const existing = sessionMap.get(key)
-          if (existing) {
-            existing.turns.push(classified)
-            if (!existing.projectPath && call.projectPath) existing.projectPath = call.projectPath
-          } else {
-            sessionMap.set(key, { project, projectPath: call.projectPath, turns: [classified] })
-          }
+          turns.push(providerCallToCachedTurn(call))
         }
+        section.files[source.path] = { fingerprint: fp, mcpInventory: [], turns }
+        didParse = true
       } catch (err) {
         if (isSqliteBusyError(err)) {
           warnProviderReadFailureOnce(providerName, err)
@@ -1478,13 +1725,57 @@ async function parseProviderSources(
       }
     }
   } finally {
-    if (providerName === 'codex') await flushCodexCache()
-    if (providerName === 'antigravity') {
+    if (didParse && providerName === 'codex') await flushCodexCache()
+    if (didParse && providerName === 'antigravity') {
       const liveIds = new Set(sources.map(s => basename(s.path, '.pb')))
       await flushAntigravityCache(liveIds)
     }
   }
 
+  // Remove deleted files from cache
+  for (const cachedPath of Object.keys(section.files)) {
+    if (!allDiscoveredFiles.has(cachedPath)) {
+      delete section.files[cachedPath]
+    }
+  }
+
+  // Query-time: derive SessionSummary from all cached turns.
+  // Uses seenKeys (shared across providers) for cross-provider dedup.
+  const sessionMap = new Map<string, { project: string; projectPath?: string; turns: ClassifiedTurn[] }>()
+
+  for (const source of sources) {
+    const cachedFile = section.files[source.path]
+    if (!cachedFile) continue
+
+    for (const turn of cachedFile.turns) {
+      const hasDup = turn.calls.some(c => seenKeys.has(c.deduplicationKey))
+      if (hasDup) continue
+
+      for (const c of turn.calls) seenKeys.add(c.deduplicationKey)
+
+      if (dateRange) {
+        const callTs = turn.calls[0]?.timestamp
+        if (!callTs) continue
+        const ts = new Date(callTs)
+        if (ts < dateRange.start || ts > dateRange.end) continue
+      }
+
+      const classified = cachedTurnToClassified(turn)
+      const project = turn.calls[0]?.project ?? source.project
+      const key = `${providerName}:${turn.sessionId}:${project}`
+
+      const existing = sessionMap.get(key)
+      if (existing) {
+        existing.turns.push(classified)
+        if (!existing.projectPath && turn.calls[0]?.projectPath) {
+          existing.projectPath = turn.calls[0]!.projectPath
+        }
+      } else {
+        sessionMap.set(key, { project, projectPath: turn.calls[0]?.projectPath, turns: [classified] })
+      }
+    }
+  }
+
   const projectMap = new Map<string, { projectPath?: string; sessions: SessionSummary[] }>()
   for (const [key, { project, projectPath, turns }] of sessionMap) {
     const sessionId = key.split(':')[1] ?? key
@@ -1602,6 +1893,9 @@ export async function parseAllSessions(dateRange?: DateRange, providerFilter?: s
   const cached = sessionCache.get(key)
   if (cached && Date.now() - cached.ts < CACHE_TTL_MS) return cached.data
 
+  const diskCache = await loadCache()
+  await cleanupOrphanedTempFiles()
+
   const seenMsgIds = new Set<string>()
   const seenKeys = new Set<string>()
   const allSources = await discoverAllSessions(providerFilter)
@@ -1610,7 +1904,7 @@ export async function parseAllSessions(dateRange?: DateRange, providerFilter?: s
   const nonClaudeSources = allSources.filter(s => s.provider !== 'claude')
 
   const claudeDirs = claudeSources.map(s => ({ path: s.path, name: s.project }))
-  const claudeProjects = await scanProjectDirs(claudeDirs, seenMsgIds, dateRange)
+  const claudeProjects = await scanProjectDirs(claudeDirs, seenMsgIds, diskCache, dateRange)
 
   const providerGroups = new Map<string, Array<{ path: string; project: string }>>()
   for (const source of nonClaudeSources) {
@@ -1621,10 +1915,12 @@ export async function parseAllSessions(dateRange?: DateRange, providerFilter?: s
 
   const otherProjects: ProjectSummary[] = []
   for (const [providerName, sources] of providerGroups) {
-    const projects = await parseProviderSources(providerName, sources, seenKeys, dateRange)
+    const projects = await parseProviderSources(providerName, sources, seenKeys, diskCache, dateRange)
     otherProjects.push(...projects)
   }
 
+  try { await saveCache(diskCache) } catch {}
+
   const mergedMap = new Map<string, ProjectSummary>()
   for (const p of [...claudeProjects, ...otherProjects]) {
     const existing = mergedMap.get(p.project)

src/session-cache.ts

@@ -0,0 +1,319 @@
+import { readFile, stat, open, rename, unlink, readdir, mkdir } from 'fs/promises'
+import { existsSync } from 'fs'
+import { createHash, randomBytes } from 'crypto'
+import { join } from 'path'
+import { homedir } from 'os'
+
+// ── Types ──────────────────────────────────────────────────────────────
+
+export type CachedUsage = {
+  inputTokens: number
+  outputTokens: number
+  cacheCreationInputTokens: number
+  cacheReadInputTokens: number
+  cachedInputTokens: number
+  reasoningTokens: number
+  webSearchRequests: number
+  cacheCreationOneHourTokens: number
+}
+
+export type CachedCall = {
+  provider: string
+  model: string
+  usage: CachedUsage
+  speed: 'standard' | 'fast'
+  timestamp: string
+  tools: string[]
+  bashCommands: string[]
+  skills: string[]
+  deduplicationKey: string
+  project?: string
+  projectPath?: string
+}
+
+export type CachedTurn = {
+  timestamp: string
+  sessionId: string
+  userMessage: string
+  calls: CachedCall[]
+}
+
+export type FileFingerprint = {
+  dev: number
+  ino: number
+  mtimeMs: number
+  sizeBytes: number
+}
+
+export type CachedFile = {
+  fingerprint: FileFingerprint
+  lastCompleteLineOffset?: number
+  canonicalCwd?: string
+  mcpInventory: string[]
+  turns: CachedTurn[]
+}
+
+export type ProviderSection = {
+  envFingerprint: string
+  files: Record<string, CachedFile>
+}
+
+export type SessionCache = {
+  version: number
+  providers: Record<string, ProviderSection>
+}
+
+// ── Constants ──────────────────────────────────────────────────────────
+
+export const CACHE_VERSION = 1
+
+const CACHE_FILE = 'session-cache.json'
+const TEMP_FILE_MAX_AGE_MS = 5 * 60 * 1000
+
+const PROVIDER_ENV_VARS: Record<string, string[]> = {
+  claude: ['CLAUDE_CONFIG_DIRS', 'CLAUDE_CONFIG_DIR'],
+  codex: ['CODEX_HOME'],
+  droid: ['FACTORY_DIR'],
+  cursor: ['XDG_DATA_HOME'],
+  'cursor-agent': ['XDG_DATA_HOME'],
+  opencode: ['XDG_DATA_HOME'],
+  goose: ['XDG_DATA_HOME'],
+  crush: ['XDG_DATA_HOME'],
+  antigravity: ['CODEBURN_CACHE_DIR'],
+  qwen: ['QWEN_DATA_DIR'],
+  'ibm-bob': ['XDG_CONFIG_HOME'],
+}
+
+// ── Cache Dir ──────────────────────────────────────────────────────────
+
+function getCacheDir(): string {
+  return process.env['CODEBURN_CACHE_DIR'] ?? join(homedir(), '.cache', 'codeburn')
+}
+
+function getCachePath(): string {
+  return join(getCacheDir(), CACHE_FILE)
+}
+
+// ── Env Fingerprint ────────────────────────────────────────────────────
+
+export function computeEnvFingerprint(provider: string): string {
+  const vars = PROVIDER_ENV_VARS[provider] ?? []
+  const parts = vars.map(v => `${v}=${process.env[v] ?? ''}`)
+  return createHash('sha256').update(parts.join('\0')).digest('hex').slice(0, 16)
+}
+
+// ── Load / Save ────────────────────────────────────────────────────────
+
+export function emptyCache(): SessionCache {
+  return { version: CACHE_VERSION, providers: {} }
+}
+
+function isNum(v: unknown): v is number {
+  return typeof v === 'number' && Number.isFinite(v)
+}
+
+function isStringArray(v: unknown): v is string[] {
+  return Array.isArray(v) && v.every(e => typeof e === 'string')
+}
+
+function isOptionalString(v: unknown): boolean {
+  return v === undefined || typeof v === 'string'
+}
+
+function isOptionalNum(v: unknown): boolean {
+  return v === undefined || isNum(v)
+}
+
+function validateFingerprint(fp: unknown): fp is FileFingerprint {
+  if (!fp || typeof fp !== 'object') return false
+  const f = fp as Record<string, unknown>
+  return isNum(f['dev']) && isNum(f['ino']) && isNum(f['mtimeMs']) && isNum(f['sizeBytes'])
+}
+
+function validateUsage(u: unknown): u is CachedUsage {
+  if (!u || typeof u !== 'object') return false
+  const o = u as Record<string, unknown>
+  return isNum(o['inputTokens']) && isNum(o['outputTokens'])
+    && isNum(o['cacheCreationInputTokens']) && isNum(o['cacheReadInputTokens'])
+    && isNum(o['cachedInputTokens']) && isNum(o['reasoningTokens'])
+    && isNum(o['webSearchRequests']) && isNum(o['cacheCreationOneHourTokens'])
+}
+
+function validateCall(c: unknown): c is CachedCall {
+  if (!c || typeof c !== 'object') return false
+  const o = c as Record<string, unknown>
+  return typeof o['provider'] === 'string'
+    && typeof o['model'] === 'string'
+    && typeof o['deduplicationKey'] === 'string'
+    && typeof o['timestamp'] === 'string'
+    && (o['speed'] === 'standard' || o['speed'] === 'fast')
+    && isStringArray(o['tools'])
+    && isStringArray(o['bashCommands'])
+    && isStringArray(o['skills'])
+    && isOptionalString(o['project'])
+    && isOptionalString(o['projectPath'])
+    && validateUsage(o['usage'])
+}
+
+function validateTurn(t: unknown): t is CachedTurn {
+  if (!t || typeof t !== 'object') return false
+  const o = t as Record<string, unknown>
+  return typeof o['timestamp'] === 'string'
+    && typeof o['sessionId'] === 'string'
+    && typeof o['userMessage'] === 'string'
+    && Array.isArray(o['calls'])
+    && (o['calls'] as unknown[]).every(validateCall)
+}
+
+function validateCachedFile(f: unknown): f is CachedFile {
+  if (!f || typeof f !== 'object') return false
+  const o = f as Record<string, unknown>
+  return validateFingerprint(o['fingerprint'])
+    && isOptionalNum(o['lastCompleteLineOffset'])
+    && isOptionalString(o['canonicalCwd'])
+    && isStringArray(o['mcpInventory'])
+    && Array.isArray(o['turns'])
+    && (o['turns'] as unknown[]).every(validateTurn)
+}
+
+function validateProviderSection(s: unknown): s is ProviderSection {
+  if (!s || typeof s !== 'object') return false
+  const o = s as Record<string, unknown>
+  if (typeof o['envFingerprint'] !== 'string') return false
+  if (!o['files'] || typeof o['files'] !== 'object' || Array.isArray(o['files'])) return false
+  return Object.values(o['files'] as Record<string, unknown>).every(validateCachedFile)
+}
+
+function validateCache(raw: unknown): raw is SessionCache {
+  if (!raw || typeof raw !== 'object') return false
+  const o = raw as Record<string, unknown>
+  if (o['version'] !== CACHE_VERSION) return false
+  if (!o['providers'] || typeof o['providers'] !== 'object' || Array.isArray(o['providers'])) return false
+  return Object.values(o['providers'] as Record<string, unknown>).every(validateProviderSection)
+}
+
+export async function loadCache(): Promise<SessionCache> {
+  try {
+    const raw = await readFile(getCachePath(), 'utf-8')
+    const parsed = JSON.parse(raw)
+    if (!validateCache(parsed)) return emptyCache()
+    return parsed
+  } catch {
+    return emptyCache()
+  }
+}
+
+export async function saveCache(cache: SessionCache): Promise<void> {
+  const dir = getCacheDir()
+  if (!existsSync(dir)) await mkdir(dir, { recursive: true })
+
+  const finalPath = getCachePath()
+  const tempPath = `${finalPath}.${randomBytes(8).toString('hex')}.tmp`
+  const payload = JSON.stringify(cache)
+
+  const handle = await open(tempPath, 'w', 0o600)
+  try {
+    await handle.writeFile(payload, { encoding: 'utf-8' })
+    await handle.sync()
+  } finally {
+    await handle.close()
+  }
+
+  try {
+    await rename(tempPath, finalPath)
+  } catch (err) {
+    try { await unlink(tempPath) } catch {}
+    throw err
+  }
+}
+
+// ── File Fingerprinting ────────────────────────────────────────────────
+
+export async function fingerprintFile(filePath: string): Promise<FileFingerprint | null> {
+  try {
+    const s = await stat(filePath)
+    return { dev: s.dev, ino: s.ino, mtimeMs: s.mtimeMs, sizeBytes: s.size }
+  } catch {
+    return null
+  }
+}
+
+// ── Reconciliation ─────────────────────────────────────────────────────
+
+export type ReconcileAction =
+  | { action: 'unchanged' }
+  | { action: 'appended'; readFromOffset: number }
+  | { action: 'modified' }
+  | { action: 'new' }
+
+export function reconcileFile(
+  current: FileFingerprint,
+  cached: CachedFile | undefined,
+): ReconcileAction {
+  if (!cached) return { action: 'new' }
+
+  const fp = cached.fingerprint
+
+  if (
+    fp.dev === current.dev &&
+    fp.ino === current.ino &&
+    fp.mtimeMs === current.mtimeMs &&
+    fp.sizeBytes === current.sizeBytes
+  ) {
+    return { action: 'unchanged' }
+  }
+
+  if (
+    cached.lastCompleteLineOffset !== undefined &&
+    fp.dev === current.dev &&
+    fp.ino === current.ino &&
+    current.sizeBytes > fp.sizeBytes
+  ) {
+    return { action: 'appended', readFromOffset: cached.lastCompleteLineOffset }
+  }
+
+  return { action: 'modified' }
+}
+
+// ── Dedup Merge ────────────────────────────────────────────────────────
+// When appending incremental data, streaming Claude messages can re-emit
+// the same dedup key with updated usage. Merge by key: keep the earliest
+// timestamp, take incoming usage/tools/bashCommands/skills (latest wins).
+
+export function mergeCallByDedupKey(
+  existing: CachedCall,
+  incoming: CachedCall,
+): CachedCall {
+  return {
+    ...incoming,
+    timestamp: existing.timestamp < incoming.timestamp
+      ? existing.timestamp
+      : incoming.timestamp,
+  }
+}
+
+// ── Temp Cleanup ───────────────────────────────────────────────────────
+
+export async function cleanupOrphanedTempFiles(): Promise<void> {
+  const dir = getCacheDir()
+  if (!existsSync(dir)) return
+
+  try {
+    const entries = await readdir(dir)
+    const now = Date.now()
+
+    const prefix = 'session-cache.json.'
+    for (const entry of entries) {
+      if (!entry.startsWith(prefix) || !entry.endsWith('.tmp')) continue
+      try {
+        const fullPath = join(dir, entry)
+        const s = await stat(fullPath)
+        if (now - s.mtimeMs > TEMP_FILE_MAX_AGE_MS) {
+          await unlink(fullPath)
+        }
+      } catch {}
+    }
+  } catch {}
+}
+
+

src/types.ts

@@ -83,6 +83,7 @@ export type ParsedApiCall = {
   timestamp: string
   bashCommands: string[]
   deduplicationKey: string
+  cacheCreationOneHourTokens?: number
 }
 
 export type TaskCategory =