perf: optimize subagent transcript lookup with cache, meta-based resolution and startup index

src/server/routes/message.ts

@@ -15,6 +15,9 @@ import { getSubagentProgress } from '../sessionMessageRouter.js'
 
 function findParentCwd(sessionManager: SessionManager, id: string): string | undefined {
   for (const handle of sessionManager.getAllSessions()) {
+    if (handle.subagentIndex.has(id)) {
+      return handle.spawnCwd ?? handle.cwd
+    }
     if (handle.activeSubagents.has(id)) {
       return handle.spawnCwd ?? handle.cwd
     }

src/server/sessionHandle.ts

@@ -1,5 +1,8 @@
 import { type ChildProcess, spawn } from 'child_process'
 import { createInterface } from 'readline'
+import { readdir, stat, readFile } from 'fs/promises'
+import { existsSync } from 'fs'
+import { join } from 'path'
 import { jsonParse, jsonStringify } from '../utils/slowOperations.js'
 import { logError } from '../utils/log.js'
 import type { EventBus } from './eventBus.js'
@@ -10,10 +13,10 @@ import {
 } from './childSpawn.js'
 import { ControlChannel } from './sessionControlChannel.js'
 import {
+  type SubagentInfo,
   routeMessage,
   type StdoutMessage,
   type MessageRouterCtx,
-  type SubagentInfo,
 } from './sessionMessageRouter.js'
 import type {
   SessionBusyStatus,
@@ -24,6 +27,7 @@ import type {
 } from './types.js'
 import type { DisposableChildProcess } from '../utils/killOnDrop.js'
 import type { SessionMessage } from './transcriptReader.js'
+import { getProjectDir, findProjectDir } from '../utils/sessionStoragePortable.js'
 
 export type { InitData, PendingPermission, PendingQuestion }
 export { getScriptArgsForChild }
@@ -88,6 +92,11 @@ export class SessionHandle implements DisposableChildProcess {
   private _messageBuffer: SessionMessage[] = []
   private _tombstonedUuids = new Set<string>()
   private _activeSubagents = new Map<string, SubagentInfo>()
+  private _subagentIndex = new Map<string, { transcriptPath: string; meta: Record<string, unknown> }>()
+
+  get subagentIndex(): ReadonlyMap<string, { transcriptPath: string; meta: Record<string, unknown> }> {
+    return this._subagentIndex
+  }
 
   get tombstonedUuids(): ReadonlySet<string> {
     return this._tombstonedUuids
@@ -215,6 +224,28 @@ export class SessionHandle implements DisposableChildProcess {
     }
   }
 
+  async buildSubagentIndex(): Promise<void> {
+    const projectDir = getProjectDir(this.cwd)
+    const sessionDir = join(projectDir, this.sessionId, 'subagents')
+    if (!existsSync(sessionDir)) return
+
+    try {
+      const entries = await readdir(sessionDir)
+      for (const entry of entries) {
+        if (!entry.startsWith('agent-') || !entry.endsWith('.jsonl')) continue
+        const agentId = entry.slice('agent-'.length, -'.jsonl'.length)
+        const transcriptPath = join(sessionDir, entry)
+        const metaPath = transcriptPath.replace(/\.jsonl$/, '.meta.json')
+        let meta: Record<string, unknown> = {}
+        try {
+          const raw = await readFile(metaPath, 'utf-8')
+          meta = JSON.parse(raw)
+        } catch {}
+        this._subagentIndex.set(agentId, { transcriptPath, meta })
+      }
+    } catch {}
+  }
+
   spawn(): void {
     const printArgs = [
       '--print',

src/server/sessionManager.ts

@@ -248,6 +248,7 @@ export class SessionManager {
 
     try {
       handle.spawn()
+      handle.buildSubagentIndex().catch(() => {})
     } catch (err) {
       this.sessions.delete(sessionId)
       this.eventBus.unregisterSessionCwd(sessionId)

src/server/transcriptReader.ts

@@ -175,6 +175,23 @@ const SKIP_TYPES = new Set([
 ])
 
 const pathCache = new Map<string, string | null>()
+const subagentPathCache = new Map<string, string | null>()
+
+type AgentMeta = {
+  parent_session_id?: string
+  agentType?: string
+  description?: string
+  prompt?: string
+}
+
+async function readAgentMeta(metaPath: string): Promise<AgentMeta | null> {
+  try {
+    const raw = await readFile(metaPath, 'utf-8')
+    return JSON.parse(raw) as AgentMeta
+  } catch {
+    return null
+  }
+}
 
 async function resolveTranscriptPath(
   sessionId: string,
@@ -307,10 +324,40 @@ function readMessagesFromLines(
 async function findSubagentTranscriptPath(
   agentId: string,
   cwd?: string,
+): Promise<string | null> {
+  const cacheKey = `${agentId}:${cwd ?? ''}`
+  const cached = subagentPathCache.get(cacheKey)
+  if (cached !== undefined) return cached
+
+  const result = await findSubagentTranscriptPathUncached(agentId, cwd)
+  if (result) subagentPathCache.set(cacheKey, result)
+  return result
+}
+
+async function findSubagentTranscriptPathUncached(
+  agentId: string,
+  cwd?: string,
 ): Promise<string | null> {
   const fileName = `agent-${agentId}.jsonl`
+  const metaFileName = `agent-${agentId}.meta.json`
+
+  const tryDirect = async (projectDir: string): Promise<string | null> => {
+    const metaPath = join(projectDir, metaFileName)
+    const meta = await readAgentMeta(metaPath)
+    if (meta?.parent_session_id) {
+      const direct = join(projectDir, meta.parent_session_id, 'subagents', fileName)
+      if (existsSync(direct)) {
+        const s = await stat(direct)
+        if (s.isFile() && s.size > 0) return direct
+      }
+    }
+    return null
+  }
 
   const searchProject = async (projectDir: string): Promise<string | null> => {
+    const directHit = await tryDirect(projectDir)
+    if (directHit) return directHit
+
     let sessionDirs: string[]
     try {
       sessionDirs = await readdir(projectDir)
@@ -322,8 +369,7 @@ async function findSubagentTranscriptPath(
       try {
         const s = await stat(direct)
         if (s.isFile() && s.size > 0) return direct
-      } catch {
+      } catch {}
-      }
       const nestedSubagentsDir = join(projectDir, sessionDir, 'subagents')
       let subdirs: string[]
       try {
@@ -336,8 +382,7 @@ async function findSubagentTranscriptPath(
         try {
           const s = await stat(candidate)
           if (s.isFile() && s.size > 0) return candidate
-        } catch {
+        } catch {}
-        }
       }
     }
     return null
@@ -705,4 +750,5 @@ export async function readSessionTasks(opts: {
 
 export function clearPathCache(): void {
   pathCache.clear()
+  subagentPathCache.clear()
 }