feat(anthropic-auto-compact): Add tool output truncation recovery layer for token limit handling (#63)

- Add storage.ts: Functions to find and truncate largest tool results
- Add TruncateState and TRUNCATE_CONFIG for truncation tracking
- Implement truncate-first recovery: truncate largest output -> retry (10x) -> compact (2x) -> revert (3x)
- Move session error handling to immediate recovery instead of session.idle wait
- Add compactionInProgress tracking to prevent concurrent execution

This fixes GitHub issue #63: "prompt is too long" errors now trigger immediate recovery by truncating the largest tool outputs first before attempting compaction.

🤖 Generated with assistance of OhMyOpenCode (https://github.com/code-yeongyu/oh-my-opencode)

src/hooks/anthropic-auto-compact/storage.ts

@@ -0,0 +1,163 @@
+import { existsSync, readdirSync, readFileSync, writeFileSync } from "node:fs"
+import { join } from "node:path"
+import { xdgData } from "xdg-basedir"
+
+const OPENCODE_STORAGE = join(xdgData ?? "", "opencode", "storage")
+const MESSAGE_STORAGE = join(OPENCODE_STORAGE, "message")
+const PART_STORAGE = join(OPENCODE_STORAGE, "part")
+
+const TRUNCATION_MESSAGE =
+  "[TOOL RESULT TRUNCATED - Context limit exceeded. Original output was too large and has been truncated to recover the session. Please re-run this tool if you need the full output.]"
+
+interface StoredToolPart {
+  id: string
+  sessionID: string
+  messageID: string
+  type: "tool"
+  callID: string
+  tool: string
+  state: {
+    status: "pending" | "running" | "completed" | "error"
+    input: Record<string, unknown>
+    output?: string
+    error?: string
+  }
+  truncated?: boolean
+  originalSize?: number
+}
+
+export interface ToolResultInfo {
+  partPath: string
+  partId: string
+  messageID: string
+  toolName: string
+  outputSize: number
+}
+
+function getMessageDir(sessionID: string): string {
+  if (!existsSync(MESSAGE_STORAGE)) return ""
+
+  const directPath = join(MESSAGE_STORAGE, sessionID)
+  if (existsSync(directPath)) {
+    return directPath
+  }
+
+  for (const dir of readdirSync(MESSAGE_STORAGE)) {
+    const sessionPath = join(MESSAGE_STORAGE, dir, sessionID)
+    if (existsSync(sessionPath)) {
+      return sessionPath
+    }
+  }
+
+  return ""
+}
+
+function getMessageIds(sessionID: string): string[] {
+  const messageDir = getMessageDir(sessionID)
+  if (!messageDir || !existsSync(messageDir)) return []
+
+  const messageIds: string[] = []
+  for (const file of readdirSync(messageDir)) {
+    if (!file.endsWith(".json")) continue
+    const messageId = file.replace(".json", "")
+    messageIds.push(messageId)
+  }
+
+  return messageIds
+}
+
+export function findToolResultsBySize(sessionID: string): ToolResultInfo[] {
+  const messageIds = getMessageIds(sessionID)
+  const results: ToolResultInfo[] = []
+
+  for (const messageID of messageIds) {
+    const partDir = join(PART_STORAGE, messageID)
+    if (!existsSync(partDir)) continue
+
+    for (const file of readdirSync(partDir)) {
+      if (!file.endsWith(".json")) continue
+      try {
+        const partPath = join(partDir, file)
+        const content = readFileSync(partPath, "utf-8")
+        const part = JSON.parse(content) as StoredToolPart
+
+        if (part.type === "tool" && part.state?.output && !part.truncated) {
+          results.push({
+            partPath,
+            partId: part.id,
+            messageID,
+            toolName: part.tool,
+            outputSize: part.state.output.length,
+          })
+        }
+      } catch {
+        continue
+      }
+    }
+  }
+
+  return results.sort((a, b) => b.outputSize - a.outputSize)
+}
+
+export function findLargestToolResult(sessionID: string): ToolResultInfo | null {
+  const results = findToolResultsBySize(sessionID)
+  return results.length > 0 ? results[0] : null
+}
+
+export function truncateToolResult(partPath: string): {
+  success: boolean
+  toolName?: string
+  originalSize?: number
+} {
+  try {
+    const content = readFileSync(partPath, "utf-8")
+    const part = JSON.parse(content) as StoredToolPart
+
+    if (!part.state?.output) {
+      return { success: false }
+    }
+
+    const originalSize = part.state.output.length
+    const toolName = part.tool
+
+    part.truncated = true
+    part.originalSize = originalSize
+    part.state.output = TRUNCATION_MESSAGE
+
+    writeFileSync(partPath, JSON.stringify(part, null, 2))
+
+    return { success: true, toolName, originalSize }
+  } catch {
+    return { success: false }
+  }
+}
+
+export function getTotalToolOutputSize(sessionID: string): number {
+  const results = findToolResultsBySize(sessionID)
+  return results.reduce((sum, r) => sum + r.outputSize, 0)
+}
+
+export function countTruncatedResults(sessionID: string): number {
+  const messageIds = getMessageIds(sessionID)
+  let count = 0
+
+  for (const messageID of messageIds) {
+    const partDir = join(PART_STORAGE, messageID)
+    if (!existsSync(partDir)) continue
+
+    for (const file of readdirSync(partDir)) {
+      if (!file.endsWith(".json")) continue
+      try {
+        const content = readFileSync(join(partDir, file), "utf-8")
+        const part = JSON.parse(content)
+        if (part.truncated === true) {
+          count++
+        }
+      } catch {
+        continue
+      }
+    }
+  }
+
+  return count
+}