fix: harden resume after compaction failures (#195)

* fix: harden resume after compaction failures

* test: cover resume compaction safeguards

* fix: address resume safeguard review findings

src/utils/conversationRecovery.test.ts

@@ -0,0 +1,79 @@
+import { afterEach, expect, test } from 'bun:test'
+import { mkdtemp, rm, writeFile } from 'node:fs/promises'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+
+import {
+  loadConversationForResume,
+  ResumeTranscriptTooLargeError,
+} from './conversationRecovery.ts'
+
+const tempDirs: string[] = []
+const originalSimple = process.env.CLAUDE_CODE_SIMPLE
+const sessionId = '00000000-0000-4000-8000-000000001999'
+const ts = '2026-04-02T00:00:00.000Z'
+
+function id(n: number): string {
+  return `00000000-0000-4000-8000-${String(n).padStart(12, '0')}`
+}
+
+function user(uuid: string, content: string) {
+  return {
+    type: 'user',
+    uuid,
+    parentUuid: null,
+    timestamp: ts,
+    cwd: '/tmp',
+    userType: 'external',
+    sessionId,
+    version: 'test',
+    isSidechain: false,
+    isMeta: false,
+    message: {
+      role: 'user',
+      content,
+    },
+  }
+}
+
+async function writeJsonl(entry: unknown): Promise<string> {
+  const dir = await mkdtemp(join(tmpdir(), 'openclaude-conversation-recovery-'))
+  tempDirs.push(dir)
+  const filePath = join(dir, 'resume.jsonl')
+  await writeFile(filePath, `${JSON.stringify(entry)}\n`)
+  return filePath
+}
+
+afterEach(async () => {
+  process.env.CLAUDE_CODE_SIMPLE = originalSimple
+  await Promise.all(tempDirs.splice(0).map(dir => rm(dir, { recursive: true, force: true })))
+})
+
+test('loadConversationForResume accepts a small transcript from jsonl path', async () => {
+  process.env.CLAUDE_CODE_SIMPLE = '1'
+  const path = await writeJsonl(user(id(1), 'hello'))
+
+  const result = await loadConversationForResume('fixture', path)
+  expect(result).not.toBeNull()
+  expect(result?.sessionId).toBe(sessionId)
+  expect(result?.messages.length).toBeGreaterThan(0)
+})
+
+test('loadConversationForResume rejects oversized reconstructed transcripts', async () => {
+  process.env.CLAUDE_CODE_SIMPLE = '1'
+  const hugeContent = 'x'.repeat(8 * 1024 * 1024 + 32 * 1024)
+  const path = await writeJsonl(user(id(2), hugeContent))
+
+  let caught: unknown
+  try {
+    await loadConversationForResume('fixture', path)
+  } catch (error) {
+    caught = error
+  }
+
+  expect(caught).toBeInstanceOf(ResumeTranscriptTooLargeError)
+  expect((caught as Error).message).toContain(
+    'Reconstructed transcript is too large to resume safely',
+  )
+})
+