fix: reduce activity history disk writes during streaming

Save only changed activity records instead of rewriting the entire history snapshot. Migrate existing history to schema 44 while preserving order and duplicate IDs.

Run unit tests with up to four workers and keep the configured integration phase serial. Include activity-history I/O, storage-upgrade, settings, and OpenCode isolation regression coverage.

Validation: 4 related test files / 123 tests passed; typecheck and lint passed.

Release note: Reduce disk writes while agent activity updates stream in, preserving existing activity history.

src/main/assistant/activity-history-io.test.ts

@@ -0,0 +1,62 @@
+// @vitest-environment node
+import { randomUUID } from 'node:crypto'
+import { mkdtempSync, rmSync, statSync } from 'node:fs'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+import type { DatabaseSync } from 'node:sqlite'
+import { expect, it } from 'vitest'
+import { AssistantDatabase } from './assistant-database'
+import { upgradeAssistantStorage } from './assistant-storage-upgrade'
+
+it('migrates activity history and writes only changed records during streaming', () => {
+  const directory = mkdtempSync(join(tmpdir(), 'goodbuddy-save-io-'))
+  const path = join(directory, 'assistant.sqlite')
+  const database = new AssistantDatabase(path)
+  try {
+    database.initialize(directory)
+    const raw = (database as unknown as { database: DatabaseSync }).database
+    const records = Array.from({ length: 10_000 }, (_, index) => ({
+      id: String(index), conversationId: randomUUID(), requestId: randomUUID(),
+      scope: { kind: 'global' as const }, kind: 'tool' as const,
+      title: 'Tool', detail: 'h'.repeat(280),
+      status: 'running' as const, createdAt: Date.now()
+    }))
+    // Build a released schema-43 snapshot, including an allowed duplicate ID.
+    records[1]!.id = records[0]!.id
+    raw.exec(`DROP TABLE activity_history_records;
+      ALTER TABLE activity_history RENAME COLUMN record_order_json TO records_json;
+      PRAGMA user_version=43`)
+    const legacySave = raw.prepare('UPDATE activity_history SET records_json = ?, legacy_history_may_be_incomplete = 1')
+    legacySave.run(JSON.stringify(records))
+    raw.exec('PRAGMA wal_checkpoint(TRUNCATE); PRAGMA wal_autocheckpoint=0')
+    for (let index = 0; index < 10; index++) {
+      records[0]!.detail += 'x'
+      legacySave.run(JSON.stringify(records))
+    }
+    const beforeBytes = statSync(`${path}-wal`).size
+    database.close()
+    upgradeAssistantStorage(path, () => undefined)
+    database.initialize(directory)
+    expect(database.getActivityHistory()).toEqual({ records, legacyHistoryMayBeIncomplete: true })
+    const migrated = (database as unknown as { database: DatabaseSync }).database
+    migrated.exec('PRAGMA wal_checkpoint(TRUNCATE); PRAGMA wal_autocheckpoint=0')
+    for (let index = 0; index < 10; index++) {
+      records[0]!.detail += 'x'
+      database.replaceActivityHistory({ records, legacyHistoryMayBeIncomplete: true })
+    }
+    const afterBytes = statSync(`${path}-wal`).size
+    console.log({ beforeBytes, afterBytes })
+    expect(afterBytes).toBeLessThan(beforeBytes / 100)
+    database.replaceActivityHistory({ records, legacyHistoryMayBeIncomplete: true })
+    expect(statSync(`${path}-wal`).size).toBe(afterBytes)
+    records.unshift(records.pop()!)
+    records.splice(2, 1)
+    database.replaceActivityHistory({ records, legacyHistoryMayBeIncomplete: false })
+    database.close()
+    database.initialize(directory)
+    expect(database.getActivityHistory()).toEqual({ records, legacyHistoryMayBeIncomplete: false })
+  } finally {
+    database.close()
+    rmSync(directory, { recursive: true, force: true })
+  }
+})