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.

BUILD.md

@@ -43,6 +43,22 @@ npm run typecheck
 npm run lint
 ```
 
+Vitest runs two ordered projects from `vitest.config.ts`. The `unit` project runs
+first with up to four workers, bounded by Node's available CPU parallelism. Once
+it finishes, the `integration` project runs with one worker. The serial group
+contains all test files under `tests/` (including `*.electron.test.ts`),
+`src/main/agent/**/*runtime*.test.ts`, and
+`src/agent-daemon/private-endpoint.test.ts`. Other tests remain in the unit group.
+Both projects inherit the React plugin, jsdom environment, renderer setup, and
+existing exclusions; test-file isolation remains enabled.
+
+This preserves serialization for the process/socket tests that previously timed
+out on Linux with two workers (commit `93721d6`). `sequence.groupOrder` keeps the
+two phases from overlapping. Existing file filters still work, for example
+`npm test -- src/main/agent/opencode-runtime.test.ts`. To select a whole phase,
+use `npm test -- --project unit` or `npm test -- --project integration`. To inspect
+file selection without running tests, use `npx vitest list --filesOnly`.
+
 监听模式：
 
 ```bash