test(core): await debounced sessions.json flush in plan-store test

[thomas-yanga]

Issue for this PR

Closes #

(no tracking issue — this fixes the unit (macos) CI failure seen on #89)

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

c0b79979 ("perf(core): 修复启动慢根因 — sessions.json 防抖") changed session-state.ts saveToDisk() from a synchronous write to a debounced
setImmediate(flushToDisk). The I33-1 plan-store test (packages/core/test/deepagent/plan-store.test.ts) predates that change and still assumed synchronous
persistence:

SessionState.setPlan("s3", p)   // only schedules setImmediate(flushToDisk), nothing on disk yet
const raw = readFileSync(path.join(stateDir, "sessions.json"), "utf8")  // ENOENT

The test body is fully synchronous, so whether the file exists at read time depends on event-loop timing — on the macOS runner it consistently fails with
ENOENT, which is what failed unit (macos) (@deepagent-code/core#test:ci exit 1) on #89. The linux/windows jobs in that run were cancelled (fail-fast) before
executing, so this is not actually macOS-specific.

Fix: make the test async and yield one event-loop turn (await new Promise((resolve) => setImmediate(resolve))) after setPlan, so the debounced flushToDisk lands
sessions.json before the assertion reads it. No production code changes. I also replaced the inline require("node:fs").readFileSync with the top-level
readFileSync import.

I verified the root cause by checking out c0b7997^ in a worktree: the test passes there and fails at dev HEAD, so the debounce commit is what broke it.

How did you verify your code works?

• cd packages/core && bun test test/deepagent/plan-store.test.ts → 8 pass / 0 fail (previously 7 pass / 1 fail with ENOENT)
• Full package suite bun test (2236 tests / 225 files): this test was the only failure before the fix
• bun run typecheck in packages/core passes

Screenshots / recordings

If this is a UI change, please include a screenshot or recording.

N/A — test-only change.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

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