fix(seed): wait for L2/L3 before closing pipeline

[RerankerGuo]

Description | 描述

Fix the remaining seed lifecycle defect from #115: the seed runtime previously waited only for L1 to become idle, then called the gateway-oriented destroy() path. That path has an intentional 2-second shutdown budget and marks the scheduler destroyed before flushing, so a scheduled/running L2 extraction or the L3 persona task triggered by L2 could be skipped or interrupted before artifacts reached disk.

This PR adds a finite-batch completion barrier:

• Add MemoryPipelineManager.flushAll() to drain pending L1 work, flush scheduled L2 work, then wait for L3.
• Wait for L2 and L3 sequentially. The old concurrent wait could observe an initially-idle L3 queue before L2 enqueued the L3 task.
• Cancel recurring L2 timers after the finite batch drain, preventing the following destroy() call from triggering a duplicate L2 pass.
• Replace seed's final L1-only polling barrier with flushAll() so scene and persona artifacts are complete before storage resources close.
• Add a regression test with independently blocked L2 and L3 runners. It proves the barrier does not resolve during either phase and that destroy does not run a second extraction afterward.

Scope boundary: this does not change the JSON correction/retry behavior already covered by #190, or the seed tail-batch flush behavior covered by #507.

Related Issue | 关联 Issue

Refs #115

Change Type | 修改类型

• Bug fix | Bug 修复
• New feature | 新功能
• Documentation update | 文档更新
• Code optimization | 代码优化

Self-test Checklist | 自测清单

• Verified locally | 本地验证通过
• No existing features affected | 无影响现有功能

Additional Notes | 其他说明

Validation (Node v26.5.0, npm v11.17.0):

npm test -- src/utils/pipeline-manager.test.ts
# 1 file, 1 test passed

npm test
# 5 files, 68 tests passed

npm run build
# plugin bundle + all three script TypeScript builds passed

git diff --check
# passed

No configuration, storage schema, or public HTTP API changes.

[Maxwell-Code07]

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