[BUG] DisruptorProviderManage.startup is not idempotent — leaks disruptor + executor on re-entry

• Severity: Medium
• Location: shenyu-disruptor/src/main/java/org/apache/shenyu/disruptor/DisruptorProviderManage.java:98-134

Description: startup() unconditionally constructs a new OrderlyExecutor, a new Disruptor, new QueueConsumers, and overwrites this.provider without shutting down any prior instance. No guard (provider != null) and no shutdown of previously-assigned disruptor/executor. Threads are daemon=false.

Impact: Any code path calling startup() a second time (reconnect, re-init, retry, test re-entry) leaks the previous Disruptor's non-daemon provider threads plus OrderlyExecutor/SingletonExecutor threads; prevents JVM exit and grows thread counts.

Suggested fix: Guard with AtomicBoolean started; on re-entry if (provider != null) shutdown() first; make startup idempotent.

Confidence: Medium

• Related existing: none — #6262 is shutdown() not closing executor; this is startup() not closing the previous instance on re-entry.

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Identified during the 2026-08-02 deep re-scan; full list in docs/scan2-2026-08-02/06-medium-tiers.md.