[BUG] Replaced ext-lib JAR is never reloaded (version check is dead code)

- Severity: Medium-High
- Location:
`shenyu-web/src/main/java/org/apache/shenyu/web/loader/ShenyuExtPathPluginJarLoader.java:54-56` (`if (pluginJarName.contains(absolutePath)) { continue; }`); `shenyu-web/src/main/java/org/apache/shenyu/web/loader/ShenyuPluginClassLoader.java:212-219` (`compareVersion` — zero call sites)
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Description:
`loadExtendPlugins` keys only on the file's absolute path. If the path is already known, the jar is silently skipped — content/version is never re-examined. `ShenyuPluginClassLoader.compareVersion(...)` would detect a version change but has zero call sites.
-
Impact:
Operator replaces `ext-lib/foo.jar` with a new build (same filename) and expects hot reload. The scheduler rescans, sees the path known, silently ignores. Gateway keeps running the old plugin indefinitely. Only delete-then-re-add triggers reload.
-
Suggested fix:
Track `(path, version)` or `(path, lastModified/hash)`; when path exists but version differs, `removePluginClassLoader(path)` and re-parse. Wire `compareVersion` into this check.
-
Confidence: High
- Related existing: none

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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`](docs/scan2-2026-08-02/06-medium-tiers.md)._

Start in shenyu-web/src/main/java/org/apache/shenyu/web/loader/ShenyuExtPathPluginJarLoader.java at loadExtendPlugins and inspect the path-based skip at lines 54-56. Then read compareVersion in ShenyuPluginClassLoader.java:212-219 and trace how the scheduler rescans ext-lib. Done means replacing a JAR at the same path is detected and the updated plugin is reloaded without deleting the file first.

Written by the indexing model from the issue text.