[xiaobaicai66695]

What does this PR do?

Fixes #16548.

• Store the script rule and compiled script router in one immutable state and publish it through a single volatile reference.
• Clear that state when a configuration DELETED event arrives, so routing passes through to the healthy provider candidates.
• Add a regression test for rule addition, deletion, and republishing.

Why?

In 3.3.6, AppScriptStateRouter.process(DELETED) clears scriptRule but leaves scriptRouter non-null. The next invocation passes the null-router guard and dereferences scriptRule.isValid(). DynamicDirectory catches the exception and returns an empty invoker list, causing No provider available even when providers are healthy. Publishing the rule and compiled router together also prevents an invocation from observing values from different configuration revisions.

This bug reproduces with a single service reference on unmodified 3.3.6. It is independent of the cross-service chain issue in #16545 and #16546.

How was this tested?

• The new AppScriptStateRouterTest case fails with a NullPointerException at doRoute on unmodified 3.3 source, then passes with this change.
• ./mvnw -pl dubbo-cluster -Dtest=AppScriptStateRouterTest -Dsurefire.failIfNoSpecifiedTests=false test: 2 tests, 0 failures, 0 errors.
• Local real-RPC E2E with Nacos 2.5.2, an embedded ZooKeeper registry, two Order provider JVMs, and one consumer JVM:
  • With the original 3.3.6 router factory and one reference: before deletion v2=5; after Nacos returned 404, v1=2/v2=3; after republishing v2=5.
  • With the separate per-service router-factory fix and two references: the same sequence and counts.
  • No router NPE or provider-unavailable error after deletion.

No production cluster changes are included in this PR.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 69.23077% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 60.92%. Comparing base (843b98b) to head (5156fdc).

Files with missing lines	Patch %	Lines
...ter/router/script/config/AppScriptStateRouter.java	69.23%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                3.3   #16549      +/-   ##
============================================
+ Coverage     60.90%   60.92%   +0.01%     
- Complexity       15       30      +15     
============================================
  Files          1953     1953              
  Lines         89280    89286       +6     
  Branches      13476    13478       +2     
============================================
+ Hits          54376    54394      +18     
+ Misses        29323    29311      -12     
  Partials       5581     5581              

Flag	Coverage Δ
integration-tests-java21	32.08% <7.69%> (+<0.01%)	⬆️
integration-tests-java8	32.21% <7.69%> (+0.06%)	⬆️
samples-tests-java21	32.11% <7.69%> (-0.02%)	⬇️
samples-tests-java8	29.80% <7.69%> (+0.02%)	⬆️
unit-tests-java11	59.19% <69.23%> (+0.08%)	⬆️
unit-tests-java17	58.61% <7.69%> (+0.01%)	⬆️
unit-tests-java21	58.61% <7.69%> (-0.03%)	⬇️
unit-tests-java25	58.55% <7.69%> (-0.05%)	⬇️
unit-tests-java8	59.16% <69.23%> (+0.01%)	⬆️

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[EarthChen]

LGTM. Confirmed the bug: after a rule is deleted, scriptRule is null but scriptRouter stays non-null, so doRoute hits an NPE on scriptRule.isValid(). Merging rule and router into one immutable RouterState published through a volatile field fixes it and removes the null-check/dereference race. A failed ScriptStateRouter construction now keeps the old state.

Verified locally: AppScriptStateRouterTest passes with this PR, and fails with an NPE in doRoute when the main class is reverted to 3.3.