Fix non-idiomatic patterns: raw EventContext, string concat in errors, pre-Java 16 stream collection

[Schmarvinius]

Summary

Fix three non-idiomatic patterns identified by comparison with cds-services conventions.

Changes

1. ActionHandler: Replace raw context.put("result") with context.setResult()

File: cds-feature-ai-core/.../handler/ActionHandler.java:36-37

// Before
context.put("result", result);
context.setCompleted();

// After
context.setResult(result);  // setResult() calls setCompleted() automatically

In cds-services, setResult() implicitly calls setCompleted(). The explicit context.put("result", ...) + setCompleted() pattern bypasses this and is non-standard.

2. AICoreSetupHandler: Replace string concatenation with {} placeholders

File: cds-feature-ai-core/.../AICoreSetupHandler.java (3 locations)

// Before (line 44)
throw new ServiceException(ErrorStatuses.SERVER_ERROR,
    "Failed to create AI Core resources for tenant: " + tenantId, e);

// After
throw new ServiceException(ErrorStatuses.SERVER_ERROR,
    "Failed to create AI Core resources for tenant: {}", tenantId, e);

Same for lines 82 and 106. ServiceException uses MessageFormatter.arrayFormat() internally and detects the last Throwable arg as the cause.

3. AbstractCrudHandler: Replace Collectors.toList() with .toList() and new ArrayList<>() with List.of()

File: cds-feature-ai-core/.../handler/AbstractCrudHandler.java:36-38

// Before
protected static <T, R> List<R> mapResources(List<T> resources, Function<T, R> mapper) {
  if (resources == null) return new ArrayList<>();
  return resources.stream().map(mapper).collect(Collectors.toList());
}

// After
protected static <T, R> List<R> mapResources(List<T> resources, Function<T, R> mapper) {
  if (resources == null) return List.of();
  return resources.stream().map(mapper).toList();
}

Remove unused imports: java.util.ArrayList, java.util.stream.Collectors.

Verification

• All existing tests should pass unchanged (return values flow into context.setResult() which accepts any Iterable).
• The returned lists are never mutated by callers (verified: all go to context.setResult()).

Rationale

Aligns with idiomatic patterns observed in cds-services:

• setResult() is the standard way to complete ON handlers
• SLF4J-style placeholders enable localization and consistent formatting
• .toList() is the Java 16+ standard; List.of() signals immutability intent

[github-actions]

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