Replace exception-only retry policy with Result-aware retry logic

[Copilot]

Webhook handlers wrap errors in Result<,> types rather than throwing exceptions. The existing retry policy only caught exceptions, so retries never triggered when handlers returned wrapped errors.

Changes

Upgraded to Polly v8 ResiliencePipeline with result-based retry logic:

• Retries on IStatusCodeHttpResult with 5xx status codes (transient failures)
• Retries on uncaught exceptions (infrastructure failures)
• Skips retries for 4xx responses (permanent failures)

Added observability:

• Activity events track retry attempts with status codes

Implementation

private static readonly ResiliencePipeline<IResult> ResultAwareRetryPolicy = 
    new ResiliencePipelineBuilder<IResult>()
        .AddRetry(new RetryStrategyOptions<IResult> {
            ShouldHandle = new PredicateBuilder<IResult>()
                .HandleInner<Exception>()
                .HandleResult(result => result is IStatusCodeHttpResult statusResult &&
                                       statusResult.StatusCode >= 500),
            BackoffType = DelayBackoffType.Exponential,
            UseJitter = true,
            MaxRetryAttempts = 5,
            Delay = TimeSpan.FromSeconds(1)
        })
        .Build();

Handlers catch and wrap permanent failures → return 400 → no retry
Handlers catch and wrap transient failures → return 500 → retry
Uncaught exceptions are infrastructure failures → retry

Original prompt

Work on TODO: look into better retry logic since I'm using Result<,> now. (from dotnet/Nudges.Webhooks/Program.cs)

Created from VS Code via the GitHub Pull Request extension.

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