feat(amazonq): adding classification based retry strategy for chat

[ashishrp-aws]

Copy of #2234 for main branch

Problem

Current chat request strategy is insufficient and we need to be in parity with Q CLI's unified approach.

Solution

Implements a simplified AWS retry strategy for agentic chat operations that matches AWS CLI behavior with exponential backoff and proper error handling.

Changes Made

• New AwsRetryStrategy class with AWS SDK-compatible retry logic
• 3-attempt retry pattern with exponential backoff (1s, 2s, 4s base delays)
• Jitter implementation (50-100%) to prevent thundering herd
• 10-second maximum delay cap to match AWS SDK adaptive strategy
• Comprehensive error classification for retry vs non-retry scenarios

Key Features

• Smart error handling: Distinguishes between retryable (throttling, high load) and non-retryable errors (usage limits, input too long)
• Monthly limit detection: Prevents unnecessary retries on quota exhaustion
• Model unavailability handling: Provides appropriate messaging for capacity issues
• Abort signal support: Respects cancellation requests
• Delay notifications: Informs users about retry delays > 2 seconds
• Request ID preservation: Maintains AWS request IDs for debugging

Error Types Handled

• Usage limit errors (monthly quotas)
• Throttling exceptions (429, service overload)
• Model capacity issues (insufficient capacity)
• Input validation errors (too long)
• Abort/cancellation requests

Testing

• Follows AWS SDK adaptive retry patterns
• Matches existing CLI behavior
• Preserves error context and request IDs

License

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 90.31414% with 74 lines in your changes missing coverage. Please review.
✅ Project coverage is 62.25%. Comparing base (a908195) to head (067e293).

Files with missing lines	Patch %	Lines
...uage-server/agenticChat/agenticChatResultStream.ts	9.09%	20 Missing ⚠️
...guage-server/agenticChat/retry/errorTransformer.ts	93.21%	14 Missing and 1 partial ⚠️
...nguage-server/agenticChat/retry/retryClassifier.ts	93.37%	9 Missing and 2 partials ⚠️
...isperer/src/language-server/chat/chatController.ts	0.00%	6 Missing ⚠️
...-server/workspaceContext/workspaceFolderManager.ts	0.00%	6 Missing ⚠️
...nguage-server/agenticChat/agenticChatController.ts	50.00%	4 Missing ⚠️
...rer/src/language-server/agenticChat/retry/index.ts	0.00%	3 Missing ⚠️
...codewhisperer/src/shared/streamingClientService.ts	93.87%	3 Missing ⚠️
server/aws-lsp-codewhisperer/src/shared/utils.ts	83.33%	2 Missing and 1 partial ⚠️
...anguage-server/agenticChat/retry/qRetryStrategy.ts	98.87%	1 Missing ⚠️
... and 2 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2409      +/-   ##
==========================================
+ Coverage   61.87%   62.25%   +0.38%     
==========================================
  Files         261      266       +5     
  Lines       58505    59090     +585     
  Branches     3672     3786     +114     
==========================================
+ Hits        36199    36788     +589     
+ Misses      22235    22227       -8     
- Partials       71       75       +4     

Flag	Coverage Δ
unittests	62.25% <90.31%> (+0.38%)	⬆️

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