fix: use correct slice index for Bedrock tool result coalescing

[Aias00]

Description

Fix two bugs in the Anthropic-to-Bedrock translator message merging logic at internal/translator/anthropic_awsbedrock.go.

Bug 1: Wrong slice index (original report)

When system messages are present in the request body, promoteAnthropicSystemMessagesToParam filters them out, producing a shorter messages slice. The coalescing loop was using body.Messages[i+1] (the original unfiltered slice) instead of messages[i+1] (the filtered slice), causing index misalignment that could read wrong messages or panic with out-of-bounds access.

Bug 2: Coalescing logic was unreachable (root cause)

Tool result messages have Role: "user", so they match case anthropicschema.MessageRoleUser and go through convertUserMessage() — which handles tool results individually but never coalesces consecutive ones. The coalescing logic in the default branch was dead code for tool results since they never reach that branch.

Changes

• Moved the hasToolResult check + coalescing loop into the MessageRoleUser case branch
• Non-tool-result user messages still go through convertUserMessage()
• Changed body.Messages[i+1] → messages[i+1] to use the correct filtered slice
• Simplified the default branch to just return an error for unexpected roles
• Updated existing test to expect coalesced output (3 messages instead of 4)
• Added regression test with system messages to verify index alignment

Testing

• All existing translator tests pass
• New TestAnthropicToAWSBedrockTranslator_RequestBody_ToolResultMessagesWithSystemMessages verifies the fix works when system messages are present alongside consecutive tool results

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

This PR fixes tool_result message coalescing in the Anthropic→AWS Bedrock translator (especially when Anthropic system messages are promoted/filtered), and updates tests to match the new behavior.

Changes:

• Coalesce consecutive Anthropic tool_result messages into a single Bedrock message content array.
• Fix coalescing loop to iterate over the filtered messages slice (avoids index misalignment when system messages are promoted).
• Add a regression test covering system-message promotion + tool_result coalescing; update .gitignore for worktree directories.

Reviewed changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated 1 comment.

File	Description
internal/translator/anthropic_awsbedrock.go	Fixes coalescing to use the filtered messages slice and properly handles tool_result within the user role path.
internal/translator/anthropic_awsbedrock_test.go	Updates expectations for coalesced tool results and adds a regression test with system-message promotion.
.gitignore	Ignores local .worktrees/ directory.

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[Aias00]

Good point about test brittleness. However, promoteAnthropicSystemMessagesToParam uses strings.Join to concatenate all system message texts into a single string, then creates a single SystemPrompt{Text: ...} entry. So Len == 1 is deterministic and correct — there will always be exactly one system block regardless of how many system messages were in the input. I kept the assertion tight to catch any future regression in the system message promotion logic.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 92.85714% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 84.84%. Comparing base (3456009) to head (f22a9c3).

Files with missing lines	Patch %	Lines
internal/translator/anthropic_awsbedrock.go	92.85%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2237      +/-   ##
==========================================
+ Coverage   84.70%   84.84%   +0.14%     
==========================================
  Files         144      144              
  Lines       21250    21246       -4     
==========================================
+ Hits        17999    18026      +27     
+ Misses       2166     2137      -29     
+ Partials     1085     1083       -2     

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[Aias00]

CI failed on E2E Test for Upgrades (k8s v1.33.4) - this appears to be a flaky test unrelated to the PR changes (translator code). Other k8s versions (v1.32.8/v1.34.3/v1.35.0) all passed. Requesting re-run.

[Aias00]

close: #2278