fix(amazon-bedrock): do not replay unsigned reasoning content in multi-turn messages

[KiraPC]

PR #13972 fixed a bug where trimIfLast() invalidated Anthropic reasoning signatures by trimming trailing whitespace. During that refactoring, the code structure in convert-to-bedrock-chat-messages.ts changed from:

if (reasoningMetadata != null) {
  if (reasoningMetadata.signature != null) { /* replay with trim */ }
  else if (reasoningMetadata.redactedData != null) { /* replay redacted */ }
}
// unsigned reasoning → silently dropped (no else branch)

to:

if (reasoningMetadata?.signature != null) { /* replay without trim  */ }
else if (reasoningMetadata?.redactedData != null) { /* replay redacted */ }
else { /* replay unsigned reasoning as reasoningContent ← NEW catch-all */ }

The outer if (reasoningMetadata != null) guard was removed and replaced with optional chaining. This inadvertently introduced an else catch-all that replays unsigned reasoning (reasoning parts with no providerMetadata) as reasoningContent blocks — a case that was previously silently dropped.

The PR #13972 commit message states: "reasoning blocks without a signature still get trimmed as before", but Anthropic models always include a signature. The only case reaching the else branch is unsigned reasoning from non-Anthropic models (e.g., OpenAI extended thinking on Bedrock), which should not be replayed.

Summary

• Remove the else catch-all branch in the reasoning case of convertToBedrockChatMessages
• Reasoning parts without signature or redactedData are now silently dropped (restoring pre-fix(amazon-bedrock): preserve reasoning text when signature is present #13972 behavior for this specific case)
• Signed reasoning (Anthropic) and redacted reasoning remain completely unaffected
• Add comment explaining why unsigned reasoning is intentionally not replayed
• Update tests to verify unsigned reasoning is dropped rather than replayed

Why the else branch is unnecessary

• Anthropic always includes a cryptographic signature → handled by the if branch
• Anthropic redacted reasoning always has redactedData → handled by the else if branch
• Non-Anthropic models (OpenAI) produce unsigned reasoning that should not be replayed — replaying it causes the model to leak raw <reasoning> tags into the visible text response

Manual Verification

Tested against real Bedrock models with a multi-turn agent + tool-use scenario (non-streaming generateText):

Model	Without fix	With fix
openai.gpt-oss-120b-1:0	Leaks <reasoning> tags (33-100% of runs)	No leak
us.anthropic.claude-sonnet-4-20250514-v1:0	OK (reasoning with signature)	OK
moonshotai.kimi-k2.5	OK (no reasoning blocks)	OK
amazon.nova-pro-v1:0	OK (no reasoning blocks)	OK

Checklist

• Tests have been added / updated (for bug fixes / features)
• Documentation has been added / updated (for bug fixes / features)
• A patch changeset for relevant packages has been added (for bug fixes / features - run pnpm changeset in the project root)
• I have reviewed this pull request (self-review)

Related Issues

• Fixes bug(amazon-bedrock): <reasoning> tags leaked into text response for OpenAI models on Bedrock during multi-turn tool use #14720
• Caused by fix(amazon-bedrock): preserve reasoning text when signature is present #13972 (backported in Backport: fix(amazon-bedrock): preserve reasoning text when signature is present #13979)
• Related: fix(amazon-bedrock): preserve empty text blocks when reasoning content is present #14175 (empty text blocks with reasoning — same code area)

[aayush-kapoor]

signed github commits are needed for community PRs

[aayush-kapoor]

continued in #15181; will add you as a co-author