VincentLambert 8f87e19120 feat(llm): add AWS Bedrock reranker connector (#16960) ...

## What

Adds a reranker connector for the **Bedrock** factory, which previously
offered
chat/embedding/CV models but no reranker — selecting a Bedrock rerank
model
raised `Factory not in rerank model`.

## How

`BedrockRerank` calls the `bedrock-agent-runtime` Rerank API. It reuses
the same
JSON key protocol as `BedrockEmbed` (`auth_mode` / `bedrock_region` /
`bedrock_ak` / `bedrock_sk`, with `access_key_secret` / `iam_role` /
`assume_role` modes). Documents are truncated to the model window
(Cohere Rerank
v3.5 ~2k of its shared 4k window, Amazon Rerank v1 8k) on top of
Bedrock's own
internal truncation. Scores are returned in `[0, 1]`, so the shared
`Base.similarity` normalization applies unchanged.

Verified against `amazon.rerank-v1:0` and `cohere.rerank-v3-5:0` in
`eu-central-1`.

> Note: this PR adds the connector only. Bedrock rerank models can be
selected by
> adding the relevant entries to `conf/llm_factories.json` under the
Bedrock
> provider; that catalog change is intentionally left out of this PR.

## Tests

`test/unit_test/rag/llm/test_bedrock_rerank.py` — boto3 is mocked (no
AWS call):
score-by-index mapping, per-model document truncation, model ARN
construction,
auth-mode validation and the empty-input short-circuit. `pytest` green
alongside
the existing reranker normalization suite.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

2026-07-16 11:06:20 +08:00

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