Fixes #184.

Problem

The research sub-agent hard-codes bedrock/us.anthropic.claude-sonnet-4-6, which AWS Bedrock rejects with "The provided model identifier is invalid." whenever the caller's region/account cannot reach the us.* cross-region inference profile (e.g. ap-northeast-1). The main agent itself is unaffected because the user-chosen profile id is passed straight through to LiteLLM — only the sub-agent overrides it.

Fix

Inherit the inference-profile prefix from the main model. If the user is running bedrock/jp.anthropic.claude-opus-4-7, the sub-agent now picks bedrock/jp.anthropic.claude-sonnet-4-6; same for global., apac., etc. The sub-agent stays on the cheaper Sonnet model — only the prefix follows the main agent's choice, matching the project's existing convention of letting the user's explicit profile selection drive Bedrock routing.

if main_model.startswith("bedrock/") and "anthropic" in main_model:
    head = main_model.split("/", 1)[1]
    region_prefix = head.split(".", 1)[0]
    return f"bedrock/{region_prefix}.anthropic.claude-sonnet-4-6"

The existing us. test case is preserved (the new logic still produces us. for a us. main model), and a new test covers global. / apac. prefixes.

Verification

Direct LiteLLM call from ap-northeast-1 before/after, against the same model the function returns:

bedrock/us.anthropic.claude-sonnet-4-6  -> BedrockException "The provided model identifier is invalid."  (the reported bug)
bedrock/jp.anthropic.claude-sonnet-4-6  -> OK   (what the patched function emits for the user's main model)

Unit tests pass:

$ pytest tests/unit/test_cli_rendering.py
======================== 7 passed, 5 warnings in 6.51s =========================

Caveats

This makes the sub-agent work for every prefix under which claude-sonnet-4-6 is published on Bedrock (currently us., jp., global.). If a user is on an exotic prefix that has no sonnet-4-6 variant, the sub-agent will still fail on that environment — but that's also true of the main agent on that prefix today, and addressing it would expand the scope beyond this fix.