fix(vertexai): recognize "adaptive" thinking in _thinking_in_params

[Humphrey (HumphreySun98)]

Description

_thinking_in_params in libs/vertexai/langchain_google_vertexai/_anthropic_utils.py only matched thinking.type == "enabled". When callers set thinking.type = "adaptive" — Anthropic's recommended thinking mode for Claude 4.6+, and the only mode supported by Claude Opus 4.7 — the helper returns False. In model_garden.py (and the streaming counterpart at L520), that flips coerce_content_to_string to True for both _generate and _stream, so the response's structured thinking blocks get silently flattened to a plain string. Net effect: ChatAnthropicVertex cannot return thinking blocks for Claude Opus 4.7 at all.

The fix is to match "adaptive" alongside "enabled":

def _thinking_in_params(params: dict) -> bool:
    return params.get("thinking", {}).get("type") in ("enabled", "adaptive")

Relevant issues

Fixes #1711

Type

🐛 Bug Fix

Changes

• libs/vertexai/langchain_google_vertexai/_anthropic_utils.py: accept both "enabled" and "adaptive".
• libs/vertexai/tests/unit_tests/test_anthropic_utils.py: add test_thinking_in_params_adaptive next to the existing enabled / disabled cases.

Testing

$ uv run pytest libs/vertexai/tests/unit_tests/test_anthropic_utils.py -k thinking_in_params -v
test_thinking_in_params_true                  PASSED
test_thinking_in_params_false_different_type  PASSED
test_thinking_in_params_adaptive              PASSED
3 passed in 11.90s

Reverting only the one-line _anthropic_utils.py change while keeping the new test makes that test fail with AssertionError, confirming the regression coverage pins the buggy behavior.

ruff check and ruff format --check pass on both files.

Note

The fix is intentionally minimal — a tuple-membership check that mirrors what the issue reporter proposed. No behavior changes for callers using "enabled" or any other value.

Disclaimer: this PR was prepared with the assistance of an AI agent (Claude Code). All code and test changes were reviewed by the author before submission.