fix(aws): accept tool_call content blocks in convertAIMessageToConverseMessage

[Lukas Buck (L4XB)]

Fixes #11476.

The bug

convertAIMessageToConverseMessage walks an assistant message's content array and throws on any block type it does not recognise:

Unsupported content block type: tool_call with content of { ... }

A tool_call block is one of those, even though the same call is serialized a few lines below from msg.tool_calls. An AIMessage carries both views — content blocks and tool_calls — so the converter rejected a message shape this class produces itself. Any agent loop that replays assistant turns as standard content blocks hits it.

The fix

Handle tool_call before the throw. When msg.tool_calls already carries the same id and name, the block is the duplicate and is skipped, so the toolUse is emitted exactly once, from the existing tool_calls pass.

When it does not, the block is converted to a toolUse here instead of being skipped. That branch matters: core only syncs content and tool_calls when an AIMessage is constructed with contentBlocks (libs/langchain-core/src/messages/ai.ts), so a message assembled through content can carry the block with tool_calls empty. A blanket skip would drop that call silently — which is the failure the throw was there to prevent in the first place.

Scope is the standard tool_call block. Anthropic's provider-shaped tool_use is not produced by this class, so it stays with the existing throw rather than being mapped on a guess about which of args/input it carries.

Tests

Three cases in libs/providers/langchain-aws/src/tests/chat_models.test.ts:

• a message holding the call both as a tool_call block and in tool_calls converts without throwing, and yields one toolUse, in the block's position relative to the text;
• a message holding only the block converts it, so nothing is dropped;
• an actually unknown block type still throws, unchanged.

npx vitest run src/tests/chat_models.test.ts    # 70 passed, no type errors

Checked against mutants rather than only against the fix: on main the first two fail and the third passes; skipping the block unconditionally (the shape the issue suggests) fails the second; emitting it without the duplicate check fails the first, with two toolUse blocks for one call.

oxlint and oxfmt --check are clean, and a changeset is included.

[changeset-bot]

🦋 Changeset detected

Latest commit: 8c1ff18

The changes in this PR will be included in the next version bump.

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@langchain/aws	Patch

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