fix(core): strip null id/name from tool-call-chunk deltas in compat bridge

[Christian Bromann (christian-bromann)]

Many provider integrations (notably Anthropic's input_json_delta path) attach the tool-call id and name only to the first tool_use chunk; subsequent per-chunk slices carry id=None, name=None and just the fresh args segment. The compat bridge forwarded those None values verbatim, producing wire payloads like {"type": "tool_call_chunk", "id": null, "name": null, "args": "..."}.

Consumers that fold deltas via a naive {...target, ...delta} spread (e.g. the langgraph-js SDK's MessageAssembler.applyContentDelta) interpret those as "identifier reset to null" and lose the id/name captured from content-block-start. Downstream extractors then drop the chunk until the final content-block-finish arrives — visible to end users as tool-call cards appearing all-at-once at the end of a turn instead of streaming in incrementally (the Deep Agent example rendering four subagents in a single flicker rather than one after another).

Introduce _to_protocol_delta_block and route every content-block-delta emission (sync / async chunk streams and the message_to_events replay path) through it. For tool_call_chunk and server_tool_call_chunk shapes, drop id / name keys when they would serialize to null. This matches the wire shape produced by langgraph-js's toProtocolDeltaBlock, where identifiers are only surfaced when they carry a real value.

[codspeed-hq]

Merging this PR will not alter performance

✅ 13 untouched benchmarks
⏩ 2 skipped benchmarks¹

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_{Comparing cb/new-streaming (bd8ab55) with nh/middleware-transformer (494a472)²}

Footnotes

1. 2 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

2. No successful run was found on nh/middleware-transformer (03e2eb7) during the generation of this report, so 4c32454 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩