fix(js): avoid false tool-call capture on plain tool_calls prose

[CJackHwang]

Motivation

• JS stream sieve could enter JSON capture mode when a tool keyword (e.g. tool_calls) appeared in normal prose, causing the client stream to appear truncated after the keyword.
• The goal is to prevent plain explanatory text that mentions tool_calls from being misdetected as the start of a tool-call JSON payload.

Description

• Tighten detection in internal/js/helpers/stream-tool-sieve/sieve.js so capture only starts when there is an actual { before a matched tool keyword (change in findToolSegmentStart).
• Add a regression test tests/node/stream-tool-sieve.test.js (new case: "sieve does not start capture on plain "tool_calls" prose without opening json brace") to ensure plain mentions are preserved as text.
• Commit message: fix(js): avoid false tool-call capture on plain tool_calls prose and included the updated files internal/js/helpers/stream-tool-sieve/sieve.js and tests/node/stream-tool-sieve.test.js.

Testing

• Ran Node unit tests with bash tests/scripts/run-unit-node.sh, all JS tests passed (48/48).
• Ran Go unit tests with bash tests/scripts/run-unit-go.sh, all Go unit tests passed (cached/ok results shown).
• Performed a live end-to-end run with real account via go run ./cmd/ds2api-tests --config /tmp/ds2api-live-config.json --admin-key admin --no-preflight --timeout 90 --retries 1 --keep 1; tool-related streaming cases passed and overall live run produced 28 passed / 2 failures that are unrelated to this fix (embeddings_contract and error_contract_invalid_model).

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Codex Task

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Project	Deployment	Actions	Updated (UTC)
ds2api	Ready	Preview, Comment	Mar 30, 2026 7:59am

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