Third-party gateways can trickle content deltas (e.g. a large tool_use
input_json_delta) just under the idle-watchdog window and never send
message_stop. Each delta resets the idle timer, so the in-kernel watchdog
never fires and the request hangs forever — the desktop shows "running"
with slowly growing tokens and a permanently-pending trace span (#766).
Add an overall-duration watchdog (CLAUDE_STREAM_MAX_DURATION_MS) that is
armed once and never reset by incoming chunks; the desktop injects 600000ms
via buildChildEnv. Orthogonal to the idle watchdog: idle catches a fully
silent stream, this catches an endless trickle that never completes. CLI
default stays 0 (disabled) for backward compatibility.
Verified end-to-end by replaying the issue's real captured SSE against the
actual kernel: trickle hangs without the cap, aborts cleanly with it.
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