[Bug] Anthropic API: Opus 4.7/4.8 Missing Tool Use Block with tool_use Stop Reason

Bug Description
Opus 4.7 AND 4.8 both produce silent stuck-turns:
the assistant message has stop_reason="tool_use" but no
tool_use block in content (it stops right after a thinking
block). Local transcript scan, aggregated at message.id
level, denominator = turns with stop_reason==tool_use:
opus-4-7 218/3066 = 7.11% (ongoing since 2026-05-23, not
converged), opus-4-8 14/105 = 13.33% (2026-05-29),
sonnet-4-6 0/2097 = 0.00% on the same machine over the same
period. Hang signature is identical across 4.7 and 4.8 (95%
thinking-only, 5% thinking+text). The fact it spans 4.7->4.8
while Sonnet 4.6 is completely clean points to a
server-side issue in the Opus thinking->tool_use transition,
not a client/version/file-structure problem. Related closed
issue: #50727 (was reported as 4.7-only).

Environment Info

• Platform: darwin
• Terminal: vscode
• Version: 2.1.156
• Feedback ID: 9e2f89b6-a60b-473e-bd08-cab968ee9d82

Errors

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