Summary

• When the Claude SDK reports stop_reason: "max_tokens", the ACP adapter now returns { stopReason: "max_tokens" } instead of throwing a RequestError.internalError (JSON-RPC -32603)
• Scoped to success and error_during_execution result subtypes only — error_max_turns / error_max_budget_usd still correctly map to max_turn_requests

Problem

When tokens are exhausted, the SDK sends a result message with stop_reason: "max_tokens" and is_error: true. The adapter hit the is_error check first and threw an internal error, so ACP clients never received the stopReason field. Downstream tools like toad saw a JSON-RPC exception instead of a clean stop reason.

Fix

Check stop_reason === "max_tokens" before the is_error throw in the success and error_during_execution branches. Token exhaustion is a normal stop condition, not an internal error.

Test plan

• Added 5 unit tests covering:
  • success + max_tokens + is_error: false → returns max_tokens
  • success + max_tokens + is_error: true → returns max_tokens (main bug)
  • error_during_execution + max_tokens + is_error: true → returns max_tokens
  • success + null stop_reason → still returns end_turn (no regression)
  • success + is_error: true + non-max_tokens → still throws (no regression)
• All 100 tests pass
• Build passes

Fixes #235

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