Agent Response Interruption: Anthropic API Message Sequence Error

Bug Description
Claude Code stops responding when generating a partial answer or during the initial response. Additionally, an error message appears:

Error: Agent 1: Last message was not an assistant message

Currently, Claude Code is unusable due to this issue.

Environment Info

• Platform: darwin
• Terminal: Apple_Terminal
• Version: 1.0.53
• Feedback ID: f18d5a89-521c-4099-b1f2-a7a6571c3e59

Errors

[{"error":"Error: Command failed: security find-generic-password -a $USER -w -s \"Claude Code\"\nsecurity: SecKeychainSearchCopyNext: The specified item could not be found in the keychain.\n\n    at genericNodeError (node:internal/errors:983:15)\n    at wrappedFn (node:internal/errors:537:14)\n    at checkExecSyncError (node:child_process:882:11)\n    at execSync (node:child_process:954:15)\n    at AI (file:///Users/admin/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:728:6320)\n    at file:///Users/admin/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:640:16554\n    at Q (file:///Users/admin/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:542:14406)\n    at MF (file:///Users/admin/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:640:14339)\n    at zX (file:///Users/admin/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:640:13205)\n    at MB (file:///Users/admin/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:640:19174)","timestamp":"2025-07-17T04:14:40.253Z"},{"error":"Error: Agent 1: Last message was not an assistant message\n    at q5A (file:///Users/admin/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:2335:1588)\n    at process.processTicksAndRejections (node:internal/process/task_queues:105:5)\n    at async Object.call (file:///Users/admin/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:2337:791)\n    at async J44 (file:///Users/admin/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:2223:9788)\n    at async a$1 (file:///Users/admin/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:2223:6451)\n    at async Dp (file:///Users/admin/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:1621:1318)\n    at async W44 (file:///Users/admin/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:2223:5596)\n    at async Z44 (file:///Users/admin/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:2223:5081)\n    at async AH (file:///Users/admin/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:2223:3533)\n    at async TQ (file:///Users/admin/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:2633:2662)","timestamp":"2025-07-17T04:15:09.226Z"}]