fix(hook): add tool_use/tool_result pair validator to prevent API errors

Adds a defensive tool-pair-validator hook that runs as the final step in
the messages transform pipeline. When compaction or context-window recovery
removes user messages containing tool_result blocks without removing the
preceding assistant message with tool_use blocks, this validator detects
the mismatch and either:

1. Injects missing tool_result parts into the next user message, or
2. Creates a synthetic user message with placeholder tool_results

This prevents Anthropic API errors like 'tool_use ids found without
tool_result blocks immediately after'.

Fixes #3014

src/hooks/index.ts

@@ -26,6 +26,7 @@ export { createNonInteractiveEnvHook } from "./non-interactive-env";
 export { createInteractiveBashSessionHook } from "./interactive-bash-session";
 
 export { createThinkingBlockValidatorHook } from "./thinking-block-validator";
+export { createToolPairValidatorHook } from "./tool-pair-validator";
 export { createCategorySkillReminderHook } from "./category-skill-reminder";
 export { createRalphLoopHook, type RalphLoopHook } from "./ralph-loop";
 export { createNoSisyphusGptHook } from "./no-sisyphus-gpt";