fix: prevent protected tools from being pruned

Author: Tarquinen

lib/prompts/tool.txt

@@ -1,7 +1,7 @@
 Prunes tool outputs from context to manage conversation size and reduce noise.
 
 ## IMPORTANT: The Prunable List
-A `<prunable-tools>` list is injected into user messages showing available tool outputs you can prune. Each line has the format `ID: tool, parameter` (e.g., `20: read, /path/to/file.ts`). Use these numeric IDs to select which tools to prune.
+A `<prunable-tools>` list is injected into user messages showing available tool outputs you can prune. Each line has the format `ID: tool, parameter` (e.g., `20: read, /path/to/file.ts`). You MUST only use numeric IDs that appear in this list to select which tools to prune.
 
 ## CRITICAL: When and How to Prune
 

lib/strategies/prune-tool.ts

@@ -71,6 +71,14 @@ export function createPruneTool(
             const currentAgent: string | undefined = findCurrentAgent(messages)
             const toolIdList: string[] = buildToolIdList(messages)
             const pruneToolIds: string[] = getPruneToolIds(numericToolIds, toolIdList)
+                .filter(id => {
+                    const metadata = state.toolParameters.get(id)
+                    if (metadata && config.strategies.pruneTool.protectedTools.includes(metadata.tool)) {
+                        logger.warn("Blocked attempt to prune protected tool", { tool: metadata.tool, id })
+                        return false
+                    }
+                    return true
+                })
             state.prune.toolIds.push(...pruneToolIds)
 
             const toolMetadata = new Map<string, ToolParameterEntry>()