Q16: compact older tool results inside a run

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/main/services/run-context-compaction.ts

@@ -0,0 +1,27 @@
+import type { AgentTurnMessage } from "./provider-tool-turn";
+
+const KEEP_RECENT_TOOL_TURNS = 3;
+const ELIDE_ABOVE_CHARS = 600;
+const PREVIEW_CHARS = 300;
+
+/** Older tool results shrink to a preview; the latest turns stay verbatim. */
+export function compactToolHistory(messages: AgentTurnMessage[]): { messages: AgentTurnMessage[]; elided: number } {
+  const toolTurnIndexes = messages.flatMap((message, index) => (message.role === "tool" ? [index] : []));
+  const compactBefore = toolTurnIndexes.length > KEEP_RECENT_TOOL_TURNS
+    ? toolTurnIndexes[toolTurnIndexes.length - KEEP_RECENT_TOOL_TURNS]
+    : 0;
+  let elided = 0;
+  const compacted = messages.map((message, index) => {
+    if (message.role !== "tool" || index >= compactBefore) return message;
+    const results = message.results.map((result) => {
+      if (result.output.length <= ELIDE_ABOVE_CHARS || result.output.startsWith("[Earlier result of ")) return result;
+      elided += 1;
+      return {
+        ...result,
+        output: `[Earlier result of ${result.toolName} elided to save context (${result.output.length} chars). It began: ${result.output.slice(0, PREVIEW_CHARS)}… Call ${result.toolName} again if you need the full result.]`,
+      };
+    });
+    return { ...message, results };
+  });
+  return { messages: compacted, elided };
+}