fix(core): reject empty compaction summaries and offer no tools to compaction requests (#84)

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

packages/core/src/trace/resume.ts

@@ -226,14 +226,21 @@ export function resumeTrace(messages: OmniMessage[]): ResumeResult {
         renderMessages: [],
         meta,
       };
-      if (p.mode === "summarize") {
-        // Reconstruct the summary from the compaction request's output (the assistant text of
-        // the last completed Request). Always rebuilt in the current [context_summary] form —
-        // extractSummary itself still accepts the old <summary> tags an old Trace may contain.
-        const summaryText = lastCompletedRequestText(messages);
-        result.pendingSummary = userText(buildContextSummaryText(extractSummary(summaryText)));
+      if (p.mode !== "summarize") return result;
+      // Reconstruct the summary from the compaction request's output (the assistant text of
+      // the last completed Request). Always rebuilt in the current [context_summary] form —
+      // extractSummary itself still accepts the old <summary> tags an old Trace may contain.
+      const summaryText = extractSummary(lastCompletedRequestText(messages));
+      if (summaryText !== "") {
+        result.pendingSummary = userText(buildContextSummaryText(summaryText));
+        return result;
       }
-      return result;
+      // The compaction output extracts to an **empty** summary: only a pre-#83 engine could
+      // have written such a "completed" closure (compaction now fails instead of committing an
+      // empty summary, which would erase the task state). Mirror the current contract: void
+      // the closure and fall through to turn-by-turn replay — the original context this file
+      // still holds is restored, and the committed compaction turn stays in history like any
+      // committed turn.
     }
   }
 
@@ -320,7 +327,11 @@ export function resumeTrace(messages: OmniMessage[]): ResumeResult {
             committedCallIds.add(p.tool_call_id);
           }
         }
-        sessionTurns += 1;
+        // A committed request inside a compaction span enters history as usual (AgentHub
+        // committed it — e.g. an invalid-summary attempt of a compaction that then failed),
+        // but does not count as a Session turn: in-process only runTurn increments the
+        // counter, never runCompactionRequest.
+        if (!inCompaction) sessionTurns += 1;
         snapshot = [];
         outputs = [];
         inRequest = false;
@@ -433,8 +444,9 @@ function lastCompletedRequestText(messages: OmniMessage[]): string {
       {
         // A completed request with empty text still overwrites (we take the text of “the last
         // completed request”, even if empty) — otherwise a textless compaction output would fall
-        // back to an earlier turn's normal reply and get mistakenly injected as the summary; the
-        // in-process path yields an empty summary here (extractSummary(“”)).
+        // back to an earlier turn's normal reply and get mistakenly injected as the summary. The
+        // caller treats the resulting empty extract as a void closure (a pre-#83 trace shape)
+        // and replays the original context instead.
         if (msg.payload.status === "completed") text = current;
         inRequest = false;
       }