fix(cli-runner): cap summary block plus marker against maxHistoryChars

adele-with-a-b · adele-with-a-b · commit fef60907cd9d · 2026-05-23T17:25:12.000-04:00
ClawSweeper P2 on #83117 flagged that when `summaryRendered.length` is less than `maxHistoryChars` but `summaryBlock.length` (summary + `\n\n` separator) meets or exceeds it, the `remainingBudget <= 0` arm of `buildCliSessionHistoryPrompt` appends the truncation marker after the already-full summary block. A 199-char rendered summary under a 200-char cap produced a 257-char history block — defeating the cap that prevents reseeding fresh CLI sessions with unexpectedly huge prompts. Fix the budget edge by truncating the summary in this branch as well so `summary + separator + marker` stays within `maxHistoryChars`. The tail still drops (the summary alone consumes the budget) and the marker still leads its own line so the prompt announces what was discarded. Mirrors the existing oversize-summary branch's pattern of head-slicing the summary against an explicit budget that reserves marker + separator. Add a focused regression in `session-history.test.ts` covering exactly the gap the finding called out: `summaryRendered.length < maxHistoryChars` with a non-empty post-summary tail. Asserts the rendered history block stays within `maxHistoryChars` and the truncation marker is present.
diff --git a/src/agents/cli-runner/session-history.test.ts b/src/agents/cli-runner/session-history.test.ts
@@ -696,4 +696,41 @@ describe("buildCliSessionHistoryPrompt", () => {
     expect(prompt).toContain("POST_SUMMARY_ASSISTANT_DROPPED");
     expect(prompt).toContain("<next_user_message>\nnext ask\n</next_user_message>");
   });
+
+  it("honors the cap when the summary block plus marker crosses it", () => {
+    // Edge case: `summaryRendered.length < maxHistoryChars` (the gate that
+    // routes to the oversize-summary branch is not taken) BUT
+    // `summaryBlock.length >= maxHistoryChars` once the `\n\n` separator
+    // is appended, making `remainingBudget <= 0`. Without summary
+    // truncation in that branch, the rendered history block is
+    // `summary + separator + marker` — well over `maxHistoryChars`. A
+    // 199-char rendered summary under a 200-char cap would otherwise
+    // produce a 257-char history block.
+    const maxHistoryChars = 200;
+    // `renderHistoryMessage` prefixes "Compaction summary: " (20 chars)
+    // before the summary text, so a 179-char summary renders to 199 chars
+    // — strictly less than the cap, but `summaryBlock = rendered + "\n\n"`
+    // is 201 chars and `remainingBudget` is negative.
+    const summaryPrefix = "Compaction summary: ";
+    const summaryText = "S".repeat(maxHistoryChars - 1 - summaryPrefix.length);
+    const prompt = buildCliSessionHistoryPrompt({
+      messages: [
+        { role: "compactionSummary", summary: summaryText },
+        { role: "user", content: "POST_SUMMARY_TAIL_USER" },
+        { role: "assistant", content: "POST_SUMMARY_TAIL_ASSISTANT" },
+      ],
+      prompt: "next ask",
+      maxHistoryChars,
+    });
+
+    expect(prompt).toBeDefined();
+    const historyMatch = prompt?.match(
+      /<conversation_history>\n([\s\S]*?)\n<\/conversation_history>/,
+    );
+    expect(historyMatch).not.toBeNull();
+    const renderedHistory = historyMatch?.[1] ?? "";
+    expect(renderedHistory.length).toBeLessThanOrEqual(maxHistoryChars);
+    // Marker is still present so the prompt announces what was discarded.
+    expect(prompt).toContain("[OpenClaw reseed history truncated; older turns dropped]");
+  });
 });
diff --git a/src/agents/cli-runner/session-history.ts b/src/agents/cli-runner/session-history.ts
@@ -200,11 +200,18 @@ export function buildCliSessionHistoryPrompt(params: {
       const remainingBudget = maxHistoryChars - summaryBlock.length;
       if (remainingBudget <= 0) {
         // `tailRaw.slice(-0)` would return the entire tail (JS quirk:
-        // `-0 === 0`), so guard explicitly: the summary plus its
-        // separator already consumes the full budget. Drop the tail
-        // entirely and lead with the marker so the prompt still announces
-        // what was discarded.
-        renderedHistory = `${summaryBlock}${truncationMarker}`;
+        // `-0 === 0`), so guard explicitly. The summary plus its
+        // separator already meets or exceeds the cap, so the tail must
+        // drop. The summary itself must also be truncated so that
+        // `summary + separator + marker` stays within budget — appending
+        // the marker after a full-budget summary block would otherwise
+        // blow past `maxHistoryChars` (a 199-char summary under a
+        // 200-char cap would render a 257-char history block).
+        const summaryBudget = Math.max(0, maxHistoryChars - truncationMarker.length - 2);
+        const summaryTruncated = summaryRendered.slice(0, summaryBudget).trimEnd();
+        renderedHistory = summaryTruncated
+          ? `${summaryTruncated}\n\n${truncationMarker}`
+          : truncationMarker;
       } else if (tailRaw.length > remainingBudget) {
         renderedHistory = `${summaryBlock}${truncationMarker}\n${tailRaw.slice(-remainingBudget).trimStart()}`;
       } else {
