fix: replay a compaction summary by its flag, not its framing (#1536)

Fixes #1535

A compaction summary on replay was only sent as a `compaction_update` if
its text also parsed, so a change in Claude Code's framing turned it
into a `user_message_chunk`, shown as text the user typed. That is what
happens to summaries from Claude Code 2.1.312 and 2.1.316.

`isCompactSummary` now decides on its own. A summary whose framing isn't
recognized is sent as a completed `compaction_update` without summary
text. This reverses the choice to keep such text visible: the
model-facing framing isn't kept as a summary either way, and showing it
as the user's words is the worse failure.

`PERSISTED_PREAMBLE` also allows content before the `Summary:` line, so
current summaries keep their text. All 31 summaries in my own
transcripts now parse, and a real `session/load` on one from 2.1.316
sends a `compaction_update` with its text and no summary
`user_message_chunk`.

src/acp-agent.ts

@@ -10051,9 +10051,10 @@ export class ClaudeAcpAgent {
       // The entity is keyed by the summary message's uuid, which differs from
       // the live id (the `compacting` status uuid) — replay is terminal-first
       // by the RFD, and no client merges a replay into a live entity store.
-      // A subagent's own compaction summary is not the root session's, and a
-      // summary whose framing is unrecognized stays visible as transcript
-      // text rather than vanishing behind a summary-less entity.
+      // A subagent's own compaction summary is not the root session's. A summary
+      // whose framing is unrecognized is still this compaction, without summary
+      // text: isCompactSummary says what it is, and the framing is Claude Code's
+      // to change.
       if (
         replayCompactionUpdates &&
         isCompactSummaryMessage(message) &&
@@ -10069,10 +10070,9 @@ export class ClaudeAcpAgent {
             airClient: this.toolCallCapabilities.air.client,
           },
         );
-        if (replayCompaction.recordSummary(assistantMessageText(message.message))) {
-          await replayCompaction.finish(message.uuid, "completed");
-          return;
-        }
+        replayCompaction.recordSummary(assistantMessageText(message.message));
+        await replayCompaction.finish(message.uuid, "completed");
+        return;
       }
 
       for (const notification of toAcpNotifications(

src/context-compaction.ts

@@ -67,7 +67,7 @@ const ANALYSIS_BLOCKS = [
  *  it as the post-compaction user message. */
 const CONTINUATION_PREAMBLE = /^\s*This session is being continued from a previous conversation/i;
 const PERSISTED_PREAMBLE =
-  /^\s*This session is being continued from a previous conversation[^\n]*\n+Summary:[ \t]*\r?\n/;
+  /^\s*This session is being continued from a previous conversation[^\n]*\n(?:[\s\S]*?\n)?Summary:[ \t]*\r?\n/;
 const PERSISTED_TRAILERS = [
   /\n+If you need specific details from before compaction[\s\S]*$/,
   /\n+(?:Please )?[Cc]ontinue the conversation from where it left (?:it )?off[\s\S]*$/,

src/tests/acp-agent.test.ts

@@ -18610,8 +18610,8 @@ describe("assembled assistant text fallback", () => {
     ]);
     expect(child.some((update) => update.sessionUpdate === "compaction_update")).toBe(false);
 
-    // Unrecognized framing: the text stays visible rather than vanishing
-    // behind a summary-less entity.
+    // Unrecognized framing: still the compaction isCompactSummary says it is,
+    // without summary text, and never a message from the user.
     const unknownFraming = await replay(true, [
       {
         ...summaryMessage("odd-summary"),
@@ -18622,12 +18622,14 @@ describe("assembled assistant text fallback", () => {
         },
       },
     ]);
-    expect(unknownFraming.some((update) => update.sessionUpdate === "compaction_update")).toBe(
-      false,
-    );
-    expect(unknownFraming.some((update) => update.sessionUpdate === "user_message_chunk")).toBe(
-      true,
-    );
+    expect(unknownFraming).toEqual([
+      {
+        sessionUpdate: "compaction_update",
+        compactionId: "odd-summary",
+        status: "completed",
+        _meta: { jetbrains: { air: { version: 1, contextCompaction: { version: 1 } } } },
+      },
+    ]);
   });
 
   it("preserves the model response after multiple compactions in one turn", async () => {

src/tests/context-compaction.test.ts

@@ -130,6 +130,17 @@ describe("compactionSummaryText", () => {
     );
   });
 
+  it("strips the framing when other content sits before the Summary line", () => {
+    expect(
+      compactionSummaryText(
+        "This session is being continued from a previous conversation that ran out of context. The summary below covers the earlier portion of the conversation.\n\n" +
+          "<system-reminder>\n<tools-used-before-summary>Read, Bash</tools-used-before-summary>\n</system-reminder>\n" +
+          "Summary:\n1. Primary Request and Intent:\n   Count upward.\n\n" +
+          "Continue the conversation from where it left off without asking the user any further questions.",
+      ),
+    ).toBe("1. Primary Request and Intent:\n   Count upward.");
+  });
+
   it("strips the older tagged transcript framing", () => {
     expect(
       compactionSummaryText(