feat: inject post-compaction workspace context as system event (#18023)

src/auto-reply/reply/post-compaction-context.ts

@@ -0,0 +1,86 @@
+import fs from "node:fs";
+import path from "node:path";
+
+const MAX_CONTEXT_CHARS = 3000;
+
+/**
+ * Read critical sections from workspace AGENTS.md for post-compaction injection.
+ * Returns formatted system event text, or null if no AGENTS.md or no relevant sections.
+ */
+export async function readPostCompactionContext(workspaceDir: string): Promise<string | null> {
+  const agentsPath = path.join(workspaceDir, "AGENTS.md");
+
+  try {
+    if (!fs.existsSync(agentsPath)) {
+      return null;
+    }
+
+    const content = await fs.promises.readFile(agentsPath, "utf-8");
+
+    // Extract "## Session Startup" and "## Red Lines" sections
+    // Each section ends at the next "## " heading or end of file
+    const sections = extractSections(content, ["Session Startup", "Red Lines"]);
+
+    if (sections.length === 0) {
+      return null;
+    }
+
+    const combined = sections.join("\n\n");
+    const safeContent =
+      combined.length > MAX_CONTEXT_CHARS
+        ? combined.slice(0, MAX_CONTEXT_CHARS) + "\n...[truncated]..."
+        : combined;
+
+    return (
+      "[Post-compaction context refresh]\n\n" +
+      "Session was just compacted. The conversation summary above is a hint, NOT a substitute for your startup sequence. " +
+      "Execute your Session Startup sequence now — read the required files before responding to the user.\n\n" +
+      "Critical rules from AGENTS.md:\n\n" +
+      safeContent
+    );
+  } catch {
+    return null;
+  }
+}
+
+/**
+ * Extract named H2 sections from markdown content.
+ * Matches "## SectionName" and captures until the next "## " or end of string.
+ */
+function extractSections(content: string, sectionNames: string[]): string[] {
+  const results: string[] = [];
+  const lines = content.split("\n");
+
+  for (const name of sectionNames) {
+    let sectionLines: string[] = [];
+    let inSection = false;
+
+    for (const line of lines) {
+      // Check if this is the start of our target section
+      if (line.match(new RegExp(`^##\\s+${escapeRegExp(name)}\\s*$`))) {
+        inSection = true;
+        sectionLines = [line];
+        continue;
+      }
+
+      // If we're in the section, check if we've hit another H2 heading
+      if (inSection) {
+        if (line.match(/^##\s+/)) {
+          // Hit another H2 heading, stop collecting
+          break;
+        }
+        sectionLines.push(line);
+      }
+    }
+
+    if (sectionLines.length > 0) {
+      results.push(sectionLines.join("\n").trim());
+    }
+  }
+
+  return results;
+}
+
+function escapeRegExp(str: string): string {
+  return str.replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
+}