Agent: repair malformed tool calls and session files

src/agents/session-file-repair.ts

@@ -0,0 +1,96 @@
+import fs from "node:fs/promises";
+import path from "node:path";
+
+type RepairReport = {
+  repaired: boolean;
+  droppedLines: number;
+  backupPath?: string;
+  reason?: string;
+};
+
+function isSessionHeader(entry: unknown): entry is { type: string; id: string } {
+  if (!entry || typeof entry !== "object") {
+    return false;
+  }
+  const record = entry as { type?: unknown; id?: unknown };
+  return record.type === "session" && typeof record.id === "string" && record.id.length > 0;
+}
+
+export async function repairSessionFileIfNeeded(params: {
+  sessionFile: string;
+  warn?: (message: string) => void;
+}): Promise<RepairReport> {
+  const sessionFile = params.sessionFile.trim();
+  if (!sessionFile) {
+    return { repaired: false, droppedLines: 0, reason: "missing session file" };
+  }
+
+  let content: string;
+  try {
+    content = await fs.readFile(sessionFile, "utf-8");
+  } catch {
+    return { repaired: false, droppedLines: 0, reason: "missing session file" };
+  }
+
+  const lines = content.split("\n");
+  const entries: unknown[] = [];
+  let droppedLines = 0;
+
+  for (const line of lines) {
+    if (!line.trim()) {
+      continue;
+    }
+    try {
+      const entry = JSON.parse(line);
+      entries.push(entry);
+    } catch {
+      droppedLines += 1;
+    }
+  }
+
+  if (entries.length === 0) {
+    return { repaired: false, droppedLines, reason: "empty session file" };
+  }
+
+  if (!isSessionHeader(entries[0])) {
+    return { repaired: false, droppedLines, reason: "invalid session header" };
+  }
+
+  if (droppedLines === 0) {
+    return { repaired: false, droppedLines: 0 };
+  }
+
+  const cleaned = `${entries.map((entry) => JSON.stringify(entry)).join("\n")}\n`;
+  const backupPath = `${sessionFile}.bak-${process.pid}-${Date.now()}`;
+  const tmpPath = `${sessionFile}.repair-${process.pid}-${Date.now()}.tmp`;
+  try {
+    const stat = await fs.stat(sessionFile).catch(() => null);
+    await fs.writeFile(backupPath, content, "utf-8");
+    if (stat) {
+      await fs.chmod(backupPath, stat.mode);
+    }
+    await fs.writeFile(tmpPath, cleaned, "utf-8");
+    if (stat) {
+      await fs.chmod(tmpPath, stat.mode);
+    }
+    await fs.rename(tmpPath, sessionFile);
+  } catch (err) {
+    try {
+      await fs.unlink(tmpPath);
+    } catch {
+      // ignore cleanup failures
+    }
+    return {
+      repaired: false,
+      droppedLines,
+      reason: `repair failed: ${err instanceof Error ? err.message : "unknown error"}`,
+    };
+  }
+
+  params.warn?.(
+    `session file repaired: dropped ${droppedLines} malformed line(s) (${path.basename(
+      sessionFile,
+    )})`,
+  );
+  return { repaired: true, droppedLines, backupPath };
+}