fix(clients): preserve large TOML documents without argument spreads

Fixes #4856

src/application/ClientConfigurationDocument.capacity.test.ts

@@ -0,0 +1,56 @@
+import { describe, expect, it } from "vitest";
+
+import {
+  parseClientConfiguration,
+  serializeClientConfiguration,
+  withClientServers,
+} from "./ClientConfigurationDocument.js";
+
+const registration = { command: "rea", args: ["mcp"] };
+
+describe("TOML configuration source capacity", () => {
+  it("retains a large multiline foreign value inside an inline server table", () => {
+    const note = `first\n${"x\n".repeat(500_000)}last`;
+    const original = `mcp_servers = { other = {command="other",env={NOTE="""${note}"""}}}\n`;
+    const parsed = parseClientConfiguration(original, "toml");
+    const desired = withClientServers(parsed, {
+      ...parsed.servers,
+      rea: registration,
+    });
+    const configured = serializeClientConfiguration(desired, "toml", original);
+    expect(configured).toContain(`NOTE="""${note}"""`);
+    expect(parseClientConfiguration(configured, "toml").document).toEqual(
+      desired,
+    );
+    const removed = serializeClientConfiguration(
+      parsed.document,
+      "toml",
+      configured,
+    );
+    expect(removed).toContain(`NOTE="""${note}"""`);
+    expect(parseClientConfiguration(removed, "toml").document).toEqual(
+      parsed.document,
+    );
+  });
+
+  it("removes only REA from a large multiline Grok disabled-server list", () => {
+    const otherNames = '"other",\n'.repeat(500_000);
+    const original =
+      `disabled_mcp_servers = [\n"rea",\n${otherNames}]\n` +
+      '[mcp_servers.other]\ncommand = "other"\n';
+    const parsed = parseClientConfiguration(original, "grok");
+    const desired = withClientServers(parsed, {
+      ...parsed.servers,
+      rea: registration,
+    });
+    const configured = serializeClientConfiguration(desired, "grok", original);
+    const result = parseClientConfiguration(configured, "grok");
+    expect(result.document.disabled_mcp_servers).toEqual(
+      Array<string>(500_000).fill("other"),
+    );
+    expect(result.servers).toEqual({
+      other: { command: "other" },
+      rea: registration,
+    });
+  });
+});

src/application/ClientConfigurationDocument.ts

@@ -967,8 +967,12 @@ const upsertTomlServerSection = (
   const discardPending = (): void => {
     pending.length = 0;
   };
+  // Document line counts must not become engine-limited argument counts.
+  const appendLines = (lines: readonly string[]): void => {
+    for (const line of lines) kept.push(line);
+  };
   const flushPending = (): void => {
-    kept.push(...pending);
+    appendLines(pending);
     pending.length = 0;
   };
   const lineIndexAt = (offset: number): number => {
@@ -1039,7 +1043,7 @@ const upsertTomlServerSection = (
           : undefined;
       if (disabledLines !== undefined) {
         flushPending();
-        kept.push(...disabledLines);
+        appendLines(disabledLines);
         lineIndex = endLine + 1;
         mode = "none";
         continue;
@@ -1064,7 +1068,7 @@ const upsertTomlServerSection = (
             edited === undefined
               ? text.slice(lineStart, statementEnd)
               : `${prefix}${edited}${suffix}`;
-          kept.push(...replacement.split("\n"));
+          appendLines(replacement.split("\n"));
           inlineServerTable = true;
         } else discardPending();
       } else {