test(mcp): drift-guard HOST_CONTRACT_METHODS against DocmostClientLike both ways

The contract test only checked one direction (each name in
HOST_CONTRACT_METHODS exists on the real DocmostClient). But
HOST_CONTRACT_METHODS is itself a hand-copy of the server's
DocmostClientLike interface (docmost-client.loader.ts), and that
list<->interface link was untested: a method added to the interface +
consumed by the adapter but forgotten in the list (or removed from the
interface but left in the list) would escape both the server typecheck
(the pkg emits no .d.ts) and the existing test (name not in the list) ->
a runtime "x is not a function" in a tool call.

Parse the method names from the DocmostClientLike interface body (read
the .ts source via import.meta.url, scan member-signature lines) and
assert.deepEqual them against HOST_CONTRACT_METHODS BOTH ways. Lists are
currently identical (39=39), so this is a coverage hole closed, not a
live bug.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/mcp/test/unit/client-host-contract.test.mjs

@@ -1,5 +1,8 @@
 import { test } from "node:test";
 import assert from "node:assert/strict";
+import { readFileSync } from "node:fs";
+import { fileURLToPath } from "node:url";
+import { dirname, resolve } from "node:path";
 
 import { DocmostClient } from "../../build/index.js";
 
@@ -98,3 +101,72 @@ test("HOST_CONTRACT_METHODS has no duplicates", () => {
     HOST_CONTRACT_METHODS.length,
   );
 });
+
+// Parse the method names declared in the server's `DocmostClientLike` interface
+// body. We read the .ts source as plain text (no TS compiler dep, and the file
+// lives in the CJS server tree across the ESM boundary): scan from the
+// `export interface DocmostClientLike {` line to its closing brace at column 0,
+// matching member-signature lines like `  methodName(`. Nested param-object
+// braces (`opts: { ... }`) are indented, so only the interface's own closing
+// `}` (column 0) ends the scan.
+function parseDocmostClientLikeMethods() {
+  const here = dirname(fileURLToPath(import.meta.url));
+  // packages/mcp/test/unit -> repo root is four levels up.
+  const loaderPath = resolve(
+    here,
+    "../../../../apps/server/src/core/ai-chat/tools/docmost-client.loader.ts",
+  );
+  const source = readFileSync(loaderPath, "utf8");
+  const lines = source.split(/\r?\n/);
+
+  const startIdx = lines.findIndex((l) =>
+    /^export interface DocmostClientLike\s*\{/.test(l),
+  );
+  assert.notEqual(
+    startIdx,
+    -1,
+    `Could not find "export interface DocmostClientLike {" in ${loaderPath}. ` +
+      `If the interface was renamed/moved, update this drift-guard test.`,
+  );
+
+  const methods = [];
+  let closed = false;
+  for (let i = startIdx + 1; i < lines.length; i++) {
+    const line = lines[i];
+    if (/^\}/.test(line)) {
+      closed = true;
+      break;
+    }
+    const m = /^\s*([a-zA-Z]+)\(/.exec(line);
+    if (m) methods.push(m[1]);
+  }
+  assert.ok(
+    closed,
+    `Did not find the closing brace of DocmostClientLike in ${loaderPath}.`,
+  );
+  assert.ok(
+    methods.length > 0,
+    `Parsed zero methods from DocmostClientLike in ${loaderPath} — the parser ` +
+      `is likely out of date with the interface formatting.`,
+  );
+  return methods;
+}
+
+// The point of the guard is to protect the DocmostClientLike mirror <-> client.ts
+// link, but HOST_CONTRACT_METHODS is itself a HAND-COPY of that interface kept in
+// sync manually. The list<->interface link must be tested too: a method consumed
+// by the adapter and added to DocmostClientLike but forgotten here (or removed
+// from the interface but left here) would otherwise escape both the server
+// typecheck (pkg emits no .d.ts) and the first test above (name not in the list).
+// Assert the two agree BOTH ways.
+test("HOST_CONTRACT_METHODS exactly mirrors the server's DocmostClientLike interface", () => {
+  const interfaceMethods = parseDocmostClientLikeMethods();
+  assert.deepEqual(
+    [...HOST_CONTRACT_METHODS].sort(),
+    [...interfaceMethods].sort(),
+    `HOST_CONTRACT_METHODS has drifted from the DocmostClientLike interface in ` +
+      `apps/server/src/core/ai-chat/tools/docmost-client.loader.ts. Add/remove ` +
+      `method names in HOST_CONTRACT_METHODS so it lists EXACTLY the methods ` +
+      `declared in that interface (both directions are checked).`,
+  );
+});