diff --git a/apps/server/src/integrations/mcp/mcp-login-gate-coupling.contract.spec.ts b/apps/server/src/integrations/mcp/mcp-login-gate-coupling.contract.spec.ts
new file mode 100644
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+++ b/apps/server/src/integrations/mcp/mcp-login-gate-coupling.contract.spec.ts
@@ -0,0 +1,183 @@
+import * as fs from 'node:fs';
+import * as path from 'node:path';
+import * as ts from 'typescript';
+
+/**
+ * Coupling / drift-guard contract for the pre-token SSO/MFA gate (Gitea #91).
+ *
+ * There are TWO independent code paths that must run the SAME pre-token gate
+ * before any token is minted from a password:
+ *
+ *   1) AuthController.login (core/auth/auth.controller.ts) — the normal
+ *      /api/auth/login path. Before issuing a token it runs:
+ *        validateSsoEnforcement(workspace)
+ *        -> lazy require('./../../ee/mfa/services/mfa.service')
+ *        -> mfaService.checkMfaRequirements(...)
+ *
+ *   2) McpService.enforceBasicLoginGate (integrations/mcp/mcp.service.ts) —
+ *      the /mcp HTTP-Basic path. It re-implements EXACTLY the same pre-token
+ *      sequence so the Basic path is not an SSO/MFA bypass.
+ *
+ * These two implementations are physically separate (no shared helper — Option 1
+ * would extract one, but that refactor is deliberately skipped in this batch).
+ * If a future edit drops the SSO check or the MFA check from one side, the two
+ * paths silently DRIFT and the dropped side re-opens an SSO/MFA bypass. This
+ * test asserts BOTH method bodies still contain BOTH gate calls, so such a drift
+ * fails the build.
+ *
+ * Why a SOURCE-LEVEL (AST) contract test rather than live instances: neither
+ * AuthController nor McpService can be constructed — or even imported — under
+ * this jest config without mocking their heavy transitive graph (the
+ * @docmost/transactional React-email templates and the lib0/ESM collaboration
+ * chain that ts-jest's transformIgnorePatterns cannot load). This mirrors the
+ * existing AST-contract approach in
+ * core/auth/services/verify-user-credentials.contract.spec.ts: read the real
+ * source, extract the relevant method bodies, and assert each contains the
+ * required calls.
+ */
+
+// The exact symbols BOTH pre-token paths must share. Drop any of these from one
+// side and that side stops enforcing SSO/MFA before minting a token.
+const SSO_GATE = 'validateSsoEnforcement';
+// The lazy EE-MFA require specifier — byte-for-byte identical in both files (a
+// fork WITHOUT the EE module bundled behaves the same on both sides: no module,
+// no MFA gate).
+const MFA_REQUIRE = "require('./../../ee/mfa/services/mfa.service')";
+// The MFA requirement check both paths call on the lazily-loaded service.
+const MFA_CHECK = 'checkMfaRequirements';
+
+/**
+ * Strip all comments from a chunk of TS source, leaving only real CODE tokens.
+ *
+ * This is load-bearing: the method bodies we inspect DOCUMENT the gate they run
+ * (e.g. "// 1) validateSsoEnforcement(workspace) — reject if ..."), so a naive
+ * substring match on the raw body text would still pass even if the actual call
+ * were deleted and only the comment survived. We tokenize with the TS scanner
+ * and re-emit only non-comment token text, so the assertions below see code, not
+ * prose. (A deleted/commented-out gate call therefore correctly fails the test.)
+ */
+function stripComments(text: string): string {
+  const scanner = ts.createScanner(
+    ts.ScriptTarget.Latest,
+    /* skipTrivia */ false,
+    ts.LanguageVariant.Standard,
+    text,
+  );
+  let out = '';
+  let kind = scanner.scan();
+  while (kind !== ts.SyntaxKind.EndOfFileToken) {
+    if (
+      kind !== ts.SyntaxKind.SingleLineCommentTrivia &&
+      kind !== ts.SyntaxKind.MultiLineCommentTrivia
+    ) {
+      out += scanner.getTokenText();
+    } else {
+      // Preserve a separator so adjacent tokens around a comment don't merge.
+      out += ' ';
+    }
+    kind = scanner.scan();
+  }
+  return out;
+}
+
+/**
+ * Return the COMMENT-STRIPPED source text of a named method body (a class
+ * MethodDeclaration). Throws if the method is not found so a rename can never
+ * silently make this test vacuous.
+ */
+function methodBodyText(
+  source: string,
+  fileLabel: string,
+  methodName: string,
+): string {
+  const sf = ts.createSourceFile(
+    fileLabel,
+    source,
+    ts.ScriptTarget.Latest,
+    /* setParentNodes */ true,
+  );
+
+  let found: string | null = null;
+  const visit = (node: ts.Node): void => {
+    if (
+      ts.isMethodDeclaration(node) &&
+      node.name &&
+      ts.isIdentifier(node.name) &&
+      node.name.text === methodName &&
+      node.body
+    ) {
+      found = node.body.getText(sf);
+      return;
+    }
+    ts.forEachChild(node, visit);
+  };
+  visit(sf);
+
+  if (found === null) {
+    throw new Error(`method ${methodName} not found in ${fileLabel}`);
+  }
+  return stripComments(found);
+}
+
+describe('pre-token SSO/MFA gate coupling contract (Gitea #91)', () => {
+  const controllerPath = path.join(
+    __dirname,
+    '..',
+    '..',
+    'core',
+    'auth',
+    'auth.controller.ts',
+  );
+  const mcpServicePath = path.join(__dirname, 'mcp.service.ts');
+
+  const controllerSource = fs.readFileSync(controllerPath, 'utf8');
+  const mcpServiceSource = fs.readFileSync(mcpServicePath, 'utf8');
+
+  // The real login pre-token gate lives inline in AuthController.login.
+  const loginBody = methodBodyText(
+    controllerSource,
+    'auth.controller.ts',
+    'login',
+  );
+  // The /mcp Basic-path mirror lives in McpService.enforceBasicLoginGate.
+  const gateBody = methodBodyText(
+    mcpServiceSource,
+    'mcp.service.ts',
+    'enforceBasicLoginGate',
+  );
+
+  it('AuthController.login runs the full pre-token gate (SSO + MFA)', () => {
+    expect(loginBody).toContain(SSO_GATE);
+    expect(loginBody).toContain(MFA_REQUIRE);
+    expect(loginBody).toContain(MFA_CHECK);
+  });
+
+  it('McpService.enforceBasicLoginGate runs the full pre-token gate (SSO + MFA)', () => {
+    expect(gateBody).toContain(SSO_GATE);
+    expect(gateBody).toContain(MFA_REQUIRE);
+    expect(gateBody).toContain(MFA_CHECK);
+  });
+
+  it('both paths share EVERY gate symbol (no drift between the two)', () => {
+    // The drift guard: if a future edit drops a gate call from exactly one
+    // side, that side fails here while the other still passes — pinpointing the
+    // bypass. Both sides carrying the same set keeps them semantically coupled.
+    for (const symbol of [SSO_GATE, MFA_REQUIRE, MFA_CHECK]) {
+      const inLogin = loginBody.includes(symbol);
+      const inGate = gateBody.includes(symbol);
+      expect({ symbol, inLogin, inGate }).toEqual({
+        symbol,
+        inLogin: true,
+        inGate: true,
+      });
+    }
+  });
+
+  it('the EE-MFA require specifier is byte-for-byte identical on both sides', () => {
+    // A drift in the require PATH (not just its presence) would load a different
+    // module on one side — e.g. the controller gating on MFA while the Basic
+    // path silently requires a non-existent path and skips MFA. Pin the literal.
+    expect(loginBody).toContain(MFA_REQUIRE);
+    expect(gateBody).toContain(MFA_REQUIRE);
+  });
+});