Yet in the light of day, the holes in the rescue plan are plain to see. The scheme is confused and unconvincing. Confused, because its financial engineering is too clever by half and vulnerable to unintended consequences. Unconvincing, because too many details are missing and the scheme at its core is not up to the job of safeguarding the euro.

This is the euro zone’s third comprehensive package this year. It is unlikely to be its last.

Words are cheap…

The summit’s most notable achievement was to forge an agreement to write down the Greek debt held by the private sector by 50%. This newspaper has long argued for such a move. Yet an essential counterpart to the Greek writedown is a credible firewall around heavily indebted yet solvent borrowers such as Italy. That is the only way of restoring confidence and protecting European banks’ balance-sheets, thus ensuring that they can get on with the business of lending.

Unfortunately the euro zone’s firewall is the weakest part of the deal (see article). Europe’s main rescue fund, the European Financial Stability Facility (EFSF), does not have enough money to withstand a run on Italy and Spain. Germany and the European Central Bank (ECB) have ruled out the only source of unlimited support: the central bank itself. The euro zone’s northern creditor governments have refused to put more of their own money into the pot.

Instead they have come up with two schemes to stretch the EFSF. One is to use it to insure the first losses if any new bonds are written down. In theory, this means that the rescue fund’s power could be magnified several times. But in practice, such “credit enhancement” may not yield much. Bond markets may be suspicious of guarantees made by countries that would themselves be vulnerable if their over-indebted neighbours suffered turmoil.

Under the second scheme, the EFSF would create a set of special-purpose vehicles financed by other investors, including sovereign-wealth funds. Again, there are reasons to doubt whether this will work. Each vehicle seems to be dedicated to a single country, so risk is not spread. And why should China or Brazil invest a lot in them when Germany is holding back from putting in more money?

Together, these schemes are supposed to extend the value of the EFSF to €1 trillion ($1.4 trillion) or more. Sadly, that looks more like an aspiration than a prediction. And because the EFSF bears the first losses, its capital is at greater risk of being wiped out than under a loan programme. This could taint France, which finances the rescue fund and has recently seen its AAA credit rating come under threat. Since the EFSF depends partly on France for its own credit rating, a French downgrade could undermine the rescue fund just when it is most needed.

If the foundations of the firewall are too shallow, then the bank plan plunges too deep. By the end of June 2012, banks are expected to establish a core-capital ratio of 9%. In principle, that is laudable. But if banks have months to reach their target, they can avoid raising new equity, which would dilute their shareholders' stakes, and instead move to the required ratio by shrinking their balance-sheets. That would be a terrible outcome: by depriving Europe’s economy of credit, it would worsen the downturn.

Then there is Greece. Although the size of the writedown is welcome, euro-zone leaders are desperate for it to be “voluntary”. That is because a default would trigger the bond-insurance contracts called credit-default swaps (CDSs). The fear is that a default could lead to chaos, because the CDS market is untested. That is true, but this implausibly large “voluntary” writedown will lead investors in other European sovereign bonds to doubt whether CDSs offer much protection. So while the EFSF scheme is designed to offer insurance to bondholders, the European leaders’ insistence that the Greek writedown be voluntary will make euro-zone debt harder to insure.

…but trust is nowhere to be found

Europe has got to this point because German politicians are convinced that without market pressure the euro zone’s troubled economies will slacken their efforts at reform (see article). Despite a list of promises presented to the summit by Silvio Berlusconi, Italy’s prime minister (see article), Germany has good reason to worry. But it needs to concentrate on institutional ways of disciplining profligate governments, rather than starving the rescue package of funds. As it is, this deal at best fails to solve the euro crisis; at worst it may even make it worse. As the shortcomings of each component become clear, investors’ fears will surely return, bond yields will rise and banks’ funding problems will worsen.

Yet again, disaster will loom. And yet again, the ECB will end up staving it off. Fortunately, Mario Draghi, the ECB’s incoming president, made it clear this week that he realises that is his job. But therein lies the tragedy of this summit. An ECB pledge of unlimited backing for solvent governments would have had a far better chance of solving the crisis months ago, and remains the best option today.