Bots that attack, units that look like units

The planner worked one unit at a time, picking each one's best destination
independently. That is why nothing was ever taken: a defended province is
attacked by a single unit, bounces, and is attacked again next year for ever.
It now works the other way round -- list what is worth having, work out how
many units it takes, and commit that many or none. A province you cannot take
is not worth one unit.

Three things came out of that. A single unit still walks at an *empty*
province, since the worst case is a bounce and it might be free, but never at
a garrison. Garrisoning now needs two neighbours rather than one, because one
unit cannot dislodge another -- with one counting as a threat, almost every
centre on a crowded board was threatened, almost every unit stood still, and
nothing happened for two centuries. And an attack is priced at two units
unless the defender has two friends near enough to prop it up; assuming one
was enough meant almost every attack was priced at three, which nobody can
afford.

Asking for help now works from what a power wanted and could not have. It
used to read the moves already planned, which was exactly backwards once the
planner learned not to attack what it cannot take: the target is no longer in
the plan, so the bot stopped asking precisely when it needed to.

The game is now called at the end of 1912. This game has no clock of its own
and seven cautious powers will hold a standoff for ever -- a run to 2198 had
the board still alive and nobody near eighteen. Eighteen wins outright and
otherwise the survivors draw, which is a proper ending here and the commonest
way real games finish.

Units are a soldier and a ship rather than two wedges. A helmet and square
shoulders read as troops at any size; a triangle above a curved hull is a
boat before anybody has decided to look. Both in the power's colour with one
flat highlight, and a shadow so they sit on the ground instead of floating
over a border.

README.md

@@ -213,15 +213,23 @@ answer on the merits, and what they agree binds that turn and is judged at
 the end of it. Approaches to the human are handed back rather than answered
 for them.
 
-**What it does not do yet is finish.** Played out to 2149 the board is alive
-and nobody has soloed: the powers take the neutrals in the first few years
-and then hold each other off indefinitely. Taking a defended centre needs two
-units on it, and the bots do not reliably arrange that even with deals being
-struck every turn. That is the next piece of work and it is a fact about the
-bots, not the loop, so the test says what the loop guarantees and no more.
+**The game is called at the end of 1912.** Diplomacy has no clock of its own:
+it ends on eighteen centres, or when the players agree to stop -- and
+agreeing to stop is a conversation seven computer powers are never going to
+have. Left alone they reach a standoff and hold it, which is what a table of
+equally cautious players does and is why real games are called.
+
+So: eighteen centres wins outright, and if nobody has them by the end of 1912
+the survivors draw. Twelve years is a long evening and a real tournament
+length, and **the draw is a proper ending here rather than a failure to
+finish** -- it is the commonest way this game actually ends.
+
+Worth saying plainly: seven bots left alone draw. They take centres off each
+other now, which they could not do at all before, but none of them breaks
+away to a solo. Beating six of them is the game.
 
 ## Still to build
 
-- bots that can actually finish a game: coordinated attacks on defended centres
 - the press in front of the player, rather than only between the bots
+- bots strong enough to solo against each other, not only to draw
 - the music, the battle sound, the four endings