* fix: return error when clone stalls with phantoms outstanding

Clone's convergence loop broke out of its round loop as soon as the phantom count stopped decreasing and returned success, even when the phantom table was still non-empty. That leaves the caller holding a repository missing content with no error and exit code 0.

Stopping on a stall is still correct — spinning forever would be worse — but reporting it as success is not. checkStop now returns a PhantomStallError when the loop halts with phantoms remaining, giving the caller a programmatically-reachable count plus a sample of the missing UUIDs for diagnosis. A clean clone still returns nil with an empty phantom table.

Fixes #64.

* fix: preserve partial CloneResult when Clone returns an error

Clone's named result return was never assigned on the error paths — cs.run's cloneResult stayed in a local variable, so a caller catching a PhantomStallError (or a crosslink failure) got a nil result even though a partial one, with the round/blob counts collected so far, was sitting right there. Assign it before returning on both paths.

* fix: make phantom stall error sample deterministic

newPhantomStallError previously took an arbitrary 10 entries from map iteration order before sorting, so the sample was nondeterministic across runs when more than 10 phantoms were outstanding. Sort all UUIDs first, then take the lexicographically-smallest 10, matching what the doc comment already implied.

Addresses a non-blocking nit from review on #64. check-in: e5be6a9199 user: [email protected] tags: trunk