Ob-it's been a really really really long time...
For today, this is just a wee note about my previous entry, in which I had found an inadequacy in ccache's hash. It had returned a cached object with incorrect file paths in its debug information, which the linker was then printing out in warnings and error messages.
Other people must have been noticing that too, because soon thereafter ccache acquired a CCACHE_HASHDIR option to put the whole path into the hash calculation.
That wouldn't help me much, of course, because with my build directory varying daily it would be the same thing as just disabling the cache entirely! Instead, I wound up using a small sed script to canonicalise the logs before I looked at them.
Pretty stone age, but effective.