Instead, store only the action's name, and look it up upon searching.

Keeping a reference to the actions in the history extended the lifetime of
actions that sohuld have otherwise died, leading to all sorts of nastiness.  In
particular, the Alt+[n] actions to switch between images would remain bound to
their accelerator after the image has been closed, holding a dangling display
pointer, which would lead to a segfault, or fail with a CRITICAL message, when
using the accelerator again.