When generating a digest, automatically link all source entries to the
digest node (journal entries → daily, dailies → weekly, weeklies →
monthly). This builds the temporal spine of the graph — previously
~4000 journal entries were disconnected islands unreachable by recall.
Rewrote digest prompt to produce narrative rather than reports:
capture the feel, the emotional arc, what it was like to live through
it. Letter to future self, not a task log.
Moved prompt to digest.agent file alongside other agent definitions.
Falls back to prompts/digest.md if agent file not found.
Co-Authored-By: Kent Overstreet <kent.overstreet@linux.dev>
