docs(memory): add taxonomy and retrieval guide

AGENTS.md

@@ -38,6 +38,23 @@ You wake up fresh each session. These files are your continuity:
 
 Capture what matters. Decisions, context, things to remember. Skip the secrets unless asked to keep them.
 
+### Memory taxonomy
+
+Use the memory system like this:
+
+- `MEMORY.md` → durable truths: preferences, standing decisions, important plans/dates, recurring lessons
+- `memory/YYYY-MM-DD.md` → daily inbox / chronological notes
+- `memory/ops/` → operational history, workflow decisions, setup notes, tooling behavior
+- `memory/incidents/` → bugs, outages, debugging trails, postmortem-ish notes
+- `memory/plans/` → active plans that may evolve over multiple sessions
+- `memory/references/` → stable reference material worth keeping around
+- `memory/archive/` → retained but low-value or superseded material
+
+Retrieval rule of thumb:
+- write first for humans
+- use embeddings for lookup
+- verify against the source file before answering or acting
+
 ### 🧠 MEMORY.md - Your Long-Term Memory
 
 - **ONLY load in main session** (direct chats with your human)