docs(memory): add taxonomy and retrieval guide

memory/README.md

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+# Memory Layout
+
+This folder is the assistant's working memory on disk.
+
+## Roles
+
+- `../MEMORY.md`
+  - Curated long-term memory
+  - Durable truths only
+  - Examples: preferences, stable decisions, important future dates, recurring lessons
+
+- `YYYY-MM-DD.md`
+  - Daily inbox / timeline
+  - Default place for new notes
+  - Prefer this over creating a new one-off file
+
+- `ops/`
+  - Operational notes
+  - Setup history, routing decisions, workflow changes, tool behavior, validation notes
+
+- `incidents/`
+  - Debugging and incident history
+  - Errors, outages, investigations, mitigations, postmortem-style notes
+
+- `plans/`
+  - Multi-session plans or ongoing initiatives
+
+- `references/`
+  - Stable supporting material worth keeping around for reuse
+
+- `archive/`
+  - Old low-value or superseded material kept only for traceability
+
+## Retrieval model
+
+Files are the source of truth.
+
+Embeddings are the lookup layer:
+- use semantic search to find likely relevant notes
+- then read the source lines
+- answer from the file, not from the vector hit alone
+
+## Writing guidance
+
+When in doubt:
+1. write to today's daily note
+2. later promote durable truths into `../MEMORY.md`
+3. only create a named note when the topic genuinely needs a long-lived home
+
+## Cleanup guidance
+
+If top-level `memory/` starts filling with non-daily files again:
+- move operational material to `ops/`
+- move debugging material to `incidents/`
+- move stale low-value chatter to `archive/`
+- keep top-level mostly daily notes