docs(graphs): add generated documentation atlas

docs/graphs/session-surface.md

@@ -0,0 +1,25 @@
+<!-- Generated by scripts/gen-doc-graphs.ts - do not edit by hand.
+     Run `pnpm run gen-doc-graphs` to regenerate. -->
+
+# Session Surface And Message Projection
+
+Maintenance mode: curated Mermaid dataflow; exact event/type shapes live in core-data-structures.
+
+This graph separates the append-only log from the derived message surface the next model request sees.
+
+```mermaid
+flowchart LR
+  append["Session.append(type, data)"]
+  log["Append-only SessionEvent log"]
+  surface["SurfaceManager linked list<br/>surfaceOp + sourceEventSeqs"]
+  derive["deriveMessages()"]
+  model["GenerateOptions.messages"]
+  persist["JSONL / SQLite persistence"]
+  replay["load / replay / fork seed"]
+  append --> log
+  log --> surface
+  surface --> derive --> model
+  log --> persist --> replay --> log
+```
+
+See [core-data-structures/session.md](../core-data-structures/session.md) for the full `SessionEventMap`, surface operations, and turn-enclosure invariant.