skills: v6.6.0 catch-up

references/architecture.md

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+# Architecture
+
+## State Storage: SeiDB
+
+Sei uses **SeiDB** for state storage. As of the IAVL removal, SeiDB state-commit (SC) is **mandatory** — the legacy IAVL backend has been fully removed and is no longer available as a fallback.
+
+### State Commit (SC)
+
+The state-commit layer is backed by **memIAVL** (an in-memory IAVL implementation with a write-ahead log and snapshotting). It is enabled via `sc-enable` in `app.toml`:
+
+```toml
+[state-commit]
+# Enable defines if the state-commit should be enabled.
+sc-enable = true
+```
+
+**`sc-enable` must be `true`.** If it is `false`, the node panics on startup:
+
+```
+panic: SeiDB state-commit (SC) must be enabled; IAVL backend has been fully deprecated
+```
+
+There is no IAVL fallback. memIAVL is the sole state-commit backend; it does not "override" or coexist with an IAVL db backend — the IAVL backend does not exist anymore.
+
+### State Store (SS)
+
+The optional state-store layer provides historical state for queries and is configured under `[state-store]`:
+
+```toml
+[state-store]
+ss-enable = true
+ss-backend = "pebbledb"
+```
+
+## Migration Notes
+
+Node operators upgrading from a version that supported the IAVL backend must ensure `sc-enable = true` before upgrading. The following have been removed and no longer take effect:
+
+### Removed CLI commands
+
+- `seid compact` — compacted the application levelDB
+- `seid debug dump-iavl [height]` (with `--db-path`/`-d`, `--output-dir`, `--module`/`-m`) — dumped IAVL data
+- `seid prune` (with `--home`, `--app-db-backend`, `--pruning`, `--pruning-keep-recent`, etc.) — pruned app history states
+- `seid latest_version` — printed the latest app DB version
+
+### Removed `start` flags
+
+- `--separate-orphan-storage`
+- `--separate-orphan-versions-to-keep`
+- `--num-orphan-per-file`
+- `--orphan-dir`
+- `--iavl-disable-fastnode`
+
+### Removed `app.toml` config fields
+
+- `iavl-cache-size`
+- `iavl-disable-fastnode`
+- `no-versioning`
+- `separate-orphan-storage`
+- `separate-orphan-versions-to-keep`
+- `num-orphan-per-file`
+- `orphan-dir`
+- The entire `[iavl]` section (including `iavl.pruning`, `iavl.pruning-keep-recent`, `iavl.pruning-keep-every`, `iavl.pruning-interval`)
+
+Only the top-level `pruning`, `pruning-keep-recent`, `pruning-keep-every`, and `pruning-interval` flags remain.
+
+### Snapshots / restore
+
+Legacy IAVL snapshot and restore via the rootmulti store are no longer supported. Attempting the legacy IAVL path returns an error:
+
+```
+legacy IAVL snapshots are no longer supported
+legacy IAVL restore is no longer supported
+```