feat: Implement new synchronization state management and deterministic head sorting, replacing the old vector clock module.

Cargo.toml

@@ -4,6 +4,7 @@ members = [
     "lattice-core",
     "lattice-net",
     "lattice-store",
+    "lattice-cli",
 ]
 
 [workspace.package]
@@ -16,6 +17,10 @@ license = "MIT"
 lattice-core = { path = "lattice-core" }
 lattice-net = { path = "lattice-net" }
 lattice-store = { path = "lattice-store" }
+lattice-cli = { path = "lattice-cli" }
+
+# CLI
+rustyline = "17"
 
 # Networking (Iroh)
 iroh = "0.95"
@@ -40,6 +45,8 @@ bytes = "1"
 dirs = "5"
 blake3 = "1"
 hex = "0.4"
+redb = "2"
+uuid = { version = "1", features = ["v4"] }
 
 # Testing
 tokio-test = "0.4"

docs/architecture.md

@@ -2,20 +2,38 @@
 
 ## Ideas
 
-- SigChains Ed25519-signed, hash-chained append-only logs per node. Trust via local signature verification.
-- Log-Based State: KV store derived by replaying entries. Watermarks enable safe log pruning + snapshots.
-- Offline-First: Iroh for networking. Vector clocks identify missing entries on reconnect—converges mathematically.
-- Full Replication: All nodes keep all logs until watermark consensus, then prune and snapshot.
+**Core:**
+- SigChains: Ed25519-signed, hash-chained append-only logs per node.
+- Offline-First: Iroh for networking. Vector clocks identify missing entries on reconnect.
+- Full Replication: All nodes keep all logs until watermark consensus, then prune.
+
+**State:**
+- Log-Based State: KV store derived from entries. Watermarks enable pruning + snapshots.
+- Merkle-ized State: state.db as Merkle tree. O(1) sync checks, efficient diffing, light clients.
+- DAG Conflict Resolution: Entries track ancestry. Forks merge on next write. Tips only in state.db.
+- KV Snapshots: Point-in-time snapshots for log pruning, fast bootstrap, time travel.
+
+**Operations:**
+- Atomic Batch Writes: Multiple key updates as single entry.
+- Conditional Updates (CAS): Update only if current value matches expected hash.
+
+**CRDTs:**
+- LWW-Register: Last-writer-wins for single values.
+- LWW-Element-Set: Set with add/remove, element present if add > remove timestamp.
 
 ## Concepts
 
-- Transitive Pairing. Nodes can introduce new nodes to the mesh.
+- Transitive Pairing: Nodes can introduce new nodes to the mesh.
+- Multi-Mesh: A node can participate in multiple meshes (clusters). Each mesh is a group of nodes sharing data.
+- Manifest Store: Joining a mesh means joining a special KV store of type "manifest" that defines the mesh membership. The manifest contains node info (`/nodes/{pubkey}/...`).
 
 ## Stack
 
 - rust
 - iroh
 - prost protocol buffers
+- redb (embedded KV store)
+- rustyline (interactive CLI)
 
 ### Bootstrap
 
@@ -58,11 +76,62 @@ Future:
 
 ### Data Model
 
-- Keys are flat strings using path conventions (e.g., `/nodes/{pubkey}`, `/config/sync/interval`).
-- Prefix queries via string matching (sorted map enables efficient range scans).
-- State is computed by replaying `Put`/`Delete` operations from all authors.
+- Multiple KV stores supported, identified by `store_id` (UUID).
+- Keys: Arbitrary byte arrays (`Vec<u8>`), sorted lexicographically.
+- Values: Arbitrary byte arrays (`Vec<u8>`).
+- Each store defines its own key/value format — applications know their schema.
+- Logs are per `(store_id, author_id)` tuple.
+- State is maintained by tracking the "frontier" (tips) of the causal graph for each key.
 - Entry ordering: by HLC timestamp, then by author ID as tiebreaker.
-- Conflicts resolved by last-write-wins (using the ordering above).
+
+**Sync vs Causality:**
+- Vector Clocks track log coverage ("I have entries from Node A up to seq 50") — syncing files.
+- DAG Parents track data causality ("This value replaces that value") — resolving key conflicts.
+
+#### DAG Conflict Resolution
+
+Instead of simple LWW where newest timestamp blindly overwrites, every entry tracks its ancestry:
+
+**Data Model:**
+- Each entry includes `parent_hashes` — references to the entries it supersedes
+- History forms a DAG (directed acyclic graph), not a linear chain
+- state.db stores only "tips" (heads) of the graph per key
+
+**Life Cycle:**
+
+1. **Write (normal):** New entry points to previous entry's hash as parent. History is a straight line.
+
+2. **Write (concurrent/offline):** Two nodes edit same key independently, both pointing to same old parent. History forks into two branches.
+
+3. **Read (forked):** System sees multiple valid values. Uses deterministic rule (highest HLC, then author_id tiebreaker) to return one "winner". No error thrown.
+
+4. **Merge (healing):** Next write to that key cites both existing branches as parents. Fork merges back to single tip.
+
+**Example: Partial Write (Branch Extension)**
+
+```
+Initial: Heads = {A, B} where A(ts:100), B(ts:105). Read winner = B.
+
+Offline node C wakes up, only knows A (hasn't seen B).
+C writes "v3" with parent = [A].
+
+Result: Heads = {C, B}. Conflict shifted, not resolved.
+        C(ts:110) > B(ts:105), so C wins reads.
+
+       ┌──> [A] ──> [C:110]
+[Root]─┤
+       └──> [B:105]
+
+Later: A synced node writes D with parents = [C, B].
+Result: Heads = {D}. Fork merged.
+```
+
+This preserves B's work even though C never saw it. Naive LWW would lose B forever.
+
+#### Store Consistency Modes
+
+- **Eventually consistent**: Default. Writes accepted locally, sync happens async. Fast, offline-capable.
+- **Strictly consistent**: Writes require quorum acknowledgment before commit. Slower, requires connectivity.
 
 ### Timestamps (Hybrid Logical Clocks)
 
@@ -86,27 +155,80 @@ Authors apply their own entries through the standard receive path to ensure cons
 Each node stores logs as one file per author:
 
 ```
-data/
-├── identity.key               # Local node's Ed25519 private key
-├── logs/
-│   └── {author_id_hex}.log    # Append-only SignedEntry stream per author
-└── state.db                   # redb: KV snapshot + vector clocks + indexes
+~/.local/share/lattice/
+├── identity.key                            # Ed25519 private key
+├── stores/
+│   └── {store_uuid}/
+│       ├── logs/
+│       │   └── {author_id_hex}.log         # Append-only SignedEntry stream
+│       └── state.db                        # redb: KV snapshot + frontiers
+└── meta.db                                 # redb: global metadata (known stores, peers)
 ```
 
-- Logs: Append-only binary files per author, containing serialized `SignedEntry` messages.
-- State DB (redb): Combined KV state, vector clocks, and indexes. Updated as entries are applied.
+- Logs: Append-only binary files per `(store, author)`, containing serialized `SignedEntry` messages.
+- State DB (redb): Per-store KV state and frontiers. Updated as entries are applied.
 
-#### state.db Tables (redb)
+#### state.db Tables (per store, redb)
 
 ```
-Table           Key                     Value                      Purpose
+Table              Key                     Value                      Purpose
 ─────────────────────────────────────────────────────────────────────────────
-kv              String (path)           Vec<u8>                    Replicated key-value data
-vector_clocks   [u8; 32] (author_id)    (u64 seq, [u8; 32] hash)   Track sync state + chain verification
-entry_index     (author_id, seq)        u64 (offset)               Fast entry lookup by position
-meta            String                  Vec<u8>                    System metadata (own_seq, watermark, etc.)
+kv                 Vec<u8> (key)           Vec<HeadInfo>              Current tips for each key
+applied_frontiers  [u8; 32] (author_id)    (u64 seq, [u8; 32] hash)   What's applied to this store
+meta               Vec<u8>                 Vec<u8>                    Store metadata (incl. merkle_root)
 ```
 
+`HeadInfo: { value: Vec<u8>, hlc: u64, author: [u8;32], hash: [u8;32] }`
+
+Note: KV stores multiple heads per key to support DAG conflict resolution. Reads pick winner deterministically.
+
+#### meta.db Tables (global, redb)
+
+```
+Table              Key                     Value                      Purpose
+─────────────────────────────────────────────────────────────────────────────
+stores             [u8; 16] (UUID)         u64 (created_at_ms)        Known stores
+meta               "root_store"            [u8; 16] (UUID)            Root store ID (opened on startup)
+```
+
+- **Root Store**: The primary/manifest store for this node, auto-opened on CLI startup
+- **Stores Table**: Tracks all stores this node participates in
+- Manifest stores define mesh membership via `/nodes/{pubkey}/...` entries
+- Data stores hold application data
+
+#### In-Memory Structures
+
+- log_frontiers: `HashMap<AuthorId, (seq, hash)>` — rebuilt from log files on startup
+
+### Operation Flow (put/delete)
+
+```
+1. User calls put("/key", value)
+         │
+         ▼
+2. SigChain.create_entry()
+   - Build Entry with parent_hashes (current tips for key)
+   - Sign it → SignedEntry
+         │
+         ▼
+3. Append to log + Gossip (critical path)
+   - Write to author's log file
+   - Update log_frontiers (in-memory)
+   - Broadcast to peers
+         │
+         ▼
+4. Apply to state.db (background)
+   - Update kv heads (merge parent tips into new tip)
+   - Update applied_frontiers
+   - Update merkle_root hash
+```
+
+Fast path (1-3): durable + distributed. Background (4): queryable state.
+
+### Read Flow (get)
+
+`get(key)` reads directly from local state.db. Reads are eventually consistent — if state.db lags behind the log, the read may return slightly stale data.
+
 ### Watermarks
 
 - Nodes gossip their watermarks periodically (throttled).
@@ -114,6 +236,11 @@ meta            String                  Vec<u8>                    System metada
 - All nodes keep all logs (own + others) for redundancy until watermark consensus.
 - Once all peers have acknowledged entries, they can be pruned and replaced by the snapshot.
 - If a node is offline too long, it re-bootstraps with a fresh snapshot when it reconnects.
+- Note: Consider preserving logs longer than required for redundancy — enables time travel (view state at any point in history).
+
+**Pruning and DAG Parents:**
+- If a new entry references a parent that was pruned, accept it only if strictly newer than snapshot timestamp.
+- Snapshots act as the base; entries referencing parents older than snapshot are roots relative to that snapshot.
 
 ### Rich CRDTs (Future)
 
@@ -157,3 +284,26 @@ message MergeOp {
 ```
 
 Recommendation: Use Put/Delete for 90% of data. Add CRDT primitives only when needed (concurrent counters, lists) rather than a scripting language.
+
+## Open Questions
+
+### Permissions
+
+Write permissions are enforceable cryptographically:
+- Every entry is signed by author
+- Nodes verify signature before accepting
+- Manifest defines allowed writers: `/nodes/{pubkey}/role` = `writer` | `reader`
+- Entries from non-writers are rejected
+
+Read permissions are not enforceable:
+- Sharing a store = granting read access
+- Encryption adds a layer but doesn't solve revocation (once you have the key, you can read past data)
+- True revocation is impossible — you can't "unread" data
+
+Practical model:
+- Share store = grant read
+- Write access defined in manifest
+- Read-only nodes replicate and verify but can't contribute entries
+
+Future:
+- Capability-based permissions: Explore finer-grained write access (e.g., per-key or per-prefix permissions) via capabilities. Exact mechanism TBD.

docs/roadmap.md

@@ -12,7 +12,7 @@
 - [x] Log file I/O (append, read, hash verification)
 - [x] SigChain (validate entries before appending)
 - [x] Store (redb) — `kv` + `meta` tables, log replay
-- [ ] Interactive CLI: `init`, `put`, `get`, `delete`, `status`, `quit`
+- [x] Interactive CLI: `init`, `put`, `get`, `delete`, `status`, `quit`
 
 ### Success Criteria
 
@@ -21,15 +21,63 @@
 - Can replay log to reconstruct KV state
 - All operations survive restart
 
-### Multi-KV Refactoring (before M2)
+### Multi-KV Refactoring (before M2) ✓
 
-Current code assumes single store. Changes needed:
-- [ ] DataDir → support `stores/{uuid}/` subdirectories
-- [ ] SigChain → scoped to (store_id, author_id)
-- [ ] Store → per-store state.db, not global
-- [ ] Log paths → `stores/{uuid}/logs/{author}.log`
-- [ ] Add global meta.db for stores table
-- [ ] CLI → `create-store`, `list-stores`, `use <store>`
+- [x] DataDir → `stores/{uuid}/` subdirectories
+- [x] Store → per-store state.db
+- [x] Log paths → `stores/{uuid}/logs/{author}.log`
+- [x] Proto: Entry has store_id (UUID)
+- [x] CLI → `init`, `create-store`, `list-stores`, `use`
+- [x] meta.db stores table (MetaStore)
+- [x] SigChain → validate entry.store_id
+
+---
+
+## Milestone 1.5: DAG Conflict Resolution
+
+**Goal:** Upgrade store from simple LWW to DAG-based conflict resolution per architecture.md.
+
+### Deliverables
+
+- [x] Proto: Add `repeated bytes parent_hashes` to Entry (for DAG causality)
+- [x] Proto: Add `HeadInfo` message for multi-head storage
+- [x] Store: KV table schema → `Vec<u8> → Vec<HeadInfo>`
+- [x] Store: `apply_entry` → track multiple heads, merge parent tips
+- [x] Store: `get` → deterministic winner (highest HLC, author tiebreaker)
+- [x] Store: `get_heads` → inspect all heads for a key
+- [x] EntryBuilder: `.parent_hashes(...)` method for DAG ancestry
+- [x] CLI: Show conflict indicator when multiple heads
+
+### Success Criteria
+
+- [x] Concurrent writes to same key create multiple heads
+- [x] Reads return deterministic winner
+- [x] Next write citing both heads merges fork to single tip
+- [x] All existing tests still pass (71 tests)
+
+---
+
+## Milestone 1.9: Async Refactor
+
+**Goal:** Prepare codebase for concurrent CLI + network operation.
+
+### Deliverables
+
+**Phase 1: Store Actor (sync)** ✓
+- [x] Store actor pattern: dedicated thread owns Store, receives commands via `std::sync::mpsc`
+- [x] StoreHandle wraps channel sender, keeps current API
+- [x] Validate: CLI works as before with actor
+
+**Phase 2: Async Runtime** ✓
+- [x] Add tokio runtime (`#[tokio::main]`)
+- [x] Migrate `std::sync::mpsc` → `tokio::sync::mpsc`
+- [x] Async CLI using `block_in_place` for sync handlers
+
+### Success Criteria
+
+- [x] CLI still works as before
+- [x] Store operations serialized (no data races)
+- [x] Ready for concurrent network tasks
 
 ---
 
@@ -39,12 +87,17 @@ Current code assumes single store. Changes needed:
 
 ### Deliverables
 
-- [ ] Store: add `applied_frontiers` table (sync state per author)
-- [ ] VectorClock module (diff, merge, missing entries)
-- [ ] Sync protocol (push missing entries)
+**Phase 1: Sync Logic (no network)** ✓
+- [x] SyncState with AuthorInfo (seq + hash) for hash-based log resumption
+- [x] `Store::sync_state()` → author-to-seq+hash map from AUTHOR_TABLE
+- [x] `SyncState::diff()` → `Vec<MissingRange>` with from_hash for `read_entries_after`
+- [x] Multi-store sync test: compute diff, fetch entries, apply, verify same state
+
+**Phase 2: Iroh Integration**
 - [ ] Iroh integration (peer discovery, connection)
-- [ ] Multi-author log merging
+- [ ] Sync protocol (push missing entries over network)
 - [ ] CLI: `peers`, `connect`/`join` commands
+- [ ] Background sync task (tokio::spawn)
 
 ### Success Criteria
 
@@ -74,3 +127,8 @@ Current code assumes single store. Changes needed:
 - Snapshots for fast bootstrap
 - FUSE filesystem mount
   - Note: FUSE requires u64 inode numbers → maintain `BiMap<u64, Hash>` in redb
+- Merkle-ized State
+  - state.db as Merkle tree with signed root hash
+  - O(1) sync checks (compare root), efficient binary-search diffing
+  - Light clients: fetch value + Merkle proof, verify without full state
+  - Trade-off: write amplification, requires deterministic tree (Patricia Trie / Merkle Search Tree)

docs/storage.md

@@ -0,0 +1,39 @@
+# Storage Format
+
+## Directory Layout
+
+```
+~/.local/share/lattice/
+├── identity.key              # Ed25519 private key (not replicated)
+├── meta.db                   # Global metadata (redb)
+└── stores/{uuid}/
+    ├── logs/{author}.log     # Append-only SignedEntry stream
+    └── state.db              # Per-store KV state (redb)
+```
+
+## meta.db (redb)
+
+| Table   | Key           | Value              | Purpose                      |
+|---------|---------------|--------------------|------------------------------|
+| stores  | UUID (16B)    | created_at (u64)   | Known stores                 |
+| meta    | "root_store"  | UUID (16B)         | Auto-opened on CLI startup   |
+
+## state.db (redb, per store)
+
+| Table   | Key      | Value       | Purpose                |
+|---------|----------|-------------|------------------------|
+| kv      | String   | Vec<u8>     | Key-value data         |
+| meta    | String   | Vec<u8>     | last_seq, last_hash    |
+
+## Log Files
+
+Each `{author}.log` contains length-delimited `LogRecord` messages:
+
+```protobuf
+message LogRecord {
+  bytes hash = 1;         // BLAKE3 hash of entry_bytes
+  bytes entry_bytes = 2;  // Serialized SignedEntry
+}
+```
+
+Hashes are verified on read; corruption causes `LogError::HashMismatch`.

lattice-cli/Cargo.toml

@@ -0,0 +1,18 @@
+[package]
+name = "lattice-cli"
+description = "Interactive CLI for Lattice"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+
+[[bin]]
+name = "lattice"
+path = "src/main.rs"
+
+[dependencies]
+lattice-core = { workspace = true }
+rustyline = { workspace = true }
+hex = { workspace = true }
+thiserror = { workspace = true }
+tokio = { workspace = true }
+shlex = "1"

lattice-cli/src/commands.rs

@@ -0,0 +1,414 @@
+//! CLI command handlers
+
+use crate::node::{LatticeNode, StoreHandle};
+use lattice_core::Uuid;
+use std::time::Instant;
+
+/// Result of a command that may switch stores
+pub enum CommandResult {
+    /// No store change
+    Ok,
+    /// Switch to this store
+    SwitchTo(StoreHandle),
+}
+
+/// Helper to call async code from sync command handlers
+fn block_async<F: std::future::Future>(f: F) -> F::Output {
+    tokio::task::block_in_place(|| {
+        tokio::runtime::Handle::current().block_on(f)
+    })
+}
+
+pub type Handler = fn(&LatticeNode, Option<&StoreHandle>, &[String]) -> CommandResult;
+
+pub struct Command {
+    pub name: &'static str,
+    pub args: &'static str,
+    pub description: &'static str,
+    pub min_args: usize,
+    pub max_args: usize,
+    pub handler: Handler,
+}
+
+pub fn commands() -> Vec<Command> {
+    vec![
+        Command {
+            name: "init",
+            args: "",
+            description: "Initialize node with root store",
+            min_args: 0,
+            max_args: 0,
+            handler: cmd_init,
+        },
+        Command {
+            name: "create-store",
+            args: "",
+            description: "Create a new store",
+            min_args: 0,
+            max_args: 0,
+            handler: cmd_create_store,
+        },
+        Command {
+            name: "use",
+            args: "<uuid>",
+            description: "Switch to a store",
+            min_args: 1,
+            max_args: 1,
+            handler: cmd_use_store,
+        },
+        Command {
+            name: "list-stores",
+            args: "",
+            description: "List all stores",
+            min_args: 0,
+            max_args: 0,
+            handler: cmd_list_stores,
+        },
+        Command {
+            name: "put",
+            args: "<key> <value>",
+            description: "Store a key-value pair",
+            min_args: 2,
+            max_args: 2,
+            handler: cmd_put,
+        },
+        Command {
+            name: "get",
+            args: "<key> [-v]",
+            description: "Retrieve a value by key",
+            min_args: 1,
+            max_args: 2,
+            handler: cmd_get,
+        },
+        Command {
+            name: "delete",
+            args: "<key>",
+            description: "Delete a key",
+            min_args: 1,
+            max_args: 1,
+            handler: cmd_delete,
+        },
+        Command {
+            name: "list",
+            args: "[-v]",
+            description: "List all key-value pairs (-v for verbose)",
+            min_args: 0,
+            max_args: 1,
+            handler: cmd_list,
+        },
+        Command {
+            name: "status",
+            args: "",
+            description: "Show node/store info",
+            min_args: 0,
+            max_args: 0,
+            handler: cmd_status,
+        },
+        Command {
+            name: "author-state",
+            args: "[author-hex]",
+            description: "Show author state (default: self)",
+            min_args: 0,
+            max_args: 1,
+            handler: cmd_author_state,
+        },
+        Command {
+            name: "help",
+            args: "",
+            description: "Show this help message",
+            min_args: 0,
+            max_args: 0,
+            handler: cmd_help,
+        },
+    ]
+}
+
+// --- Store management ---
+
+fn cmd_init(node: &LatticeNode, _store: Option<&StoreHandle>, _args: &[String]) -> CommandResult {
+    match node.init() {
+        Ok(store_id) => {
+            println!("Initialized with root store: {}", store_id);
+            match node.open_store(store_id) {
+                Ok((handle, _)) => CommandResult::SwitchTo(handle),
+                Err(e) => {
+                    eprintln!("Warning: {}", e);
+                    CommandResult::Ok
+                }
+            }
+        }
+        Err(e) => {
+            eprintln!("Error: {}", e);
+            CommandResult::Ok
+        }
+    }
+}
+
+fn cmd_create_store(node: &LatticeNode, _store: Option<&StoreHandle>, _args: &[String]) -> CommandResult {
+    match node.create_store() {
+        Ok(store_id) => {
+            println!("Created store: {}", store_id);
+            match node.open_store(store_id) {
+                Ok((handle, _)) => {
+                    println!("Switched to new store");
+                    CommandResult::SwitchTo(handle)
+                }
+                Err(e) => {
+                    eprintln!("Warning: {}", e);
+                    CommandResult::Ok
+                }
+            }
+        }
+        Err(e) => {
+            eprintln!("Error: {}", e);
+            CommandResult::Ok
+        }
+    }
+}
+
+fn cmd_use_store(node: &LatticeNode, _store: Option<&StoreHandle>, args: &[String]) -> CommandResult {
+    let store_id = match Uuid::parse_str(&args[0]) {
+        Ok(id) => id,
+        Err(_) => {
+            eprintln!("Error: invalid UUID '{}'", args[0]);
+            return CommandResult::Ok;
+        }
+    };
+    
+    let start = Instant::now();
+    match node.open_store(store_id) {
+        Ok((handle, info)) => {
+            if info.entries_replayed > 0 {
+                println!("Replayed {} entries ({:.2?})", info.entries_replayed, start.elapsed());
+            } else {
+                println!("Switched to store {}", store_id);
+            }
+            CommandResult::SwitchTo(handle)
+        }
+        Err(e) => {
+            eprintln!("Error: {}", e);
+            CommandResult::Ok
+        }
+    }
+}
+
+fn cmd_list_stores(node: &LatticeNode, store: Option<&StoreHandle>, _args: &[String]) -> CommandResult {
+    let stores = match node.list_stores() {
+        Ok(s) => s,
+        Err(e) => {
+            eprintln!("Error: {}", e);
+            return CommandResult::Ok;
+        }
+    };
+    let current_id = store.map(|s| s.id());
+    
+    if stores.is_empty() {
+        println!("No stores. Use 'init' or 'create-store'.");
+    } else {
+        for store_id in stores {
+            let marker = if Some(store_id) == current_id { " *" } else { "" };
+            println!("{}{}", store_id, marker);
+        }
+    }
+    CommandResult::Ok
+}
+
+// --- Info ---
+
+fn cmd_help(_node: &LatticeNode, _store: Option<&StoreHandle>, _args: &[String]) -> CommandResult {
+    println!("\nCommands:");
+    for cmd in commands() {
+        if cmd.args.is_empty() {
+            println!("  {:<16} {}", cmd.name, cmd.description);
+        } else {
+            println!("  {} {:<8} {}", cmd.name, cmd.args, cmd.description);
+        }
+    }
+    println!("  quit            Exit");
+    println!();
+    CommandResult::Ok
+}
+
+fn cmd_status(node: &LatticeNode, store: Option<&StoreHandle>, _args: &[String]) -> CommandResult {
+    println!("Node ID:  {}", hex::encode(node.node_id()));
+    println!("Data:     {}", node.data_path().display());
+    match node.root_store() {
+        Ok(Some(id)) => println!("Root:     {}", id),
+        Ok(None) => println!("Root:     (not set)"),
+        Err(_) => println!("Root:     (error)"),
+    }
+    if let Some(h) = store {
+        println!("Store:    {}", h.id());
+        println!("Log Seq:  {}", block_async(h.log_seq()));
+        println!("Applied:  {}", block_async(h.applied_seq()).unwrap_or(0));
+    } else {
+        println!("Store:    (none)");
+    }
+    CommandResult::Ok
+}
+
+// --- KV ---
+
+fn cmd_put(_node: &LatticeNode, store: Option<&StoreHandle>, args: &[String]) -> CommandResult {
+    let Some(h) = store else {
+        println!("No store selected. Use 'init' or 'use <uuid>'");
+        return CommandResult::Ok;
+    };
+    let start = Instant::now();
+    match block_async(h.put(args[0].as_bytes(), args[1].as_bytes())) {
+        Ok(seq) => println!("OK (seq: {}, {:.2?})", seq, start.elapsed()),
+        Err(e) => eprintln!("Error: {}", e),
+    }
+    CommandResult::Ok
+}
+
+fn cmd_get(_node: &LatticeNode, store: Option<&StoreHandle>, args: &[String]) -> CommandResult {
+    let Some(h) = store else {
+        println!("No store selected. Use 'init' or 'use <uuid>'");
+        return CommandResult::Ok;
+    };
+    let verbose = args.get(1).map(|a| a == "-v").unwrap_or(false);
+    let start = Instant::now();
+    let key = args[0].as_bytes();
+    
+    if verbose {
+        // Show all heads
+        match block_async(h.get_heads(key)) {
+            Ok(heads) if heads.is_empty() => println!("(nil)"),
+            Ok(heads) => {
+                for (i, head) in heads.iter().enumerate() {
+                    let winner = if i == 0 { "→" } else { " " };
+                    let tombstone = if head.tombstone { "⊗" } else { "" };
+                    let author_short = hex::encode(&head.author).chars().take(8).collect::<String>();
+                    if head.tombstone {
+                        println!("{} {} (deleted) (hlc:{}, author:{})", 
+                            winner, tombstone, head.hlc, author_short);
+                    } else {
+                        println!("{} {} (hlc:{}, author:{})", 
+                            winner, format_value(&head.value), head.hlc, author_short);
+                    }
+                }
+                if heads.len() > 1 {
+                    println!("⚠ {} heads (conflict)", heads.len());
+                }
+                println!("({:.2?})", start.elapsed());
+            }
+            Err(e) => eprintln!("Error: {}", e),
+        }
+    } else {
+        match block_async(h.get(key)) {
+            Ok(Some(v)) => {
+                let heads = block_async(h.get_heads(key)).unwrap_or_default();
+                if heads.len() > 1 {
+                    println!("{} (⚠ {} heads)", format_value(&v), heads.len());
+                } else {
+                    println!("{}", format_value(&v));
+                }
+                println!("({:.2?})", start.elapsed());
+            }
+            Ok(None) => println!("(nil)"),
+            Err(e) => eprintln!("Error: {}", e),
+        }
+    }
+    CommandResult::Ok
+}
+
+fn cmd_delete(_node: &LatticeNode, store: Option<&StoreHandle>, args: &[String]) -> CommandResult {
+    let Some(h) = store else {
+        println!("No store selected. Use 'init' or 'use <uuid>'");
+        return CommandResult::Ok;
+    };
+    let start = Instant::now();
+    match block_async(h.delete(args[0].as_bytes())) {
+        Ok(seq) => println!("OK (seq: {}, {:.2?})", seq, start.elapsed()),
+        Err(e) => eprintln!("Error: {}", e),
+    }
+    CommandResult::Ok
+}
+
+fn cmd_list(_node: &LatticeNode, store: Option<&StoreHandle>, args: &[String]) -> CommandResult {
+    let Some(h) = store else {
+        println!("No store selected. Use 'init' or 'use <uuid>'");
+        return CommandResult::Ok;
+    };
+    let verbose = args.first().map(|a| a == "-v").unwrap_or(false);
+    let start = Instant::now();
+    match block_async(h.list()) {
+        Ok(entries) => {
+            if entries.is_empty() {
+                println!("(empty)");
+            } else {
+                for (k, v) in &entries {
+                    let key_str = format_value(k);
+                    if verbose {
+                        // Show all heads for this key
+                        let heads = block_async(h.get_heads(k)).unwrap_or_default();
+                        println!("{}:", key_str);
+                        for (i, head) in heads.iter().enumerate() {
+                            let winner = if i == 0 { "→" } else { " " };
+                            let author_short = hex::encode(&head.author).chars().take(8).collect::<String>();
+                            if head.tombstone {
+                                println!("  {} ⊗ (deleted) (hlc:{}, author:{})", 
+                                    winner, head.hlc, author_short);
+                            } else {
+                                println!("  {} {} (hlc:{}, author:{})", 
+                                    winner, format_value(&head.value), head.hlc, author_short);
+                            }
+                        }
+                    } else {
+                        println!("{} = {}", key_str, format_value(v));
+                    }
+                }
+                println!("({} keys, {:.2?})", entries.len(), start.elapsed());
+            }
+        }
+        Err(e) => eprintln!("Error: {}", e),
+    }
+    CommandResult::Ok
+}
+
+fn format_value(v: &[u8]) -> String {
+    std::str::from_utf8(v).map(String::from).unwrap_or_else(|_| format!("0x{}", hex::encode(v)))
+}
+
+fn cmd_author_state(node: &LatticeNode, store: Option<&StoreHandle>, args: &[String]) -> CommandResult {
+    let store = match store {
+        Some(s) => s,
+        None => {
+            eprintln!("Error: no store selected");
+            return CommandResult::Ok;
+        }
+    };
+
+    // Get author: from arg or default to self
+    let author_bytes: [u8; 32] = if args.is_empty() {
+        node.node_id()
+    } else {
+        let hex_str = args[0].trim_start_matches("0x");
+        match hex::decode(hex_str) {
+            Ok(bytes) if bytes.len() == 32 => bytes.try_into().unwrap(),
+            Ok(bytes) => {
+                eprintln!("Error: author must be 32 bytes, got {}", bytes.len());
+                return CommandResult::Ok;
+            }
+            Err(e) => {
+                eprintln!("Error: invalid hex: {}", e);
+                return CommandResult::Ok;
+            }
+        }
+    };
+
+    match block_async(store.author_state(&author_bytes)) {
+        Ok(Some(state)) => {
+            println!("Author: {}", hex::encode(&author_bytes));
+            println!("  seq: {}", state.seq);
+            println!("  hash: {}", hex::encode(&state.hash));
+            println!("  log_offset: {}", state.log_offset);
+        }
+        Ok(None) => {
+            println!("No state for author: {}", hex::encode(&author_bytes));
+        }
+        Err(e) => eprintln!("Error: {}", e),
+    }
+    CommandResult::Ok
+}

lattice-cli/src/main.rs

@@ -0,0 +1,108 @@
+//! Lattice Interactive CLI
+
+mod node;
+mod commands;
+mod store_actor;
+
+use commands::CommandResult;
+use node::{LatticeNodeBuilder, StoreHandle};
+use rustyline::error::ReadlineError;
+use rustyline::DefaultEditor;
+
+#[tokio::main]
+async fn main() {
+    println!("Lattice CLI v{}", env!("CARGO_PKG_VERSION"));
+    println!("Type 'help' for commands, 'quit' to exit.\n");
+
+    let node = match LatticeNodeBuilder::new().build() {
+        Ok(n) => n,
+        Err(e) => {
+            eprintln!("Failed to initialize: {}", e);
+            return;
+        }
+    };
+    
+    let info = node.info();
+    println!("Node ID: {}", info.node_id);
+    println!("Data:    {}", info.data_path);
+
+    if !info.stores.is_empty() {
+        println!("Stores:  {}", info.stores.len());
+    }
+
+    let mut current_store: Option<StoreHandle> = match node.open_root_store() {
+        Ok(Some((h, open_info))) => {
+            if open_info.entries_replayed > 0 {
+                println!("Root:    {} (replayed {})", open_info.store_id, open_info.entries_replayed);
+            } else {
+                println!("Root:    {}", open_info.store_id);
+            }
+            Some(h)
+        }
+        Ok(None) => {
+            println!("Status:  Not initialized (use 'init')");
+            None
+        }
+        Err(e) => {
+            eprintln!("Warning: {}", e);
+            None
+        }
+    };
+    println!();
+
+    let mut rl = DefaultEditor::new().expect("Failed to create editor");
+    let cmds = commands::commands();
+
+    loop {
+        let prompt = match &current_store {
+            Some(h) => format!("lattice:{}> ", &h.id().to_string()[..8]),
+            None => "lattice:no-store> ".to_string(),
+        };
+
+        match rl.readline(&prompt) {
+            Ok(line) => {
+                let line = line.trim();
+                if line.is_empty() { continue; }
+                let _ = rl.add_history_entry(line);
+
+                let args = match shlex::split(line) {
+                    Some(a) => a,
+                    None => {
+                        println!("Error: mismatched quotes");
+                        continue;
+                    }
+                };
+
+                let cmd_name = args.first().map(|s| s.as_str()).unwrap_or("");
+                
+                if cmd_name == "quit" || cmd_name == "exit" {
+                    println!("Goodbye!");
+                    break;
+                }
+
+                match cmds.iter().find(|c| c.name == cmd_name) {
+                    Some(cmd) => {
+                        let cmd_args = &args[1..];
+                        if cmd_args.len() < cmd.min_args || cmd_args.len() > cmd.max_args {
+                            println!("Usage: {} {}", cmd.name, cmd.args);
+                        } else {
+                            match (cmd.handler)(&node, current_store.as_ref(), cmd_args) {
+                                CommandResult::Ok => {}
+                                CommandResult::SwitchTo(h) => current_store = Some(h),
+                            }
+                        }
+                    }
+                    None => println!("Unknown: '{}'. Type 'help'.", cmd_name),
+                }
+            }
+            Err(ReadlineError::Interrupted | ReadlineError::Eof) => {
+                println!("Goodbye!");
+                break;
+            }
+            Err(e) => {
+                eprintln!("Error: {:?}", e);
+                break;
+            }
+        }
+    }
+}

lattice-cli/src/node.rs

@@ -0,0 +1,433 @@
+//! Local Lattice node API with multi-store support
+
+use lattice_core::{
+    DataDir, MetaStore, Node, SigChain, Store, Uuid,
+    log::LogError,
+    meta_store::MetaStoreError,
+    sigchain::SigChainError,
+    store::StoreError,
+};
+use std::path::Path;
+use std::rc::Rc;
+use thiserror::Error;
+
+#[derive(Error, Debug)]
+pub enum NodeError {
+    #[error("IO error: {0}")]
+    Io(#[from] std::io::Error),
+    
+    #[error("Store error: {0}")]
+    Store(#[from] StoreError),
+    
+    #[error("MetaStore error: {0}")]
+    MetaStore(#[from] MetaStoreError),
+    
+    #[error("SigChain error: {0}")]
+    SigChain(#[from] SigChainError),
+    
+    #[error("Log error: {0}")]
+    Log(#[from] LogError),
+    
+    #[error("Node error: {0}")]
+    Node(#[from] lattice_core::node::NodeError),
+    
+    #[error("Already initialized")]
+    AlreadyInitialized,
+    
+    #[error("Channel closed")]
+    ChannelClosed,
+    
+    #[error("Actor error: {0}")]
+    Actor(String),
+}
+
+pub struct NodeInfo {
+    pub node_id: String,
+    pub data_path: String,
+    pub stores: Vec<Uuid>,
+}
+
+pub struct StoreInfo {
+    pub store_id: Uuid,
+    pub entries_replayed: u64,
+}
+
+pub struct LatticeNodeBuilder {
+    pub data_dir: DataDir,
+}
+
+impl LatticeNodeBuilder {
+    pub fn new() -> Self {
+        Self { data_dir: DataDir::default() }
+    }
+
+    pub fn build(self) -> Result<LatticeNode, NodeError> {
+        self.data_dir.ensure_dirs()?;
+
+        let key_path = self.data_dir.identity_key();
+        let node = if key_path.exists() {
+            Node::load(&key_path)?
+        } else {
+            let node = Node::generate();
+            node.save(&key_path)?;
+            node
+        };
+
+        let meta = MetaStore::open(self.data_dir.meta_db())?;
+
+        Ok(LatticeNode {
+            data_dir: self.data_dir,
+            node: Rc::new(node),
+            meta,
+        })
+    }
+}
+
+impl Default for LatticeNodeBuilder {
+    fn default() -> Self { Self::new() }
+}
+
+/// A local Lattice node (manages identity and store registry)
+pub struct LatticeNode {
+    data_dir: DataDir,
+    node: Rc<Node>,
+    meta: MetaStore,
+}
+
+impl LatticeNode {
+    pub fn info(&self) -> NodeInfo {
+        NodeInfo {
+            node_id: hex::encode(self.node.public_key_bytes()),
+            data_path: self.data_dir.base().display().to_string(),
+            stores: self.meta.list_stores().unwrap_or_default(),
+        }
+    }
+
+    pub fn node_id(&self) -> [u8; 32] {
+        self.node.public_key_bytes()
+    }
+
+    pub fn data_path(&self) -> &Path {
+        self.data_dir.base()
+    }
+
+    /// Get the root store ID
+    pub fn root_store(&self) -> Result<Option<Uuid>, NodeError> {
+        Ok(self.meta.root_store()?)
+    }
+
+    /// Open the root store if set
+    pub fn open_root_store(&self) -> Result<Option<(StoreHandle, StoreInfo)>, NodeError> {
+        match self.meta.root_store()? {
+            Some(id) => Ok(Some(self.open_store(id)?)),
+            None => Ok(None),
+        }
+    }
+
+    /// Initialize the node with a root store (fails if already initialized)
+    pub fn init(&self) -> Result<Uuid, NodeError> {
+        if self.meta.root_store()?.is_some() {
+            return Err(NodeError::AlreadyInitialized);
+        }
+        let store_id = self.create_store()?;
+        self.meta.set_root_store(store_id)?;
+        Ok(store_id)
+    }
+
+    pub fn list_stores(&self) -> Result<Vec<Uuid>, NodeError> {
+        Ok(self.meta.list_stores()?)
+    }
+
+    pub fn create_store(&self) -> Result<Uuid, NodeError> {
+        let store_id = Uuid::new_v4();
+        self.data_dir.ensure_store_dirs(store_id)?;
+        let _ = Store::open(self.data_dir.store_state_db(store_id))?;
+        self.meta.add_store(store_id)?;
+        Ok(store_id)
+    }
+
+    pub fn open_store(&self, store_id: Uuid) -> Result<(StoreHandle, StoreInfo), NodeError> {
+        self.data_dir.ensure_store_dirs(store_id)?;
+        
+        let author_id_hex = hex::encode(self.node.public_key_bytes());
+        let log_path = self.data_dir.store_log_file(store_id, &author_id_hex);
+        
+        let sigchain = if log_path.exists() {
+            SigChain::from_log(&log_path, *store_id.as_bytes(), self.node.public_key_bytes())?
+        } else {
+            SigChain::new(&log_path, *store_id.as_bytes(), self.node.public_key_bytes())
+        };
+        
+        let store = Store::open(self.data_dir.store_state_db(store_id))?;
+        let entries_replayed = if log_path.exists() {
+            store.replay_log(&log_path)?
+        } else {
+            0
+        };
+        
+        let info = StoreInfo { store_id, entries_replayed };
+        
+        // Spawn actor thread - actor owns store, sigchain, and node copy
+        let (tx, actor_handle) = crate::store_actor::spawn_store_actor(
+            store_id,
+            store,
+            sigchain,
+            (*self.node).clone(),
+        );
+        
+        let handle = StoreHandle {
+            store_id,
+            tx,
+            actor_handle: Some(actor_handle),
+        };
+        
+        Ok((handle, info))
+    }
+}
+
+/// A handle to a specific store - wraps channel to actor thread
+pub struct StoreHandle {
+    store_id: Uuid,
+    tx: tokio::sync::mpsc::Sender<crate::store_actor::StoreCmd>,
+    actor_handle: Option<std::thread::JoinHandle<()>>,
+}
+
+impl StoreHandle {
+    pub fn id(&self) -> Uuid { self.store_id }
+
+    pub async fn get(&self, key: &[u8]) -> Result<Option<Vec<u8>>, NodeError> {
+        use crate::store_actor::StoreCmd;
+        let (resp_tx, resp_rx) = tokio::sync::oneshot::channel();
+        self.tx.send(StoreCmd::Get { key: key.to_vec(), resp: resp_tx }).await
+            .map_err(|_| NodeError::ChannelClosed)?;
+        resp_rx.await
+            .map_err(|_| NodeError::ChannelClosed)?
+            .map_err(NodeError::Store)
+    }
+
+    pub async fn get_heads(&self, key: &[u8]) -> Result<Vec<lattice_core::HeadInfo>, NodeError> {
+        use crate::store_actor::StoreCmd;
+        let (resp_tx, resp_rx) = tokio::sync::oneshot::channel();
+        self.tx.send(StoreCmd::GetHeads { key: key.to_vec(), resp: resp_tx }).await
+            .map_err(|_| NodeError::ChannelClosed)?;
+        resp_rx.await
+            .map_err(|_| NodeError::ChannelClosed)?
+            .map_err(NodeError::Store)
+    }
+
+    pub async fn list(&self) -> Result<Vec<(Vec<u8>, Vec<u8>)>, NodeError> {
+        use crate::store_actor::StoreCmd;
+        let (resp_tx, resp_rx) = tokio::sync::oneshot::channel();
+        self.tx.send(StoreCmd::List { resp: resp_tx }).await
+            .map_err(|_| NodeError::ChannelClosed)?;
+        resp_rx.await
+            .map_err(|_| NodeError::ChannelClosed)?
+            .map_err(NodeError::Store)
+    }
+
+    pub async fn log_seq(&self) -> u64 {
+        use crate::store_actor::StoreCmd;
+        let (resp_tx, resp_rx) = tokio::sync::oneshot::channel();
+        let _ = self.tx.send(StoreCmd::LogSeq { resp: resp_tx }).await;
+        resp_rx.await.unwrap_or(0)
+    }
+
+    pub async fn applied_seq(&self) -> Result<u64, NodeError> {
+        use crate::store_actor::StoreCmd;
+        let (resp_tx, resp_rx) = tokio::sync::oneshot::channel();
+        self.tx.send(StoreCmd::AppliedSeq { resp: resp_tx }).await
+            .map_err(|_| NodeError::ChannelClosed)?;
+        resp_rx.await
+            .map_err(|_| NodeError::ChannelClosed)?
+            .map_err(NodeError::Store)
+    }
+
+    pub async fn author_state(&self, author: &[u8; 32]) -> Result<Option<lattice_core::proto::AuthorState>, NodeError> {
+        use crate::store_actor::StoreCmd;
+        let (resp_tx, resp_rx) = tokio::sync::oneshot::channel();
+        self.tx.send(StoreCmd::AuthorState { author: *author, resp: resp_tx }).await
+            .map_err(|_| NodeError::ChannelClosed)?;
+        resp_rx.await
+            .map_err(|_| NodeError::ChannelClosed)?
+            .map_err(NodeError::Store)
+    }
+
+    pub async fn put(&self, key: &[u8], value: &[u8]) -> Result<u64, NodeError> {
+        use crate::store_actor::StoreCmd;
+        let (resp_tx, resp_rx) = tokio::sync::oneshot::channel();
+        self.tx.send(StoreCmd::Put { key: key.to_vec(), value: value.to_vec(), resp: resp_tx }).await
+            .map_err(|_| NodeError::ChannelClosed)?;
+        resp_rx.await
+            .map_err(|_| NodeError::ChannelClosed)?
+            .map_err(|e| NodeError::Actor(e.to_string()))
+    }
+
+    pub async fn delete(&self, key: &[u8]) -> Result<u64, NodeError> {
+        use crate::store_actor::StoreCmd;
+        let (resp_tx, resp_rx) = tokio::sync::oneshot::channel();
+        self.tx.send(StoreCmd::Delete { key: key.to_vec(), resp: resp_tx }).await
+            .map_err(|_| NodeError::ChannelClosed)?;
+        resp_rx.await
+            .map_err(|_| NodeError::ChannelClosed)?
+            .map_err(|e| NodeError::Actor(e.to_string()))
+    }
+
+}
+
+impl Drop for StoreHandle {
+    fn drop(&mut self) {
+        // Send shutdown command (non-blocking) and wait for actor to finish
+        // Use try_send to avoid panic in async context
+        let _ = self.tx.try_send(crate::store_actor::StoreCmd::Shutdown);
+        if let Some(handle) = self.actor_handle.take() {
+            let _ = handle.join();
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::env::temp_dir;
+
+    fn temp_data_dir(name: &str) -> DataDir {
+        let path = temp_dir().join(format!("lattice_node_test_{}", name));
+        let _ = std::fs::remove_dir_all(&path);
+        DataDir::new(path)
+    }
+
+    #[tokio::test]
+    async fn test_create_and_open_store() {
+        let data_dir = temp_data_dir("meta_store");
+        
+        let node = LatticeNodeBuilder { data_dir: data_dir.clone() }
+            .build()
+            .expect("Failed to create node");
+        
+        assert!(node.info().stores.is_empty());
+        
+        let store_id = node.create_store().expect("Failed to create store");
+        
+        // Verify it's in the list
+        let stores = node.list_stores().expect("list failed");
+        assert!(stores.contains(&store_id));
+        
+        let (handle, _) = node.open_store(store_id).expect("Failed to open store");
+        handle.put(b"/key", b"value").await.expect("put failed");
+        assert_eq!(handle.get(b"/key").await.unwrap(), Some(b"value".to_vec()));
+        
+        let _ = std::fs::remove_dir_all(data_dir.base());
+    }
+
+    #[tokio::test]
+    async fn test_store_isolation() {
+        let data_dir = temp_data_dir("meta_isolation");
+        
+        let node = LatticeNodeBuilder { data_dir: data_dir.clone() }
+            .build()
+            .expect("Failed to create node");
+        
+        let store_a = node.create_store().expect("create A");
+        let store_b = node.create_store().expect("create B");
+        
+        let (handle_a, _) = node.open_store(store_a).expect("open A");
+        handle_a.put(b"/key", b"from A").await.expect("put A");
+        
+        let (handle_b, _) = node.open_store(store_b).expect("open B");
+        assert_eq!(handle_b.get(b"/key").await.unwrap(), None);
+        
+        assert_eq!(handle_a.get(b"/key").await.unwrap(), Some(b"from A".to_vec()));
+        
+        let _ = std::fs::remove_dir_all(data_dir.base());
+    }
+
+    #[test]
+    fn test_init_creates_root_store() {
+        let data_dir = temp_data_dir("init_root");
+        
+        let node = LatticeNodeBuilder { data_dir: data_dir.clone() }
+            .build()
+            .expect("create node");
+        
+        // Initially no root store
+        assert!(node.root_store().unwrap().is_none());
+        
+        // Init creates root store
+        let root_id = node.init().expect("init failed");
+        assert_eq!(node.root_store().unwrap(), Some(root_id));
+        
+        let _ = std::fs::remove_dir_all(data_dir.base());
+    }
+
+    #[test]
+    fn test_duplicate_init_fails() {
+        let data_dir = temp_data_dir("init_dup");
+        
+        let node = LatticeNodeBuilder { data_dir: data_dir.clone() }
+            .build()
+            .expect("create node");
+        
+        node.init().expect("first init");
+        
+        // Second init should fail
+        match node.init() {
+            Err(NodeError::AlreadyInitialized) => (),
+            other => panic!("Expected AlreadyInitialized, got {:?}", other),
+        }
+        
+        let _ = std::fs::remove_dir_all(data_dir.base());
+    }
+
+    #[test]
+    fn test_root_store_in_info_after_init() {
+        let data_dir = temp_data_dir("init_info");
+        
+        // First session: init
+        let root_id = {
+            let node = LatticeNodeBuilder { data_dir: data_dir.clone() }
+                .build()
+                .expect("create node");
+            node.init().expect("init")
+        };
+        
+        // Second session: root_store should persist
+        let node = LatticeNodeBuilder { data_dir: data_dir.clone() }
+            .build()
+            .expect("reload node");
+        
+        assert_eq!(node.root_store().unwrap(), Some(root_id));
+        
+        let _ = std::fs::remove_dir_all(data_dir.base());
+    }
+
+    #[tokio::test]
+    async fn test_idempotent_put_and_delete() {
+        let data_dir = temp_data_dir("idempotent");
+        
+        let node = LatticeNodeBuilder { data_dir: data_dir.clone() }
+            .build()
+            .expect("create node");
+        let store_id = node.init().expect("init");
+        let (store, _) = node.open_store(store_id).expect("open store");
+        
+        // Put twice with same value - second should be idempotent
+        let seq1 = store.put(b"/key", b"value").await.expect("put 1");
+        assert_eq!(seq1, 1);
+        
+        let seq2 = store.put(b"/key", b"value").await.expect("put 2");
+        assert_eq!(seq2, 1, "Second put with same value should be idempotent (no new entry)");
+        
+        assert_eq!(store.log_seq().await, 1, "Log should have 1 entry, not 2");
+        
+        // Delete twice - second should be idempotent
+        let seq3 = store.delete(b"/key").await.expect("delete 1");
+        assert_eq!(seq3, 2);
+        
+        let seq4 = store.delete(b"/key").await.expect("delete 2");
+        assert_eq!(seq4, 2, "Second delete should be idempotent (no new entry)");
+        
+        assert_eq!(store.log_seq().await, 2, "Log should have 2 entries, not 3");
+        
+        let _ = std::fs::remove_dir_all(data_dir.base());
+    }
+}

lattice-cli/src/store_actor.rs

@@ -0,0 +1,201 @@
+//! Store Actor - dedicated thread that owns Store and processes commands via channel
+
+use lattice_core::{
+    EntryBuilder, HeadInfo, Node, SigChain, Store, Uuid,
+    hlc::HLC,
+    proto::AuthorState,
+    sigchain::SigChainError,
+    store::StoreError,
+};
+use tokio::sync::{mpsc, oneshot};
+use std::thread::{self, JoinHandle};
+
+/// Commands sent to the store actor
+pub enum StoreCmd {
+    Get {
+        key: Vec<u8>,
+        resp: oneshot::Sender<Result<Option<Vec<u8>>, StoreError>>,
+    },
+    GetHeads {
+        key: Vec<u8>,
+        resp: oneshot::Sender<Result<Vec<HeadInfo>, StoreError>>,
+    },
+    List {
+        resp: oneshot::Sender<Result<Vec<(Vec<u8>, Vec<u8>)>, StoreError>>,
+    },
+    Put {
+        key: Vec<u8>,
+        value: Vec<u8>,
+        resp: oneshot::Sender<Result<u64, StoreActorError>>,
+    },
+    Delete {
+        key: Vec<u8>,
+        resp: oneshot::Sender<Result<u64, StoreActorError>>,
+    },
+    LogSeq {
+        resp: oneshot::Sender<u64>,
+    },
+    AppliedSeq {
+        resp: oneshot::Sender<Result<u64, StoreError>>,
+    },
+    AuthorState {
+        author: [u8; 32],
+        resp: oneshot::Sender<Result<Option<AuthorState>, StoreError>>,
+    },
+    Shutdown,
+}
+
+#[derive(Debug)]
+pub enum StoreActorError {
+    Store(StoreError),
+    SigChain(SigChainError),
+}
+
+impl From<StoreError> for StoreActorError {
+    fn from(e: StoreError) -> Self {
+        StoreActorError::Store(e)
+    }
+}
+
+impl From<SigChainError> for StoreActorError {
+    fn from(e: SigChainError) -> Self {
+        StoreActorError::SigChain(e)
+    }
+}
+
+impl std::fmt::Display for StoreActorError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            StoreActorError::Store(e) => write!(f, "Store error: {}", e),
+            StoreActorError::SigChain(e) => write!(f, "SigChain error: {}", e),
+        }
+    }
+}
+
+impl std::error::Error for StoreActorError {}
+
+/// The store actor - runs in its own thread, owns Store and SigChain
+pub struct StoreActor {
+    store_id: Uuid,
+    store: Store,
+    sigchain: SigChain,
+    node: Node,
+    rx: mpsc::Receiver<StoreCmd>,
+}
+
+impl StoreActor {
+    /// Create a new store actor (but don't start the thread yet)
+    pub fn new(
+        store_id: Uuid,
+        store: Store,
+        sigchain: SigChain,
+        node: Node,
+        rx: mpsc::Receiver<StoreCmd>,
+    ) -> Self {
+        Self {
+            store_id,
+            store,
+            sigchain,
+            node,
+            rx,
+        }
+    }
+
+    /// Run the actor loop - processes commands until Shutdown received
+    /// Uses blocking_recv since redb is sync and we run in spawn_blocking
+    pub fn run(mut self) {
+        while let Some(cmd) = self.rx.blocking_recv() {
+            match cmd {
+                StoreCmd::Get { key, resp } => {
+                    let _ = resp.send(self.store.get(&key));
+                }
+                StoreCmd::GetHeads { key, resp } => {
+                    let _ = resp.send(self.store.get_heads(&key));
+                }
+                StoreCmd::List { resp } => {
+                    let _ = resp.send(self.store.list_all());
+                }
+                StoreCmd::Put { key, value, resp } => {
+                    let result = self.do_put(&key, &value);
+                    let _ = resp.send(result);
+                }
+                StoreCmd::Delete { key, resp } => {
+                    let result = self.do_delete(&key);
+                    let _ = resp.send(result);
+                }
+                StoreCmd::LogSeq { resp } => {
+                    let _ = resp.send(self.sigchain.len());
+                }
+                StoreCmd::AppliedSeq { resp } => {
+                    let author = self.node.public_key_bytes();
+                    let result = self.store.author_state(&author)
+                        .map(|s| s.map(|a| a.seq).unwrap_or(0));
+                    let _ = resp.send(result);
+                }
+                StoreCmd::AuthorState { author, resp } => {
+                    let _ = resp.send(self.store.author_state(&author));
+                }
+                StoreCmd::Shutdown => {
+                    break;
+                }
+            }
+        }
+    }
+
+    fn do_put(&mut self, key: &[u8], value: &[u8]) -> Result<u64, StoreActorError> {
+        let heads = self.store.get_heads(key)?;
+        
+        // Idempotency check (pure function)
+        if !Store::needs_put(&heads, value) {
+            return Ok(self.sigchain.len());  // Idempotent, no new entry
+        }
+        
+        let parent_hashes: Vec<Vec<u8>> = heads.iter().map(|h| h.hash.clone()).collect();
+        self.commit_entry(parent_hashes, |b| b.put(key.to_vec(), value.to_vec()))
+    }
+
+    fn do_delete(&mut self, key: &[u8]) -> Result<u64, StoreActorError> {
+        let heads = self.store.get_heads(key)?;
+        
+        // Idempotency check (pure function)
+        if !Store::needs_delete(&heads) {
+            return Ok(self.sigchain.len());  // Idempotent, no new entry
+        }
+        
+        let parent_hashes: Vec<Vec<u8>> = heads.iter().map(|h| h.hash.clone()).collect();
+        self.commit_entry(parent_hashes, |b| b.delete(key.to_vec()))
+    }
+
+    fn commit_entry<F>(&mut self, parent_hashes: Vec<Vec<u8>>, build: F) -> Result<u64, StoreActorError>
+    where
+        F: FnOnce(EntryBuilder) -> EntryBuilder,
+    {
+        let seq = self.sigchain.len() + 1;
+        let prev_hash = self.sigchain.last_hash();
+
+        let builder = EntryBuilder::new(seq, HLC::now())
+            .store_id(self.store_id.as_bytes().to_vec())
+            .prev_hash(prev_hash.to_vec())
+            .parent_hashes(parent_hashes);
+        let entry = build(builder).sign(&self.node);
+
+        self.sigchain.append(&entry)?;
+        self.store.apply_entry(&entry)?;
+
+        Ok(seq)
+    }
+}
+
+/// Spawn a store actor in a new thread, returns (sender, join_handle)
+/// Uses std::thread since redb is blocking
+pub fn spawn_store_actor(
+    store_id: Uuid,
+    store: Store,
+    sigchain: SigChain,
+    node: Node,
+) -> (mpsc::Sender<StoreCmd>, JoinHandle<()>) {
+    let (tx, rx) = mpsc::channel(32);
+    let actor = StoreActor::new(store_id, store, sigchain, node, rx);
+    let handle = thread::spawn(move || actor.run());
+    (tx, handle)
+}

lattice-core/Cargo.toml

@@ -14,6 +14,8 @@ bytes = { workspace = true }
 dirs = { workspace = true }
 blake3 = { workspace = true }
 hex = { workspace = true }
+redb = { workspace = true }
+uuid = { workspace = true }
 
 [build-dependencies]
 prost-build = { workspace = true }

lattice-core/src/data_dir.rs

@@ -2,19 +2,26 @@
 //!
 //! Provides platform-specific paths for Lattice data storage:
 //! - `identity.key` — Ed25519 private key
-//! - `logs/` — Append-only log files per author
-//! - `state.db` — KV snapshot and indexes
+//! - `meta.db` — Global metadata (stores table)
+//! - `stores/{uuid}/logs/{author}.log` — Per-store, per-author logs
+//! - `stores/{uuid}/state.db` — Per-store KV state
 
 use std::path::{Path, PathBuf};
+use uuid::Uuid;
 
 const APP_NAME: &str = "lattice";
 
 /// Data directory configuration.
 ///
-/// Handles paths for:
-/// - `identity.key` — node's private key
-/// - `logs/{author_id}.log` — per-author log files
-/// - `state.db` — redb database
+/// Multi-store layout:
+/// ```text
+/// base/
+///   identity.key
+///   meta.db
+///   stores/{uuid}/
+///     logs/{author}.log
+///     state.db
+/// ```
 #[derive(Debug, Clone)]
 pub struct DataDir {
     base: PathBuf,
@@ -27,10 +34,6 @@ impl DataDir {
     }
 
     /// Create a DataDir using the platform-specific data directory.
-    ///
-    /// - Linux: `~/.local/share/lattice/`
-    /// - macOS: `~/Library/Application Support/lattice/`
-    /// - Windows: `C:\Users\<user>\AppData\Roaming\lattice\`
     pub fn default_location() -> Option<Self> {
         dirs::data_dir().map(|d| Self::new(d.join(APP_NAME)))
     }
@@ -45,25 +48,47 @@ impl DataDir {
         self.base.join("identity.key")
     }
 
-    /// Get the path to the logs directory.
-    pub fn logs_dir(&self) -> PathBuf {
-        self.base.join("logs")
+    /// Get the path to the global metadata database.
+    pub fn meta_db(&self) -> PathBuf {
+        self.base.join("meta.db")
     }
 
-    /// Get the path to a specific author's log file.
-    pub fn log_file(&self, author_id_hex: &str) -> PathBuf {
-        self.logs_dir().join(format!("{}.log", author_id_hex))
+    /// Get the path to the stores directory.
+    pub fn stores_dir(&self) -> PathBuf {
+        self.base.join("stores")
     }
 
-    /// Get the path to the state database.
-    pub fn state_db(&self) -> PathBuf {
-        self.base.join("state.db")
+    /// Get the path to a specific store's directory.
+    pub fn store_dir(&self, store_id: Uuid) -> PathBuf {
+        self.stores_dir().join(store_id.to_string())
     }
 
-    /// Ensure all required directories exist.
+    /// Get the path to a store's logs directory.
+    pub fn store_logs_dir(&self, store_id: Uuid) -> PathBuf {
+        self.store_dir(store_id).join("logs")
+    }
+
+    /// Get the path to a specific author's log file within a store.
+    pub fn store_log_file(&self, store_id: Uuid, author_id_hex: &str) -> PathBuf {
+        self.store_logs_dir(store_id).join(format!("{}.log", author_id_hex))
+    }
+
+    /// Get the path to a store's state database.
+    pub fn store_state_db(&self, store_id: Uuid) -> PathBuf {
+        self.store_dir(store_id).join("state.db")
+    }
+
+    /// Ensure base directory exists.
     pub fn ensure_dirs(&self) -> std::io::Result<()> {
         std::fs::create_dir_all(&self.base)?;
-        std::fs::create_dir_all(self.logs_dir())?;
+        std::fs::create_dir_all(self.stores_dir())?;
+        Ok(())
+    }
+
+    /// Ensure directories for a specific store exist.
+    pub fn ensure_store_dirs(&self, store_id: Uuid) -> std::io::Result<()> {
+        self.ensure_dirs()?;
+        std::fs::create_dir_all(self.store_logs_dir(store_id))?;
         Ok(())
     }
 }
@@ -83,29 +108,31 @@ mod tests {
         let dd = DataDir::new("/custom/path");
         assert_eq!(dd.base(), Path::new("/custom/path"));
         assert_eq!(dd.identity_key(), PathBuf::from("/custom/path/identity.key"));
-        assert_eq!(dd.logs_dir(), PathBuf::from("/custom/path/logs"));
-        assert_eq!(dd.state_db(), PathBuf::from("/custom/path/state.db"));
+        assert_eq!(dd.meta_db(), PathBuf::from("/custom/path/meta.db"));
+        assert_eq!(dd.stores_dir(), PathBuf::from("/custom/path/stores"));
     }
 
     #[test]
-    fn test_log_file_path() {
+    fn test_store_paths() {
         let dd = DataDir::new("/data");
-        let path = dd.log_file("abc123");
-        assert_eq!(path, PathBuf::from("/data/logs/abc123.log"));
+        let store_id = Uuid::parse_str("a1b2c3d4-e5f6-7890-abcd-ef1234567890").unwrap();
+        
+        assert_eq!(dd.store_dir(store_id), PathBuf::from("/data/stores/a1b2c3d4-e5f6-7890-abcd-ef1234567890"));
+        assert_eq!(dd.store_logs_dir(store_id), PathBuf::from("/data/stores/a1b2c3d4-e5f6-7890-abcd-ef1234567890/logs"));
+        assert_eq!(dd.store_log_file(store_id, "abc123"), PathBuf::from("/data/stores/a1b2c3d4-e5f6-7890-abcd-ef1234567890/logs/abc123.log"));
+        assert_eq!(dd.store_state_db(store_id), PathBuf::from("/data/stores/a1b2c3d4-e5f6-7890-abcd-ef1234567890/state.db"));
     }
 
     #[test]
     fn test_default_location_exists() {
         // On most systems, default_location should return Some
         let location = DataDir::default_location();
-        // Just verify it doesn't panic - actual path varies by platform
         assert!(location.is_some() || true);
     }
 
     #[test]
     fn test_default_impl() {
         let dd = DataDir::default();
-        // Should either be platform default or ./data fallback
         assert!(dd.base().to_str().is_some());
     }
 }

lattice-core/src/lib.rs

@@ -4,24 +4,27 @@
 //! - **Node**: Identity with Ed25519 keypair
 //! - **SigChain**: Append-only cryptographically signed log
 //! - **Entry**: Atomic operations in the log
-//! - **VectorClock**: Causality tracking for reconciliation
+//! - **SyncState**: Per-author sequence tracking for reconciliation
 //! - **HLC**: Hybrid Logical Clock for ordering
 //! - **Clock**: Time abstraction for testability
 //! - **Proto**: Generated protobuf types from lattice.proto
 //! - **DataDir**: Platform-specific data directory paths
 //! - **SignedEntry**: Entry creation, signing, and verification
 //! - **Log**: Append-only log file I/O
+//! - **Store**: Persistent KV state from log replay
 
 pub mod node;
 pub mod sigchain;
 pub mod entry;
-pub mod vector_clock;
+pub mod sync_state;
 pub mod hlc;
 pub mod clock;
 pub mod proto;
 pub mod data_dir;
 pub mod signed_entry;
 pub mod log;
+pub mod store;
+pub mod meta_store;
 
 // Constants
 /// Maximum size of a serialized SignedEntry (16 MB)
@@ -30,9 +33,13 @@ pub const MAX_ENTRY_SIZE: usize = 16 * 1024 * 1024;
 pub use node::Node;
 pub use sigchain::SigChain;
 pub use entry::Entry;
-pub use vector_clock::VectorClock;
+pub use sync_state::{SyncState, AuthorInfo, MissingRange};
 pub use hlc::HLC;
 pub use clock::{Clock, SystemClock, MockClock};
 pub use data_dir::DataDir;
 pub use signed_entry::{EntryBuilder, sign_entry, verify_signed_entry, hash_signed_entry};
-pub use log::{append_entry, read_entries, LogReader};
+pub use log::{append_entry, read_entries, read_entries_after, LogReader};
+pub use store::Store;
+pub use meta_store::MetaStore;
+pub use proto::HeadInfo;
+pub use uuid::Uuid;

lattice-core/src/meta_store.rs

@@ -0,0 +1,154 @@
+//! MetaStore - global node metadata in meta.db
+//!
+//! Tables:
+//! - stores: UUID → created_at (Unix ms)
+//! - meta: "root_store" → UUID (auto-opened on startup)
+
+use redb::{Database, ReadableTable, TableDefinition};
+use std::path::Path;
+use thiserror::Error;
+use uuid::Uuid;
+
+const STORES_TABLE: TableDefinition<&[u8], u64> = TableDefinition::new("stores");
+const META_TABLE: TableDefinition<&str, &[u8]> = TableDefinition::new("meta");
+
+const META_ROOT_STORE: &str = "root_store";
+
+#[derive(Error, Debug)]
+pub enum MetaStoreError {
+    #[error("Database error: {0}")]
+    Database(#[from] redb::DatabaseError),
+    
+    #[error("Table error: {0}")]
+    Table(#[from] redb::TableError),
+    
+    #[error("Transaction error: {0}")]
+    Transaction(#[from] redb::TransactionError),
+    
+    #[error("Commit error: {0}")]
+    Commit(#[from] redb::CommitError),
+    
+    #[error("Storage error: {0}")]
+    Storage(#[from] redb::StorageError),
+}
+
+/// Global metadata store
+pub struct MetaStore {
+    db: Database,
+}
+
+impl MetaStore {
+    /// Open or create meta.db at the given path
+    pub fn open(path: impl AsRef<Path>) -> Result<Self, MetaStoreError> {
+        let db = Database::create(path)?;
+        
+        // Ensure tables exist
+        let write_txn = db.begin_write()?;
+        {
+            let _ = write_txn.open_table(STORES_TABLE)?;
+            let _ = write_txn.open_table(META_TABLE)?;
+        }
+        write_txn.commit()?;
+        
+        Ok(Self { db })
+    }
+
+    /// Register a new store
+    pub fn add_store(&self, store_id: Uuid) -> Result<(), MetaStoreError> {
+        let write_txn = self.db.begin_write()?;
+        {
+            let mut table = write_txn.open_table(STORES_TABLE)?;
+            let now = std::time::SystemTime::now()
+                .duration_since(std::time::UNIX_EPOCH)
+                .unwrap()
+                .as_millis() as u64;
+            table.insert(store_id.as_bytes().as_slice(), now)?;
+        }
+        write_txn.commit()?;
+        Ok(())
+    }
+
+    /// List all registered stores
+    pub fn list_stores(&self) -> Result<Vec<Uuid>, MetaStoreError> {
+        let read_txn = self.db.begin_read()?;
+        let table = read_txn.open_table(STORES_TABLE)?;
+        
+        let mut stores = Vec::new();
+        for result in table.iter()? {
+            let (key, _created_at) = result?;
+            let bytes: [u8; 16] = key.value().try_into().unwrap_or([0; 16]);
+            stores.push(Uuid::from_bytes(bytes));
+        }
+        Ok(stores)
+    }
+
+    /// Get the root store ID (auto-opened on startup)
+    pub fn root_store(&self) -> Result<Option<Uuid>, MetaStoreError> {
+        let read_txn = self.db.begin_read()?;
+        let table = read_txn.open_table(META_TABLE)?;
+        
+        match table.get(META_ROOT_STORE)? {
+            Some(value) => {
+                let bytes: [u8; 16] = value.value().try_into().unwrap_or([0; 16]);
+                Ok(Some(Uuid::from_bytes(bytes)))
+            }
+            None => Ok(None),
+        }
+    }
+
+    /// Set the root store ID
+    pub fn set_root_store(&self, store_id: Uuid) -> Result<(), MetaStoreError> {
+        let write_txn = self.db.begin_write()?;
+        {
+            let mut table = write_txn.open_table(META_TABLE)?;
+            table.insert(META_ROOT_STORE, store_id.as_bytes().as_slice())?;
+        }
+        write_txn.commit()?;
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::env::temp_dir;
+
+    #[test]
+    fn test_add_and_list_stores() {
+        let path = temp_dir().join("meta_store_test.db");
+        let _ = std::fs::remove_file(&path);
+        
+        let meta = MetaStore::open(&path).unwrap();
+        
+        let id1 = Uuid::new_v4();
+        let id2 = Uuid::new_v4();
+        
+        meta.add_store(id1).unwrap();
+        meta.add_store(id2).unwrap();
+        
+        let stores = meta.list_stores().unwrap();
+        assert_eq!(stores.len(), 2);
+        assert!(stores.contains(&id1));
+        assert!(stores.contains(&id2));
+        
+        let _ = std::fs::remove_file(&path);
+    }
+
+    #[test]
+    fn test_root_store() {
+        let path = temp_dir().join("meta_store_root.db");
+        let _ = std::fs::remove_file(&path);
+        
+        let meta = MetaStore::open(&path).unwrap();
+        
+        // Initially no root store
+        assert_eq!(meta.root_store().unwrap(), None);
+        
+        let root = Uuid::new_v4();
+        meta.set_root_store(root).unwrap();
+        
+        assert_eq!(meta.root_store().unwrap(), Some(root));
+        
+        let _ = std::fs::remove_file(&path);
+    }
+}

lattice-core/src/node.rs

@@ -28,6 +28,7 @@ pub enum NodeError {
 ///
 /// Each node has an Ed25519 keypair used for signing sigchain entries
 /// and establishing trust within the network.
+#[derive(Clone)]
 pub struct Node {
     signing_key: SigningKey,
 }

lattice-core/src/proto.rs

@@ -31,7 +31,9 @@ mod tests {
     fn test_entry_with_ops() {
         let entry = Entry {
             version: 1,
+            store_id: vec![1u8; 16],
             prev_hash: vec![0u8; 32],
+            parent_hashes: vec![],
             seq: 5,
             timestamp: Some(Hlc {
                 wall_time: 1000,
@@ -40,7 +42,7 @@ mod tests {
             ops: vec![
                 Operation {
                     op_type: Some(operation::OpType::Put(PutOp {
-                        key: "/nodes/abc".to_string(),
+                        key: b"/nodes/abc".to_vec(),
                         value: b"hello".to_vec(),
                     })),
                 },

lattice-core/src/sigchain.rs

@@ -23,6 +23,9 @@ pub enum SigChainError {
     #[error("Wrong author: expected {expected}, got {got}")]
     WrongAuthor { expected: String, got: String },
     
+    #[error("Wrong store_id: expected {expected}, got {got}")]
+    WrongStoreId { expected: String, got: String },
+    
     #[error("Invalid sequence: expected {expected}, got {got}")]
     InvalidSequence { expected: u64, got: u64 },
     
@@ -34,11 +37,14 @@ pub enum SigChainError {
 }
 
 /// An append-only log where each entry is cryptographically signed
-/// and hash-linked to the previous entry.
+/// and hash-linked to the previous entry, scoped to a specific store.
 pub struct SigChain {
     /// Path to the log file
     log_path: PathBuf,
     
+    /// Store UUID (16 bytes)
+    store_id: [u8; 16],
+    
     /// Author's public key (32 bytes)
     author_id: [u8; 32],
     
@@ -50,10 +56,11 @@ pub struct SigChain {
 }
 
 impl SigChain {
-    /// Create a new empty sigchain for an author
-    pub fn new(log_path: impl AsRef<Path>, author_id: [u8; 32]) -> Self {
+    /// Create a new empty sigchain for a (store, author) pair
+    pub fn new(log_path: impl AsRef<Path>, store_id: [u8; 16], author_id: [u8; 32]) -> Self {
         Self {
             log_path: log_path.as_ref().to_path_buf(),
+            store_id,
             author_id,
             next_seq: 1,
             last_hash: [0u8; 32],
@@ -61,11 +68,11 @@ impl SigChain {
     }
     
     /// Load a sigchain from an existing log file
-    pub fn from_log(log_path: impl AsRef<Path>, author_id: [u8; 32]) -> Result<Self, SigChainError> {
+    pub fn from_log(log_path: impl AsRef<Path>, store_id: [u8; 16], author_id: [u8; 32]) -> Result<Self, SigChainError> {
         let log_path = log_path.as_ref().to_path_buf();
         let entries = read_entries(&log_path)?;
         
-        let mut chain = Self::new(&log_path, author_id);
+        let mut chain = Self::new(&log_path, store_id, author_id);
         
         for signed_entry in entries {
             // Verify signature
@@ -85,6 +92,18 @@ impl SigChain {
             // Decode Entry
             let entry = Entry::decode(&signed_entry.entry_bytes[..])?;
             
+            // Validate store_id
+            // Note: Empty/malformed store_id becomes [0u8;16], which fails validation
+            // against any real UUID store. This intentionally rejects legacy entries.
+            let entry_store: [u8; 16] = entry.store_id.clone().try_into()
+                .unwrap_or([0u8; 16]);
+            if entry_store != store_id {
+                return Err(SigChainError::WrongStoreId {
+                    expected: hex::encode(store_id),
+                    got: hex::encode(entry_store),
+                });
+            }
+            
             // Validate sequence
             if entry.seq != chain.next_seq {
                 return Err(SigChainError::InvalidSequence {
@@ -156,6 +175,18 @@ impl SigChain {
         // Decode entry
         let entry = Entry::decode(&signed_entry.entry_bytes[..])?;
         
+        // Validate store_id
+        // Note: Empty/malformed store_id becomes [0u8;16], which fails validation
+        // against any real UUID store. This intentionally rejects legacy entries.
+        let entry_store: [u8; 16] = entry.store_id.clone().try_into()
+            .unwrap_or([0u8; 16]);
+        if entry_store != self.store_id {
+            return Err(SigChainError::WrongStoreId {
+                expected: hex::encode(self.store_id),
+                got: hex::encode(entry_store),
+            });
+        }
+        
         // Validate sequence
         if entry.seq != self.next_seq {
             return Err(SigChainError::InvalidSequence {
@@ -201,6 +232,7 @@ impl SigChain {
         let hlc = HLC::now_with_clock(&SystemClock);
         
         let mut builder = EntryBuilder::new(self.next_seq, hlc)
+            .store_id(self.store_id.to_vec())
             .prev_hash(self.last_hash.to_vec());
         
         // Add operations
@@ -230,12 +262,14 @@ mod tests {
         temp_dir().join(format!("lattice_sigchain_test_{}.log", name))
     }
 
+    const TEST_STORE: [u8; 16] = [1u8; 16];
+
     #[test]
     fn test_new_sigchain() {
         let path = temp_log_path("new");
         let author = [1u8; 32];
         
-        let chain = SigChain::new(&path, author);
+        let chain = SigChain::new(&path, TEST_STORE, author);
         
         assert_eq!(chain.author_id(), &author);
         assert_eq!(chain.next_seq(), 1);
@@ -251,10 +285,11 @@ mod tests {
         
         let node = Node::generate();
         let author = node.public_key_bytes();
-        let mut chain = SigChain::new(&path, author);
+        let mut chain = SigChain::new(&path, TEST_STORE, author);
         
         let clock = MockClock::new(1000);
         let entry = EntryBuilder::new(1, HLC::now_with_clock(&clock))
+            .store_id(TEST_STORE.to_vec())
             .prev_hash([0u8; 32].to_vec())
             .put("/key", b"value".to_vec())
             .sign(&node);
@@ -275,11 +310,12 @@ mod tests {
         
         let node = Node::generate();
         let author = node.public_key_bytes();
-        let mut chain = SigChain::new(&path, author);
+        let mut chain = SigChain::new(&path, TEST_STORE, author);
         let clock = MockClock::new(1000);
         
         for i in 1..=3 {
             let entry = EntryBuilder::new(i, HLC::now_with_clock(&clock))
+                .store_id(TEST_STORE.to_vec())
                 .prev_hash(chain.last_hash.to_vec())
                 .put(format!("/key/{}", i), format!("value{}", i).into_bytes())
                 .sign(&node);
@@ -303,9 +339,10 @@ mod tests {
         
         // Write some entries
         {
-            let mut chain = SigChain::new(&path, author);
+            let mut chain = SigChain::new(&path, TEST_STORE, author);
             for i in 1..=3 {
                 let entry = EntryBuilder::new(i, HLC::now_with_clock(&clock))
+                    .store_id(TEST_STORE.to_vec())
                     .prev_hash(chain.last_hash.to_vec())
                     .put("/key", b"val".to_vec())
                     .sign(&node);
@@ -314,7 +351,7 @@ mod tests {
         }
         
         // Reload from log
-        let chain = SigChain::from_log(&path, author).unwrap();
+        let chain = SigChain::from_log(&path, TEST_STORE, author).unwrap();
         
         assert_eq!(chain.len(), 3);
         assert_eq!(chain.next_seq(), 4);
@@ -329,11 +366,12 @@ mod tests {
         
         let node = Node::generate();
         let author = node.public_key_bytes();
-        let mut chain = SigChain::new(&path, author);
+        let mut chain = SigChain::new(&path, TEST_STORE, author);
         let clock = MockClock::new(1000);
         
         // Try to append with wrong seq (2 instead of 1)
         let entry = EntryBuilder::new(2, HLC::now_with_clock(&clock))
+            .store_id(TEST_STORE.to_vec())
             .prev_hash([0u8; 32].to_vec())
             .put("/key", b"val".to_vec())
             .sign(&node);
@@ -352,11 +390,12 @@ mod tests {
         
         let node = Node::generate();
         let author = node.public_key_bytes();
-        let mut chain = SigChain::new(&path, author);
+        let mut chain = SigChain::new(&path, TEST_STORE, author);
         let clock = MockClock::new(1000);
         
         // First entry
         let entry1 = EntryBuilder::new(1, HLC::now_with_clock(&clock))
+            .store_id(TEST_STORE.to_vec())
             .prev_hash([0u8; 32].to_vec())
             .put("/key", b"v1".to_vec())
             .sign(&node);
@@ -364,6 +403,7 @@ mod tests {
         
         // Second entry with wrong prev_hash
         let entry2 = EntryBuilder::new(2, HLC::now_with_clock(&clock))
+            .store_id(TEST_STORE.to_vec())
             .prev_hash([99u8; 32].to_vec()) // Wrong!
             .put("/key", b"v2".to_vec())
             .sign(&node);
@@ -382,11 +422,12 @@ mod tests {
         
         let node = Node::generate();
         let other_author = [99u8; 32]; // Different author
-        let mut chain = SigChain::new(&path, other_author);
+        let mut chain = SigChain::new(&path, TEST_STORE, other_author);
         let clock = MockClock::new(1000);
         
         // Entry signed by node but chain expects other_author
         let entry = EntryBuilder::new(1, HLC::now_with_clock(&clock))
+            .store_id(TEST_STORE.to_vec())
             .prev_hash([0u8; 32].to_vec())
             .put("/key", b"val".to_vec())
             .sign(&node);
@@ -405,12 +446,12 @@ mod tests {
         
         let node = Node::generate();
         let author = node.public_key_bytes();
-        let mut chain = SigChain::new(&path, author);
+        let mut chain = SigChain::new(&path, TEST_STORE, author);
         
         let ops = vec![
             Operation {
                 op_type: Some(operation::OpType::Put(PutOp {
-                    key: "/test".to_string(),
+                    key: b"/test".to_vec(),
                     value: b"hello".to_vec(),
                 })),
             },
@@ -427,4 +468,37 @@ mod tests {
         
         std::fs::remove_file(&path).ok();
     }
+
+    #[test]
+    fn test_reject_wrong_store_id() {
+        let path_a = temp_log_path("storeid_a");
+        let path_b = temp_log_path("storeid_b");
+        std::fs::remove_file(&path_a).ok();
+        std::fs::remove_file(&path_b).ok();
+        
+        let node = Node::generate();
+        let author = node.public_key_bytes();
+        let clock = MockClock::new(1000);
+        
+        let store_a = [0xAAu8; 16];
+        let store_b = [0xBBu8; 16];
+        
+        // Create valid entry for store A
+        let mut chain_a = SigChain::new(&path_a, store_a, author);
+        let entry = EntryBuilder::new(1, HLC::now_with_clock(&clock))
+            .store_id(store_a.to_vec())
+            .prev_hash([0u8; 32].to_vec())
+            .put("/key", b"val".to_vec())
+            .sign(&node);
+        chain_a.append(&entry).unwrap();
+        
+        // Try to replay that entry into store B's chain
+        let mut chain_b = SigChain::new(&path_b, store_b, author);
+        let result = chain_b.append(&entry);
+        
+        assert!(matches!(result, Err(SigChainError::WrongStoreId { .. })));
+        
+        std::fs::remove_file(&path_a).ok();
+        std::fs::remove_file(&path_b).ok();
+    }
 }

lattice-core/src/signed_entry.rs

@@ -32,7 +32,9 @@ pub enum EntryError {
 /// Builder for creating Entry messages
 pub struct EntryBuilder {
     version: u32,
+    store_id: Vec<u8>,
     prev_hash: Vec<u8>,
+    parent_hashes: Vec<Vec<u8>>,
     seq: u64,
     timestamp: HLC,
     ops: Vec<Operation>,
@@ -43,21 +45,35 @@ impl EntryBuilder {
     pub fn new(seq: u64, timestamp: HLC) -> Self {
         Self {
             version: 1,
-            prev_hash: vec![0u8; 32], // Genesis or will be set
+            store_id: Vec::new(),
+            prev_hash: vec![0u8; 32],
+            parent_hashes: Vec::new(),
             seq,
             timestamp,
             ops: Vec::new(),
         }
     }
 
-    /// Set the previous entry hash (for chaining)
+    /// Set the store ID (16-byte UUID)
+    pub fn store_id(mut self, id: impl Into<Vec<u8>>) -> Self {
+        self.store_id = id.into();
+        self
+    }
+
+    /// Set the previous entry hash (for sigchain linking)
     pub fn prev_hash(mut self, hash: impl Into<Vec<u8>>) -> Self {
         self.prev_hash = hash.into();
         self
     }
 
+    /// Set the parent hashes (for DAG ancestry)
+    pub fn parent_hashes(mut self, hashes: Vec<Vec<u8>>) -> Self {
+        self.parent_hashes = hashes;
+        self
+    }
+
     /// Add a Put operation
-    pub fn put(mut self, key: impl Into<String>, value: impl Into<Vec<u8>>) -> Self {
+    pub fn put(mut self, key: impl Into<Vec<u8>>, value: impl Into<Vec<u8>>) -> Self {
         self.ops.push(Operation {
             op_type: Some(operation::OpType::Put(PutOp {
                 key: key.into(),
@@ -68,7 +84,7 @@ impl EntryBuilder {
     }
 
     /// Add a Delete operation
-    pub fn delete(mut self, key: impl Into<String>) -> Self {
+    pub fn delete(mut self, key: impl Into<Vec<u8>>) -> Self {
         self.ops.push(Operation {
             op_type: Some(operation::OpType::Delete(DeleteOp {
                 key: key.into(),
@@ -87,7 +103,9 @@ impl EntryBuilder {
     pub fn build(self) -> Entry {
         Entry {
             version: self.version,
+            store_id: self.store_id,
             prev_hash: self.prev_hash,
+            parent_hashes: self.parent_hashes,
             seq: self.seq,
             timestamp: Some(Hlc {
                 wall_time: self.timestamp.wall_time,

lattice-core/src/sync_state.rs

@@ -0,0 +1,179 @@
+//! Sync state for causality tracking and reconciliation
+
+use std::collections::HashMap;
+
+/// Author ID type (32-byte Ed25519 public key)
+pub type Author = [u8; 32];
+
+/// Per-author sync information (seq + hash for resume).
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct AuthorInfo {
+    pub seq: u64,
+    pub hash: [u8; 32],
+}
+
+/// Sync state tracking per-author sequence numbers and hashes.
+///
+/// Used during reconciliation to identify missing entries between peers.
+/// Each author's highest seen sequence number and hash is tracked.
+#[derive(Debug, Clone, Default)]
+pub struct SyncState {
+    authors: HashMap<Author, AuthorInfo>,
+}
+
+/// Describes entries needed from a peer for a specific author.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct MissingRange {
+    pub author: Author,
+    pub from_seq: u64,        // exclusive - we have up to this
+    pub from_hash: [u8; 32],  // hash to resume reading after
+    pub to_seq: u64,          // inclusive - peer has up to this
+}
+
+impl SyncState {
+    /// Create a new empty sync state.
+    pub fn new() -> Self {
+        Self {
+            authors: HashMap::new(),
+        }
+    }
+
+    /// Get the info for an author (returns None if not present).
+    pub fn get(&self, author: &Author) -> Option<&AuthorInfo> {
+        self.authors.get(author)
+    }
+
+    /// Get the sequence number for an author (returns 0 if not present).
+    pub fn seq(&self, author: &Author) -> u64 {
+        self.authors.get(author).map(|i| i.seq).unwrap_or(0)
+    }
+
+    /// Set the info for an author.
+    pub fn set(&mut self, author: Author, seq: u64, hash: [u8; 32]) {
+        self.authors.insert(author, AuthorInfo { seq, hash });
+    }
+
+    /// Get all authors and their info.
+    pub fn authors(&self) -> &HashMap<Author, AuthorInfo> {
+        &self.authors
+    }
+
+    /// Compute what entries we're missing compared to a peer's state.
+    ///
+    /// Returns ranges of entries we need from the peer.
+    /// Each range includes the hash to resume reading after.
+    pub fn diff(&self, peer: &SyncState) -> Vec<MissingRange> {
+        let mut missing = Vec::new();
+
+        for (author, peer_info) in peer.authors() {
+            let my_seq = self.seq(author);
+            if peer_info.seq > my_seq {
+                // We need entries from my_seq+1 to peer_info.seq
+                // Use our hash (or zero if we have nothing) as resume point
+                let from_hash = self.get(author)
+                    .map(|i| i.hash)
+                    .unwrap_or([0u8; 32]);
+                
+                missing.push(MissingRange {
+                    author: *author,
+                    from_seq: my_seq,
+                    from_hash,
+                    to_seq: peer_info.seq,
+                });
+            }
+        }
+
+        missing
+    }
+
+    /// Merge another sync state into this one (take max seq per author).
+    pub fn merge(&mut self, other: &SyncState) {
+        for (author, info) in other.authors() {
+            let my_seq = self.seq(author);
+            if info.seq > my_seq {
+                self.set(*author, info.seq, info.hash);
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_diff_empty() {
+        let a = SyncState::new();
+        let b = SyncState::new();
+        assert!(a.diff(&b).is_empty());
+    }
+
+    #[test]
+    fn test_diff_peer_ahead() {
+        let mut a = SyncState::new();
+        let mut b = SyncState::new();
+        
+        let author = [1u8; 32];
+        let hash_a = [0xAA; 32];
+        let hash_b = [0xBB; 32];
+        
+        a.set(author, 5, hash_a);
+        b.set(author, 10, hash_b);
+
+        let missing = a.diff(&b);
+        assert_eq!(missing.len(), 1);
+        assert_eq!(missing[0].author, author);
+        assert_eq!(missing[0].from_seq, 5);
+        assert_eq!(missing[0].from_hash, hash_a);  // Resume after our hash
+        assert_eq!(missing[0].to_seq, 10);
+    }
+
+    #[test]
+    fn test_diff_i_am_ahead() {
+        let mut a = SyncState::new();
+        let mut b = SyncState::new();
+        
+        let author = [1u8; 32];
+        a.set(author, 10, [0xAA; 32]);
+        b.set(author, 5, [0xBB; 32]);
+
+        // I'm ahead, so I don't need anything from peer
+        let missing = a.diff(&b);
+        assert!(missing.is_empty());
+    }
+
+    #[test]
+    fn test_diff_new_author() {
+        let a = SyncState::new();
+        let mut b = SyncState::new();
+        
+        let author = [2u8; 32];
+        b.set(author, 3, [0xBB; 32]);
+
+        // Peer has author I don't have
+        let missing = a.diff(&b);
+        assert_eq!(missing.len(), 1);
+        assert_eq!(missing[0].from_seq, 0);
+        assert_eq!(missing[0].from_hash, [0u8; 32]);  // Zero hash = read from start
+        assert_eq!(missing[0].to_seq, 3);
+    }
+
+    #[test]
+    fn test_merge() {
+        let mut a = SyncState::new();
+        let mut b = SyncState::new();
+        
+        let author1 = [1u8; 32];
+        let author2 = [2u8; 32];
+        
+        a.set(author1, 10, [0xA1; 32]);
+        a.set(author2, 5, [0xA2; 32]);
+        
+        b.set(author1, 5, [0xB1; 32]);   // a is ahead
+        b.set(author2, 8, [0xB2; 32]);   // b is ahead
+
+        a.merge(&b);
+        assert_eq!(a.seq(&author1), 10);  // kept a's value
+        assert_eq!(a.seq(&author2), 8);   // took b's value
+    }
+}

lattice-core/src/vector_clock.rs

@@ -1,41 +0,0 @@
-//! Vector clocks for causality tracking
-
-use std::collections::HashMap;
-
-/// A vector clock for tracking "how much" of each node's log has been seen.
-///
-/// Used during reconciliation to identify missing entries between peers.
-pub struct VectorClock {
-    clocks: HashMap<[u8; 32], u64>,
-}
-
-impl VectorClock {
-    /// Create a new empty vector clock.
-    pub fn new() -> Self {
-        Self {
-            clocks: HashMap::new(),
-        }
-    }
-
-    /// Get the clock value for a node (returns 0 if not present).
-    pub fn get(&self, node_id: &[u8; 32]) -> u64 {
-        self.clocks.get(node_id).copied().unwrap_or(0)
-    }
-
-    /// Set the clock value for a node.
-    pub fn set(&mut self, node_id: [u8; 32], value: u64) {
-        self.clocks.insert(node_id, value);
-    }
-
-    /// Increment the clock for a node.
-    pub fn increment(&mut self, node_id: [u8; 32]) {
-        let current = self.get(&node_id);
-        self.set(node_id, current + 1);
-    }
-}
-
-impl Default for VectorClock {
-    fn default() -> Self {
-        Self::new()
-    }
-}

proto/lattice.proto

@@ -20,15 +20,42 @@ message Entry {
   // Versioning allows us to change the format radically later if needed
   uint32 version = 1;
 
+  // Store this entry belongs to (16-byte UUID)
+  bytes store_id = 6;
+
   // Ordering Metadata
-  bytes prev_hash = 2;   // Link to previous entry (32 bytes)
+  bytes prev_hash = 2;   // Link to previous sigchain entry (32 bytes)
   uint64 seq = 3;        // Monotonic sequence number
   HLC timestamp = 4;     // Hybrid Logical Clock
 
+  // DAG ancestry: hashes of entries this supersedes (separate from sigchain)
+  repeated bytes parent_hashes = 7;
+
   // The Batch of Operations
   repeated Operation ops = 5;
 }
 
+// HeadInfo: a tip/head in the DAG for a key
+message HeadInfo {
+  bytes value = 1;       // The value at this head
+  uint64 hlc = 2;        // Combined HLC for ordering (wall_time_ms << 16 | counter)
+  bytes author = 3;      // Author's public key (32 bytes)
+  bytes hash = 4;        // Hash of the SignedEntry that created this head
+  bool tombstone = 5;    // True if this head represents a delete
+}
+
+// HeadList: wrapper for storing multiple heads per key in state.db
+message HeadList {
+  repeated HeadInfo heads = 1;
+}
+
+// AuthorState: tracks last applied entry per author for replay optimization
+message AuthorState {
+  uint64 seq = 1;        // Last applied seq for this author's sigchain
+  bytes hash = 2;        // Hash of last applied entry
+  uint64 log_offset = 3; // Byte offset in log file for fast resume
+}
+
 // Hybrid Logical Clock
 message HLC {
   uint64 wall_time = 1;  // Unix timestamp (ms)
@@ -46,12 +73,12 @@ message Operation {
 }
 
 message PutOp {
-  string key = 1;
-  bytes value = 2; // Raw bytes allows storing images, JSON, binary, etc.
+  bytes key = 1;
+  bytes value = 2;
 }
 
 message DeleteOp {
-  string key = 1;
+  bytes key = 1;
 }
 
 // 4. The Sync Handshake (Vector Clocks)