# Logseq Blocks Support - Architecture Design

## Problem Statement

Logseq uses **content blocks** as the fundamental unit of information, not full documents. Each block can have:

- **Properties**: `#card`, `TODO`, `DONE`, custom properties
- **Tags**: Inline tags like `#flashcard`, `#important`
- **References**: Block references `((block-id))`, page references `[[page]]`
- **Nesting**: Outliner-style hierarchy (parent-child blocks)
- **Metadata**: Block-level properties (unlike page-level frontmatter)

**Current KB limitation**: Nodes only have `content: String` (flat markdown). Importing from Logseq loses block structure and properties.

**Requirement**: Support round-trip import/export with full block fidelity:

```text
Logseq Graph → KOGRAL Import → KOGRAL Storage → KOGRAL Export → Logseq Graph
     (blocks preserved)                    (blocks preserved)
```

## Use Cases

### 1. Flashcards (`#card`)

**Logseq**:

```markdown
- What is Rust's ownership model? #card
  - Rust uses ownership, borrowing, and lifetimes
  - Three rules: one owner, many borrows XOR one mutable
```

**KB needs to preserve**:
- Block with `#card` property
- Nested answer blocks
- Ability to query all cards

### 2. Task Tracking (`TODO`/`DONE`)

**Logseq**:

```markdown
- TODO Implement block parser #rust
  - DONE Research block structure
  - TODO Write parser tests
```

**KB needs to preserve**:
- Task status per block
- Hierarchical task breakdown
- Tags on tasks

### 3. Block References

**Logseq**:

```markdown
- Core concept: ((block-uuid-123))
  - See also: [[Related Page]]
```

**KB needs to preserve**:
- Block-to-block links (not just page-to-page)
- UUID references

### 4. Block Properties

**Logseq**:

```markdown
- This is a block with properties
  property1:: value1
  property2:: value2
```

**KB needs to preserve**:
- Custom key-value properties per block
- Property inheritance/override

## Design Options

### Option A: Blocks as First-Class Data Structure

**Add `blocks` field to Node**:

```rust
pub struct Node {
    // ... existing fields ...
    pub content: String,              // Backward compat: flat markdown
    pub blocks: Option<Vec<Block>>,   // NEW: Structured blocks
}

pub struct Block {
    pub id: String,                   // UUID or auto-generated
    pub content: String,              // Block text
    pub properties: BlockProperties,  // Tags, status, custom props
    pub children: Vec<Block>,         // Nested blocks
    pub created: DateTime<Utc>,
    pub modified: DateTime<Utc>,
}

pub struct BlockProperties {
    pub tags: Vec<String>,            // #card, #important
    pub status: Option<TaskStatus>,   // TODO, DONE, WAITING
    pub custom: HashMap<String, String>, // property:: value
}

pub enum TaskStatus {
    Todo,
    Doing,
    Done,
    Waiting,
    Cancelled,
}
```

**Pros**:
- ✅ Type-safe, explicit structure
- ✅ Queryable (find all #card blocks)
- ✅ Preserves hierarchy
- ✅ Supports block-level operations

**Cons**:
- ❌ Adds complexity to Node
- ❌ Dual representation (content + blocks)
- ❌ Requires migration of existing data

### Option B: Parser-Only Approach

**Keep `content: String`, parse blocks on-demand**:

```rust
pub struct BlockParser;

impl BlockParser {
    // Parse markdown content into block structure
    fn parse(content: &str) -> Vec<Block>;

    // Serialize blocks back to markdown
    fn serialize(blocks: &[Block]) -> String;
}

// Usage
let blocks = BlockParser::parse(&node.content);
let filtered = blocks.iter().filter(|b| b.properties.tags.contains("card"));
```

**Pros**:
- ✅ No schema changes
- ✅ Backward compatible
- ✅ Simple storage (still just String)

**Cons**:
- ❌ Parse overhead on every access
- ❌ Can't query blocks in database (SurrealDB)
- ❌ Harder to index/search blocks

### Option C: Hybrid Approach (RECOMMENDED)

**Combine both: structured storage + lazy parsing**:

```rust
pub struct Node {
    // ... existing fields ...
    pub content: String,              // Source of truth (markdown)

    #[serde(skip_serializing_if = "Option::is_none")]
    pub blocks: Option<Vec<Block>>,   // Cached structure (parsed)
}

impl Node {
    // Parse blocks from content if not already cached
    pub fn get_blocks(&mut self) -> &Vec<Block> {
        if self.blocks.is_none() {
            self.blocks = Some(BlockParser::parse(&self.content));
        }
        self.blocks.as_ref().unwrap()
    }

    // Update content from blocks (when blocks modified)
    pub fn sync_blocks_to_content(&mut self) {
        if let Some(ref blocks) = self.blocks {
            self.content = BlockParser::serialize(blocks);
        }
    }
}
```

**Storage Strategy**:

1. **Filesystem** - Store as markdown (Logseq compatible):

   ```markdown
   - Block 1 #card
     - Nested block
   - Block 2 TODO
   ```

2. **SurrealDB** - Store both:

   ```sql
   DEFINE TABLE block SCHEMAFULL;
   DEFINE FIELD node_id ON block TYPE record(node);
   DEFINE FIELD block_id ON block TYPE string;
   DEFINE FIELD content ON block TYPE string;
   DEFINE FIELD properties ON block TYPE object;
   DEFINE FIELD parent_id ON block TYPE option<string>;

   -- Index for queries
   DEFINE INDEX block_tags ON block COLUMNS properties.tags;
   DEFINE INDEX block_status ON block COLUMNS properties.status;
   ```

**Pros**:
- ✅ Best of both worlds
- ✅ Filesystem stays Logseq-compatible
- ✅ SurrealDB can query blocks
- ✅ Lazy parsing (only when needed)
- ✅ Backward compatible

**Cons**:
- ⚠️ Need to keep content/blocks in sync
- ⚠️ More complex implementation

## Recommended Implementation

**Phase 1: Data Model**

```rust
// crates/kogral-core/src/models/block.rs

use chrono::{DateTime, Utc};
use serde::{Deserialize, Serialize};
use std::collections::HashMap;

/// A content block (Logseq-style)
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct Block {
    /// Unique block identifier (UUID)
    pub id: String,

    /// Block content (markdown text, excluding nested blocks)
    pub content: String,

    /// Block properties (tags, status, custom)
    pub properties: BlockProperties,

    /// Child blocks (nested hierarchy)
    #[serde(default)]
    pub children: Vec<Block>,

    /// Creation timestamp
    pub created: DateTime<Utc>,

    /// Last modification timestamp
    pub modified: DateTime<Utc>,

    /// Parent block ID (if nested)
    #[serde(skip_serializing_if = "Option::is_none")]
    pub parent_id: Option<String>,
}

/// Block-level properties
#[derive(Debug, Clone, Default, Serialize, Deserialize)]
pub struct BlockProperties {
    /// Tags (e.g., #card, #important)
    #[serde(default)]
    pub tags: Vec<String>,

    /// Task status (TODO, DONE, etc.)
    #[serde(skip_serializing_if = "Option::is_none")]
    pub status: Option<TaskStatus>,

    /// Custom properties (property:: value)
    #[serde(default)]
    pub custom: HashMap<String, String>,

    /// Block references ((uuid))
    #[serde(default)]
    pub block_refs: Vec<String>,

    /// Page references ([[page]])
    #[serde(default)]
    pub page_refs: Vec<String>,
}

/// Task status for TODO blocks
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "UPPERCASE")]
pub enum TaskStatus {
    Todo,
    Doing,
    Done,
    Later,
    Now,
    Waiting,
    Cancelled,
}

impl Block {
    /// Create a new block with content
    pub fn new(content: String) -> Self {
        use uuid::Uuid;
        Self {
            id: Uuid::new_v4().to_string(),
            content,
            properties: BlockProperties::default(),
            children: Vec::new(),
            created: Utc::now(),
            modified: Utc::now(),
            parent_id: None,
        }
    }

    /// Add a child block
    pub fn add_child(&mut self, mut child: Block) {
        child.parent_id = Some(self.id.clone());
        self.children.push(child);
        self.modified = Utc::now();
    }

    /// Add a tag to this block
    pub fn add_tag(&mut self, tag: String) {
        if !self.properties.tags.contains(&tag) {
            self.properties.tags.push(tag);
            self.modified = Utc::now();
        }
    }

    /// Set task status
    pub fn set_status(&mut self, status: TaskStatus) {
        self.properties.status = Some(status);
        self.modified = Utc::now();
    }

    /// Get all blocks (self + descendants) as flat list
    pub fn flatten(&self) -> Vec<&Block> {
        let mut result = vec![self];
        for child in &self.children {
            result.extend(child.flatten());
        }
        result
    }

    /// Find block by ID in tree
    pub fn find(&self, id: &str) -> Option<&Block> {
        if self.id == id {
            return Some(self);
        }
        for child in &self.children {
            if let Some(found) = child.find(id) {
                return Some(found);
            }
        }
        None
    }
}
```

**Phase 2: Update Node Model**

```rust
// crates/kogral-core/src/models.rs (modifications)

use crate::models::block::Block;

pub struct Node {
    // ... existing fields ...
    pub content: String,

    /// Structured blocks (optional, parsed from content)
    #[serde(skip_serializing_if = "Option::is_none")]
    pub blocks: Option<Vec<Block>>,
}

impl Node {
    /// Get blocks, parsing from content if needed
    pub fn get_blocks(&mut self) -> Result<&Vec<Block>> {
        if self.blocks.is_none() {
            self.blocks = Some(crate::parser::BlockParser::parse(&self.content)?);
        }
        Ok(self.blocks.as_ref().unwrap())
    }

    /// Update content from blocks
    pub fn sync_blocks_to_content(&mut self) {
        if let Some(ref blocks) = self.blocks {
            self.content = crate::parser::BlockParser::serialize(blocks);
        }
    }

    /// Find all blocks with a specific tag
    pub fn find_blocks_by_tag(&mut self, tag: &str) -> Result<Vec<&Block>> {
        let blocks = self.get_blocks()?;
        let mut result = Vec::new();
        for block in blocks {
            for b in block.flatten() {
                if b.properties.tags.iter().any(|t| t == tag) {
                    result.push(b);
                }
            }
        }
        Ok(result)
    }

    /// Find all TODO blocks
    pub fn find_todos(&mut self) -> Result<Vec<&Block>> {
        let blocks = self.get_blocks()?;
        let mut result = Vec::new();
        for block in blocks {
            for b in block.flatten() {
                if matches!(b.properties.status, Some(TaskStatus::Todo)) {
                    result.push(b);
                }
            }
        }
        Ok(result)
    }
}
```

**Phase 3: Block Parser**

```rust
// crates/kogral-core/src/parser/block_parser.rs

use crate::models::block::{Block, BlockProperties, TaskStatus};
use regex::Regex;

pub struct BlockParser;

impl BlockParser {
    /// Parse markdown content into block structure
    ///
    /// Handles:
    /// - Outliner format (- prefix with indentation)
    /// - Tags (#card, #important)
    /// - Task status (TODO, DONE)
    /// - Properties (property:: value)
    /// - Block references (((uuid)))
    /// - Page references ([[page]])
    pub fn parse(content: &str) -> Result<Vec<Block>> {
        let mut blocks = Vec::new();
        let mut stack: Vec<(usize, Block)> = Vec::new(); // (indent_level, block)

        for line in content.lines() {
            // Detect indentation level
            let indent = count_indent(line);
            let trimmed = line.trim_start();

            // Skip empty lines
            if trimmed.is_empty() {
                continue;
            }

            // Parse block line
            if let Some(block_content) = trimmed.strip_prefix("- ") {
                let mut block = Self::parse_block_line(block_content)?;

                // Pop stack until we find parent level
                while let Some((level, _)) = stack.last() {
                    if *level < indent {
                        break;
                    }
                    stack.pop();
                }

                // Add as child to parent or as root
                if let Some((_, parent)) = stack.last_mut() {
                    parent.add_child(block.clone());
                } else {
                    blocks.push(block.clone());
                }

                stack.push((indent, block));
            }
        }

        Ok(blocks)
    }

    /// Parse a single block line (after "- " prefix)
    fn parse_block_line(line: &str) -> Result<Block> {
        let mut block = Block::new(String::new());
        let mut properties = BlockProperties::default();

        // Extract task status (TODO, DONE, etc.)
        let (status, remaining) = Self::extract_task_status(line);
        properties.status = status;

        // Extract tags (#card, #important)
        let (tags, remaining) = Self::extract_tags(remaining);
        properties.tags = tags;

        // Extract properties (property:: value)
        let (custom_props, remaining) = Self::extract_properties(remaining);
        properties.custom = custom_props;

        // Extract block references (((uuid)))
        let (block_refs, remaining) = Self::extract_block_refs(remaining);
        properties.block_refs = block_refs;

        // Extract page references ([[page]])
        let (page_refs, content) = Self::extract_page_refs(remaining);
        properties.page_refs = page_refs;

        block.content = content.trim().to_string();
        block.properties = properties;

        Ok(block)
    }

    /// Serialize blocks back to markdown
    pub fn serialize(blocks: &[Block]) -> String {
        let mut result = String::new();
        for block in blocks {
            Self::serialize_block(&mut result, block, 0);
        }
        result
    }

    fn serialize_block(output: &mut String, block: &Block, indent: usize) {
        // Write indent
        for _ in 0..indent {
            output.push_str("  ");
        }

        // Write prefix
        output.push_str("- ");

        // Write task status
        if let Some(status) = block.properties.status {
            output.push_str(&format!("{:?} ", status).to_uppercase());
        }

        // Write content
        output.push_str(&block.content);

        // Write tags
        for tag in &block.properties.tags {
            output.push_str(&format!(" #{}", tag));
        }

        // Write properties
        if !block.properties.custom.is_empty() {
            output.push('\n');
            for (key, value) in &block.properties.custom {
                for _ in 0..=indent {
                    output.push_str("  ");
                }
                output.push_str(&format!("{}:: {}\n", key, value));
            }
        }

        output.push('\n');

        // Write children recursively
        for child in &block.children {
            Self::serialize_block(output, child, indent + 1);
        }
    }

    // Helper methods for extraction
    fn extract_task_status(line: &str) -> (Option<TaskStatus>, &str) {
        let line = line.trim_start();
        if let Some(rest) = line.strip_prefix("TODO ") {
            (Some(TaskStatus::Todo), rest)
        } else if let Some(rest) = line.strip_prefix("DONE ") {
            (Some(TaskStatus::Done), rest)
        } else if let Some(rest) = line.strip_prefix("DOING ") {
            (Some(TaskStatus::Doing), rest)
        } else if let Some(rest) = line.strip_prefix("LATER ") {
            (Some(TaskStatus::Later), rest)
        } else if let Some(rest) = line.strip_prefix("NOW ") {
            (Some(TaskStatus::Now), rest)
        } else if let Some(rest) = line.strip_prefix("WAITING ") {
            (Some(TaskStatus::Waiting), rest)
        } else if let Some(rest) = line.strip_prefix("CANCELLED ") {
            (Some(TaskStatus::Cancelled), rest)
        } else {
            (None, line)
        }
    }

    fn extract_tags(line: &str) -> (Vec<String>, String) {
        let tag_regex = Regex::new(r"#(\w+)").unwrap();
        let mut tags = Vec::new();
        let mut result = line.to_string();

        for cap in tag_regex.captures_iter(line) {
            if let Some(tag) = cap.get(1) {
                tags.push(tag.as_str().to_string());
                result = result.replace(&format!("#{}", tag.as_str()), "");
            }
        }

        (tags, result.trim().to_string())
    }

    fn extract_properties(line: &str) -> (HashMap<String, String>, String) {
        let prop_regex = Regex::new(r"(\w+)::\s*([^\n]+)").unwrap();
        let mut props = HashMap::new();
        let mut result = line.to_string();

        for cap in prop_regex.captures_iter(line) {
            if let (Some(key), Some(value)) = (cap.get(1), cap.get(2)) {
                props.insert(key.as_str().to_string(), value.as_str().trim().to_string());
                result = result.replace(&cap[0], "");
            }
        }

        (props, result.trim().to_string())
    }

    fn extract_block_refs(line: &str) -> (Vec<String>, String) {
        let ref_regex = Regex::new(r"\(\(([^)]+)\)\)").unwrap();
        let mut refs = Vec::new();
        let mut result = line.to_string();

        for cap in ref_regex.captures_iter(line) {
            if let Some(uuid) = cap.get(1) {
                refs.push(uuid.as_str().to_string());
                result = result.replace(&cap[0], "");
            }
        }

        (refs, result.trim().to_string())
    }

    fn extract_page_refs(line: &str) -> (Vec<String>, String) {
        let page_regex = Regex::new(r"\[\[([^\]]+)\]\]").unwrap();
        let mut pages = Vec::new();
        let result = line.to_string();

        for cap in page_regex.captures_iter(line) {
            if let Some(page) = cap.get(1) {
                pages.push(page.as_str().to_string());
                // Keep [[page]] in content for now (backward compat)
            }
        }

        (pages, result)
    }
}

fn count_indent(line: &str) -> usize {
    line.chars().take_while(|c| c.is_whitespace()).count() / 2
}
```

**Phase 4: Logseq Import/Export**

```rust
// crates/kogral-core/src/logseq.rs

use crate::models::{Node, NodeType};
use crate::models::block::Block;
use crate::parser::BlockParser;

pub struct LogseqImporter;

impl LogseqImporter {
    /// Import a Logseq page (markdown file) as a Node
    pub fn import_page(path: &Path) -> Result<Node> {
        let content = std::fs::read_to_string(path)?;

        // Extract frontmatter if present
        let (frontmatter, body) = Self::split_frontmatter(&content);

        // Parse blocks from body
        let blocks = BlockParser::parse(&body)?;

        // Create node with blocks
        let mut node = Node::new(NodeType::Note, Self::extract_title(path));
        node.content = body;
        node.blocks = Some(blocks);

        // Apply frontmatter properties
        if let Some(fm) = frontmatter {
            Self::apply_frontmatter(&mut node, &fm)?;
        }

        Ok(node)
    }

    fn split_frontmatter(content: &str) -> (Option<String>, String) {
        if content.starts_with("---\n") {
            if let Some(end) = content[4..].find("\n---\n") {
                let frontmatter = content[4..4 + end].to_string();
                let body = content[4 + end + 5..].to_string();
                return (Some(frontmatter), body);
            }
        }
        (None, content.to_string())
    }

    fn extract_title(path: &Path) -> String {
        path.file_stem()
            .and_then(|s| s.to_str())
            .unwrap_or("Untitled")
            .to_string()
    }

    fn apply_frontmatter(node: &mut Node, frontmatter: &str) -> Result<()> {
        // Parse YAML frontmatter and apply to node
        // ... implementation ...
        Ok(())
    }
}

pub struct LogseqExporter;

impl LogseqExporter {
    /// Export a Node to Logseq page format
    pub fn export_page(node: &Node, path: &Path) -> Result<()> {
        let mut output = String::new();

        // Generate frontmatter
        output.push_str("---\n");
        output.push_str(&Self::generate_frontmatter(node)?);
        output.push_str("---\n\n");

        // Serialize blocks or use content
        if let Some(ref blocks) = node.blocks {
            output.push_str(&BlockParser::serialize(blocks));
        } else {
            output.push_str(&node.content);
        }

        std::fs::write(path, output)?;
        Ok(())
    }

    fn generate_frontmatter(node: &Node) -> Result<String> {
        let mut fm = String::new();
        fm.push_str(&format!("title: {}\n", node.title));
        fm.push_str(&format!("tags: {}\n", node.tags.join(", ")));
        // ... more frontmatter fields ...
        Ok(fm)
    }
}
```

## Query API Extensions

```rust
// New methods in Graph or Query module

impl Graph {
    /// Find all blocks with a specific tag across all nodes
    pub fn find_blocks_by_tag(&mut self, tag: &str) -> Vec<(&Node, &Block)> {
        let mut results = Vec::new();
        for node in self.nodes.values_mut() {
            if let Ok(blocks) = node.find_blocks_by_tag(tag) {
                for block in blocks {
                    results.push((node as &Node, block));
                }
            }
        }
        results
    }

    /// Find all flashcards (#card blocks)
    pub fn find_flashcards(&mut self) -> Vec<(&Node, &Block)> {
        self.find_blocks_by_tag("card")
    }

    /// Find all TODO items across knowledge base
    pub fn find_all_todos(&mut self) -> Vec<(&Node, &Block)> {
        let mut results = Vec::new();
        for node in self.nodes.values_mut() {
            if let Ok(todos) = node.find_todos() {
                for block in todos {
                    results.push((node as &Node, block));
                }
            }
        }
        results
    }
}
```

## MCP Tool Extensions

```json
{
  "name": "kogral/find_blocks",
  "description": "Find blocks by tag, status, or properties",
  "inputSchema": {
    "type": "object",
    "properties": {
      "tag": { "type": "string", "description": "Filter by tag (e.g., 'card')" },
      "status": { "type": "string", "enum": ["TODO", "DONE", "DOING"] },
      "property": { "type": "string", "description": "Custom property key" },
      "value": { "type": "string", "description": "Property value to match" }
    }
  }
}
```

## Configuration

```nickel
# schemas/contracts.ncl (additions)

BlockConfig = {
  enabled | Bool
    | doc "Enable block-level parsing and storage"
    | default = true,

  preserve_hierarchy | Bool
    | doc "Preserve block nesting on import/export"
    | default = true,

  parse_on_load | Bool
    | doc "Automatically parse blocks when loading nodes"
    | default = false,  # Lazy parsing by default

  supported_statuses | Array String
    | doc "Supported task statuses"
    | default = ["TODO", "DONE", "DOING", "LATER", "NOW", "WAITING", "CANCELLED"],
}

KbConfig = {
  # ... existing fields ...

  blocks | BlockConfig
    | doc "Block-level features configuration"
    | default = {},
}
```

## Migration Path

**Phase 1**: Add Block models (no behavior change)
**Phase 2**: Add BlockParser (opt-in via config)
**Phase 3**: Update Logseq import/export
**Phase 4**: Add block queries to CLI/MCP
**Phase 5**: SurrealDB block indexing

**Backward Compatibility**:
- Existing nodes without `blocks` field work as before
- `content` remains source of truth
- `blocks` is optional cache/structure
- Config flag `blocks.enabled` to opt-in

## Testing Strategy

```rust
#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_parse_simple_block() {
        let content = "- This is a block #card";
        let blocks = BlockParser::parse(content).unwrap();

        assert_eq!(blocks.len(), 1);
        assert_eq!(blocks[0].content, "This is a block");
        assert_eq!(blocks[0].properties.tags, vec!["card"]);
    }

    #[test]
    fn test_parse_nested_blocks() {
        let content = r#"
- Parent block
  - Child block 1
  - Child block 2
    - Grandchild
"#;
        let blocks = BlockParser::parse(content).unwrap();

        assert_eq!(blocks.len(), 1);
        assert_eq!(blocks[0].children.len(), 2);
        assert_eq!(blocks[0].children[1].children.len(), 1);
    }

    #[test]
    fn test_parse_todo() {
        let content = "- TODO Implement feature #rust";
        let blocks = BlockParser::parse(content).unwrap();

        assert_eq!(blocks[0].properties.status, Some(TaskStatus::Todo));
        assert_eq!(blocks[0].content, "Implement feature");
        assert_eq!(blocks[0].properties.tags, vec!["rust"]);
    }

    #[test]
    fn test_roundtrip() {
        let original = r#"- Block 1 #card
  - Nested
- TODO Block 2
  priority:: high
"#;
        let blocks = BlockParser::parse(original).unwrap();
        let serialized = BlockParser::serialize(&blocks);
        let reparsed = BlockParser::parse(&serialized).unwrap();

        assert_eq!(blocks.len(), reparsed.len());
        assert_eq!(blocks[0].properties, reparsed[0].properties);
    }
}
```

## Summary

**Recommended Approach**: Hybrid (Option C)

- **Add** `Block` struct with properties, hierarchy
- **Extend** `Node` with optional `blocks: Option<Vec<Block>>`
- **Implement** bidirectional parser (markdown ↔ blocks)
- **Preserve** `content` as source of truth (backward compat)
- **Enable** block queries in CLI/MCP
- **Support** round-trip Logseq import/export

**Benefits**:
- ✅ Full Logseq compatibility
- ✅ Queryable blocks (find #card, TODO, etc.)
- ✅ Backward compatible
- ✅ Extensible (custom properties)
- ✅ Type-safe structure

**Trade-offs**:
- ⚠️ Added complexity
- ⚠️ Need to sync content ↔ blocks
- ⚠️ More storage for SurrealDB backend

**Next Steps**:
1. Review and approve design
2. Implement Phase 1 (Block models)
3. Implement Phase 2 (BlockParser)
4. Update Logseq import/export
5. Add block queries to MCP/CLI