docs(blocks): add manual sections for ConcatenateListsBlock and documentation guidelines

Fill in the how_it_works and use_case manual sections for the new
Concatenate Lists block documentation. Add CLAUDE.md with formatting
guidelines for future block documentation updates.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docs/CLAUDE.md

@@ -0,0 +1,44 @@
+# Documentation Guidelines
+
+## Block Documentation Manual Sections
+
+When updating manual sections (`<!-- MANUAL: ... -->`) in block documentation files (e.g., `docs/integrations/basic.md`), follow these formats:
+
+### How It Works Section
+
+Provide a technical explanation of how the block functions:
+- Describe the processing logic in 1-2 paragraphs
+- Mention any validation, error handling, or edge cases
+- Use code examples with backticks when helpful (e.g., `[[1, 2], [3, 4]]` becomes `[1, 2, 3, 4]`)
+
+Example:
+```markdown
+<!-- MANUAL: how_it_works -->
+The block iterates through each list in the input and extends a result list with all elements from each one. It processes lists in order, so `[[1, 2], [3, 4]]` becomes `[1, 2, 3, 4]`.
+
+The block includes validation to ensure each item is actually a list. If a non-list value is encountered, the block outputs an error message instead of proceeding.
+<!-- END MANUAL -->
+```
+
+### Use Case Section
+
+Provide 3 practical use cases in this format:
+- **Bold Heading**: Short one-sentence description
+
+Example:
+```markdown
+<!-- MANUAL: use_case -->
+**Paginated API Merging**: Combine results from multiple API pages into a single list for batch processing or display.
+
+**Parallel Task Aggregation**: Merge outputs from parallel workflow branches that each produce a list of results.
+
+**Multi-Source Data Collection**: Combine data collected from different sources (like multiple RSS feeds or API endpoints) into one unified list.
+<!-- END MANUAL -->
+```
+
+### Style Guidelines
+
+- Keep descriptions concise and action-oriented
+- Focus on practical, real-world scenarios
+- Use consistent terminology with other blocks
+- Avoid overly technical jargon unless necessary

docs/integrations/README.md

@@ -31,6 +31,7 @@ Below is a comprehensive list of all available blocks, categorized by their prim
 | [Agent Time Input](basic.md#agent-time-input) | Block for time input |
 | [Agent Toggle Input](basic.md#agent-toggle-input) | Block for boolean toggle input |
 | [Block Installation](basic.md#block-installation) | Given a code string, this block allows the verification and installation of a block code into the system |
+| [Concatenate Lists](basic.md#concatenate-lists) | Concatenates multiple lists into a single list |
 | [Dictionary Is Empty](basic.md#dictionary-is-empty) | Checks if a dictionary is empty |
 | [File Store](basic.md#file-store) | Stores the input file in the temporary directory |
 | [Find In Dictionary](basic.md#find-in-dictionary) | A block that looks up a value in a dictionary, list, or object by key or index and returns the corresponding value |

docs/integrations/basic.md

@@ -634,6 +634,42 @@ This enables extensibility by allowing custom blocks to be added without modifyi
 
 ---
 
+## Concatenate Lists
+
+### What it is
+Concatenates multiple lists into a single list. All elements from all input lists are combined in order.
+
+### How it works
+<!-- MANUAL: how_it_works -->
+The block iterates through each list in the input and extends a result list with all elements from each one. It processes lists in order, so `[[1, 2], [3, 4]]` becomes `[1, 2, 3, 4]`.
+
+The block includes validation to ensure each item is actually a list. If a non-list value (like a string or number) is encountered, the block outputs an error message instead of proceeding. None values are skipped automatically.
+<!-- END MANUAL -->
+
+### Inputs
+
+| Input | Description | Type | Required |
+|-------|-------------|------|----------|
+| lists | A list of lists to concatenate together. All lists will be combined in order into a single list. | List[List[Any]] | Yes |
+
+### Outputs
+
+| Output | Description | Type |
+|--------|-------------|------|
+| error | Error message if concatenation failed due to invalid input types. | str |
+| concatenated_list | The concatenated list containing all elements from all input lists in order. | List[Any] |
+
+### Possible use case
+<!-- MANUAL: use_case -->
+**Paginated API Merging**: Combine results from multiple API pages into a single list for batch processing or display.
+
+**Parallel Task Aggregation**: Merge outputs from parallel workflow branches that each produce a list of results.
+
+**Multi-Source Data Collection**: Combine data collected from different sources (like multiple RSS feeds or API endpoints) into one unified list.
+<!-- END MANUAL -->
+
+---
+
 ## Dictionary Is Empty
 
 ### What it is