# Implementation Summary: Fetch Recent Threads Command

## Overview
Added a new CLI command `threads` to fetch recent threads from a LangSmith project and save each thread to a separate JSON file.

## Changes Made

### 1. Core Fetching Logic (`src/langsmith_cli/fetchers.py`)
- Added `fetch_recent_threads()` function that:
  - Queries the LangSmith API for root runs in a project
  - Extracts unique thread_ids from run metadata
  - Fetches full message data for each thread using the existing `fetch_thread()` function
  - Returns a list of tuples: `(thread_id, messages)`
  - Supports configurable limit for number of threads
  - Handles deduplication of thread_ids
  - Gracefully handles threads without thread_id metadata

### 2. CLI Command (`src/langsmith_cli/cli.py`)
- Added new `threads` command with:
  - Required argument: `OUTPUT_DIR` - Directory where thread files will be saved
  - Options:
    - `--project-uuid UUID`: Override project UUID from config
    - `--limit N` or `-n N`: Limit number of threads (default: 10)
- Creates output directory if it doesn't exist
- Saves each thread to a separate JSON file named by thread_id
- Provides progress feedback to user
- Updated main help text to include new command

### 3. Documentation (`README.md`)
- Updated feature list to include thread fetching
- Added usage examples for the `threads` command
- Updated quickstart section

### 4. Tests
Added comprehensive test coverage:

**CLI Tests** (`tests/test_cli.py`):
- `TestThreadsCommand::test_threads_default_limit`: Tests default behavior
- `TestThreadsCommand::test_threads_custom_limit`: Tests custom limit parameter
- `TestThreadsCommand::test_threads_no_project_uuid`: Tests error handling

**Fetcher Tests** (`tests/test_fetchers.py`):
- `TestFetchRecentThreads::test_fetch_recent_threads_success`: Tests successful fetching
- `TestFetchRecentThreads::test_fetch_recent_threads_respects_limit`: Tests limit parameter
- `TestFetchRecentThreads::test_fetch_recent_threads_handles_missing_thread_id`: Tests graceful handling of missing metadata
- `TestFetchRecentThreads::test_fetch_recent_threads_deduplicates`: Tests thread_id deduplication

## Usage Examples

```bash
# Fetch 10 most recent threads (default) to ./my-threads directory
langsmith-fetch threads ./my-threads

# Fetch 25 most recent threads
langsmith-fetch threads ./my-threads --limit 25

# Override project UUID
langsmith-fetch threads ./my-threads --project-uuid 80f1ecb3-a16b-411e-97ae-1c89adbb5c49
```

## Output
- Creates one JSON file per thread in the specified directory
- Files are named `{thread_id}.json`
- Each file contains all messages from all traces in that thread
- Format is consistent with existing thread fetch output

## API Integration
The implementation uses the LangSmith API:
1. **Runs Query Endpoint** (`POST /runs/query`): Fetches root runs with filters for project and thread metadata
2. **Thread Endpoint** (`GET /runs/threads/{thread_id}`): Fetches complete thread data (reuses existing logic)

## Test Results
All 41 tests pass, including:
- 6 new CLI tests
- 4 new fetcher tests
- All existing tests remain passing
