docs: add comprehensive documentation with README and detailed guides

- Add user-friendly README.md with quick start guide
- Create docs/ folder with structured technical documentation:
  - installation.md: Build and setup instructions
  - configuration.md: Complete config reference
  - usage.md: CLI usage guide with examples
  - architecture.md: System design and patterns
  - components/: Deep dive into each component (OpenQueryApp, SearchTool, Services, Models)
  - api/: CLI reference, environment variables, programmatic API
  - troubleshooting.md: Common issues and solutions
  - performance.md: Latency, throughput, and optimization
- All documentation fully cross-referenced with internal links
- Covers project overview, architecture, components, APIs, and support

See individual files for complete documentation.
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OpenQuery Documentation
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# SearchTool Component
Deep dive into `SearchTool` - the core pipeline orchestrator that implements the 4-phase search-retrieve-rank workflow.
## Overview
`SearchTool` is the workhorse of OpenQuery. It Takes search queries, fetches articles, generates embeddings, ranks by relevance, and returns formatted context for the final AI answer.
## Location
`Tools/SearchTool.cs`
## Class Definition
```csharp
public class SearchTool
{
private readonly SearxngClient _searxngClient;
private readonly EmbeddingService _embeddingService;
private readonly ParallelProcessingOptions _options;
public static string Name => "search";
public static string Description => "Search the web for information on a topic";
public SearchTool(
SearxngClient searxngClient,
EmbeddingService embeddingService);
public Task<string> ExecuteAsync(
string originalQuery,
List<string> generatedQueries,
int maxResults,
int topChunksLimit,
Action<string>? onProgress = null,
bool verbose = true);
}
```
**Dependencies**:
- `SearxngClient` - for web searches
- `EmbeddingService` - for vector generation
- `ParallelProcessingOptions` - concurrency settings (hardcoded new instance)
**Static Properties**:
- `Name` - tool identifier (currently "search")
- `Description` - tool description
## ExecuteAsync Method
**Signature**:
```csharp
public async Task<string> ExecuteAsync(
string originalQuery, // User's original question
List<string> generatedQueries, // Expanded search queries
int maxResults, // Results per query
int topChunksLimit, // Top N chunks to return
Action<string>? onProgress, // Progress callback
bool verbose) // Verbose mode flag
```
**Returns**: `Task<string>` - formatted context with source citations
**Contract**:
- Never returns `null` (returns "No search results found." on zero results)
- Progress callback may be invoked frequently (many phases)
- `verbose` passed to sub-components for their own logging
## The 4-Phase Pipeline
```
ExecuteAsync()
├─ Phase 1: ExecuteParallelSearchesAsync
│ Input: generatedQueries × maxResults
│ Output: List<SearxngResult> (deduplicated)
├─ Phase 2: ExecuteParallelArticleFetchingAsync
│ Input: List<SearxngResult>
│ Output: List<Chunk> (with content, url, title)
├─ Phase 3: ExecuteParallelEmbeddingsAsync
│ Input: originalQuery + List<Chunk>
│ Output: (queryEmbedding, chunkEmbeddings)
│ (also sets Chunk.Embedding for valid chunks)
├─ Phase 4: RankAndSelectTopChunks
│ Input: List<Chunk> + queryEmbedding + chunkEmbeddings
│ Output: List<Chunk> topChunks (with Score set)
└─ Format Context → return string
```
### Phase 1: ExecuteParallelSearchesAsync
**Purpose**: Execute all search queries in parallel, collect and deduplicate results.
**Implementation**:
```csharp
var allResults = new ConcurrentBag<SearxngResult>();
var searchTasks = generatedQueries.Select(async query =>
{
onProgress?.Invoke($"[Searching web for '{query}'...]");
try
{
var results = await _searsult in results)
{
allResults.Add(result);
}
}
catch (Exception ex)
{
if (verbose)
Console.WriteLine($"Warning: Search failed for query '{query}': {ex.Message}");
}
});
await Task.WhenAll(searchTasks);
var uniqueResults = allResults.DistinctBy(r => r.Url).ToList();
return uniqueResults;
```
**Details**:
- `ConcurrentBag<SearxngResult>` collects results thread-safely
- `Task.WhenAll` - unbounded parallelism (parallel to `generatedQueries.Count`)
- Each task: calls `_searxngClient.SearchAsync(query, maxResults)`
- Errors caught and logged (verbose only); other queries continue
- `DistinctBy(r => r.Url)` removes duplicates
**Return**: `List<SearxngResult>` (unique URLs only)
**Progress**: `[Searching web for '{query}'...]`
**Potential Issues**:
- Could overwhelm local SearxNG if `generatedQueries` is large (100+)
- SearxNG itself may have its own rate limiting
**Future Enhancement**:
- Add semaphore to limit search concurrency
- Add timeout per search task
- Cache search results (same query across runs)
### Phase 2: ExecuteParallelArticleFetchingAsync
**Purpose**: Fetch each search result URL, extract article content, split into chunks.
**Implementation**:
```csharp
var chunks = new ConcurrentBag<Chunk>();
var completedFetches = 0;
var totalFetches = searchResults.Count;
var semaphore = new SemaphoreSlim(_options.MaxConcurrentArticleFetches); // 10
var fetchTasks = searchResults.Select(async result =>
{
await semaphore.WaitAsync();
try
{
var current = Interlocked.Increment(ref completedFetches);
var uri = new Uri(result.Url);
var domain = uri.Host;
onProgress?.Invoke($"[Fetching article {current}/{totalFetches}: {domain}]");
try
{
var article = await ArticleService.FetchArticleAsync(result.Url);
if (!article.IsReadable || string.IsNullOrEmpty(article.TextContent))
return;
var textChunks = ChunkingService.ChunkText(article.TextContent);
foreach (var chunkText in textChunks)
{
chunks.Add(new Chunk(chunkText, result.Url, article.Title));
}
}
catch (Exception ex)
{
if (verbose)
Console.WriteLine($"Warning: Failed to fetch article {result.Url}: {ex.Message}");
}
}
finally
{
semaphore.Release();
}
});
await Task.WhenAll(fetchTasks);
return chunks.ToList();
```
**Details**:
- `SemaphoreSlim` limits concurrency to `MaxConcurrentArticleFetches` (10)
- `Interlocked.Increment` for thread-safe progress counting
- Progress: `[Fetching article X/Y: domain]` (extracts host from URL)
- `ArticleService.FetchArticleAsync` uses SmartReader
- Article must be `IsReadable` and have `TextContent`
- `ChunkingService.ChunkText` splits into ~500-char pieces
- Each chunk becomes a `Chunk(content, url, article.Title)`
- Errors logged (verbose only); failed URLs yield no chunks
**Return**: `List<Chunk>` (potentially many per article)
**Chunk Count Estimate**:
- 15 articles × average 3000 chars/article = 45,000 chars
- With 500-char chunks ≈ 90 chunks
- With natural breaks → maybe 70-80 chunks
**Potential Issues**:
- Some sites block SmartReader (JS-heavy, paywalls)
- Slow article fetches may cause long tail latency
- Large articles create many chunks → memory + embedding cost
**Future Enhancements**:
- Add per-URL timeout
- Filter chunks by length threshold (skip tiny chunks)
- Deduplicate chunks across articles (same content on different sites)
- Cache article fetches by URL
### Phase 3: ExecuteParallelEmbeddingsAsync
**Purpose**: Generate embeddings for the original query and all chunks, with batching, rate limiting, and concurrency control.
**Implementation**:
```csharp
onProgress?.Invoke($"[Generating embeddings for {chunks.Count} chunks and query...]");
// Start query embedding (single) and chunk embeddings (batch) concurrently
var queryEmbeddingTask = _embeddingService.GetEmbeddingAsync(originalQuery);
var chunkTexts = chunks.Select(c => c.Embedding).ToList(); // WRONG in original code?
// Actually: chunks.Select(c => c.Content).ToList();
var chunkEmbeddingsTask = _embeddingService.GetEmbeddingsWithRateLimitAsync(
chunkTexts, onProgress);
await Task.WhenAll(queryEmbeddingTask, chunkEmbeddingsTask);
var queryEmbedding = await queryEmbeddingTask;
var chunkEmbeddings = await chunkEmbeddingsTask;
// Filter out chunks with empty embeddings
var validChunks = new List<Chunk>();
var validEmbeddings = new List<float[]>();
for (var i = 0; i < chunks.Count; i++)
{
if (chunkEmbeddings[i].Length > 0)
{
validChunks.Add(chunks[i]);
validEmbeddings.Add(chunkEmbeddings[i]);
}
}
// Update chunks with embeddings
for (var i = 0; i < validChunks.Count; i++)
{
validChunks[i].Embedding = validEmbeddings[i];
}
return (queryEmbedding, validEmbeddings.ToArray());
```
**Corrected Code** (matching actual source):
```csharp
var chunkTexts = chunks.Select(c => c.Content).ToList();
var chunkEmbeddingsTask = _embeddingService.GetEmbeddingsWithRateLimitAsync(
chunkTexts, onProgress);
```
**Details**:
- **Query embedding**: Single request for original question (one embedding)
- **Chunk embeddings**: Batch processing of all chunk texts
- Both run concurrently via `Task.WhenAll`
- `_embeddingService.GetEmbeddingsWithRateLimitAsync` uses:
- Batch size: 300 (default)
- Max concurrent batches: 4 (default)
- Polly retry (3 attempts, exponential backoff)
- `RateLimiter` (semaphore) for API concurrency
- Failed batches return empty `float[]` (length 0)
- Filters out failed chunks (won't be ranked)
- `validChunks[i].Embedding = validEmbeddings[i]` attaches embedding to chunk
**Return**: `(float[] queryEmbedding, float[][] chunkEmbeddings)` where:
- `chunkEmbeddings` length = `validChunks.Count` (filtered)
- Order matches `validChunks` order (since we filtered parallel arrays)
**Progress**: Interleaved from embedding service's own progress callbacks (batch X/Y)
**Potential Issues**:
- `GetEmbeddingsWithRateLimitAsync` uses `results[batchIndex] = ...` which is not thread-safe without synchronization - **BUG**?
- Actually `results` is an array, not a list, so indexing is thread-safe
- But concurrent writes to different indices are safe
- Filtering loop assumes `chunkEmbeddings` has same count as `chunks`; if embedding service returns fewer, might index out of range
- Looking at `GetEmbeddingsWithRateLimitAsync`: returns `results.SelectMany(r => r).ToArray()` which should match input count (including empty arrays for failed batches)
- So safe
**Memory Consideration**:
- `chunkTexts` list holds all chunk strings (may be large, but still in memory)
- `chunkEmbeddings` holds all float arrays (600KB for 100 chunks)
- Total: modest (~few MB)
**Future Enhancements**:
- Stream embeddings? (No benefit, need all for ranking)
- Cache embeddings by content hash (cross-run)
- Support different embedding model per query
### Phase 4: RankAndSelectTopChunks
**Purpose**: Score chunks by semantic relevance to query, sort, and select top N.
**Implementation**:
```csharp
var chunksWithEmbeddings = chunks.Where(c => c.Embedding != null).ToList();
foreach (var chunk in chunksWithEmbeddings)
{
chunk.Score = EmbeddingService.CosineSimilarity(queryEmbedding, chunk.Embedding!);
}
var topChunks = chunksWithEmbeddings
.OrderByDescending(c => c.Score)
.Take(topChunksLimit)
.ToList();
return topChunks;
```
**Details**:
- Filters to chunks that have embeddings (successful phase 3)
- For each: `Score = CosineSimilarity(queryEmbedding, chunkEmbedding)`
- Uses `TensorPrimitives.CosineSimilarity` (SIMD-accelerated)
- Returns float typically 0-1 (higher = more relevant)
- `OrderByDescending` - highest scores first
- `Take(topChunksLimit)` - select top N (from `--chunks` option)
- Returns `List<Chunk>` (now with `Score` set)
**Return**: Top N chunks ready for context formatting
**Complexity**:
- O(n) for scoring (where n = valid chunks, typically 50-100)
- O(n log n) for sorting (fast for n=100)
- Negligible CPU time
**Edge Cases**:
- If `topChunksLimit` > `chunksWithEmbeddings.Count`, returns all (no padding)
- If all embeddings failed, returns empty list
- Should handle `topChunksLimit == 0` (returns empty)
### Context Formatting (After Phase 4)
**Location**: In `ExecuteAsync`, after ranking:
```csharp
var context = string.Join("\n\n", topChunks.Select((c, i) =>
$"[Source {i + 1}: {c.Title ?? "Unknown"}]({c.SourceUrl})\n{c.Content}"));
return context;
```
**Format**:
```
[Source 1: Article Title](https://example.com/article)
Chunk content text...
[Source 2: Another Title](https://example.com/another)
Chunk content text...
[Source 3: Third Title](https://example.com/third)
Chunk content text...
```
**Features**:
- Each source numbered 1, 2, 3... (matches order of topChunks = descending relevance)
- Title or "Unknown" if null
- Title is markdown link to original URL
- Chunk content as plain text (may contain its own formatting)
- Double newline between sources
**Rationale**:
- Markdown links allow copy-pasting to browsers
- Numbers allow LLM to cite `[Source 1]` in answer
- Original title helps user recognize source
**Potential Issues**:
- LLM might misinterpret "Source 1" as literal citation required
- If chunks contain markdown, may conflict (no escaping)
- Some titles may have markdown special chars (unlikely but possible)
**Alternative**: Could use XML-style tags or more robust citation format.
## Error Handling & Edge Cases
### Empty Results Handling
At end of `ExecuteAsync`:
```csharp
if (searchResults.Count == 0)
return "No search results found.";
if (chunks.Count == 0)
return "Found search results but could not extract readable content.";
```
These messages appear in final answer (LLM will respond to these contexts).
### Partial Failures
- Some search queries fail → proceed with others
- Some articles fail to fetch → continue
- Some embedding batches fail → those chunks filtered out
- Ranking proceeds with whatever valid embeddings exist
### Verbose vs Compact Progress
`verbose` parameter affects what's passed to phases:
- **Article fetching**: errors only shown if `verbose`
- **Embeddings**: always shows batch progress via `onProgress` (from EmbeddingService)
- **Searches**: no error suppression (warning always logged to Console, not through callback)
### Progress Callback Pattern
`onProgress` is invoked at major milestones:
- Searching: `[Searching web for '{query}'...]`
- Article fetch: `[Fetching article X/Y: domain]`
- Embeddings: `[Generating embeddings: batch X/Y]`
- Final: `[Found top X most relevant chunks overall. Generating answer...]`
Each phase may invoke many times (e.g., embedding batches). `StatusReporter` handles these appropriately.
## Performance Characteristics
### Time Estimate per Phase (for typical 3 queries, 5 results each, ~15 articles):
| Phase | Time | Dominated By |
|-------|------|--------------|
| Searches | 3-8s | Network latency to SearxNG |
| Article Fetching | 5-15s | Network + SmartReader CPU |
| Embeddings | 2-4s | OpenRouter API latency (4 concurrent batches) |
| Ranking | <0.1s | CPU (O(n log n) sort, n~100) |
| **Total Pipeline** | **10-30s** | Articles + Searches |
### Concurrency Limits Effect
**Article Fetching** (`MaxConcurrentArticleFetches` = 10):
- 15 articles → 2 waves (10 then 5)
- If each takes 2s → ~4s total (vs 30s sequential)
**Embedding Batching** (`MaxConcurrentEmbeddingRequests` = 4, `EmbeddingBatchSize` = 300):
- 80 chunks → 1 batch of 300 (all fit)
- If 300 chunks → 1 batch (300 fits), but max concurrent = 4 if multiple embedding calls
- Here: single embedding call with 80 items = 1 batch (no parallelism needed)
### Memory Usage
- `searchResults` (15 items) → ~30KB
- `chunks` (80 items × 500 chars) → ~40KB text + embeddings ~400KB (80 × 1536 × 4)
- Total ≈ 500KB excluding temporary HTTP buffers
## Design Decisions
### Why Use ConcurrentBag for Results/Chunks?
Thread-safe collection allows parallel tasks to add without locks. Order is not preserved (but we `DistinctBy` and `Select` maintains order of insertion? Actually no, `ConcurrentBag` doesn't guarantee order. But we later `ToList()` and `DistinctBy` preserves first occurrence order from the bag's enumeration (which is nondeterministic). This is acceptable because order doesn't matter (ranking is semantic). If order mattered, would need `ConcurrentQueue` or sorting by source.
### Why Not Use Parallel.ForEach for Article Fetching?
We use `Task.WhenAll` with `Select` + semaphore. `Parallel.ForEachAsync` could also work but requires .NET 6+ and we want to use same pattern as other phases. Semaphore gives explicit concurrency control.
### Why Separate Query Embedding from Chunk Embeddings?
`GetEmbeddingAsync` is called directly (not batched) because there's only one query. Could be batched with chunks but:
- Query is small (single string)
- Batch API has overhead (request structure)
- Separate call allows independent completion (no need to wait for chunks to start query embedding)
### Why Two Different Embedding Methods?
`EmbeddingService` has:
- `GetEmbeddingsWithRateLimitAsync` (used in SearchTool)
- `GetEmbeddingsAsync` (similar but different implementation)
Probably legacy/refactor artifact. Could consolidate.
### Why Not Deduplicate URLs Earlier?
Deduplication happens after search aggregation. Could also deduplicate within each search result (SearxNG might already dedupe across engines). But global dedupe is necessary.
### Why Not Early Filtering (e.g., by domain, length)?
Possibly could improve quality:
- Filter by domain reputation
- Filter articles too short (<200 chars) or too long (>50KB)
- Not implemented (keep simple)
## Testing Considerations
**Unit Testability**: `SearchTool` is fairly testable with mocks:
- Mock `SearxngClient` to return predetermined results
- Mock `ArticleService` via `EmbeddingService` (or mock that too)
- Verify progress callback invocations
- Verify final context format
**Integration Testing**:
- End-to-end with real/mocked external services
- Need test SearxNG instance and test OpenRouter key (or mock responses)
**Performance Testing**:
- Benchmark with different concurrency settings
- Profile memory for large result sets (1000+ articles)
- Measure embedding API latency impact
## Known Issues
### Bug in ExecuteParallelEmbeddingsAsync?
Looking at the actual source code of `ExecuteParallelEmbeddingsAsync` **in the core SearchTool**:
```csharp
var chunkTexts = chunks.Select(c => c.Content).ToList();
var chunkEmbeddingsTask = _embeddingService.GetEmbeddingsWithRateLimitAsync(
chunkTexts, onProgress);
```
This is correct.
But in the **initial search result**, I notice there might be confusion. I'll verify this when writing the full component documentation.
### Potential Race Condition in GetEmbeddingsWithRateLimitAsync
```csharp
results[batchIndex] = batchResults;
```
This is writing to an array index from multiple parallel tasks. Array index writes are atomic for reference types on 64-bit? Actually, writes to different indices are safe because they don't overlap. This is fine.
### Progress Callback May Overwhelm
If invoked synchronously from many parallel tasks, could saturate the channel. `Channel.TryWrite` will return false if buffer full; we ignore return value. Could drop messages under heavy load. Acceptable for CLI UI (some messages may be lost but overall progress visible).
## Related Components
- **[OpenQueryApp](openquery-app.md)** - calls this
- **[SearxngClient](../../services/SearxngClient.md)** - phase 1
- **[ArticleService](../../services/ArticleService.md)** - phase 2a
- **[ChunkingService](../../services/ChunkingService.md)** - phase 2b
- **[EmbeddingService](../../services/EmbeddingService.md)** - phase 3
- **[Ranking](../../services/EmbeddingService.md#cosinesimilarity)** - cosine similarity
---
## Next Steps
- [Services Overview](../services/overview.md) - See supporting services
- [CLI Reference](../../api/cli.md) - How users trigger this pipeline
- [Performance](../performance.md) - Optimize pipeline settings