chore: remove stale YDB, YTSaurus, Greenplum, OpenSearch, S3 provider references

- Remove YDB debezium emitter/receiver and tests
- Remove YTSaurus logging, KV wrapper, and recipe helpers
- Remove Greenplum and OpenSearch connection code
- Remove S3 example (s3sqs2ch) and docs references
- Remove Elasticsearch and Delta docs references
- Clean up error codes for removed providers
- Update .mapping.json to remove deleted file entries
- Add .claude/ and reports/ to .gitignore

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

Author: bvt123

.gitignore

@@ -9,3 +9,5 @@ report
 docs-html
 _docs-lint
 trcli
+.claude/
+reports/

.mapping.json

@@ -0,0 +1,213 @@
+# AGENTS.md - AI Agent & Contributor Guidelines
+
+This document provides essential context for AI agents (Claude, Copilot, etc.) and human contributors working on the Transferia codebase.
+
+## Project Overview
+
+**Transferia** is an open-source, cloud-native ELT (Extract, Load, Transform) ingestion engine built in Go. It enables seamless, high-performance data movement between diverse database systems at scale.
+
+### Key Capabilities
+- **Snapshot**: One-time bulk data transfer with table-level consistency
+- **Replication**: Continuous CDC (Change Data Capture) streaming
+- **Transformations**: Row-level transformations during transfer (rename, mask, filter, SQL)
+- **Multi-source**: PostgreSQL, MySQL, MongoDB, Kafka, S3, and more
+- **Multi-destination**: ClickHouse, PostgreSQL, Kafka, S3, and more
+
+## Repository Structure
+
+```
+transferia/
+├── cmd/trcli/          # CLI entry point (replicate, upload, check, validate)
+├── pkg/
+│   ├── abstract/       # Core interfaces (Source, Sink, Storage, Transfer)
+│   ├── providers/      # Database adapters (postgres, mysql, mongo, clickhouse, kafka)
+│   ├── dataplane/      # Runtime execution engine
+│   ├── middlewares/    # Cross-cutting concerns (retry, filter, metrics)
+│   ├── transformer/    # Pluggable transformers
+│   ├── parsers/        # Data format parsers (JSON, Avro, Parquet)
+│   ├── coordinator/    # Multi-node coordination (memory, S3)
+│   └── connection/     # Connection management
+├── internal/           # Internal packages (logger, config, metrics)
+├── tests/
+│   ├── e2e-core/       # End-to-end tests (pg2ch, mysql2ch, mongo2ch)
+│   ├── helpers/        # Test utilities and helpers
+│   ├── canon/          # Type/schema validation tests
+│   └── storage/        # Provider storage tests
+├── recipe/             # Test container recipes
+├── examples/           # Configuration examples
+└── docs/               # Documentation
+```
+
+## Core Abstractions
+
+### Key Interfaces (pkg/abstract/)
+
+1. **Storage** - One-time data reader for snapshots
+2. **Source** - Streaming data reader for CDC replication
+3. **Sink** - Data writer with async push semantics
+4. **Transformer** - Row-level data transformation
+5. **ChangeItem** - Core unit of data transfer (represents a row operation)
+
+### Provider Pattern
+
+All providers in `pkg/providers/` follow this structure:
+```go
+type Provider struct {
+    logger   log.Logger
+    registry metrics.Registry
+    cp       coordinator.Coordinator
+    transfer *model.Transfer
+}
+```
+
+Providers register via `init()` with:
+- `providers.Register(ProviderType, New)`
+- `model.RegisterSource/RegisterDestination`
+- `abstract.RegisterProviderName`
+
+## Coding Guidelines
+
+### Error Handling
+
+- Use `xerrors.Errorf("context: %w", err)` for wrapping
+- Domain-specific error types exist:
+  - `FatalError` - Stops transfer, forbids restart
+  - `RetriablePartUploadError` - Transient, eligible for retry
+  - `TableUploadError` - Specific upload failures
+- Never ignore errors silently; log if not returning
+
+### Logging
+
+- Use structured logging via the `logger` package (Zap-based)
+- Prefer `logger.Log.Info("message", log.String("key", value))` over `Infof`
+- Log levels: DEBUG, INFO, WARNING, ERROR, FATAL
+- Never log credentials or sensitive data
+
+### Testing
+
+- Place tests in `tests/` directory, not alongside code
+- Use testcontainers via `recipe/` package for integration tests
+- Follow the pattern: `TestSnapshotAndIncrement`, `TestReplication`
+- Use helpers: `helpers.Activate()`, `helpers.CompareStorages()`
+- Wait helpers for async operations: `WaitEqualRowsCount()`, `WaitCond()`
+
+### Concurrency
+
+- Always use context for cancellation
+- Use `sync.WaitGroup` for goroutine lifecycle
+- Prefer buffered channels to avoid deadlocks
+- Use `sync.Once` for one-time cleanup operations
+- Avoid mutex in hot paths; consider atomics
+
+## Security Considerations
+
+### Critical Rules
+
+1. **Never hardcode credentials** - Use environment variables
+2. **Always validate TLS certificates** - Don't set `InsecureSkipVerify: true` in production
+3. **Sanitize SQL inputs** - Use parameterized queries, never string concatenation
+4. **Redact secrets in logs** - Never log passwords, tokens, or keys
+5. **Validate database filters** - User-provided filters can be injection vectors
+
+### Known Security Debt
+
+- Some TLS configurations default to `InsecureSkipVerify` when no cert provided
+- `SecretString` type alias provides no actual protection
+- Test credentials exist in recipe files (acceptable for tests only)
+
+## Provider-Specific Notes
+
+### PostgreSQL
+- Most complex provider with full replication support
+- Uses pgx library with custom type mapping
+- Has DBLog support for alternative loading
+- System tables: `__consumer_keeper`, `__data_transfer_lsn`
+
+### MySQL
+- Supports both file-based and GTID position tracking
+- Character set handling (UTF-8MB3 vs MB4)
+- System tables: `__table_transfer_progress`, `__tm_keeper`
+
+### MongoDB
+- Simpler, document-oriented provider
+- Uses cluster time instead of LSN for position
+- System collection: `__dt_cluster_time`
+
+### ClickHouse
+- **Snapshot-only** - No replication source support
+- Implements different interfaces (`Abstract2Provider`, `AsyncSinker`)
+- HTTP and Native protocol support
+
+## Common Tasks
+
+### Adding a New Provider
+
+1. Create package in `pkg/providers/newprovider/`
+2. Implement required interfaces (Storage, Source, Sink as needed)
+3. Register in `init()` function
+4. Add test recipes in `recipe/`
+5. Create e2e tests in `tests/e2e-core/`
+
+### Adding a Transformer
+
+1. Add implementation in `pkg/transformer/registry/`
+2. Register with transformer registry
+3. Update configuration model if needed
+4. Add tests
+
+### Running Tests
+
+```bash
+# Quick core tests
+make test-core
+
+# Full CDC test suite
+make test-cdc-full
+
+# Specific wave
+make test-cdc-wave WAVE=providers
+
+# Specific layer
+make test-layer LAYER=e2e-core DB=pg2ch
+```
+
+## Build Commands
+
+```bash
+make build          # Build trcli binary
+make docker         # Build Docker image
+make clean          # Remove artifacts
+make lint           # Run linters
+```
+
+## Important Files
+
+- `pkg/abstract/model/transfer.go` - Transfer model definition
+- `pkg/abstract/endpoint.go` - Provider interface definitions
+- `pkg/providers/provider.go` - Provider registration
+- `cmd/trcli/config/model.go` - CLI configuration model
+- `.golangci.yml` - Linter configuration
+
+## Code Style
+
+- Follow Go idioms and effective Go guidelines
+- Use `gofmt` and linters (`.golangci.yml` configured)
+- Interface names: clear verbs (Source, Sink, Transformer)
+- File names: lowercase with underscores
+- Keep functions focused; extract when > 50 lines
+- Comment non-obvious logic; skip obvious comments
+
+## Architecture Decisions
+
+1. **Compile-time plugins** - No runtime plugin loading; all providers compiled in
+2. **Middleware pattern** - Cross-cutting concerns via composable middlewares
+3. **Marker interfaces** - Capability detection via `Is*()` marker methods
+4. **Coordinator abstraction** - Memory (single-node) or S3 (distributed) coordination
+5. **Wave-based testing** - Tests organized in dependency waves for efficient CI
+
+## Getting Help
+
+- See `/docs/` for detailed documentation
+- Check `/examples/` for configuration patterns
+- Review existing provider implementations for patterns
+- Test recipes in `/recipe/` show infrastructure setup