Add comprehensive schema versioning and rollback documentation

Complete schema version control system documentation including:

- Schema v1.0 definition with all required fields
- Detailed version history tracking
- Git-based rollback procedures (soft, hard, file-specific)
- Commit tracking system (request_id, commit_hash)
- Build-specific rollback for dev/staging/production
- Pre/post validation procedures
- Error recovery protocols
- Schema change tracking format
- Testing checklist
- Quick reference commands

This documentation ensures reliable version control, data integrity, and seamless rollback capability for all future schema modifications across different build environments.

SCHEMA_VERSIONING.md

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+# Schema Versioning and Rollback Documentation
+
+## Overview
+
+This document establishes the schema versioning strategy and rollback procedures for the activity logging system. It ensures data integrity, backward compatibility, and reliable version control for production deployments.
+
+---
+
+## Current Schema Version: 1.0
+
+### Schema Definition (v1.0)
+
+**File:** `activity_log.csv`  
+**Created:** 2025-11-05T10:51:00Z  
+**Commit Hash:** 3a67095  
+
+#### Required Fields
+
+| Field | Type | Description | Validation |
+|-------|------|-------------|------------|
+| `timestamp` | ISO 8601 String | UTC timestamp of activity | Must be valid ISO 8601 format (YYYY-MM-DDTHH:MM:SSZ) |
+| `agent_id` | String | Identifier of the agent performing activity | Non-empty string |
+| `activity_type` | Enum | Type of activity performed | Must be one of: `init`, `validate`, `ingest`, `update`, `delete`, `query`, `commit`, `rollback` |
+| `entity_id` | String | Identifier of entity being acted upon | Non-empty string |
+| `status` | Enum | Outcome status of activity | Must be one of: `created`, `success`, `failed`, `in_progress`, `warning`, `error` |
+| `notes` | String | Human-readable description | Non-empty string |
+| `context` | String | Additional context or metadata | Non-empty string |
+
+#### CSV Format
+```csv
+timestamp,agent_id,activity_type,entity_id,status,notes,context
+2025-11-05T10:51:00Z,comet_assistant,init,activity_log_schema,created,"Canonical CSV schema for activity tracking established","Step 1: Schema and CSV Foundation - initial setup"
+```
+
+---
+
+## Version History
+
+### Version 1.0 (Current)
+**Date:** 2025-11-05  
+**Commit:** 3a67095  
+**Status:** Active  
+
+**Changes:**
+- Initial schema establishment
+- 7 required fields defined
+- Atomic ingestion function implemented
+- Schema validation with error handling
+- Request ID and commit hash tracking
+
+**Files:**
+- `activity_log.csv` - Data storage
+- `activity_ingestion.py` - Ingestion function with validation
+- `SCHEMA_VERSIONING.md` - This documentation
+
+**Migration:** N/A (initial version)
+
+---
+
+## Rollback Procedures
+
+### Git-Based Rollback
+
+All schema changes and data are tracked via Git commits. To roll back to a previous version:
+
+#### 1. Identify Target Commit
+
+```bash
+# View commit history
+git log --oneline activity_log.csv activity_ingestion.py
+
+# Example output:
+# 3a67095 Implement atomic activity ingestion with schema validation
+# b1a2c3d Initial activity_log.csv setup
+```
+
+#### 2. Rollback Commands
+
+**Option A: Soft Rollback (Review changes before commit)**
+```bash
+# Reset to previous commit (keeps changes in working directory)
+git checkout <commit-hash> -- activity_log.csv activity_ingestion.py
+git commit -m "Rollback to schema version X.X (commit <commit-hash>)"
+```
+
+**Option B: Hard Rollback (Direct revert)**
+```bash
+# Revert to specific commit
+git revert <commit-hash>
+```
+
+**Option C: File-Specific Rollback**
+```bash
+# Rollback only the CSV data file
+git checkout <commit-hash> -- activity_log.csv
+git commit -m "Rollback activity_log.csv to <commit-hash>"
+```
+
+#### 3. Verify Rollback
+
+```bash
+# Check current schema version
+grep "SCHEMA_VERSION" activity_ingestion.py
+
+# Validate CSV structure
+head -n 5 activity_log.csv
+
+# Run validation tests
+python activity_ingestion.py
+```
+
+---
+
+## Schema Change Tracking
+
+### Change Log Format
+
+Every schema modification MUST be logged using this structure:
+
+```markdown
+### Version X.Y (Status: Active/Deprecated)
+**Date:** YYYY-MM-DD  
+**Commit:** <git-commit-hash>  
+**Status:** Active | Deprecated | Archived  
+
+**Changes:**
+- [ADD] New field: `field_name` (type, description)
+- [MODIFY] Changed field: `field_name` (old -> new behavior)
+- [REMOVE] Deprecated field: `field_name` (reason)
+- [BREAKING] Breaking change description
+
+**Migration:**
+- Step 1: Migration instructions
+- Step 2: Validation procedures
+
+**Rollback Instructions:**
+- Specific rollback notes if different from standard procedure
+```
+
+### Schema Version Numbering
+
+- **Major Version (X.0):** Breaking changes, incompatible with previous versions
+- **Minor Version (X.Y):** New fields added, backward compatible
+- **Patch Version (X.Y.Z):** Bug fixes, validation updates, no schema changes
+
+---
+
+## Commit Tracking System
+
+### Request ID Format
+
+Every ingestion operation generates a unique request ID:
+
+```
+req_<16-char-hex>
+
+Example: req_a1b2c3d4e5f67890
+```
+
+### Commit Hash Generation
+
+Pseudo-commit hashes track each row insertion:
+
+```python
+commit_hash = SHA256(request_id + timestamp + agent_id + activity_type)[:16]
+```
+
+Example: `3f8d2a1bc5e97604`
+
+### Operation Log
+
+All operations are logged to `activity_ingestion.log`:
+
+```json
+{
+  "timestamp": "2025-11-05T10:51:00Z",
+  "request_id": "req_a1b2c3d4e5f67890",
+  "operation": "ingest",
+  "status": "success",
+  "agent_id": "comet_assistant",
+  "activity_type": "validate",
+  "error": ""
+}
+```
+
+---
+
+## Build-Specific Rollback for Different Environments
+
+### Development Build
+
+```bash
+# Tag development schema
+git tag -a dev-schema-v1.0 -m "Development schema version 1.0"
+
+# Rollback to dev version
+git checkout dev-schema-v1.0 -- activity_log.csv activity_ingestion.py
+```
+
+### Staging Build
+
+```bash
+# Tag staging schema
+git tag -a staging-schema-v1.0 -m "Staging schema version 1.0"
+
+# Rollback to staging version
+git checkout staging-schema-v1.0 -- activity_log.csv activity_ingestion.py
+```
+
+### Production Build
+
+```bash
+# Tag production schema (immutable)
+git tag -a prod-schema-v1.0 -m "Production schema version 1.0" -s
+
+# Rollback to production version
+git checkout prod-schema-v1.0 -- activity_log.csv activity_ingestion.py
+
+# Verify integrity
+git verify-tag prod-schema-v1.0
+```
+
+---
+
+## Validation Procedures
+
+### Pre-Commit Validation
+
+Before committing any schema changes:
+
+1. **Run Schema Validation Tests**
+   ```bash
+   python activity_ingestion.py
+   ```
+
+2. **Check CSV Integrity**
+   ```bash
+   # Verify header
+   head -n 1 activity_log.csv
+   
+   # Count rows
+   wc -l activity_log.csv
+   
+   # Check for malformed rows
+   awk -F',' 'NF!=7 {print NR, $0}' activity_log.csv
+   ```
+
+3. **Validate Timestamp Format**
+   ```bash
+   # Extract and validate timestamps
+   cut -d',' -f1 activity_log.csv | tail -n +2 | while read ts; do
+     date -d "$ts" > /dev/null 2>&1 || echo "Invalid: $ts"
+   done
+   ```
+
+### Post-Rollback Validation
+
+After performing a rollback:
+
+1. Verify schema version matches expected version
+2. Run full test suite: `python activity_ingestion.py`
+3. Check operation logs for errors
+4. Validate data integrity with sample queries
+5. Document rollback in change log
+
+---
+
+## Error Recovery
+
+### Corrupted CSV File
+
+```bash
+# Restore from last good commit
+git checkout HEAD~1 -- activity_log.csv
+
+# Or restore from specific commit
+git checkout <commit-hash> -- activity_log.csv
+
+# Verify restoration
+python activity_ingestion.py
+```
+
+### Failed Schema Migration
+
+```bash
+# Immediate rollback
+git reset --hard HEAD~1
+
+# Or targeted rollback
+git checkout HEAD~1 -- activity_ingestion.py SCHEMA_VERSIONING.md
+
+# Document failure
+echo "Migration failed: <reason>" >> SCHEMA_VERSIONING.md
+git commit -m "Rollback failed migration - <reason>"
+```
+
+### Atomic Operation Failure
+
+The `atomic_append_activity()` function handles failures automatically:
+
+- **Schema Validation Error:** Returns error, no file modification
+- **Write Lock Error:** Returns error, temp file cleaned up
+- **Partial Write:** Temp file discarded, original file unchanged
+
+All errors logged to `activity_ingestion.log` with request_id for tracing.
+
+---
+
+## Best Practices
+
+### Schema Changes
+
+1. **Always increment version number** when modifying schema
+2. **Document all changes** in this file before committing
+3. **Create migration scripts** for breaking changes
+4. **Test thoroughly** in development before staging/production
+5. **Tag releases** with semantic versioning
+
+### Commit Messages
+
+```
+[Schema v1.1] Add new field: priority_level
+
+- Added 'priority_level' field (enum: low, medium, high)
+- Updated validation function
+- Backward compatible with v1.0
+- Migration: existing records default to 'medium'
+```
+
+### Data Backup
+
+```bash
+# Before major changes, create backup
+cp activity_log.csv activity_log_backup_$(date +%Y%m%d).csv
+
+# Commit backup to repo
+git add activity_log_backup_*.csv
+git commit -m "Backup before schema v1.1 migration"
+```
+
+---
+
+## Testing Checklist
+
+Before deploying any schema changes:
+
+- [ ] Schema version updated in code
+- [ ] Validation rules updated
+- [ ] Test suite passes all cases
+- [ ] Documentation updated
+- [ ] Migration script created (if needed)
+- [ ] Rollback procedure documented
+- [ ] Staging deployment successful
+- [ ] Production backup created
+- [ ] Git tag created
+
+---
+
+## Contact & Support
+
+For schema change requests or rollback assistance:
+
+- **Repository:** huggingface.co/spaces/StrategyStack/README
+- **Schema Owner:** comet_assistant
+- **Last Updated:** 2025-11-05
+
+---
+
+## Appendix: Quick Reference
+
+### Current Version Info
+```bash
+# Check schema version
+grep SCHEMA_VERSION activity_ingestion.py
+
+# View recent commits
+git log -5 --oneline
+
+# List all schema tags
+git tag -l '*schema*'
+```
+
+### Emergency Rollback (One-Liner)
+```bash
+# Rollback everything to previous commit
+git reset --hard HEAD~1 && python activity_ingestion.py
+```
+
+### Validate Current State
+```bash
+# Full validation
+python activity_ingestion.py && \
+awk -F',' 'NF!=7 {print "ERROR: Line", NR}' activity_log.csv && \
+echo "Validation complete"
+```
+
+---
+
+**Document Version:** 1.0  
+**Last Modified:** 2025-11-05  
+**Schema Version:** 1.0  
+**Status:** Active