Add detailed bug report for legal documentation

CRITICAL_BUGS_FIXED.md

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+# Critical Bug Fixes - January 2026
+
+**Timeline**: Issues existed for 2-3 months before being fixed  
+**Impact**: Customer backup/restore operations failing through TUI  
+**Fixed in**: v3.42.5 through v3.42.10
+
+---
+
+## Root Cause Analysis
+
+### Bug #1: Encryption Detection False Positive (v3.42.5)
+**File**: `internal/backup/encryption.go:92`  
+**Issue**: `IsBackupEncrypted()` returned TRUE for ALL files  
+**Impact**: Normal (unencrypted) backups could not be restored  
+**Root Cause**: Fallback logic checked if 12 bytes could be read (nonce size) - always true for any file  
+**Fix**: Properly detect magic bytes (1f 8b for gzip, PGDMP for PostgreSQL custom format)
+
+### Bug #2-13: cmd.Wait() Deadlocks (v3.42.6-v3.42.7)
+**Files**: 
+- `internal/backup/engine.go` (4 functions)
+- `internal/restore/engine.go` (3 functions)  
+- `internal/engine/mysqldump.go` (2 functions)
+- `internal/backup/engine.go:createArchive` (tar/pigz pipeline)
+
+**Issue**: 12 functions with blocking `cmd.Wait()` calls  
+**Impact**: Processes could hang forever when context was cancelled  
+**Root Cause**: 
+```go
+// WRONG - hangs on cancellation
+if err := cmd.Wait(); err != nil {
+    return err
+}
+```
+
+**Fix**: Channel-based pattern with Process.Kill()
+```go
+// CORRECT
+cmdDone := make(chan error, 1)
+go func() { cmdDone <- cmd.Wait() }()
+select {
+case err = <-cmdDone:
+case <-ctx.Done():
+    cmd.Process.Kill()
+    <-cmdDone
+}
+```
+
+### Bug #14-20: TUI Timeout Bugs (v3.42.8-v3.42.9)
+**THE PRIMARY ISSUE** - Why backups appeared to fail for months
+
+| File | Function | Old Timeout | New Timeout | Impact |
+|------|----------|-------------|-------------|---------|
+| restore_preview.go | runSafetyChecks | 60s | 10 min | Large archives timeout before backup even starts |
+| dbselector.go | fetchDatabases | 15s | 60s | Database listing fails on busy servers |
+| status.go | fetchStatus | 10s | 30s | Status checks fail with SSL/slow networks |
+| diagnose.go | diagnoseClusterArchive | 60s | 5 min | tar -tzf times out on multi-GB archives |
+| diagnose.go | verifyWithPgRestore | 60s | 5 min | pg_restore --list times out on large dumps |
+| diagnose.go | DiagnoseClusterDumps | 120s | 10 min | Archive extraction times out |
+| engine.go | detectLargeObjectsInDumps | 10s | 2 min | Large object detection fails |
+
+**Root Cause**: User sees "context deadline exceeded" in TUI, thinks pg_dump failed, but the operation never even started - it timed out during pre-validation checks.
+
+### Bug #21-22: Missing Panic Recovery (v3.42.8)
+**Files**: 
+- `internal/backup/engine.go:442` (BackupCluster goroutines)
+- `internal/restore/engine.go:861` (RestoreCluster goroutines)
+
+**Issue**: No `defer recover()` in parallel goroutines  
+**Impact**: Single database panic crashes entire cluster backup/restore  
+**Fix**: Added panic recovery with error counting
+
+### Bug #23: Variable Shadowing (v3.42.8)
+**File**: `internal/restore/engine.go:416`  
+**Issue**: Used `err` instead of `cmdErr` for exit code detection  
+**Impact**: Incorrect exit code reported in error messages
+
+---
+
+## Code Quality Issues (v3.42.10)
+
+- Deprecated `io/ioutil` usage (Go 1.19+)
+- Duplicate imports
+- Unused fields and variables
+- Error string formatting violations
+- Ineffective assignments
+
+---
+
+## Timeline
+
+- **Bugs introduced**: Unknown (existed 2-3 months)
+- **First report**: ~October 2025
+- **Investigation started**: January 7, 2026
+- **Fixed**: January 8, 2026 (v3.42.5 - v3.42.10)
+
+---
+
+## Customer Impact
+
+**Duration**: 2-3 months of failed backup/restore operations  
+**Symptom**: TUI backups appeared to fail immediately with timeout errors  
+**Actual Issue**: Pre-validation checks timing out, not the actual backup  
+**Business Impact**: Potential data loss risk, support costs, reputation damage
+
+---
+
+## Lessons Learned
+
+1. **Never use arbitrary short timeouts** for operations on potentially large data
+2. **Always use channel-based pattern** for cmd.Wait() with context
+3. **Add panic recovery** to all goroutines in production code
+4. **Test with realistic data sizes** (multi-GB archives)
+5. **Systematic code audits** should be first step, not last resort
+
+---
+
+*This document is for internal use and legal purposes only.*