test(bf-1h5og): add test utility and error handling imports

Add comprehensive test utility and error handling imports to encryption test files:

- Added std::error::Error and std::io for error handling
- Expanded pdftract_core::diagnostics imports to include Diagnostic, DiagnosticsCollector, and ObjRef
- Ensured both test_encryption_errors.rs and test_encryption_unsupported.rs have consistent imports

All imports verified against actual crate structure and compile successfully.

Closes bf-1h5og. Verification: notes/bf-1h5og.md.

crates/pdftract-cli/tests/test_encryption_errors.rs

@@ -19,13 +19,17 @@
 //! - Plan line 1132: RC4 and AES-128/256 decryption implementation
 //! - Plan line 1149: Encrypted file with unknown handler error handling
 
+use std::error::Error;
 use std::fs;
+use std::io;
 use std::path::{Path, PathBuf};
 use std::process::Command;
 
 // CLI module imports for encryption testing
 use pdftract_cli::password;
-use pdftract_core::diagnostics::{DiagCode, DiagInfo, Severity, DIAGNOSTIC_CATALOG};
+use pdftract_core::diagnostics::{
+    DiagCode, DiagInfo, Diagnostic, DiagnosticsCollector, ObjRef, Severity, DIAGNOSTIC_CATALOG,
+};
 
 /// Get the workspace root directory
 fn workspace_root() -> PathBuf {

crates/pdftract-cli/tests/test_encryption_unsupported.rs

@@ -4,11 +4,15 @@
 //! and exits with code 3 when run on an owner-password-only encrypted PDF
 //! (or a PDF with an unsupported encryption handler like Adobe LiveCycle).
 
+use std::error::Error;
+use std::io;
 use std::process::Command;
 
 // CLI module imports for encryption testing
 use pdftract_cli::password;
-use pdftract_core::diagnostics::{DiagCode, DiagInfo, Severity, DIAGNOSTIC_CATALOG};
+use pdftract_core::diagnostics::{
+    DiagCode, DiagInfo, Diagnostic, DiagnosticsCollector, ObjRef, Severity, DIAGNOSTIC_CATALOG,
+};
 
 #[test]
 fn test_livecycle_pdf_emits_encryption_unsupported() {

notes/bf-1h5og.md

@@ -0,0 +1,50 @@
+# Verification Note: bf-1h5og - Add test utility and error handling imports
+
+## Summary
+Added comprehensive test utility and error handling imports to both encryption test files.
+
+## Changes Made
+
+### 1. Enhanced test_encryption_errors.rs imports
+Added imports:
+- `std::error::Error` - for error handling patterns
+- `std::io` - for I/O operations
+- `Diagnostic`, `DiagnosticsCollector`, `ObjRef` from `pdftract_core::diagnostics` - for detailed diagnostic testing
+
+### 2. Enhanced test_encryption_unsupported.rs imports
+Added the same comprehensive imports for consistency:
+- `std::error::Error` - for error handling patterns  
+- `std::io` - for I/O operations
+- `Diagnostic`, `DiagnosticsCollector`, `ObjRef` from `pdftract_core::diagnostics` - for detailed diagnostic testing
+
+## Verification
+
+### Compilation Status
+✅ PASS - Both test files compile successfully with `cargo test --test test_encryption_errors --test test_encryption_unsupported --no-run`
+
+### Imports Match Actual Crate Structure
+✅ PASS - All imports verified against actual exports:
+- `pdftract_core::diagnostics` exports: `DiagCode`, `DiagInfo`, `Diagnostic`, `DiagnosticsCollector`, `ObjRef`, `Severity`, `DIAGNOSTIC_CATALOG`
+- `pdftract_cli::password` - confirmed as public module
+- Standard library imports: `std::error::Error`, `std::io`, `std::fs`, `std::path`, `std::process::Command`
+
+### Test Utility Imports
+✅ PASS - Test utilities now include:
+- Error handling types (`Error`, `io`)
+- Comprehensive diagnostic types for advanced testing
+- All necessary CLI and core imports
+
+### Files Modified
+- `/home/coding/pdftract/crates/pdftract-cli/tests/test_encryption_errors.rs`
+- `/home/coding/pdftract/crates/pdftract-cli/tests/test_encryption_unsupported.rs`
+
+## Acceptance Criteria Status
+
+- ✅ Test utility imports added
+- ✅ Error handling type imports added  
+- ✅ Imports compile successfully
+- ✅ Imports match actual crate structure
+
+## References
+- Parent bead: bf-2nl4x
+- Plan line 258, Failure Mode Taxonomy: ENCRYPTION_UNSUPPORTED