fix(io): add contextual error handling with E() helper

Address CodeRabbit review feedback by wrapping raw errors with the
errors.E() helper to provide service/action context for debugging:

- pkg/cache: wrap cache.New, Get, Set, Delete, Clear errors
- pkg/devops/test: wrap LoadTestConfig path/read/parse errors
- pkg/cli/daemon: wrap PIDFile.Release path resolution error
- pkg/container/state: wrap LoadState/SaveState errors
- pkg/container/templates: wrap GetTemplate embedded/user read errors

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

pkg/cache/cache.go

@@ -7,6 +7,7 @@ import (
 	"path/filepath"
 	"time"
 
+	"github.com/host-uk/core/pkg/errors"
 	"github.com/host-uk/core/pkg/io"
 )
 
@@ -33,7 +34,7 @@ func New(baseDir string, ttl time.Duration) (*Cache, error) {
 		// Use .core/cache in current working directory
 		cwd, err := os.Getwd()
 		if err != nil {
-			return nil, err
+			return nil, errors.E("cache.New", "failed to get working directory", err)
 		}
 		baseDir = filepath.Join(cwd, ".core", "cache")
 	}
@@ -45,12 +46,12 @@ func New(baseDir string, ttl time.Duration) (*Cache, error) {
 	// Convert to absolute path for io.Local
 	absBaseDir, err := filepath.Abs(baseDir)
 	if err != nil {
-		return nil, err
+		return nil, errors.E("cache.New", "failed to resolve absolute path", err)
 	}
 
 	// Ensure cache directory exists
 	if err := io.Local.EnsureDir(absBaseDir); err != nil {
-		return nil, err
+		return nil, errors.E("cache.New", "failed to create cache directory", err)
 	}
 
 	baseDir = absBaseDir
@@ -75,7 +76,7 @@ func (c *Cache) Get(key string, dest interface{}) (bool, error) {
 		if os.IsNotExist(err) {
 			return false, nil
 		}
-		return false, err
+		return false, errors.E("cache.Get", "failed to read cache file", err)
 	}
 	data := []byte(content)
 
@@ -92,7 +93,7 @@ func (c *Cache) Get(key string, dest interface{}) (bool, error) {
 
 	// Unmarshal the actual data
 	if err := json.Unmarshal(entry.Data, dest); err != nil {
-		return false, err
+		return false, errors.E("cache.Get", "failed to unmarshal cache data", err)
 	}
 
 	return true, nil
@@ -105,7 +106,7 @@ func (c *Cache) Set(key string, data interface{}) error {
 	// Marshal the data
 	dataBytes, err := json.Marshal(data)
 	if err != nil {
-		return err
+		return errors.E("cache.Set", "failed to marshal data", err)
 	}
 
 	entry := Entry{
@@ -116,26 +117,35 @@ func (c *Cache) Set(key string, data interface{}) error {
 
 	entryBytes, err := json.MarshalIndent(entry, "", "  ")
 	if err != nil {
-		return err
+		return errors.E("cache.Set", "failed to marshal cache entry", err)
 	}
 
 	// io.Local.Write creates parent directories automatically
-	return io.Local.Write(path, string(entryBytes))
+	if err := io.Local.Write(path, string(entryBytes)); err != nil {
+		return errors.E("cache.Set", "failed to write cache file", err)
+	}
+	return nil
 }
 
 // Delete removes an item from the cache.
 func (c *Cache) Delete(key string) error {
 	path := c.Path(key)
 	err := io.Local.Delete(path)
-	if os.IsNotExist(err) {
-		return nil
+	if err != nil {
+		if os.IsNotExist(err) {
+			return nil
+		}
+		return errors.E("cache.Delete", "failed to delete cache file", err)
 	}
-	return err
+	return nil
 }
 
 // Clear removes all cached items.
 func (c *Cache) Clear() error {
-	return io.Local.DeleteAll(c.baseDir)
+	if err := io.Local.DeleteAll(c.baseDir); err != nil {
+		return errors.E("cache.Clear", "failed to clear cache directory", err)
+	}
+	return nil
 }
 
 // Age returns how old a cached item is, or -1 if not cached.

pkg/cli/daemon.go

@@ -124,9 +124,12 @@ func (p *PIDFile) Release() error {
 	defer p.mu.Unlock()
 	absPath, err := filepath.Abs(p.path)
 	if err != nil {
-		return err
+		return fmt.Errorf("failed to resolve PID file path: %w", err)
 	}
-	return io.Local.Delete(absPath)
+	if err := io.Local.Delete(absPath); err != nil {
+		return fmt.Errorf("failed to delete PID file: %w", err)
+	}
+	return nil
 }
 
 // Path returns the PID file path.

pkg/container/state.go

@@ -6,6 +6,7 @@ import (
 	"path/filepath"
 	"sync"
 
+	"github.com/host-uk/core/pkg/errors"
 	"github.com/host-uk/core/pkg/io"
 )
 
@@ -60,7 +61,7 @@ func LoadState(filePath string) (*State, error) {
 
 	absPath, err := filepath.Abs(filePath)
 	if err != nil {
-		return nil, err
+		return nil, errors.E("container.LoadState", "failed to resolve state file path", err)
 	}
 
 	content, err := io.Local.Read(absPath)
@@ -68,11 +69,11 @@ func LoadState(filePath string) (*State, error) {
 		if os.IsNotExist(err) {
 			return state, nil
 		}
-		return nil, err
+		return nil, errors.E("container.LoadState", "failed to read state file", err)
 	}
 
 	if err := json.Unmarshal([]byte(content), state); err != nil {
-		return nil, err
+		return nil, errors.E("container.LoadState", "failed to parse state file", err)
 	}
 
 	return state, nil
@@ -85,16 +86,19 @@ func (s *State) SaveState() error {
 
 	absPath, err := filepath.Abs(s.filePath)
 	if err != nil {
-		return err
+		return errors.E("container.SaveState", "failed to resolve state file path", err)
 	}
 
 	data, err := json.MarshalIndent(s, "", "  ")
 	if err != nil {
-		return err
+		return errors.E("container.SaveState", "failed to marshal state", err)
 	}
 
 	// io.Local.Write creates parent directories automatically
-	return io.Local.Write(absPath, string(data))
+	if err := io.Local.Write(absPath, string(data)); err != nil {
+		return errors.E("container.SaveState", "failed to write state file", err)
+	}
+	return nil
 }
 
 // Add adds a container to the state and persists it.

pkg/container/templates.go

@@ -8,6 +8,7 @@ import (
 	"regexp"
 	"strings"
 
+	"github.com/host-uk/core/pkg/errors"
 	"github.com/host-uk/core/pkg/io"
 )
 
@@ -63,7 +64,7 @@ func GetTemplate(name string) (string, error) {
 		if t.Name == name {
 			content, err := embeddedTemplates.ReadFile(t.Path)
 			if err != nil {
-				return "", fmt.Errorf("failed to read embedded template %s: %w", name, err)
+				return "", errors.E("container.GetTemplate", "failed to read embedded template", err)
 			}
 			return string(content), nil
 		}
@@ -76,13 +77,13 @@ func GetTemplate(name string) (string, error) {
 		if io.Local.IsFile(templatePath) {
 			content, err := io.Local.Read(templatePath)
 			if err != nil {
-				return "", fmt.Errorf("failed to read user template %s: %w", name, err)
+				return "", errors.E("container.GetTemplate", "failed to read user template", err)
 			}
 			return content, nil
 		}
 	}
 
-	return "", fmt.Errorf("template not found: %s", name)
+	return "", errors.E("container.GetTemplate", "template not found: "+name, nil)
 }
 
 // ApplyTemplate applies variable substitution to a template.

pkg/devops/test.go

@@ -7,6 +7,7 @@ import (
 	"path/filepath"
 	"strings"
 
+	"github.com/host-uk/core/pkg/errors"
 	"github.com/host-uk/core/pkg/io"
 	"gopkg.in/yaml.v3"
 )
@@ -116,17 +117,17 @@ func LoadTestConfig(projectDir string) (*TestConfig, error) {
 	path := filepath.Join(projectDir, ".core", "test.yaml")
 	absPath, err := filepath.Abs(path)
 	if err != nil {
-		return nil, err
+		return nil, errors.E("devops.LoadTestConfig", "failed to resolve path", err)
 	}
 
 	content, err := io.Local.Read(absPath)
 	if err != nil {
-		return nil, err
+		return nil, errors.E("devops.LoadTestConfig", "failed to read test config", err)
 	}
 
 	var cfg TestConfig
 	if err := yaml.Unmarshal([]byte(content), &cfg); err != nil {
-		return nil, err
+		return nil, errors.E("devops.LoadTestConfig", "failed to parse test config", err)
 	}
 
 	return &cfg, nil