refactor: extract shared SplitFrontmatter, delete 4 dead delimiter errors

Extract duplicated frontmatter splitting logic from steering/ and
skill/ into parse.SplitFrontmatter. Both callers now delegate to
the shared function and wrap errors with domain-specific context.

Delete 4 dead error constructors (MissingOpeningDelimiter,
MissingClosingDelimiter in err/steering and err/skill) and their
DescKey constants + YAML entries. Add new err/parser delimiter
constructors used by the shared function.

Spec: specs/ast-audit-contributor-guide.md
Signed-off-by: Jose Alekhinne <jose@ctx.ist>

Author: josealekhine

internal/assets/commands/text/errors.yaml

@@ -446,12 +446,8 @@ err.skill.invalid-yaml:
   short: 'skill: %s: invalid YAML frontmatter: %w'
 err.skill.load:
   short: 'skill: %s: %w'
-err.skill.missing-closing-delimiter:
-  short: missing closing frontmatter delimiter (---)
 err.skill.missing-name:
   short: 'skill: %s is missing required ''name'' field'
-err.skill.missing-opening-delimiter:
-  short: missing opening frontmatter delimiter (---)
 err.skill.not-found:
   short: 'skill %q not found'
 err.skill.not-valid-dir:
@@ -478,10 +474,6 @@ err.steering.file-exists:
   short: 'steering file already exists: %s'
 err.steering.invalid-yaml:
   short: 'steering: %s: invalid YAML frontmatter: %w'
-err.steering.missing-closing-delimiter:
-  short: missing closing frontmatter delimiter (---)
-err.steering.missing-opening-delimiter:
-  short: missing opening frontmatter delimiter (---)
 err.steering.no-tool:
   short: 'no tool specified: use --tool <tool>, --all, or set the tool field in .ctxrc'
 err.steering.output-escapes-root:
@@ -572,3 +564,7 @@ err.validation.parse-file:
   short: 'failed to parse %s: %w'
 err.validation.working-directory:
   short: 'failed to get working directory: %w'
+err.parser.missing-open-delim:
+  short: missing opening frontmatter delimiter (---)
+err.parser.missing-close-delim:
+  short: missing closing frontmatter delimiter (---)

internal/config/embed/text/err_parse.go

@@ -23,4 +23,10 @@ const (
 	DescKeyErrParserUnmarshal = "err.parser.unmarshal"
 	// DescKeyErrParserWalkDir is the text key for err parser walk dir messages.
 	DescKeyErrParserWalkDir = "err.parser.walk-dir"
+	// DescKeyErrParserMissingOpenDelim is the text key for
+	// missing opening frontmatter delimiter.
+	DescKeyErrParserMissingOpenDelim = "err.parser.missing-open-delim"
+	// DescKeyErrParserMissingCloseDelim is the text key
+	// for missing closing frontmatter delimiter.
+	DescKeyErrParserMissingCloseDelim = "err.parser.missing-close-delim"
 )

internal/config/embed/text/err_skill.go

@@ -23,15 +23,9 @@ const (
 	DescKeyErrSkillList = "err.skill.skill-list"
 	// DescKeyErrSkillLoad is the text key for err skill load messages.
 	DescKeyErrSkillLoad = "err.skill.load"
-	// DescKeyErrSkillMissingClosingDelim is the text key for err skill missing
-	// closing delim messages.
-	DescKeyErrSkillMissingClosingDelim = "err.skill.missing-closing-delimiter"
 	// DescKeyErrSkillMissingName is the text key for err skill missing name
 	// messages.
 	DescKeyErrSkillMissingName = "err.skill.missing-name"
-	// DescKeyErrSkillMissingOpeningDelim is the text key for err skill missing
-	// opening delim messages.
-	DescKeyErrSkillMissingOpeningDelim = "err.skill.missing-opening-delimiter"
 	// DescKeyErrSkillNotFound is the text key for err skill not found messages.
 	DescKeyErrSkillNotFound = "err.skill.not-found"
 	// DescKeyErrSkillNotValidDir is the text key for err skill not valid dir

internal/config/embed/text/err_steering.go

@@ -23,12 +23,6 @@ const (
 	// DescKeyErrSteeringInvalidYAML is the text key for err steering invalid yaml
 	// messages.
 	DescKeyErrSteeringInvalidYAML = "err.steering.invalid-yaml"
-	// DescKeyErrSteeringMissingClosingDelim is the text key for err steering
-	// missing closing delim messages.
-	DescKeyErrSteeringMissingClosingDelim = "err.steering.missing-closing-delimiter"
-	// DescKeyErrSteeringMissingOpeningDelim is the text key for err steering
-	// missing opening delim messages.
-	DescKeyErrSteeringMissingOpeningDelim = "err.steering.missing-opening-delimiter"
 	// DescKeyErrSteeringNoTool is the text key for err steering no tool messages.
 	DescKeyErrSteeringNoTool = "err.steering.no-tool"
 	// DescKeyErrSteeringOutputEscapesRoot is the text key for err steering output

internal/err/parser/parser.go

@@ -7,12 +7,39 @@
 package parser
 
 import (
+	"errors"
 	"fmt"
 
 	"github.com/ActiveMemory/ctx/internal/assets/read/desc"
 	"github.com/ActiveMemory/ctx/internal/config/embed/text"
 )
 
+// MissingOpenDelim returns an error for a missing
+// opening frontmatter delimiter (---).
+//
+// Returns:
+//   - error: "missing opening frontmatter delimiter"
+func MissingOpenDelim() error {
+	return errors.New(
+		desc.Text(
+			text.DescKeyErrParserMissingOpenDelim,
+		),
+	)
+}
+
+// MissingCloseDelim returns an error for a missing
+// closing frontmatter delimiter (---).
+//
+// Returns:
+//   - error: "missing closing frontmatter delimiter"
+func MissingCloseDelim() error {
+	return errors.New(
+		desc.Text(
+			text.DescKeyErrParserMissingCloseDelim,
+		),
+	)
+}
+
 // ReadFile wraps a session file read failure.
 //
 // Parameters:

internal/err/skill/skill.go

@@ -7,7 +7,6 @@
 package skill
 
 import (
-	"errors"
 	"fmt"
 
 	"github.com/ActiveMemory/ctx/internal/assets/read/desc"
@@ -94,17 +93,6 @@ func Load(name string, cause error) error {
 	)
 }
 
-// MissingClosingDelimiter returns an error for missing closing
-// frontmatter delimiter.
-//
-// Returns:
-//   - error: "missing closing frontmatter delimiter (---)"
-func MissingClosingDelimiter() error {
-	return errors.New(
-		desc.Text(text.DescKeyErrSkillMissingClosingDelim),
-	)
-}
-
 // MissingName returns an error for a skill manifest missing the
 // required name field.
 //
@@ -119,17 +107,6 @@ func MissingName(manifest string) error {
 	)
 }
 
-// MissingOpeningDelimiter returns an error for missing opening
-// frontmatter delimiter.
-//
-// Returns:
-//   - error: "missing opening frontmatter delimiter (---)"
-func MissingOpeningDelimiter() error {
-	return errors.New(
-		desc.Text(text.DescKeyErrSkillMissingOpeningDelim),
-	)
-}
-
 // NotFound returns an error when a skill cannot be found by name.
 //
 // Parameters:

internal/err/steering/steering.go

@@ -78,28 +78,6 @@ func InvalidYAML(filePath string, cause error) error {
 	)
 }
 
-// MissingClosingDelimiter returns an error for missing closing
-// frontmatter delimiter.
-//
-// Returns:
-//   - error: "missing closing frontmatter delimiter (---)"
-func MissingClosingDelimiter() error {
-	return errors.New(
-		desc.Text(text.DescKeyErrSteeringMissingClosingDelim),
-	)
-}
-
-// MissingOpeningDelimiter returns an error for missing opening
-// frontmatter delimiter.
-//
-// Returns:
-//   - error: "missing opening frontmatter delimiter (---)"
-func MissingOpeningDelimiter() error {
-	return errors.New(
-		desc.Text(text.DescKeyErrSteeringMissingOpeningDelim),
-	)
-}
-
 // NoTool returns an error when no tool is specified for sync.
 //
 // Returns:

internal/parse/markdown.go

@@ -11,6 +11,7 @@ import (
 
 	"github.com/ActiveMemory/ctx/internal/config/regex"
 	"github.com/ActiveMemory/ctx/internal/config/token"
+	errParser "github.com/ActiveMemory/ctx/internal/err/parser"
 )
 
 // StripLineNumbers removes Claude Code's line number prefixes from content.
@@ -85,3 +86,48 @@ func FenceForContent(content string) string {
 	}
 	return fence
 }
+
+// SplitFrontmatter separates YAML frontmatter from a
+// markdown body. Frontmatter must start with a ---
+// line and end with a second --- line.
+//
+// Parameters:
+//   - data: Raw file bytes
+//
+// Returns:
+//   - []byte: YAML frontmatter (between delimiters)
+//   - string: Body after the closing delimiter
+//   - error: Non-nil if delimiters are missing
+func SplitFrontmatter(
+	data []byte,
+) ([]byte, string, error) {
+	content := strings.TrimLeft(
+		string(data), token.TrimCR,
+	)
+
+	if !strings.HasPrefix(
+		content, token.FrontmatterDelimiter,
+	) {
+		return nil, "", errParser.MissingOpenDelim()
+	}
+
+	rest := content[len(token.FrontmatterDelimiter):]
+	rest = strings.TrimPrefix(rest, token.NewlineLF)
+
+	needle := token.NewlineLF +
+		token.FrontmatterDelimiter
+	idx := strings.Index(rest, needle)
+	if idx < 0 {
+		return nil, "", errParser.MissingCloseDelim()
+	}
+
+	fm := rest[:idx]
+	after := rest[idx+1+len(
+		token.FrontmatterDelimiter,
+	):]
+	after = strings.TrimPrefix(
+		after, token.NewlineLF,
+	)
+
+	return []byte(fm), after, nil
+}

internal/skill/manifest.go

@@ -7,59 +7,34 @@
 package skill
 
 import (
-	"strings"
-
 	"gopkg.in/yaml.v3"
 
-	"github.com/ActiveMemory/ctx/internal/config/token"
 	errSkill "github.com/ActiveMemory/ctx/internal/err/skill"
+	"github.com/ActiveMemory/ctx/internal/parse"
 )
 
-// parseManifest extracts YAML frontmatter and markdown body from a
-// SKILL.md file. The frontmatter is delimited by --- lines.
-func parseManifest(data []byte, name, dir string) (*Skill, error) {
-	raw, body, splitErr := splitFrontmatter(data)
+// parseManifest extracts YAML frontmatter and markdown
+// body from a SKILL.md file.
+func parseManifest(
+	data []byte, name, dir string,
+) (*Skill, error) {
+	raw, body, splitErr := parse.SplitFrontmatter(
+		data,
+	)
 	if splitErr != nil {
 		return nil, errSkill.Load(name, splitErr)
 	}
 
 	sk := &Skill{}
-	if unmarshalErr := yaml.Unmarshal(raw, sk); unmarshalErr != nil {
-		return nil, errSkill.InvalidYAML(name, unmarshalErr)
+	if unmarshalErr := yaml.Unmarshal(
+		raw, sk,
+	); unmarshalErr != nil {
+		return nil, errSkill.InvalidYAML(
+			name, unmarshalErr,
+		)
 	}
 
 	sk.Body = body
 	sk.Dir = dir
 	return sk, nil
 }
-
-// splitFrontmatter separates YAML frontmatter from the markdown body.
-// Frontmatter must start with a --- line and end with a second --- line.
-func splitFrontmatter(
-	data []byte,
-) (frontmatter []byte, body string, err error) {
-	content := strings.TrimLeft(string(data), token.TrimCR)
-
-	if !strings.HasPrefix(content, token.FrontmatterDelimiter) {
-		return nil, "", errSkill.MissingOpeningDelimiter()
-	}
-
-	// Skip the opening delimiter line.
-	rest := content[len(token.FrontmatterDelimiter):]
-	rest = strings.TrimPrefix(rest, token.NewlineLF)
-
-	needle := token.NewlineLF + token.FrontmatterDelimiter
-	idx := strings.Index(rest, needle)
-	if idx < 0 {
-		return nil, "", errSkill.MissingClosingDelimiter()
-	}
-
-	fm := rest[:idx]
-
-	// Skip past the closing delimiter line.
-	after := rest[idx+1+len(token.FrontmatterDelimiter):]
-	// Trim exactly one leading newline from the body if present.
-	after = strings.TrimPrefix(after, token.NewlineLF)
-
-	return []byte(fm), after, nil
-}

internal/steering/frontmatter.go

@@ -7,45 +7,9 @@
 package steering
 
 import (
-	"strings"
-
 	cfgSteering "github.com/ActiveMemory/ctx/internal/config/steering"
-	"github.com/ActiveMemory/ctx/internal/config/token"
-	errSteering "github.com/ActiveMemory/ctx/internal/err/steering"
 )
 
-// splitFrontmatter separates YAML frontmatter from the markdown body.
-// Frontmatter must start with a --- line and end with a second --- line.
-func splitFrontmatter(
-	data []byte,
-) (frontmatter []byte, body string, err error) {
-	content := string(data)
-	content = strings.TrimLeft(content, token.TrimCR)
-
-	if !strings.HasPrefix(content, token.FrontmatterDelimiter) {
-		return nil, "", errSteering.MissingOpeningDelimiter()
-	}
-
-	// Skip the opening delimiter line.
-	rest := content[len(token.FrontmatterDelimiter):]
-	rest = strings.TrimPrefix(rest, token.NewlineLF)
-
-	needle := token.NewlineLF + token.FrontmatterDelimiter
-	idx := strings.Index(rest, needle)
-	if idx < 0 {
-		return nil, "", errSteering.MissingClosingDelimiter()
-	}
-
-	fm := rest[:idx]
-
-	// Skip past the closing delimiter line.
-	after := rest[idx+1+len(token.FrontmatterDelimiter):]
-	// Trim exactly one leading newline from the body if present.
-	after = strings.TrimPrefix(after, token.NewlineLF)
-
-	return []byte(fm), after, nil
-}
-
 // applyDefaults sets default values for fields not present in the
 // parsed frontmatter.
 func applyDefaults(sf *SteeringFile) {