diff --git a/internal/git/git.go b/internal/git/git.go
index d8f06d0a..ead1fc1d 100644
--- a/internal/git/git.go
+++ b/internal/git/git.go
@@ -3,7 +3,6 @@ package git
 
 import (
 	"bytes"
-	"errors"
 	"fmt"
 	"os"
 	"os/exec"
@@ -34,47 +33,6 @@ func (e *GitError) Unwrap() error {
 	return e.Err
 }
 
-// HasConflict returns true if the error output indicates a merge conflict.
-// Deprecated: This exists for backwards compatibility. Agents should observe
-// Stderr directly and make their own decisions (ZFC principle).
-func (e *GitError) HasConflict() bool {
-	return strings.Contains(e.Stderr, "CONFLICT") ||
-		strings.Contains(e.Stderr, "Merge conflict") ||
-		strings.Contains(e.Stdout, "CONFLICT")
-}
-
-// HasAuthFailure returns true if the error output indicates authentication failure.
-// Deprecated: This exists for backwards compatibility. Agents should observe
-// Stderr directly and make their own decisions (ZFC principle).
-func (e *GitError) HasAuthFailure() bool {
-	return strings.Contains(e.Stderr, "Authentication failed") ||
-		strings.Contains(e.Stderr, "could not read Username")
-}
-
-// IsNotARepo returns true if the error indicates the path is not a git repository.
-// Deprecated: This exists for backwards compatibility. Agents should observe
-// Stderr directly and make their own decisions (ZFC principle).
-func (e *GitError) IsNotARepo() bool {
-	return strings.Contains(e.Stderr, "not a git repository")
-}
-
-// HasRebaseConflict returns true if the error indicates a rebase conflict.
-// Deprecated: This exists for backwards compatibility. Agents should observe
-// Stderr directly and make their own decisions (ZFC principle).
-func (e *GitError) HasRebaseConflict() bool {
-	return strings.Contains(e.Stderr, "needs merge") ||
-		strings.Contains(e.Stderr, "rebase in progress")
-}
-
-// Common errors - deprecated, kept for backwards compatibility.
-// ZFC: These should not be used; observe GitError.Stderr instead.
-var (
-	ErrNotARepo       = errors.New("not a git repository")
-	ErrMergeConflict  = errors.New("merge conflict")
-	ErrAuthFailure    = errors.New("authentication failed")
-	ErrRebaseConflict = errors.New("rebase conflict")
-)
-
 // Git wraps git operations for a working directory.
 type Git struct {
 	workDir string
@@ -470,21 +428,16 @@ func (g *Git) CheckConflicts(source, target string) ([]string, error) {
 	_, mergeErr := g.runMergeCheck("merge", "--no-commit", "--no-ff", source)
 
 	if mergeErr != nil {
-		// Check if there are unmerged files (indicates conflict)
-		conflicts, err := g.getConflictingFiles()
+		// ZFC: Use git's porcelain output to detect conflicts instead of parsing stderr.
+		// GetConflictingFiles() uses `git diff --diff-filter=U` which is the proper way.
+		conflicts, err := g.GetConflictingFiles()
 		if err == nil && len(conflicts) > 0 {
 			// Abort the test merge (best-effort cleanup)
 			_ = g.AbortMerge()
 			return conflicts, nil
 		}
 
-		// ZFC: Check if the error output indicates a conflict
-		if gitErr, ok := mergeErr.(*GitError); ok && gitErr.HasConflict() {
-			_ = g.AbortMerge() // best-effort cleanup
-			return conflicts, nil
-		}
-
-		// Some other merge error (best-effort cleanup)
+		// No unmerged files detected - this is some other merge error
 		_ = g.AbortMerge()
 		return nil, mergeErr
 	}
@@ -514,8 +467,10 @@ func (g *Git) runMergeCheck(args ...string) (string, error) {
 	return strings.TrimSpace(stdout.String()), nil
 }
 
-// getConflictingFiles returns the list of files with merge conflicts.
-func (g *Git) getConflictingFiles() ([]string, error) {
+// GetConflictingFiles returns the list of files with merge conflicts.
+// ZFC: Uses git's porcelain output (diff --diff-filter=U) instead of parsing stderr.
+// This is the proper way to detect conflicts without violating ZFC.
+func (g *Git) GetConflictingFiles() ([]string, error) {
 	// git diff --name-only --diff-filter=U shows unmerged files
 	out, err := g.run("diff", "--name-only", "--diff-filter=U")
 	if err != nil {
diff --git a/internal/git/git_test.go b/internal/git/git_test.go
index 25fd3f8c..d7d4bacd 100644
--- a/internal/git/git_test.go
+++ b/internal/git/git_test.go
@@ -214,10 +214,16 @@ func TestNotARepo(t *testing.T) {
 	g := NewGit(dir)
 
 	_, err := g.CurrentBranch()
-	// ZFC: Check for not-a-repo via GitError method instead of sentinel error
+	// ZFC: Check for GitError with raw stderr for agent observation.
+	// Agents decide what "not a git repository" means, not Go code.
 	gitErr, ok := err.(*GitError)
-	if !ok || !gitErr.IsNotARepo() {
-		t.Errorf("expected GitError with IsNotARepo(), got %v", err)
+	if !ok {
+		t.Errorf("expected GitError, got %T: %v", err, err)
+		return
+	}
+	// Verify raw stderr is available for agent observation
+	if gitErr.Stderr == "" {
+		t.Errorf("expected GitError with Stderr, got empty stderr")
 	}
 }
 
diff --git a/internal/refinery/engineer.go b/internal/refinery/engineer.go
index 15a96199..af065d45 100644
--- a/internal/refinery/engineer.go
+++ b/internal/refinery/engineer.go
@@ -311,8 +311,10 @@ func (e *Engineer) doMerge(ctx context.Context, branch, target, sourceIssue stri
 	}
 	_, _ = fmt.Fprintf(e.output, "[Engineer] Merging with message: %s\n", mergeMsg)
 	if err := e.git.MergeNoFF(branch, mergeMsg); err != nil {
-		// ZFC: Check for conflict via GitError method instead of sentinel error
-		if gitErr, ok := err.(*git.GitError); ok && gitErr.HasConflict() {
+		// ZFC: Use git's porcelain output to detect conflicts instead of parsing stderr.
+		// GetConflictingFiles() uses `git diff --diff-filter=U` which is proper.
+		conflicts, conflictErr := e.git.GetConflictingFiles()
+		if conflictErr == nil && len(conflicts) > 0 {
 			_ = e.git.AbortMerge()
 			return ProcessResult{
 				Success:  false,
diff --git a/internal/swarm/integration.go b/internal/swarm/integration.go
index 8c27ad69..c18f6f59 100644
--- a/internal/swarm/integration.go
+++ b/internal/swarm/integration.go
@@ -31,14 +31,6 @@ func (e *SwarmGitError) Error() string {
 	return fmt.Sprintf("%s: %v", e.Command, e.Err)
 }
 
-// HasConflict returns true if the error output indicates a merge conflict.
-// Deprecated: Agents should observe Stderr directly (ZFC principle).
-func (e *SwarmGitError) HasConflict() bool {
-	return strings.Contains(e.Stderr, "CONFLICT") ||
-		strings.Contains(e.Stderr, "Merge conflict") ||
-		strings.Contains(e.Stdout, "CONFLICT")
-}
-
 // CreateIntegrationBranch creates the integration branch for a swarm.
 // The branch is created from the swarm's BaseCommit and pushed to origin.
 func (m *Manager) CreateIntegrationBranch(swarmID string) error {
@@ -92,9 +84,11 @@ func (m *Manager) MergeToIntegration(swarmID, workerBranch string) error {
 		fmt.Sprintf("Merge %s into %s", workerBranch, swarm.Integration),
 		workerBranch)
 	if err != nil {
-		// ZFC: Check for conflict via SwarmGitError method
-		if gitErr, ok := err.(*SwarmGitError); ok && gitErr.HasConflict() {
-			return gitErr // Return the error with raw output for observation
+		// ZFC: Use git's porcelain output to detect conflicts instead of parsing stderr.
+		conflicts, conflictErr := m.getConflictingFiles()
+		if conflictErr == nil && len(conflicts) > 0 {
+			// Return the original error with raw output for observation
+			return err
 		}
 		return fmt.Errorf("merging: %w", err)
 	}
@@ -127,9 +121,11 @@ func (m *Manager) LandToMain(swarmID string) error {
 		fmt.Sprintf("Land swarm %s", swarmID),
 		swarm.Integration)
 	if err != nil {
-		// ZFC: Check for conflict via SwarmGitError method
-		if gitErr, ok := err.(*SwarmGitError); ok && gitErr.HasConflict() {
-			return gitErr // Return the error with raw output for observation
+		// ZFC: Use git's porcelain output to detect conflicts instead of parsing stderr.
+		conflicts, conflictErr := m.getConflictingFiles()
+		if conflictErr == nil && len(conflicts) > 0 {
+			// Return the original error with raw output for observation
+			return err
 		}
 		return fmt.Errorf("merging to %s: %w", swarm.TargetBranch, err)
 	}
@@ -207,6 +203,34 @@ func (m *Manager) getCurrentBranch() (string, error) {
 	return strings.TrimSpace(stdout.String()), nil
 }
 
+// getConflictingFiles returns the list of files with merge conflicts.
+// ZFC: Uses git's porcelain output (diff --diff-filter=U) instead of parsing stderr.
+func (m *Manager) getConflictingFiles() ([]string, error) {
+	cmd := exec.Command("git", "diff", "--name-only", "--diff-filter=U")
+	cmd.Dir = m.gitDir
+
+	var stdout bytes.Buffer
+	cmd.Stdout = &stdout
+
+	if err := cmd.Run(); err != nil {
+		return nil, err
+	}
+
+	out := strings.TrimSpace(stdout.String())
+	if out == "" {
+		return nil, nil
+	}
+
+	files := strings.Split(out, "\n")
+	var result []string
+	for _, f := range files {
+		if f != "" {
+			result = append(result, f)
+		}
+	}
+	return result, nil
+}
+
 // gitRun executes a git command.
 // ZFC: Returns SwarmGitError with raw output for agent observation.
 func (m *Manager) gitRun(args ...string) error {