Urgh I made some wrong amends and I'm too tired to separate the commits out this time

ancestor: Split out of reachability
mergebase: Add merge base routines
internal/commitquery: Add commit query context engine thingy
internal/peel: Shared tag peeling
errors: Shared object query errors
internal/testgit: Add rooted repo helpers; remove raw path access
objectstore/memory: Add in-memory object store
objectid: Add Compare helper

2 files changed, 20 insertions, 42 deletions

diff --git a/refstore/loose/loose_test.go b/refstore/loose/loose_test.go
index 7b295bbb..912d7c9e 100644
--- a/refstore/loose/loose_test.go
+++ b/refstore/loose/loose_test.go
@@ -2,8 +2,6 @@ package loose_test
 
 import (
 	"errors"
-	"os"
-	"path/filepath"
 	"slices"
 	"testing"
 
@@ -14,15 +12,10 @@ import (
 	"codeberg.org/lindenii/furgit/refstore/loose"
 )
 
-func openLooseStore(t *testing.T, repoPath string, algo objectid.Algorithm) *loose.Store {
+func openLooseStore(t *testing.T, testRepo *testgit.TestRepo, algo objectid.Algorithm) *loose.Store {
 	t.Helper()
 
-	root, err := os.OpenRoot(repoPath)
-	if err != nil {
-		t.Fatalf("OpenRoot(%q): %v", repoPath, err)
-	}
-
-	t.Cleanup(func() { _ = root.Close() })
+	root := testRepo.OpenGitRoot(t)
 
 	store, err := loose.New(root, algo)
 	if err != nil {
@@ -40,7 +33,7 @@ func TestLooseResolveAndResolveFully(t *testing.T) {
 		testRepo.UpdateRef(t, "refs/heads/main", commitID)
 		testRepo.SymbolicRef(t, "HEAD", "refs/heads/main")
 
-		store := openLooseStore(t, testRepo.Dir(), algo)
+		store := openLooseStore(t, testRepo, algo)
 
 		resolvedHead, err := store.Resolve("HEAD")
 		if err != nil {
@@ -93,7 +86,7 @@ func TestLooseResolveFullyCycle(t *testing.T) {
 		testRepo.SymbolicRef(t, "refs/heads/a", "refs/heads/b")
 		testRepo.SymbolicRef(t, "refs/heads/b", "refs/heads/a")
 
-		store := openLooseStore(t, testRepo.Dir(), algo)
+		store := openLooseStore(t, testRepo, algo)
 
 		_, err := store.ResolveFully("refs/heads/a")
 		if err == nil {
@@ -112,7 +105,7 @@ func TestLooseListPattern(t *testing.T) {
 		testRepo.UpdateRef(t, "refs/tags/v1.0.0", commitID)
 		testRepo.SymbolicRef(t, "HEAD", "refs/heads/main")
 
-		store := openLooseStore(t, testRepo.Dir(), algo)
+		store := openLooseStore(t, testRepo, algo)
 
 		allRefs, err := store.List("")
 		if err != nil {
@@ -161,7 +154,7 @@ func TestLooseListPatternMatrix(t *testing.T) {
 		testRepo.UpdateRef(t, "refs/tags/v1", commitID)
 		testRepo.SymbolicRef(t, "HEAD", "refs/heads/main")
 
-		store := openLooseStore(t, testRepo.Dir(), algo)
+		store := openLooseStore(t, testRepo, algo)
 
 		tests := []struct {
 			pattern string
@@ -223,21 +216,11 @@ func TestLooseMalformedDetachedRef(t *testing.T) {
 	testgit.ForEachAlgorithm(t, func(t *testing.T, algo objectid.Algorithm) { //nolint:thelper
 		testRepo := testgit.NewRepo(t, testgit.RepoOptions{ObjectFormat: algo, Bare: true})
 
-		refPath := filepath.Join(testRepo.Dir(), "refs", "heads", "bad")
-
-		err := os.MkdirAll(filepath.Dir(refPath), 0o755)
-		if err != nil {
-			t.Fatalf("MkdirAll: %v", err)
-		}
-
-		err = os.WriteFile(refPath, []byte("not-a-hash\n"), 0o644)
-		if err != nil {
-			t.Fatalf("WriteFile: %v", err)
-		}
+		testRepo.WriteFileAll(t, "refs/heads/bad", []byte("not-a-hash\n"), 0o755, 0o644)
 
-		store := openLooseStore(t, testRepo.Dir(), algo)
+		store := openLooseStore(t, testRepo, algo)
 
-		_, err = store.Resolve("refs/heads/bad")
+		_, err := store.Resolve("refs/heads/bad")
 		if err == nil {
 			t.Fatalf("Resolve(malformed) expected error")
 		}
@@ -253,7 +236,7 @@ func TestLooseShorten(t *testing.T) {
 		testRepo.UpdateRef(t, "refs/tags/main", commitID)
 		testRepo.UpdateRef(t, "refs/remotes/origin/main", commitID)
 
-		store := openLooseStore(t, testRepo.Dir(), algo)
+		store := openLooseStore(t, testRepo, algo)
 
 		shortHead, err := store.Shorten("refs/heads/main")
 		if err != nil {
diff --git a/refstore/packed/packed_test.go b/refstore/packed/packed_test.go
index 9d6b2fe1..e5a56dda 100644
--- a/refstore/packed/packed_test.go
+++ b/refstore/packed/packed_test.go
@@ -14,15 +14,10 @@ import (
 	"codeberg.org/lindenii/furgit/refstore/packed"
 )
 
-func openPackedRefStoreFromRepo(t *testing.T, repoPath string, algo objectid.Algorithm) *packed.Store {
+func openPackedRefStoreFromRepo(t *testing.T, testRepo *testgit.TestRepo, algo objectid.Algorithm) *packed.Store {
 	t.Helper()
 
-	root, err := os.OpenRoot(repoPath)
-	if err != nil {
-		t.Fatalf("OpenRoot(repo): %v", err)
-	}
-
-	defer func() { _ = root.Close() }()
+	root := testRepo.OpenGitRoot(t)
 
 	store, err := packed.New(root, algo)
 	if err != nil {
@@ -37,11 +32,6 @@ func openPackedRefStoreFromContent(t *testing.T, content string, algo objectid.A
 
 	dir := t.TempDir()
 
-	err := os.WriteFile(dir+"/packed-refs", []byte(content), 0o644)
-	if err != nil {
-		t.Fatalf("WriteFile(packed-refs): %v", err)
-	}
-
 	root, err := os.OpenRoot(dir)
 	if err != nil {
 		t.Fatalf("OpenRoot(temp): %v", err)
@@ -49,6 +39,11 @@ func openPackedRefStoreFromContent(t *testing.T, content string, algo objectid.A
 
 	defer func() { _ = root.Close() }()
 
+	err = root.WriteFile("packed-refs", []byte(content), 0o644)
+	if err != nil {
+		t.Fatalf("WriteFile(packed-refs): %v", err)
+	}
+
 	return packed.New(root, algo)
 }
 
@@ -61,7 +56,7 @@ func TestPackedResolveAndPeeled(t *testing.T) {
 		tagID := testRepo.TagAnnotated(t, "v1.0.0", commitID, "annotated tag")
 		testRepo.PackRefs(t, "--all", "--prune")
 
-		store := openPackedRefStoreFromRepo(t, testRepo.Dir(), algo)
+		store := openPackedRefStoreFromRepo(t, testRepo, algo)
 
 		resolvedMain, err := store.Resolve("refs/heads/main")
 		if err != nil {
@@ -125,7 +120,7 @@ func TestPackedListAndShorten(t *testing.T) {
 		testRepo.UpdateRef(t, "refs/remotes/origin/main", commitID)
 		testRepo.PackRefs(t, "--all", "--prune")
 
-		store := openPackedRefStoreFromRepo(t, testRepo.Dir(), algo)
+		store := openPackedRefStoreFromRepo(t, testRepo, algo)
 
 		all, err := store.List("")
 		if err != nil {
@@ -180,7 +175,7 @@ func TestPackedListPatternMatrix(t *testing.T) {
 		testRepo.UpdateRef(t, "refs/tags/v1", commitID)
 		testRepo.PackRefs(t, "--all", "--prune")
 
-		store := openPackedRefStoreFromRepo(t, testRepo.Dir(), algo)
+		store := openPackedRefStoreFromRepo(t, testRepo, algo)
 
 		tests := []struct {
 			pattern string