refactor: move Gitter interface to consumer package internal/cli (task p6)

Per Go best practice (100 Go Mistakes #6): interfaces belong where they are
used, not where they are implemented. Move Gitter from internal/git to
internal/cli/git.go. Compile-time assertions (var _ Gitter = ...) kept in
the new location. internal/git retains concrete *Git and *NoOp types.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

3 files changed, 17 insertions, 39 deletions

diff --git a/internal/git/git.go b/internal/git/git.go
index 72d55af..e9a1b9b 100644
--- a/internal/git/git.go
+++ b/internal/git/git.go
@@ -2,10 +2,10 @@
 // It mirrors the Git module from the original Ruby implementation (geheim.rb lines 79-123),
 // running real git subprocesses rather than using a Go git library.
 //
-// The package exposes a Gitter interface so that callers can accept either a
-// real *Git (backed by a git repository) or a *NoOp stub (for directories that
-// are not git repositories). This avoids nil-pointer panics in the CLI dispatch
-// loop and keeps git-related decisions local to this package.
+// The package exposes concrete types (*Git and *NoOp) but does NOT define a
+// Gitter interface. Per Go best practices (100 Go Mistakes #6), interfaces
+// belong in the consumer package — the Gitter interface lives in internal/cli,
+// which is the only package that needs to abstract over *Git vs *NoOp.
 package git
 
 import (
@@ -18,37 +18,11 @@ import (
 	"strings"
 )
 
-// Gitter is the interface that both *Git (real git operations) and *NoOp
-// (informational no-ops) implement. The CLI holds a Gitter so that it can be
-// freely swapped without changing any dispatch logic.
-type Gitter interface {
-	// Add stages a single file for the next commit.
-	Add(ctx context.Context, filePath string) error
-
-	// Remove stages a file deletion for the next commit.
-	Remove(ctx context.Context, filePath string) error
-
-	// Status prints the current git status of the working directory.
-	Status(ctx context.Context) error
-
-	// Commit records all staged changes with a generic commit message.
-	Commit(ctx context.Context) error
-
-	// Reset discards all uncommitted changes in the working directory.
-	Reset(ctx context.Context) error
-
-	// Sync pulls from and pushes to each configured remote repository.
-	Sync(ctx context.Context, syncRepos []string) error
-}
-
 // Git provides git operations scoped to the secret store's data directory.
 type Git struct {
 	dataDir string
 }
 
-// Compile-time assertion: *Git must satisfy Gitter.
-var _ Gitter = (*Git)(nil)
-
 // New creates a Git helper for the given data directory.
 func New(dataDir string) *Git {
 	return &Git{dataDir: dataDir}
diff --git a/internal/git/git_test.go b/internal/git/git_test.go
index 462c747..4c22fec 100644
--- a/internal/git/git_test.go
+++ b/internal/git/git_test.go
@@ -283,11 +283,14 @@ func TestIsGitRepo_outside(t *testing.T) {
 	}
 }
 
-// TestNoOp_satisfies_Gitter verifies that *git.NoOp compiles as a Gitter and
-// that all its methods return nil (no-op, no error) so they are safe to call
-// unconditionally from CLI dispatch.
-func TestNoOp_satisfies_Gitter(t *testing.T) {
-	var g git.Gitter = git.NewNoOp()
+// TestNoOp_methods verifies that all *git.NoOp methods return nil (no-op, no
+// error) so they are safe to call unconditionally from CLI dispatch.
+//
+// Note: the Gitter interface is defined in internal/cli (the consumer), not
+// here in internal/git (the producer), per Go best practice #6. The
+// compile-time assertion that *NoOp satisfies Gitter lives in internal/cli/git.go.
+func TestNoOp_methods(t *testing.T) {
+	g := git.NewNoOp()
 	ctx := context.Background()
 
 	table := []struct {
diff --git a/internal/git/noop.go b/internal/git/noop.go
index 44dc68c..f125644 100644
--- a/internal/git/noop.go
+++ b/internal/git/noop.go
@@ -9,7 +9,7 @@ import (
 // because the kdbx file is not inside a git repository.
 const noOpMessage = "kdbx file is not in a git repo; skipping"
 
-// NoOp is a Gitter implementation whose every method prints an informational
+// NoOp is a no-op git client whose every method prints an informational
 // message and returns nil. It is used when the KeePass database file lives
 // outside of a git repository so that sync/status/commit/reset commands remain
 // functional and transparent rather than crashing or returning errors.
@@ -17,11 +17,12 @@ const noOpMessage = "kdbx file is not in a git repo; skipping"
 // Keeping the no-op behaviour in its own type (rather than nil-checking in the
 // CLI dispatch) respects the Open/Closed Principle: the CLI is open for
 // extension (new backends, new git behaviours) without modification.
+//
+// NoOp satisfies the Gitter interface defined in internal/cli (the consumer),
+// not here in the producer — per Go best practice #6 from 100 Go Mistakes.
+// The compile-time assertion lives in internal/cli/git.go.
 type NoOp struct{}
 
-// Compile-time assertion: *NoOp must satisfy Gitter.
-var _ Gitter = (*NoOp)(nil)
-
 // NewNoOp returns a *NoOp that satisfies Gitter with all operations being
 // informational no-ops.
 func NewNoOp() *NoOp {