perf: batch external dep checks by project (bd-687v)

Optimize CheckExternalDeps to group refs by project and open each
external DB only once, checking all capabilities in a single query.

Before: If 10 issues depend on external:gastown:cap1, we opened
gastown's DB 10 times.

After: We open each external project's DB once, query for all
capabilities needed from that project, then close.

Also added deduplication in filterByExternalDeps to collect all
unique refs before checking, avoiding redundant checks for the
same ref across multiple issues.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

internal/storage/sqlite/ready_test.go

@@ -1513,6 +1513,140 @@ func TestCheckExternalDepInvalidFormats(t *testing.T) {
 	}
 }
 
+// TestCheckExternalDepsBatching verifies that CheckExternalDeps correctly
+// batches multiple refs to the same project and deduplicates refs (bd-687v).
+func TestCheckExternalDepsBatching(t *testing.T) {
+	ctx := context.Background()
+
+	// Initialize config (required for config.Set to work)
+	if err := config.Initialize(); err != nil {
+		t.Fatalf("failed to initialize config: %v", err)
+	}
+
+	// Create external project directory with beads database
+	externalDir, err := os.MkdirTemp("", "beads-batch-test-*")
+	if err != nil {
+		t.Fatalf("failed to create external temp dir: %v", err)
+	}
+	defer os.RemoveAll(externalDir)
+
+	// Create .beads directory and config
+	beadsDir := filepath.Join(externalDir, ".beads")
+	if err := os.MkdirAll(beadsDir, 0755); err != nil {
+		t.Fatalf("failed to create beads dir: %v", err)
+	}
+	cfg := configfile.DefaultConfig()
+	if err := cfg.Save(beadsDir); err != nil {
+		t.Fatalf("failed to save config: %v", err)
+	}
+
+	// Create external database
+	externalDBPath := filepath.Join(beadsDir, "beads.db")
+	externalStore, err := New(ctx, externalDBPath)
+	if err != nil {
+		t.Fatalf("failed to create external store: %v", err)
+	}
+
+	if err := externalStore.SetConfig(ctx, "issue_prefix", "ext"); err != nil {
+		t.Fatalf("failed to set issue_prefix: %v", err)
+	}
+
+	// Ship capability "cap1" (closed issue with provides:cap1 label)
+	cap1Issue := &types.Issue{
+		ID:        "ext-cap1",
+		Title:     "Capability 1",
+		Status:    types.StatusOpen,
+		Priority:  1,
+		IssueType: types.TypeFeature,
+	}
+	if err := externalStore.CreateIssue(ctx, cap1Issue, "test-user"); err != nil {
+		t.Fatalf("failed to create cap1 issue: %v", err)
+	}
+	if err := externalStore.AddLabel(ctx, cap1Issue.ID, "provides:cap1", "test-user"); err != nil {
+		t.Fatalf("failed to add provides:cap1 label: %v", err)
+	}
+	if err := externalStore.CloseIssue(ctx, cap1Issue.ID, "Shipped", "test-user", ""); err != nil {
+		t.Fatalf("failed to close cap1 issue: %v", err)
+	}
+
+	// Ship capability "cap2"
+	cap2Issue := &types.Issue{
+		ID:        "ext-cap2",
+		Title:     "Capability 2",
+		Status:    types.StatusOpen,
+		Priority:  1,
+		IssueType: types.TypeFeature,
+	}
+	if err := externalStore.CreateIssue(ctx, cap2Issue, "test-user"); err != nil {
+		t.Fatalf("failed to create cap2 issue: %v", err)
+	}
+	if err := externalStore.AddLabel(ctx, cap2Issue.ID, "provides:cap2", "test-user"); err != nil {
+		t.Fatalf("failed to add provides:cap2 label: %v", err)
+	}
+	if err := externalStore.CloseIssue(ctx, cap2Issue.ID, "Shipped", "test-user", ""); err != nil {
+		t.Fatalf("failed to close cap2 issue: %v", err)
+	}
+
+	// Close to checkpoint WAL before read-only access
+	externalStore.Close()
+
+	// Configure external_projects
+	oldProjects := config.GetExternalProjects()
+	t.Cleanup(func() {
+		if oldProjects != nil {
+			config.Set("external_projects", oldProjects)
+		} else {
+			config.Set("external_projects", map[string]string{})
+		}
+	})
+	config.Set("external_projects", map[string]string{
+		"batch-test": externalDir,
+	})
+
+	// Test: Check multiple refs including duplicates and mixed satisfied/unsatisfied
+	refs := []string{
+		"external:batch-test:cap1",           // satisfied
+		"external:batch-test:cap2",           // satisfied
+		"external:batch-test:cap3",           // NOT satisfied
+		"external:batch-test:cap1",           // duplicate - should still work
+		"external:unconfigured-project:cap1", // unconfigured project
+		"invalid-ref",                        // invalid format
+	}
+
+	statuses := CheckExternalDeps(ctx, refs)
+
+	// Verify we got results for all unique refs (5 unique, since cap1 appears twice)
+	expectedUnique := 5
+	if len(statuses) != expectedUnique {
+		t.Errorf("Expected %d unique statuses, got %d", expectedUnique, len(statuses))
+	}
+
+	// cap1 should be satisfied
+	if s := statuses["external:batch-test:cap1"]; s == nil || !s.Satisfied {
+		t.Error("Expected external:batch-test:cap1 to be satisfied")
+	}
+
+	// cap2 should be satisfied
+	if s := statuses["external:batch-test:cap2"]; s == nil || !s.Satisfied {
+		t.Error("Expected external:batch-test:cap2 to be satisfied")
+	}
+
+	// cap3 should NOT be satisfied
+	if s := statuses["external:batch-test:cap3"]; s == nil || s.Satisfied {
+		t.Error("Expected external:batch-test:cap3 to be unsatisfied")
+	}
+
+	// unconfigured project should NOT be satisfied
+	if s := statuses["external:unconfigured-project:cap1"]; s == nil || s.Satisfied {
+		t.Error("Expected external:unconfigured-project:cap1 to be unsatisfied")
+	}
+
+	// invalid ref should NOT be satisfied
+	if s := statuses["invalid-ref"]; s == nil || s.Satisfied {
+		t.Error("Expected invalid-ref to be unsatisfied")
+	}
+}
+
 // TestGetNewlyUnblockedByClose tests the --suggest-next functionality (GH#679)
 func TestGetNewlyUnblockedByClose(t *testing.T) {
 	env := newTestEnv(t)