diff --git a/internal/scan/evidence.go b/internal/scan/evidence.go
new file mode 100644
index 0000000..669256a
--- /dev/null
+++ b/internal/scan/evidence.go
@@ -0,0 +1,79 @@
+package scan
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"sync"
+	"time"
+
+	"github.com/kryft-dev/cdd/internal/git"
+	"github.com/kryft-dev/cdd/internal/project"
+)
+
+// workers bounds the number of concurrent git calls a Scan makes while
+// gathering each Project's evidence time, so scanning a large Root never
+// spawns one git process per Project at once.
+const workers = 8
+
+// gatherEvidence returns each Project's evidence time, keyed by Rel: the
+// Project's git.LastCommit time when it is a repository with a commit,
+// else its directory's mtime. Git calls are bounded to workers at a time.
+func gatherEvidence(ctx context.Context, root string, projects []project.Project) (map[string]time.Time, error) {
+	type result struct {
+		rel string
+		at  time.Time
+		err error
+	}
+
+	sem := make(chan struct{}, workers)
+	results := make(chan result, len(projects))
+	var wg sync.WaitGroup
+
+	for _, p := range projects {
+		wg.Add(1)
+		go func(p project.Project) {
+			defer wg.Done()
+
+			sem <- struct{}{}
+			defer func() { <-sem }()
+
+			at, err := evidenceTime(ctx, p.Abs(root))
+			results <- result{rel: p.Rel(), at: at, err: err}
+		}(p)
+	}
+
+	go func() {
+		wg.Wait()
+		close(results)
+	}()
+
+	evidence := make(map[string]time.Time, len(projects))
+	for r := range results {
+		if r.err != nil {
+			return nil, fmt.Errorf("scan: evidence time for %q: %w", r.rel, r.err)
+		}
+		evidence[r.rel] = r.at
+	}
+	return evidence, nil
+}
+
+// evidenceTime returns dir's evidence time: its git.LastCommit time when
+// dir is a repository with a commit, else dir's mtime. The result is
+// truncated to UTC second precision, matching History's own line format, so
+// repeated Scans compare equal rather than drifting on sub-second noise.
+func evidenceTime(ctx context.Context, dir string) (time.Time, error) {
+	commit, ok, err := git.LastCommit(ctx, dir)
+	if err != nil {
+		return time.Time{}, err
+	}
+	if ok {
+		return commit.UTC().Truncate(time.Second), nil
+	}
+
+	info, err := os.Stat(dir)
+	if err != nil {
+		return time.Time{}, err
+	}
+	return info.ModTime().UTC().Truncate(time.Second), nil
+}
diff --git a/internal/scan/scan.go b/internal/scan/scan.go
new file mode 100644
index 0000000..b94422c
--- /dev/null
+++ b/internal/scan/scan.go
@@ -0,0 +1,76 @@
+// Package scan discovers Projects under a Root and seeds History with one
+// Visit per Project, so a fresh cdd installation has a starting order
+// before any real Jump happens.
+package scan
+
+import (
+	"context"
+	"fmt"
+	"time"
+
+	"github.com/kryft-dev/cdd/internal/config"
+	"github.com/kryft-dev/cdd/internal/history"
+	"github.com/kryft-dev/cdd/internal/project"
+)
+
+// Summary reports what a Scan did, for the cli to print as "Seeded N
+// Visits across M Projects".
+type Summary struct {
+	// Seeded is the number of Visits actually appended to History.
+	Seeded int
+	// Projects is the number of Projects discovered under Root.
+	Projects int
+}
+
+// Run discovers Projects under cfg.Root, honoring cfg.Exclude and
+// cfg.IncludeHidden, and seeds hist with one Visit per Project. Each
+// Project's evidence time is git.LastCommit when the Project is a
+// repository with a commit, else the Project directory's mtime.
+//
+// Whether a given Project actually gains a new Visit is entirely up to
+// Seed's own idempotency rule (a Project with a newer real Visit is left
+// alone); Run does not re-implement that rule, only reports how many
+// Visits it produced.
+func Run(ctx context.Context, cfg config.Config, hist *history.History) (Summary, error) {
+	projects, err := project.Discover(cfg.Root, cfg.Exclude, cfg.IncludeHidden)
+	if err != nil {
+		return Summary{}, fmt.Errorf("scan: discover projects: %w", err)
+	}
+
+	evidence, err := gatherEvidence(ctx, cfg.Root, projects)
+	if err != nil {
+		return Summary{}, err
+	}
+
+	summary := Summary{Projects: len(projects)}
+	for _, p := range projects {
+		seeded, err := seedOne(hist, p.Rel(), evidence[p.Rel()])
+		if err != nil {
+			return Summary{}, fmt.Errorf("scan: seed %q: %w", p.Rel(), err)
+		}
+		if seeded {
+			summary.Seeded++
+		}
+	}
+
+	return summary, nil
+}
+
+// seedOne calls Seed for project and reports whether it actually appended a
+// Visit, by comparing History's Visit count for project before and after.
+// This leans on history.Count rather than re-implementing Seed's
+// idempotency rule.
+func seedOne(hist *history.History, rel string, at time.Time) (bool, error) {
+	before, err := hist.Count(rel)
+	if err != nil {
+		return false, err
+	}
+	if err := hist.Seed(rel, at); err != nil {
+		return false, err
+	}
+	after, err := hist.Count(rel)
+	if err != nil {
+		return false, err
+	}
+	return after > before, nil
+}
diff --git a/internal/scan/scan_test.go b/internal/scan/scan_test.go
new file mode 100644
index 0000000..0353c5e
--- /dev/null
+++ b/internal/scan/scan_test.go
@@ -0,0 +1,221 @@
+package scan_test
+
+import (
+	"context"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"testing"
+	"time"
+
+	"github.com/kryft-dev/cdd/internal/config"
+	"github.com/kryft-dev/cdd/internal/git"
+	"github.com/kryft-dev/cdd/internal/history"
+	"github.com/kryft-dev/cdd/internal/scan"
+)
+
+// runGit runs a git command in dir with a test identity and no system or
+// global config, failing the test on error.
+func runGit(t *testing.T, dir string, args ...string) {
+	t.Helper()
+
+	cmd := exec.Command("git", args...)
+	cmd.Dir = dir
+	cmd.Env = append(os.Environ(),
+		"GIT_CONFIG_NOSYSTEM=1",
+		"HOME=/nonexistent-cdd-test-home",
+		"GIT_AUTHOR_NAME=cdd test",
+		"GIT_AUTHOR_EMAIL=cdd-test@example.com",
+		"GIT_COMMITTER_NAME=cdd test",
+		"GIT_COMMITTER_EMAIL=cdd-test@example.com",
+	)
+
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Fatalf("git %v: %v\n%s", args, err, out)
+	}
+}
+
+// newProjectDir creates a directory for a Project at kind/name under root.
+func newProjectDir(t *testing.T, root, kind, name string) string {
+	t.Helper()
+
+	dir := filepath.Join(root, kind, name)
+	if err := os.MkdirAll(dir, 0o755); err != nil {
+		t.Fatalf("mkdir %s: %v", dir, err)
+	}
+	return dir
+}
+
+// newRepoProjectDir creates a Project directory that is also a git
+// repository with one commit, and returns its path.
+func newRepoProjectDir(t *testing.T, root, kind, name string) string {
+	t.Helper()
+
+	dir := newProjectDir(t, root, kind, name)
+	runGit(t, dir, "init", "-q", "-b", "main")
+	runGit(t, dir, "config", "user.name", "cdd test")
+	runGit(t, dir, "config", "user.email", "cdd-test@example.com")
+	if err := os.WriteFile(filepath.Join(dir, "file.txt"), []byte("hi"), 0o644); err != nil {
+		t.Fatalf("write file: %v", err)
+	}
+	runGit(t, dir, "add", ".")
+	runGit(t, dir, "commit", "-q", "-m", "init")
+	return dir
+}
+
+// newHistory opens an empty History in a fresh temp directory.
+func newHistory(t *testing.T) *history.History {
+	t.Helper()
+
+	path := filepath.Join(t.TempDir(), "history")
+	hist, err := history.Open(path, 1000)
+	if err != nil {
+		t.Fatalf("history.Open: %v", err)
+	}
+	return hist
+}
+
+func newConfig(root string, exclude []string) config.Config {
+	return config.Config{Root: root, Exclude: exclude}
+}
+
+func TestRun_RepositorySeededFromCommitTime(t *testing.T) {
+	root := t.TempDir()
+	dir := newRepoProjectDir(t, root, "tools", "cdd")
+
+	commitTime, ok, err := git.LastCommit(context.Background(), dir)
+	if err != nil || !ok {
+		t.Fatalf("git.LastCommit: ok=%v err=%v", ok, err)
+	}
+
+	hist := newHistory(t)
+	summary, err := scan.Run(context.Background(), newConfig(root, nil), hist)
+	if err != nil {
+		t.Fatalf("Run: %v", err)
+	}
+	if summary != (scan.Summary{Seeded: 1, Projects: 1}) {
+		t.Fatalf("summary = %+v, want {Seeded:1 Projects:1}", summary)
+	}
+
+	visits, err := hist.Latest()
+	if err != nil {
+		t.Fatalf("Latest: %v", err)
+	}
+	if len(visits) != 1 {
+		t.Fatalf("len(visits) = %d, want 1", len(visits))
+	}
+	if visits[0].Project != "tools/cdd" {
+		t.Fatalf("project = %q, want tools/cdd", visits[0].Project)
+	}
+	if visits[0].Source != history.SourceScan {
+		t.Fatalf("source = %q, want scan", visits[0].Source)
+	}
+	if !visits[0].At.Equal(commitTime) {
+		t.Fatalf("At = %v, want %v", visits[0].At, commitTime)
+	}
+}
+
+func TestRun_NonRepositorySeededFromMtime(t *testing.T) {
+	root := t.TempDir()
+	dir := newProjectDir(t, root, "tools", "scratch")
+
+	info, err := os.Stat(dir)
+	if err != nil {
+		t.Fatalf("Stat: %v", err)
+	}
+
+	hist := newHistory(t)
+	summary, err := scan.Run(context.Background(), newConfig(root, nil), hist)
+	if err != nil {
+		t.Fatalf("Run: %v", err)
+	}
+	if summary.Seeded != 1 {
+		t.Fatalf("Seeded = %d, want 1", summary.Seeded)
+	}
+
+	visits, err := hist.Latest()
+	if err != nil {
+		t.Fatalf("Latest: %v", err)
+	}
+	if len(visits) != 1 {
+		t.Fatalf("len(visits) = %d, want 1", len(visits))
+	}
+	want := info.ModTime().UTC().Truncate(time.Second)
+	if !visits[0].At.Equal(want) {
+		t.Fatalf("At = %v, want %v", visits[0].At, want)
+	}
+}
+
+func TestRun_AlreadyJumpedProjectNotOverwritten(t *testing.T) {
+	root := t.TempDir()
+	newProjectDir(t, root, "tools", "cdd")
+
+	hist := newHistory(t)
+	if err := hist.Record("tools/cdd"); err != nil {
+		t.Fatalf("Record: %v", err)
+	}
+	before, err := hist.Latest()
+	if err != nil {
+		t.Fatalf("Latest: %v", err)
+	}
+
+	summary, err := scan.Run(context.Background(), newConfig(root, nil), hist)
+	if err != nil {
+		t.Fatalf("Run: %v", err)
+	}
+	if summary.Seeded != 0 {
+		t.Fatalf("Seeded = %d, want 0", summary.Seeded)
+	}
+
+	after, err := hist.Latest()
+	if err != nil {
+		t.Fatalf("Latest: %v", err)
+	}
+	if len(after) != 1 || after[0].Source != history.SourceJump || !after[0].At.Equal(before[0].At) {
+		t.Fatalf("after = %+v, want unchanged jump visit %+v", after, before)
+	}
+}
+
+func TestRun_SecondRunSeedsNothingNew(t *testing.T) {
+	root := t.TempDir()
+	newProjectDir(t, root, "tools", "cdd")
+
+	hist := newHistory(t)
+	cfg := newConfig(root, nil)
+
+	if _, err := scan.Run(context.Background(), cfg, hist); err != nil {
+		t.Fatalf("first Run: %v", err)
+	}
+
+	summary, err := scan.Run(context.Background(), cfg, hist)
+	if err != nil {
+		t.Fatalf("second Run: %v", err)
+	}
+	if summary != (scan.Summary{Seeded: 0, Projects: 1}) {
+		t.Fatalf("summary = %+v, want {Seeded:0 Projects:1}", summary)
+	}
+}
+
+func TestRun_ExcludedProjectSkipped(t *testing.T) {
+	root := t.TempDir()
+	newProjectDir(t, root, "tools", "cdd")
+	newProjectDir(t, root, "tools", "scratch")
+
+	hist := newHistory(t)
+	summary, err := scan.Run(context.Background(), newConfig(root, []string{"tools/scratch"}), hist)
+	if err != nil {
+		t.Fatalf("Run: %v", err)
+	}
+	if summary != (scan.Summary{Seeded: 1, Projects: 1}) {
+		t.Fatalf("summary = %+v, want {Seeded:1 Projects:1}", summary)
+	}
+
+	visits, err := hist.Latest()
+	if err != nil {
+		t.Fatalf("Latest: %v", err)
+	}
+	if len(visits) != 1 || visits[0].Project != "tools/cdd" {
+		t.Fatalf("visits = %+v, want only tools/cdd", visits)
+	}
+}