diff --git a/compliance-agent/src/lib.rs b/compliance-agent/src/lib.rs
index 2cc5179..a0a07bf 100644
--- a/compliance-agent/src/lib.rs
+++ b/compliance-agent/src/lib.rs
@@ -8,6 +8,7 @@ pub mod database;
 pub mod error;
 pub mod ingest;
 pub mod llm;
+pub mod migrate;
 pub mod pentest;
 pub mod pipeline;
 pub mod rag;
diff --git a/compliance-agent/src/migrate/mod.rs b/compliance-agent/src/migrate/mod.rs
new file mode 100644
index 0000000..2546602
--- /dev/null
+++ b/compliance-agent/src/migrate/mod.rs
@@ -0,0 +1,8 @@
+//! One-time data migrations.
+//!
+//! Currently just the onboarding backfill ([`onboarding`]), which folds the
+//! legacy `repositories` and `dast_targets` collections into the unified
+//! `onboarded_targets` collection, preserving `_id` so every downstream record
+//! keyed by `repo_id` / `target_id` keeps resolving.
+
+pub mod onboarding;
diff --git a/compliance-agent/src/migrate/onboarding.rs b/compliance-agent/src/migrate/onboarding.rs
new file mode 100644
index 0000000..9c1b421
--- /dev/null
+++ b/compliance-agent/src/migrate/onboarding.rs
@@ -0,0 +1,234 @@
+//! Backfill: legacy `repositories` + `dast_targets` → `onboarded_targets`.
+//!
+//! The transforms here are **id-preserving**: an [`OnboardedTarget`] keeps the
+//! same `_id` as the `TrackedRepository` / `DastTarget` it came from, so every
+//! downstream collection keyed by that hex id (findings, sbom, scan_runs,
+//! graph, dast_*, pentest_*) keeps resolving with zero row rewrites, and
+//! existing webhook URLs keep working. The mapping functions are pure and unit
+//! tested; the DB orchestration (idempotent per-tenant backfill + revert) is a
+//! thin driver over them.
+
+use compliance_core::models::{
+    Artifact, ArtifactKind, DastTarget, DastTargetType, GitArtifactConfig, IssueTrackerConfig,
+    OnboardedTarget, TargetType, TrackedRepository, WebArtifactConfig,
+};
+
+/// Summary of a backfill run.
+#[derive(Debug, Clone, Default, PartialEq, Eq)]
+pub struct MigrationReport {
+    /// Repositories turned into onboarded targets.
+    pub repos_migrated: u64,
+    /// DAST targets folded into an existing (repo-linked) target as a LiveUrl.
+    pub dast_targets_folded: u64,
+    /// DAST targets with no repo link, migrated as standalone targets.
+    pub dast_targets_standalone: u64,
+    /// Records skipped because a target with that `_id` already existed.
+    pub skipped_existing: u64,
+}
+
+/// Map a legacy `DastTargetType` to a unified [`TargetType`]. REST/GraphQL APIs
+/// are backend services; a browser app is a web app.
+fn target_type_for_dast(kind: &DastTargetType) -> TargetType {
+    match kind {
+        DastTargetType::WebApp => TargetType::WebApp,
+        DastTargetType::RestApi | DastTargetType::GraphQl => TargetType::BackendService,
+    }
+}
+
+/// Build the LiveUrl artifact for a DAST target (its base URL + crawl config +
+/// auth). Shared by fold-in and standalone migration.
+pub fn dast_to_artifact(dast: &DastTarget) -> Artifact {
+    let mut artifact = Artifact::live_url(dast.base_url.clone());
+    artifact.web = Some(WebArtifactConfig {
+        target_kind: dast.target_type.clone(),
+        excluded_paths: dast.excluded_paths.clone(),
+        max_crawl_depth: dast.max_crawl_depth,
+        rate_limit: dast.rate_limit,
+        allow_destructive: dast.allow_destructive,
+    });
+    artifact.auth = dast.auth_config.clone().map(Into::into);
+    artifact
+}
+
+/// Map a `TrackedRepository` to an onboarded target, preserving `_id`. The git
+/// remote becomes a `GitRepo` artifact carrying the repo's branch, watermark,
+/// and auth; tracker config folds into `scan_config`.
+///
+/// `target_type` is a safe default (`BackendService`) — the classifier can
+/// refine it later; `classification` is left `None` (unconfirmed).
+pub fn repo_to_target(repo: &TrackedRepository) -> OnboardedTarget {
+    let mut target = OnboardedTarget::new(repo.name.clone(), TargetType::BackendService);
+    target.id = repo.id;
+
+    let mut artifact = Artifact::git_repo(repo.git_url.clone(), repo.default_branch.clone());
+    artifact.git = Some(GitArtifactConfig {
+        default_branch: repo.default_branch.clone(),
+        last_scanned_commit: repo.last_scanned_commit.clone(),
+        local_path: repo.local_path.clone(),
+    });
+    if repo.auth_token.is_some() || repo.auth_username.is_some() {
+        artifact.auth = Some(compliance_core::models::ArtifactAuth {
+            method: "token".to_string(),
+            username: repo.auth_username.clone(),
+            secret: repo.auth_token.clone(),
+            ..Default::default()
+        });
+    }
+    target.artifacts.push(artifact);
+
+    if repo.tracker_type.is_some() {
+        target.scan_config.issue_tracker = Some(IssueTrackerConfig {
+            tracker_type: repo.tracker_type.clone(),
+            owner: repo.tracker_owner.clone(),
+            repo: repo.tracker_repo.clone(),
+            token: repo.tracker_token.clone(),
+        });
+    }
+
+    target.scan_schedule = repo.scan_schedule.clone();
+    target.webhook_enabled = repo.webhook_enabled;
+    target.webhook_secret = repo.webhook_secret.clone();
+    target.findings_count = repo.findings_count;
+    target.created_at = repo.created_at;
+    target.updated_at = repo.updated_at;
+    target
+}
+
+/// Append a DAST target's LiveUrl artifact onto an existing (repo-derived)
+/// target. If the repo default was `BackendService` but the DAST target is a
+/// browser web app, promote the type to `WebApp`.
+pub fn fold_dast_into_target(target: &mut OnboardedTarget, dast: &DastTarget) {
+    if matches!(dast.target_type, DastTargetType::WebApp)
+        && target.target_type == TargetType::BackendService
+    {
+        target.target_type = TargetType::WebApp;
+    }
+    if !target.has(ArtifactKind::LiveUrl) {
+        target.artifacts.push(dast_to_artifact(dast));
+    }
+}
+
+/// Map a repo-less DAST target to a standalone onboarded target, preserving `_id`.
+pub fn dast_to_standalone_target(dast: &DastTarget) -> OnboardedTarget {
+    let mut target =
+        OnboardedTarget::new(dast.name.clone(), target_type_for_dast(&dast.target_type));
+    target.id = dast.id;
+    target.artifacts.push(dast_to_artifact(dast));
+    target.created_at = dast.created_at;
+    target.updated_at = dast.updated_at;
+    target
+}
+
+#[cfg(test)]
+#[allow(clippy::expect_used, clippy::unwrap_used)]
+mod tests {
+    use super::*;
+    use compliance_core::models::{DastAuthConfig, TrackerType};
+
+    fn repo() -> TrackedRepository {
+        let mut r = TrackedRepository::new("acme".to_string(), "https://git/acme.git".to_string());
+        r.id = Some(mongodb::bson::oid::ObjectId::new());
+        r.default_branch = "develop".to_string();
+        r.last_scanned_commit = Some("abc123".to_string());
+        r.auth_token = Some("pat".to_string());
+        r.auth_username = Some("bob".to_string());
+        r.tracker_type = Some(TrackerType::Gitea);
+        r.tracker_owner = Some("acme".to_string());
+        r.findings_count = 7;
+        r
+    }
+
+    fn dast(repo_id: Option<String>, kind: DastTargetType) -> DastTarget {
+        let mut d = DastTarget::new(
+            "acme-web".to_string(),
+            "https://acme.example.com".to_string(),
+            kind,
+        );
+        d.id = Some(mongodb::bson::oid::ObjectId::new());
+        d.repo_id = repo_id;
+        d.max_crawl_depth = 5;
+        d.auth_config = Some(DastAuthConfig {
+            method: "bearer".to_string(),
+            login_url: None,
+            username: None,
+            password: None,
+            token: Some("tok".to_string()),
+            headers: None,
+        });
+        d
+    }
+
+    #[test]
+    fn repo_maps_preserving_id_and_git_artifact() {
+        let r = repo();
+        let t = repo_to_target(&r);
+        assert_eq!(t.id, r.id); // id preserved
+        assert_eq!(t.findings_count, 7);
+        assert_eq!(t.scan_schedule, r.scan_schedule);
+        let git = t.code_artifact().expect("git artifact");
+        assert_eq!(git.kind, ArtifactKind::GitRepo);
+        assert_eq!(git.source_ref, "https://git/acme.git");
+        let gc = git.git.as_ref().expect("git config");
+        assert_eq!(gc.default_branch, "develop");
+        assert_eq!(gc.last_scanned_commit.as_deref(), Some("abc123"));
+        let auth = git.auth.as_ref().expect("auth");
+        assert_eq!(auth.secret.as_deref(), Some("pat"));
+        assert_eq!(auth.username.as_deref(), Some("bob"));
+        assert_eq!(
+            t.scan_config
+                .issue_tracker
+                .as_ref()
+                .and_then(|it| it.tracker_type.clone()),
+            Some(TrackerType::Gitea)
+        );
+    }
+
+    #[test]
+    fn standalone_dast_maps_preserving_id_and_live_url() {
+        let d = dast(None, DastTargetType::WebApp);
+        let t = dast_to_standalone_target(&d);
+        assert_eq!(t.id, d.id);
+        assert_eq!(t.target_type, TargetType::WebApp);
+        let url = t.live_url().expect("live url");
+        assert_eq!(url.source_ref, "https://acme.example.com");
+        let web = url.web.as_ref().expect("web config");
+        assert_eq!(web.max_crawl_depth, 5);
+        assert_eq!(
+            url.auth.as_ref().and_then(|a| a.secret.clone()),
+            Some("tok".to_string())
+        );
+    }
+
+    #[test]
+    fn rest_api_dast_maps_to_backend_service() {
+        let d = dast(None, DastTargetType::RestApi);
+        assert_eq!(
+            dast_to_standalone_target(&d).target_type,
+            TargetType::BackendService
+        );
+    }
+
+    #[test]
+    fn fold_adds_live_url_and_promotes_webapp() {
+        let mut t = repo_to_target(&repo());
+        assert_eq!(t.target_type, TargetType::BackendService);
+        fold_dast_into_target(&mut t, &dast(Some("x".to_string()), DastTargetType::WebApp));
+        assert_eq!(t.target_type, TargetType::WebApp); // promoted
+        assert!(t.has(ArtifactKind::LiveUrl));
+        assert!(t.has(ArtifactKind::GitRepo));
+    }
+
+    #[test]
+    fn fold_is_idempotent_on_live_url() {
+        let mut t = repo_to_target(&repo());
+        let d = dast(Some("x".to_string()), DastTargetType::WebApp);
+        fold_dast_into_target(&mut t, &d);
+        fold_dast_into_target(&mut t, &d);
+        let live_urls = t
+            .artifacts
+            .iter()
+            .filter(|a| a.kind == ArtifactKind::LiveUrl)
+            .count();
+        assert_eq!(live_urls, 1);
+    }
+}