feat: add database export, import, and copy for backup and migration

Cargo.toml

@@ -47,6 +47,7 @@ members = [
     "crates/codex-utils",
     "crates/codex-parsers",
     "crates/codex-db",
+    "crates/codex-migrate",
     "crates/codex-services",
     "crates/codex-search",
     "crates/codex-scanner",
@@ -81,6 +82,7 @@ codex-cli-common = { path = "crates/codex-cli-common", default-features = false
 codex-config = { path = "crates/codex-config" }
 codex-db = { path = "crates/codex-db" }
 codex-events = { path = "crates/codex-events" }
+codex-migrate = { path = "crates/codex-migrate" }
 codex-models = { path = "crates/codex-models" }
 codex-parsers = { path = "crates/codex-parsers", default-features = false }
 codex-scanner = { path = "crates/codex-scanner", default-features = false }
@@ -114,6 +116,7 @@ codex-cli-common = { workspace = true }
 codex-config = { workspace = true }
 codex-db = { workspace = true }
 codex-events = { workspace = true }
+codex-migrate = { workspace = true }
 codex-models = { workspace = true }
 codex-parsers = { workspace = true }
 codex-scanner = { workspace = true }

crates/codex-migrate/Cargo.toml

@@ -0,0 +1,51 @@
+[package]
+name = "codex-migrate"
+version.workspace = true
+edition.workspace = true
+publish = false
+
+[lib]
+name = "codex_migrate"
+path = "src/lib.rs"
+
+[dependencies]
+anyhow = { workspace = true }
+chrono = { workspace = true }
+serde = { workspace = true }
+tokio = { workspace = true }
+tracing = { workspace = true }
+uuid = { workspace = true }
+
+codex-db = { workspace = true }
+codex-config = { workspace = true }
+migration = { path = "../../migration" }
+
+# SeaORM — same backend feature set as codex-db so both drivers stay supported.
+sea-orm = { version = "1.1", features = [
+    "sqlx-postgres",
+    "sqlx-sqlite",
+    "runtime-tokio-rustls",
+    "macros",
+    "with-chrono",
+    "with-uuid",
+] }
+
+# NDJSON row serialization.
+serde_json = "1.0"
+# Streaming rows out of `Entity::find().stream()`.
+futures = "0.3"
+# Archive packing: gzip-compressed tar for the portable export bundle.
+tar = "0.4"
+flate2 = "1.0"
+# Parsing postgres:// connection URLs for the `copy` command.
+url = "2"
+# Staging directories for export/import at runtime.
+tempfile = { workspace = true }
+
+[dev-dependencies]
+codex-db = { workspace = true, features = ["test-utils"] }
+migration = { path = "../../migration" }
+tempfile = { workspace = true }
+tokio = { workspace = true }
+uuid = { workspace = true }
+chrono = { workspace = true }