refactor(server): move DuckLakeConfig + migration into server/ducklake

[fuziontech]

Summary

• Step 1.5 of the binary-split plan (PR refactor(duckdbservice): extract DuckDB-free arrow helpers into arrowmap subpackage #477 was step 1)
• Moves DuckLakeConfig and the entire ducklake_migration.go file out of server/ and into a new server/ducklake/ package with zero duckdb-go dependency
• go list -deps ./server/ducklake | grep duckdb returns empty
• Public symbols renamed to drop the now-redundant DuckLake prefix; some previously-private helpers exported because they cross the new package boundary
• Type alias type DuckLakeConfig = ducklake.Config left in server/ so the dozens of server.DuckLakeConfig field types compile unchanged

Why

The migration check uses pgx against the tenant's metadata Postgres — no DuckDB execution at all. But because the migration code lived in the same Go package as server.go (which imports duckdb-go), the control plane was forced to transitively link libduckdb just to call CheckMigrationVersion / BackupMetadata. Carving out the ducklake subpackage gives the CP a callable migration API without DuckDB linkage.

Renames

Public, drops DuckLake prefix (the package name now supplies the context):

Old	New
server.DefaultDuckLakeSpecVersion	ducklake.DefaultSpecVersion
server.CheckAndBackupDuckLakeMigration	ducklake.CheckAndBackupMigration
server.CheckDuckLakeMigrationVersion	ducklake.CheckMigrationVersion
server.BackupDuckLakeMetadata	ducklake.BackupMetadata
server.DefaultDeltaCatalogPath	ducklake.DefaultDeltaCatalogPath

Newly exported (cross the package boundary):

Old (private)	New
ensureDuckLakeMigrationCheck	ducklake.EnsureMigrationCheck
duckLakeMigrationNeeded	ducklake.MigrationNeeded
duckLakeMigrationCheckedVersion	ducklake.MigrationCheckedVersion
buildDuckLakeAttachStmt	ducklake.BuildAttachStmt
buildDeltaCatalogAttachStmt	ducklake.BuildDeltaAttachStmt
deltaCatalogPath	ducklake.DeltaCatalogPath

New: ducklake.MigrationCheckError(connStr) error replaces a direct read of the private migrationState sync.Map from server.go's AttachDuckLake.

Compatibility shim

server/server.go keeps two aliases to avoid touching every server.DuckLakeConfig reference in this PR:

type DuckLakeConfig = ducklake.Config
const DefaultDuckLakeSpecVersion = ducklake.DefaultSpecVersion

The remaining server.DuckLakeConfig references are struct field types (e.g. cfg.DuckLake DuckLakeConfig) — those will be migrated to ducklake.Config as part of PR #2's larger server/ split. The alias is purely a transitional measure.

Test plan

• go build ./... clean
• go build -tags kubernetes ./... clean
• go test -short ./server/ducklake/... ./server/... ./controlplane/... ./ — all green
• go test -short -tags kubernetes ./controlplane/... — green except pre-existing testcontainer Postgres failures in controlplane/admin/ (unrelated, requires Docker)
• go list -deps ./server/ducklake | grep duckdb returns empty (the load-bearing check)
• All moved tests still pass (renamed to use new symbol names)

Stack

• ✅ PR refactor(duckdbservice): extract DuckDB-free arrow helpers into arrowmap subpackage #477: extract arrow helpers into arrowmap
• ✅ This PR: extract DuckLake into server/ducklake
• ⏳ PR Add pg_catalog compatibility and binary format support #2: full server/ split into server/wire, server/exec, server/flight; rewire server.DuckLakeConfig callers to ducklake.Config directly; add CI guard that fails the build if cmd/duckgres-controlplane ever links duckdb-go
• ⏳ PR Add connection rate limiting to prevent brute-force attacks #3: introduce cmd/duckgres-controlplane and cmd/duckgres-worker
• ⏳ PR Add configurable DuckDB extension loading #4: flip CI/CD and Helm to use the split images, add per-DuckDB-version worker matrix

🤖 Generated with Claude Code