Close TD-20 sqlite pool alignment

TECHDEBTS.md

@@ -766,7 +766,16 @@ instructions (AGENTS.md) updated to mention them.
 
 ## Phase 5 — Consistency, config & hygiene
 
-### TD-20: Align SQLite pool configuration between dev and prod
+### TD-20: Align SQLite pool configuration between dev and prod ✅ DONE (2026-06-12)
+
+**Status: implemented.** The effective mismatch was narrowed to one place:
+`config.exs`, `dev.exs`, `prod.exs`, and `test.exs` were already aligned on a
+modest pool of `5`, but `config/runtime.exs` still defaulted production to
+`POOL_SIZE=1`. The prod runtime default now also uses `5`, with an inline
+comment documenting the rationale: keep SQLite concurrency behavior consistent
+across dev and prod under the existing WAL + `busy_timeout` setup unless an
+operator explicitly overrides `POOL_SIZE`. A regression test reads
+`config/runtime.exs` in `:prod` and locks that default to `5`.
 
 **Context.** Dev runs `pool_size: 5` (config.exs), prod runs `pool_size: 1`
 (runtime.exs) — so dev and prod have **different concurrency semantics**: dev

config/runtime.exs

@@ -7,9 +7,11 @@ if config_env() == :prod do
 
   File.mkdir_p!(Path.dirname(database_path))
 
+  # Keep prod on the same modest SQLite pool as dev so WAL + busy_timeout see
+  # the same concurrency behavior in both environments unless explicitly tuned.
   config :bds, BDS.Repo,
     database: database_path,
-    pool_size: String.to_integer(System.get_env("POOL_SIZE") || "1")
+    pool_size: String.to_integer(System.get_env("POOL_SIZE") || "5")
 
   # Persist downloaded embedding model files alongside the database data dir.
   config :bumblebee,

test/bds/repo/bootstrap_test.exs

@@ -85,6 +85,32 @@ defmodule BDS.Repo.BootstrapTest do
     assert repo_config[:busy_timeout] == 15_000
   end
 
+  test "prod runtime repo config defaults to the same pool size as dev" do
+    config_path = Path.expand("../../../config/runtime.exs", __DIR__)
+    database_path = Path.join(System.tmp_dir!(), "bds-runtime-#{System.unique_integer([:positive])}.db")
+
+    previous_pool_size = System.get_env("POOL_SIZE")
+    previous_database_path = System.get_env("BDS_DATABASE_PATH")
+
+    System.delete_env("POOL_SIZE")
+    System.put_env("BDS_DATABASE_PATH", database_path)
+
+    on_exit(fn ->
+      restore_env("POOL_SIZE", previous_pool_size)
+      restore_env("BDS_DATABASE_PATH", previous_database_path)
+      File.rm_rf(Path.dirname(database_path))
+    end)
+
+    config = Config.Reader.read!(config_path, env: :prod)
+
+    repo_config =
+      config
+      |> Keyword.fetch!(:bds)
+      |> Keyword.fetch!(BDS.Repo)
+
+    assert repo_config[:pool_size] == 5
+  end
+
   defmodule RepoConfigBackup do
     def put_env do
       Process.put({__MODULE__, :temp_repo_config}, Application.get_env(:bds, TempRepo))
@@ -97,4 +123,7 @@ defmodule BDS.Repo.BootstrapTest do
       end
     end
   end
+
+  defp restore_env(key, nil), do: System.delete_env(key)
+  defp restore_env(key, value), do: System.put_env(key, value)
 end