feat(db-tool): expose overridable postgresql arg and PG_CONF_FILE env

Wrap db-tool, postgres-init, postgres-cleanup with lib.makeOverridable so
consumers can inject extension-enabled PostgreSQL via .override { postgresql = ...; }.
Add PG_CONF_FILE: when set, replaces script-generated postgresql.conf entirely
(runtime port and unix_socket_directories still appended/overridden).

package/db-tool/README.md

@@ -29,9 +29,30 @@ These variables must be set for `db-tool` to function.
 | `DATABASE_SOURCE` | `${DATABASE_DIR}/src` | Directory containing source SQL files for hydration. |
 | `PG_URL_VAR` | `PGURL` | The name of the environment variable where the computed PG URL will be exported. |
 | `PG_LOG_PATH` | (unset) | Path to redirect PostgreSQL server logs. |
+| `PG_CONF_FILE` | (unset) | Path to a `postgresql.conf` file. When set, replaces the script-generated config entirely on fresh init. `port` and `unix_socket_directories` are still appended at runtime (always overridden). When set, `PG_DISABLE_LOGGING` and `PG_SHARED_PRELOAD_LIBRARIES` are ignored. |
+| `PG_SHARED_PRELOAD_LIBRARIES` | `pg_cron` | Comma-separated `shared_preload_libraries` value. Set to empty string to disable. Ignored when `PG_CONF_FILE` is set. |
+| `PG_DISABLE_LOGGING` | `0` | Set to `1` to disable PostgreSQL logging collector. Ignored when `PG_CONF_FILE` is set. |
 | `PATCH_LOG` | (stdout) | Path to log the output of database patches. |
 | `HYDRATE_LOG` | (stdout) | Path to log the output of database hydration. |
 
+## Postgres Package Override
+
+By default, `db-tool`/`postgres-init`/`postgres-cleanup` use plain `postgresql_17` from nixpkgs. If you need extensions (e.g. `pg_cron`), override the postgres package per-output:
+
+```nix
+let
+  myPg = pkgs.postgresql_17.withJIT.withPackages (_: [
+    pkgs.postgresql_17.pkgs.pg_cron
+  ]);
+in {
+  packages = [
+    (pkgs.hectic."db-tool".override          { postgresql = myPg; })
+    (pkgs.hectic."postgres-init".override    { postgresql = myPg; })
+    (pkgs.hectic."postgres-cleanup".override { postgresql = myPg; })
+  ];
+}
+```
+
 ## pull_staging Contract
 
 The `pull_staging` subcommand allows importing data from a remote staging environment into the local `test-data.sql` file. This functionality requires four specific environment variables to be defined:

package/db-tool/default.nix

@@ -2,7 +2,9 @@
 let
   shell = "${dash}/bin/dash";
 
-  database = hectic.writeShellApplication {
+  mkDatabase =
+    { postgresql ? postgresql_17 }:
+    hectic.writeShellApplication {
       inherit shell;
       bashOptions = [
         "errexit"
@@ -11,7 +13,7 @@ let
       # SC2209: false positive — PAGER_OR_CAT=cat stores the string "cat" intentionally
       excludeShellChecks = [ "SC2209" ];
       name = "database";
-    runtimeInputs = [ hectic.migrator hectic.parse-uri postgresql_17 neovim openssh coreutils gawk ];
+      runtimeInputs = [ hectic.migrator hectic.parse-uri postgresql neovim openssh coreutils gawk ];
 
       text = ''
         ${builtins.readFile hectic.helpers.posix-shell.log}
@@ -27,11 +29,13 @@ let
       };
     };
 
-  postgresInit = hectic.writeShellApplication {
+  mkPostgresInit =
+    { postgresql ? postgresql_17 }:
+    hectic.writeShellApplication {
       inherit shell;
       bashOptions = [ ];
       name = "postgres-init";
-    runtimeInputs = [ postgresql_17 coreutils ];
+      runtimeInputs = [ postgresql coreutils ];
 
       text = builtins.readFile ./postgres-init.sh;
 
@@ -41,11 +45,13 @@ let
       };
     };
 
-  postgresCleanup = hectic.writeShellApplication {
+  mkPostgresCleanup =
+    { postgresql ? postgresql_17 }:
+    hectic.writeShellApplication {
       inherit shell;
       bashOptions = [ ];
       name = "postgres-cleanup";
-    runtimeInputs = [ postgresql_17 coreutils ];
+      runtimeInputs = [ postgresql coreutils ];
 
       text = builtins.readFile ./postgres-cleanup.sh;
 
@@ -56,7 +62,7 @@ let
     };
 in
 {
-  "db-tool"          = database;
+  "db-tool"          = lib.makeOverridable mkDatabase { };
-  "postgres-init"    = postgresInit;
+  "postgres-init"    = lib.makeOverridable mkPostgresInit { };
-  "postgres-cleanup" = postgresCleanup;
+  "postgres-cleanup" = lib.makeOverridable mkPostgresCleanup { };
 }

package/db-tool/postgres-init.sh

@@ -24,7 +24,12 @@ postgres_init_main() {
     rm -rf "$data" "$sockdir" || return 1
     mkdir -p "$sockdir" || return 1
     initdb -D "$data" --no-locale -E UTF8 || return 1
+    if [ -n "${PG_CONF_FILE:-}" ]; then
+      [ -r "$PG_CONF_FILE" ] || { printf '%s\n' "postgres-init: PG_CONF_FILE not readable: $PG_CONF_FILE" >&2; return 1; }
+      cp -f -- "$PG_CONF_FILE" "$data/postgresql.conf" || return 1
+    else
       { printf '%s\n' "listen_addresses = ''"; [ "$PG_DISABLE_LOGGING" -eq 0 ] && { printf '%s\n' 'logging_collector = on'; printf '%s\n' "log_directory = 'log'"; }; [ -n "$PG_SHARED_PRELOAD_LIBRARIES" ] && { printf '%s\n' "shared_preload_libraries = '$PG_SHARED_PRELOAD_LIBRARIES'"; printf '%s\n' "cron.database_name = '$db'"; printf '%s\n' "cron.host = '$sockdir'"; }; :; } >> "$data/postgresql.conf" || return 1
+    fi
     sed -i "1ilocal all all trust" "$data/pg_hba.conf" || return 1
   fi