Postgres is never ready running `devenv test`

[crestonbunch]

Describe the bug
You cannot depend on postgres being ready during tests.

To reproduce

Here's a minimum repro:

inputs:
  nixpkgs:
    url: github:cachix/devenv-nixpkgs/rolling

{ pkgs, lib, config, ... }:
{
  services.postgres = {
    enable = true;
    port   = 5432;
  };

  tasks."db:check" = {
    description = "Verify postgres is reachable";
    exec        = "psql -c 'SELECT 1' template1";
    before      = [ "devenv:enterTest" ];
    after       = [ "devenv:processes:postgres" ];
  };
}

The db:check task never runs because postgres is never ready

$ devenv test
✓ Configuring shell                                                                                       2.8s
  └ ✓ Evaluating shell 23 files                                                                          962ms
    └ ✓ Building  devenv-files-cleanup                                                                    75ms
    └ ✓ Building  tasks.json                                                                              51ms
    └ ✓ Building  devenv-shell 1 lines                                                                   100ms
    └ ✓ Querying  devenv-shell-env from cache.nixos.org                                                  147ms
    └ ✓ Building  devenv-shell-env                                                                       219ms
✓ Evaluating Nix                                                                                           1ms
✓ Loading tasks                                                                                            1ms
  └ ✓ Evaluating devenv.config.task.config                                                                 1ms
⠹ Running tasks → 5 tasks, roots: ["devenv:enterTest"]                                                  1m 20s
  └ ⠹ devenv:enterTest pending
    └ ⠹ db:check pending
    └ ⠹ devenv:enterShell pending
      └ ⠹ devenv:files:cleanup pending
  └ ⠧ postgres running (not ready: exec) :5432                                                          1m 20s
    │ server stopped
    │ 2026-04-07 23:23:51.549 GMT [45191] LOG:  database system was shut down at 2026-04-07 23:23:51 GMT
    │ 2026-04-07 23:23:51.551 GMT [45142] LOG:  database system is ready to accept connections

Version

$ devenv --version
devenv 2.0.6 (aarch64-darwin)

[crestonbunch]

It works if I do devenv up:

$ devenv up
✓ Configuring shell                                                                                       39ms
  └ ✓ Evaluating shell cached                                                                              7ms
✓ Evaluating Nix cached                                                                                    0ms
✓ Loading tasks                                                                                            1ms
  └ ✓ Evaluating devenv.config.task.config cached                                                          0ms
✓ Running tasks                                                                                           21ms
  └ ✓ devenv:enterShell                                                                                   15ms
    └ ✓ devenv:files:cleanup                                                                               5ms
  └ ✓ devenv:enterTest skipped                                                                             0ms
✓ Running processes                                                                                       2.6s
  └ ✓ Evaluating Nix cached                                                                                0ms
  └ ✓ devenv:enterTest skipped                                                                             0ms
    └ ✓ db:check 5 lines                                                                                 277ms
  └ ⠧ postgres ready :5432                                                                               15.4s
    │ 2026-04-07 23:28:54.008 GMT [47671] LOG:  database system was shut down at 2026-04-07 23:28:53 GMT
    │ 2026-04-07 23:28:54.010 GMT [47634] LOG:  database system is ready to accept connections
    │ Exec probe succeeded - process ready
✓ Loading tasks                                                                                            1ms
  └ ✓ Evaluating devenv.config.task.config cached

I don't understand what would be different about devenv test.

[crestonbunch]

running devenv test --no-tui makes the error more obvious:

Exec probe for postgres failed to run: No such file or directory (os error 2)

Very surprising that there is a difference in behavior between test and up