--config with multiple files skips base_path resolution entirely, breaking `atmos terraform test`

[MaxymVlasov]

Describe the Bug

Loading config via --config main.yaml,supplement.yaml (multiple files) causes
atmos terraform test <component> -s <stack> to fail with Error: failed to find import, even
though the exact same settings, saved as a single file and loaded via plain auto-discovery (no
--config flag at all), work correctly end-to-end for the identical terraform test invocation.
Setting ATMOS_BASE_PATH explicitly alongside --config has no effect on the failure either -
see the root cause below for why.

Root cause, traced in source, not just symptoms: In pkg/config/load.go, LoadConfig()
branches early for the CLI-arg config path:

if len(configAndStacksInfo.AtmosConfigFilesFromArg) > 0 || len(configAndStacksInfo.AtmosConfigDirsFromArg) > 0 {
    err := loadConfigFromCLIArgs(v, configAndStacksInfo, &atmosConfig)
    if err != nil {
        return atmosConfig, err
    }
    return atmosConfig, nil   // <-- returns here
}

// Load configuration from different sources.
if err := loadConfigSources(v, configAndStacksInfo); err != nil { ... }
...
setEnv(v)                                    // binds ATMOS_BASE_PATH (and every other ATMOS_* env var)
...
err := v.Unmarshal(&atmosConfig, ...)
...
if err := applyGitRootBasePath(&atmosConfig); err != nil { ... }  // resolves empty base_path to git root

The --config/--config-path branch's early return means none of the following ever run for
that invocation: setEnv() (env var bindings, including ATMOS_BASE_PATH),
applyGitRootBasePath() (git-root resolution for an empty/default base_path), or the later
Unmarshal/fixAuthIdentities/preserveCaseSensitiveMaps steps that normal auto-discovery relies
on.

This matches the documented breaking change in Atmos v1.202.0+ ("empty base_path now triggers
git root discovery instead of defaulting to the current directory" —
https://atmos.tools/changelog/base-path-behavior-change) — my atmos.yaml has base_path: ''
(empty). Via normal auto-discovery, that empty value correctly resolves to the git repo root
through applyGitRootBasePath(). Via --config, that function is never called, so the empty
base_path is left unresolved, which is what terraform test's component-path resolution then
fails on. This is also why setting ATMOS_BASE_PATH explicitly doesn't help: setEnv(), the
function that would bind that env var to anything, is skipped by the same early return.

Relationship to existing issues: searched first to avoid a duplicate. This is related to, but
distinct from, #2183 (fixed in v1.210.1 via #2215/#2236): that issue was about
ATMOS_BASE_PATH/--base-path values being simple relative-path strings resolving against the
wrong anchor. That fix improved resolution within the pipeline that --config skips entirely —
it doesn't touch this.

Expected Behavior

--config with one or more files should resolve base_path (including the empty-string →
git-root-discovery default) the same way normal auto-discovery does, so terraform test (and
presumably other component-path-dependent commands) behaves identically regardless of whether
config was found via auto-discovery or explicitly via --config.

Steps to Reproduce

Minimal, self-contained repro. Creates a throwaway project in a temp dir (its own git init,
minimal atmos.yaml + one supplement file, one trivial component with one test), then runs the
same terraform test invocation three ways. Copy-paste the whole block into a terminal:

REPRO_DIR="$(mktemp -d)"
echo "Reproducing in: $REPRO_DIR"

# Install atmos if not already on PATH (kept outside REPRO_DIR so atmos's own
# config-file discovery doesn't try to parse the binary itself as YAML)
if ! command -v atmos >/dev/null 2>&1; then
  ATMOS_VERSION=1.224.1
  ATMOS_BIN_DIR="$(mktemp -d)"
  curl -fsSL "https://github.com/cloudposse/atmos/releases/download/v${ATMOS_VERSION}/atmos_${ATMOS_VERSION}_linux_amd64" -o "$ATMOS_BIN_DIR/atmos"
  chmod +x "$ATMOS_BIN_DIR/atmos"
  ATMOS="$ATMOS_BIN_DIR/atmos"
else
  ATMOS=atmos
fi
$ATMOS version

cd "$REPRO_DIR"
git init -q
mkdir -p stacks/deploy components/terraform/my-component

cat > atmos.yaml <<'EOF'
base_path: ''
components:
  terraform:
    base_path: components/terraform
stacks:
  base_path: stacks
  included_paths:
    - deploy/**/*
  name_pattern: '{stage}'
EOF

cat > supplement.yaml <<'EOF'
stacks:
  included_paths:
    - extra/**/*
EOF

cat > stacks/deploy/dev.yaml <<'EOF'
vars:
  stage: dev
components:
  terraform:
    my-component:
      vars: {}
EOF

cat > components/terraform/my-component/main.tf <<'EOF'
variable "stage" {
  type = string
}

output "stage" {
  value = var.stage
}
EOF

cat > components/terraform/my-component/tests.tftest.hcl <<'EOF'
run "check_stage" {
  command = plan
  variables {
    stage = "dev"
  }
  assert {
    condition     = output.stage == "dev"
    error_message = "stage mismatch"
  }
}
EOF

echo ""
echo "CASE 1: plain auto-discovery, single atmos.yaml (works)"
$ATMOS terraform test my-component -s dev

echo ""
echo "CASE 2: identical settings, split into atmos.yaml + supplement.yaml, combined via --config (fails)"
$ATMOS --config atmos.yaml,supplement.yaml terraform test my-component -s dev || true

echo ""
echo "CASE 3: same as Case 2, but with ATMOS_BASE_PATH set explicitly (fails identically - setEnv() never runs)"
ATMOS_BASE_PATH="$REPRO_DIR" $ATMOS --config atmos.yaml,supplement.yaml terraform test my-component -s dev

Case 1 prints Success! 1 passed, 0 failed.. Cases 2 and 3 both fail identically with
Error: failed to find import.

Screenshots

No screenshots — CLI output only, included in Steps to Reproduce above. The exact failure:

Error: failed to find import

💡 Verify that base_path and stacks.base_path in atmos.yaml are correct
💡 If using ATMOS_BASE_PATH, ensure the path is correct relative to the working directory
💡 Verify stacks.base_path in atmos.yaml points to the correct directory
💡 Check that the stacks directory exists and contains stack configuration files

Environment

• OS: Linux
• Atmos version: 1.224.1
• Standalone binary (linux/amd64), not run via Docker
• Config: minimal, ordinary atmos.yaml (base_path: '', stacks.base_path: stacks,
  components.terraform.base_path: components/terraform) — no custom commands, no unusual
  settings involved in triggering this

Additional Context

Suggested fix direction: either route the --config/--config-path branch through the same
setEnv() / applyGitRootBasePath() / Unmarshal steps that loadConfigSources() uses (removing
the early return and threading the CLI-supplied files in as an additional highest-priority source
rather than a fully separate pipeline), or explicitly document that --config bypasses env-var
bindings and git-root base-path resolution, with a hint added to the failed to find import error
message specifically when triggered from this code path.