feat: Environment config overrides (`.strata.<env>.yaml`)

[Lazialize]

Problem

The current .strata.yaml requires all environment configurations to be written in a single environments section. Writing production credentials (passwords, etc.) directly in the config file is a security risk, and teams managing different environments are prone to Git merge conflicts.

Proposed Solution

Support environment-specific override files .strata.<env>.yaml that are deep-merged with the base configuration.

Design

project/
├── .strata.yaml              # Base config (shared)
├── .strata.development.yaml  # Development overrides
├── .strata.staging.yaml      # Staging overrides
└── .strata.production.yaml   # Production overrides (recommended in .gitignore)

Merge Rules

1. Load .strata.yaml as the base configuration
2. If a .strata.<env>.yaml file exists for the environment specified by --env, deep-merge it into the base
3. Fields in the override file overwrite the same-named fields in the base
4. Environment variable STRATA_ENV can also specify the environment name (--env takes precedence)

Configuration Example

.strata.yaml (base):

version: "1.0"
dialect: postgresql
schema_dir: schema
migrations_dir: migrations
environments:
  development:
    host: localhost
    port: 5432
    database: myapp_dev

.strata.production.yaml (override):

environments:
  production:
    host: db.production.internal
    database: myapp_prod
    ssl_mode: require
    max_connections: 20

Implementation Plan

1. Extend Config loader (src/core/src/core/config.rs)

   • Add override file discovery logic to Config::load()
   • Implement Config::merge(base, override) method (deep merge of HashMaps)

2. Add --env CLI argument (src/cli/src/cli/cli.rs)

   • Add --env <ENV> as a global argument
   • Fall back to STRATA_ENV environment variable

3. Update .gitignore template (strata init)

   • Suggest adding .strata.production.yaml to .gitignore by default

Files Affected

• src/core/src/core/config.rs — Config::load() merge logic
• src/cli/src/cli/cli.rs — --env argument
• src/cli/src/cli/commands/command_context.rs — Config loading flow changes
• src/cli/src/cli/commands/init.rs — .gitignore template update

Alternatives Considered

• Environment variables only: Override all settings via STRATA_DB_HOST, etc. Simple but file-based management is easier to maintain
• TOML format: TOML excels at section management, but YAML consistency with the existing ecosystem is preferred
• Vault integration: HashiCorp Vault or similar secret management tools are future scope; file-based overrides come first

Additional Context

• Corresponds to "Support environment overrides in config" in ROADMAP.md
• The existing Config::validate() must also apply to the merged result
• Typical usage with Docker Compose: STRATA_ENV=production strata apply