feat: inject BRUIN_VARS_SCHEMA for type-aware variable coercion

[sabrikaragonen]

Summary

• Adds SchemaMap() method to Variables that returns type definitions without the default key
• Modifies envInjectVariables to marshal and set BRUIN_VARS_SCHEMA alongside BRUIN_VARS
• Enables the Python SDK to coerce CLI string overrides (--var count=42) to proper types

Companion PR

• Python side (reads schema and coerces): bruin-data/python-sdk — feature/type-aware-var-coercion

Test plan

• 3 unit tests for SchemaMap() in variables_test.go
• 2 unit tests for BRUIN_VARS_SCHEMA injection in env/variables_test.go
• All existing tests still pass
• E2E test after Python PR is merged

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Additional Comments (1)

pkg/env/variables.go
Asymmetric handling of empty variables

When variables is empty, BRUIN_VARS is explicitly set to "{}" but BRUIN_VARS_SCHEMA is omitted entirely. This means the Python SDK must handle two distinct cases: (1) BRUIN_VARS_SCHEMA is absent, and (2) BRUIN_VARS_SCHEMA is present with content. Consider setting BRUIN_VARS_SCHEMA to "{}" alongside BRUIN_VARS for consistency, so the companion Python SDK can always expect the env var to exist when BRUIN_VARS does.

	if len(variables) == 0 {
		env["BRUIN_VARS"] = "{}"
		env["BRUIN_VARS_SCHEMA"] = "{}"
		return env, nil
	}

Prompt To Fix With AI

This is a comment left during a code review.
Path: pkg/env/variables.go
Line: 64-67

Comment:
**Asymmetric handling of empty variables**

When `variables` is empty, `BRUIN_VARS` is explicitly set to `"{}"` but `BRUIN_VARS_SCHEMA` is omitted entirely. This means the Python SDK must handle two distinct cases: (1) `BRUIN_VARS_SCHEMA` is absent, and (2) `BRUIN_VARS_SCHEMA` is present with content. Consider setting `BRUIN_VARS_SCHEMA` to `"{}"` alongside `BRUIN_VARS` for consistency, so the companion Python SDK can always expect the env var to exist when `BRUIN_VARS` does.

```suggestion
	if len(variables) == 0 {
		env["BRUIN_VARS"] = "{}"
		env["BRUIN_VARS_SCHEMA"] = "{}"
		return env, nil
	}
```

How can I resolve this? If you propose a fix, please make it concise.