fix(cli): reject mapping keys that inject extra .env assignments #511

Description

The CLI accepts mapping keys containing equals signs and newlines. Since keys are written verbatim, one mapping creates additional environment assignments while the command reports success.

Reproduced on CLI 0.13.2, commit c317813caa358cb4fb00cebb97a069e7cd96e6fd, Windows, Node.js 24.20.0. The compiled CLI used the real AWS SDK against a local HTTP SSM/STS stub with fictional values; no real cloud credentials were used.

Reproduction

Use this map (JSON escapes represent a real newline in the parsed key):

{"SAFE=prefix\nINJECTED": "/simple"}

Have /simple return fictional value fictional-value-123, then run node lib/envilder/apps/cli/entry/Index.js --map=map.json --envfile=result.env.

Actual: exit code 0 and:

SAFE=prefix
INJECTED=fictional-value-123

Expected: reject the invalid mapping key with an actionable error before provider calls or destination writes.

Acceptance Criteria

• Should_RejectMappingKey_When_NameContainsNewlineCarriageReturnOrEquals.
• Should_PreserveDestination_When_MappingContainsInvalidVariableNames.
• Enforce the variable-name grammar already defined by the map-file specification.
• Preserve valid names and reserved metadata-key behavior.
• Tests pass: pnpm test.
• Lint passes: pnpm lint; rebuilt Action passes pnpm verify:gha.

Technical Notes

• EnvironmentVariable.ts:72 only checks for empty names.
• FileVariableStore.ts:126 interpolates keys directly.
• Related specification work: docs(architecture): add ADR-0008 map-file schema specification #212 and feat(spec): add map-file JSON Schema v1 #217. Publishing a JSON Schema does not enforce it at this runtime boundary.
• Exploitation requires control of the mapping file. This reproduction does not demonstrate remote code execution or privilege escalation.
• No matching open or closed issue was found.