[dailyun]

ffenv.Parse returns nil after its scanner stops, even when it stopped on a read error or an overlong line. A partially read .env file can therefore be accepted as successful configuration.

Return s.Err(), as ff.PlainParser already does. Clean EOF still succeeds; a read failure is returned to the caller instead of being discarded.

Added four cases: a reader failing immediately, a reader failing after a valid setting, a line exceeding the scanner limit, and clean EOF without a trailing newline. The first three fail on the base; all four pass with this change.

Validation on Go 1.26.7 / macOS arm64:

• Full go test -race ./..., go vet ./..., and staticcheck pass.
• gofmt, gofumpt, the parallel-test lint script, and git diff --check pass.
• Revive reports three existing warnings in unchanged files; no new warnings.

No dependencies or scanner size limits change. Settings processed before a reader failure remain applied; this change reports that failure rather than adding rollback.

AI assistance: implemented and tested with OpenAI Codex; no human review before submission.