Derive a Gleam module prefix from the configured output directory.

Looks for a src segment anywhere in the path and takes everything after it (Gleam module paths are rooted at src/).

Examples: “./src/generated” -> “generated” “src/generated” -> “generated” “/tmp/proj/src/api/gen” -> “api/gen” “./generated” -> “generated” (relative, assumed src-rooted) “src” or “./src” -> “” (top-level — no prefix) “/tmp/out” -> “” (absolute, no src/ — unknowable)

Returning “” disables real-import emission and falls back to a comment hint. That is always the safe answer: an unusable prefix produces a generated import that does not parse, which is worse than no import at all.