Earlier comment claimed the function "mirrors RustAstExtractor pattern" but
the two differ: RustAstExtractor joins ctx.workspace_root to handle relative
paths, while Tier 2 trusts FsSourceConnector's absolute-path invariant.
Rephrase to document the actual rationale + the Kb URI fallback.
Reviewer nit #3 (PR #153 code-reviewer).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>