[fix] [v1]: reject dupe artifact sources

[gtnv]

Prev: archive and charge every declaration before dict kept only last value.
Now: duplicate artifact declarations are resolved before colection

closes: #2198

---

Note

Low Risk
Small validation-only change in artifact collection; the only behavioral shift is failing fast on misconfigured duplicate sources instead of silent overwrite.

Overview
collect now validates the resolved entries list before tarring anything: it tracks artifact.source values and raises RuntimeError if the same source appears twice.

That replaces the previous behavior where duplicate declarations still ran collection and the returned dict silently kept only the last entry per key—aligning runtime behavior with the existing docstring that a path cannot be collected twice.

^{Reviewed by Cursor Bugbot for commit a2f9abc. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Reject duplicate artifact sources in collect

Adds a pre-collection validation step in collect that tracks seen artifact.source values and raises a RuntimeError if any source appears more than once. Risk: existing callers with duplicate artifact sources will now fail at runtime instead of silently collecting duplicates.

^{Macroscope summarized a2f9abc.}