Keep package requests from bypassing existing selection conditions #28

During a correctness pass with Astra we found the following issue:

Author's preface above. Issue details below written by Astra (AI assistant) on 2026-10-09.

rs add-package rosidlcpp jazzy takes the wrong path when deciding whether to add a package.

rosidlcpp already exists in a conditional block in shared selection, and Jazzy explicitly excludes it. I verified with the installed Vinca resolver that it is available in Jazzy but absent from Jazzy's effective selected set. The add-package code treats that as a missing shared entry and appends an unconditional entry.

[INFERENCE] Running the mutating command would broaden the selection for other distributions/platforms while still not building the package for Jazzy. I did not run that mutation during the audit.

Code: tools/maintenance.py, shared/vinca.yaml and distros/jazzy/vinca.yaml.

Suggested change

Check the existing source selection as well as the resolved selection. Distinguish an absent package from one that is excluded, skipped or platform-restricted, and explain that state in the bot reply. Do not insert an unconditional duplicate to try to resolve it.

Acceptance criteria

• Requesting rosidlcpp for Jazzy leaves the conditional shared entry unchanged and explains the exclusion.
• Requesting an already selected or platform-restricted package does not broaden its scope.
• A genuinely absent package can still be added once, in sorted order.
• Regression tests cover exclusion and platform-condition cases.