Tags: OneNoted/forgecode.fish

Allow the fish plugin loader to work from vendor install paths

The AUR package installs forgecode.fish into fish vendor directories, but
the loader assumed a normal ~/.config/fish layout and tried to source
nonexistent /usr/share/fish/functions files. This change teaches the
loader to prefer vendor_functions.d/vendor_completions.d when needed and
adds a regression test for that install shape.

Constraint: The same loader must still work for both repo/local installs and fish vendor installs
Constraint: Packaging regressions should be caught without requiring a full AUR reinstall to notice them
Rejected: Leave the code as-is and patch only the local machine | would keep the published git package broken for other users
Confidence: high
Scope-risk: narrow
Reversibility: clean
Directive: Keep conf.d/forgecode.fish install-location-aware whenever packaging layout changes
Tested: fish interactive startup after local override; bash scripts/test-fish-plugin.sh
Not-tested: Fresh reinstall of forgecode-fish-git from AUR after the fix publishes

Let the matrix workflow use container fallbacks when the host runner …

…does not match

GitHub-hosted Ubuntu did not satisfy the local ENV-1 fish 4.6.x assumption
and the ENV-3 lane failed before it could fall back to Docker because fish
was not installed on the host at all. This change makes the matrix script
robust to missing/mismatched host fish versions and lets CI use Arch/Debian
container lanes where appropriate.

Constraint: CI must preserve the documented ENV-1/ENV-3 intent even when the host runner is not the target environment
Constraint: Host runners without fish installed must still be able to reach the Docker fallback path
Rejected: Loosen ENV-1 to whatever fish version Ubuntu provides | would weaken the documented reference lane instead of honoring it
Confidence: high
Scope-risk: narrow
Reversibility: clean
Directive: Keep matrix semantics in the script, and use containers only as faithful stand-ins for the documented environments
Tested: bash scripts/run-fish-matrix.sh ENV-1; bash scripts/run-fish-matrix.sh ENV-3; Arch Linux container run of scripts/test-fish-plugin.sh reached the suite on current packaging assumptions
Not-tested: Fresh GitHub Actions rerun before push