cabal install symlinks non-existing executables

[andreasabel]

In a situation where everything is up to date, an invocation of cabal install might just symlink executables that it has not created and that do not exist.
In the wild: https://github.com/agda/agda/actions/runs/10201512448/job/28223527794?pr=7410
This workflow restores a cached ~/.cabal/store from the last run.

1. cabal build --only-dependencies reports "up to date": https://github.com/agda/agda/actions/runs/10201512448/job/28223527794?pr=7410#step:6:7
2. cabal install then succeeds within a few seconds. https://github.com/agda/agda/actions/runs/10201512448/job/28223527794?pr=7410#step:7:10
   It does not report linking anything, just

   Symlinking 'agda' to '/home/runner/.cabal/bin/agda'

3. The respective symlink points to ~/.cabal/store/ghc-9.10.1-69c3/Agda-2.7.0-878d927f716899ddbeb27d38180df34498e8681c6104fa4fb10682e20a27e3f9/bin/agda. https://github.com/agda/agda/actions/runs/10201512448/job/28223527794?pr=7410#step:8:11
4. No agda exists there because not even the bin directory exists. https://github.com/agda/agda/actions/runs/10201512448/job/28223527794?pr=7410#step:8:15

/home/runner/.cabal/store
└── ghc-9.10.1-69c3
    ├── Agda-2.7.0-878d927f716899ddbeb27d38180df34498e8681c6104fa4fb10682e20a27e3f9
    │   ├── cabal-hash.txt
    │   ├── lib
    │   └── share

5. agda is subsequently not found. https://github.com/agda/agda/actions/runs/10201512448/job/28223527794?pr=7410#step:9:11

cabal-install version is 3.12.1.0. https://github.com/agda/agda/actions/runs/10201512448/job/28223527794?pr=7410#step:3:40

[andreasabel]

Observed again today: https://github.com/agda/agda/actions/runs/10683742640/job/29612530382?pr=7469#step:7:10

I wonder what the conditions for cabal v2-install are to skip building.