## Summary
- add first-class marketplace support for git-backed plugin sources
- keep the newer marketplace parsing behavior from `main`, including
alternate manifest locations and string local sources
- materialize remote plugin sources during install, detail reads, and
non-curated cache refresh
- expose git plugin source metadata through the app-server protocol
## Details
This teaches the marketplace parser to accept all of the following:
- local string sources such as `"source": "./plugins/foo"`
- local object sources such as
`{"source":"local","path":"./plugins/foo"}`
- remote repo-root sources such as
`{"source":"url","url":"https://github.com/org/repo.git"}`
- remote subdir sources such as
`{"source":"git-subdir","url":"owner/repo","path":"plugins/foo","ref":"main","sha":"..."}`
It also preserves the newer tolerant behavior from `main`: invalid or
unsupported plugin entries are skipped instead of breaking the whole
marketplace.
## Validation
- `cargo test -p codex-core plugins::marketplace::tests`
- `just fix -p codex-core`
- `just fmt`
## Notes
- A full `cargo test -p codex-core` run still hit unrelated existing
failures in agent and multi-agent tests during this session; the
marketplace-focused suite passed after the rebase resolution.
make plugins' `defaultPrompt` an array, but keep backcompat for strings.
the array is limited by app-server to 3 entries of up to 128 chars
(drops extra entries, `None`s-out ones that are too long) without
erroring if those invariants are violating.
added tests, tested locally.
