A PR head-branch name is attacker-controllable and get_thread_id_from_branch
derives a thread_id from its first UUID with no repo binding (TID-COLLIDE-01).
The in-memory sandbox cache and the per-thread GitHub-token cache were keyed on
thread_id alone, and a cached sandbox was reused after only an echo-ping, so a
different repo's webhook could bind to another thread's sandbox or token.
Without changing the persistent thread-id scheme:
- Persist the bound repo (owner/name) in thread metadata on sandbox creation and
refuse to reuse a sandbox whose bound repo does not match the current event
(SandboxRepoMismatchError); the in-memory proxy also carries the binding.
- Bind the GitHub-token cache entries to their repo and evict on a cross-repo
read so a colliding thread_id cannot be served another repo's token.
- Thread repo through the reviewer and the webhook token resolvers.
