fix(recovery): isolate Codex titles by PTY process

[attson]

Summary

• bind Linux Codex sessions to the rollout file actually opened by the PTY process tree
• prevent concurrent same-cwd resolvers from guessing the same conversation on unsupported platforms
• add same-cwd concurrency and process-ownership regression coverage

Verification

• go test -count=1 -tags webkit2_41 -timeout 60s ./desktop/
• go test -race -tags webkit2_41 -timeout 60s ./desktop/
• go vet -tags webkit2_41 ./...