Correct behavior of "writable" Almanac service binding for repository services
Summary: Ref T13611. This property worked correctly when implemented in D19357. The behavior was broken by D20775, which tested node-level routing but did not specifically re-test the "writable" property. This was difficult to spot because ref query outcomes weren't observable in the UI, and the ref itself had the correct property value.
See D21575. After this change, the UI shows the correct state, rather than showing a read-only service ref as writable:
Maniphest Tasks: T13611
Differential Revision: https://secure.phabricator.com/D21576