🧹 Specify knapsack required branch

See inline documentation regarding purpose and intent of the hard-coded
branch logic.

Gemfile

@@ -108,11 +108,21 @@ gem 'webmock', group: %i[test]
 # and place overrides, themes and deployment code.
 #
 # When you use a knapsack for Hyku development, which we recommend, you'll want to ensure that your
-# local knapsack repository has a `main` branch (which it should by default).  Due to some
-# tomfoolery, of knapsack, the branch name (e.g. `main`) must be checked out locally in the knapsack
-# environment that you use to build Docker.
+# local knapsack repository has a `'required_for_knapsack_instances'` branch (which it should by
+# default).  Due to some tomfoolery, of knapsack, the branch name
+# (e.g. `required_for_knapsack_instances`) must be checked out locally in the knapsack environment
+# that you use to build Docker.
 #
-# tl;dr - Have a local main branch on your knapsack repository
-gem 'hyku_knapsack', github: 'samvera-labs/hyku_knapsack', branch: 'main'
+# Why not use `main`?  We need a stable SHA for building HykuKnapsack prime
+# (e.g. samvera-labs/hyku_knapsack).  Why the stable SHA?  Because when we bundle a knapsack, the
+# Hyku submodule uses the SHA of the locally checked out branch specified in the gem spec.  Which
+# can create a chicken and egg issue; namely I need to update Hyku with a new SHA for Knapsack, but
+# to update Knapsack's submodule reference to Hyku, I need a new SHA for knapsack.  Thus, I can never
+# use a "regular branch".  Instead we need to use a separate more stable for Knapsack.
+#
+# Thus the hopefully descriptive `required_for_knapsack_instances`.
+#
+# tl;dr - Have a local `required_for_knapsack_instances` branch on your knapsack repository
+gem 'hyku_knapsack', github: 'samvera-labs/hyku_knapsack', branch: 'required_for_knapsack_instances'
 
 # rubocop:enable Layout/LineLength

Gemfile.lock

@@ -95,8 +95,8 @@ GIT
 
 GIT
   remote: https://github.com/samvera-labs/hyku_knapsack.git
-  revision: 418a390fad222120a36e29271ba6c80ff91b358c
-  branch: main
+  revision: 5a7c54cace96881a3963ab2fd881ca6ea3f57372
+  branch: required_for_knapsack_instances
   specs:
     hyku_knapsack (0.0.1)
       rails (>= 5.2.0)