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+## Background
+
+- I recently used `git-filter-repo` to scrub cleartext secrets from a
+  repository.
+- We pin some services' deployments to commit SHAs.
+- These commit SHAs are no longer reachable from `origin/main`.
+
+## Problem
+
+If `git` garbage-collects any of the commits to which services are pinned, and
+that service attempts to redeploy, the deployment will fail.
+
+`git for-each-ref --contains $SHA` will report all of the refs that can reach
+some commit, `$SHA`. This may report things like:
+- `refs/replace` (i.e. `git-filter-repo` artifacts)
+- `refs/stash`
+- some local branches
+- some remote branches
+
+One solution might involve creating references to avoid garbage-collection. But
+if any of our pinned commits contains sensitive cleartext we *want* to ensure
+that `git` purges these.
+
+Instead let's find the SHAs of the new, rewritten commits and replace the pinned
+versions with those.
+
+## Solution
+
+Essentially we want to find a commit with the same *tree* state as the currently
+pinned commit. Here are two ways to get that info...
+
+This way is indirect, but provides more context about the change:
+
+```shell
+λ git cat-file -p $SHA
+tree d011a1dd4a3c5c4c6455ab3592fa2bf71d551d22 # <-- copy this tree info
+parent ba88bbf8de61be932184631244d2ec0ec8205cb8
+author William Carroll <wpcarro@gmail.com> 1664993052 -0700
+committer William Carroll <wpcarro@gmail.com> 1665116042 -0700
+
+feat(florp): Florp can now flarp
+
+You're welcome :)
+```
+
+This way is more direct (read: code-golf-friendly):
+
+```shell
+λ git log -1 --format=%T $SHA
+```
+
+Now that we have the SHA of the desired tree state, let's use it to query `git`
+for commits with the same tree SHA.
+
+```shell
+λ git log --format='%H %T' | grep $(git log --format=%T -1 $SHA) | awk '{ print $1 }'
+```
+
+Hopefully this helps!