diff --git a/installer/PLAN.md b/installer/PLAN.md
index d2edf7d..2b068c0 100644
--- a/installer/PLAN.md
+++ b/installer/PLAN.md
@@ -894,12 +894,13 @@ operators who downloaded a bare binary being told to re-download a package. Defe
 costs nothing: nothing is published from `edge`, and the guide's Appendix A is the supported path
 meanwhile.
 
-| Item | Decision |
-|---|---|
-| `.deb` for uo-link | **Dropped** (§5.1) |
-| Windows MSI | **Dropped** (§5.1) |
-| arm64 cross build | **Build** — Linux `aarch64`, both components (§5.2) |
-| Backup before upgrade | **Build** — on by default, scoped to what a run overwrites (§5.3) |
+| Item | Decision | State |
+|---|---|---|
+| `.deb` for uo-link | **Dropped** (§5.1) | — |
+| Windows MSI | **Dropped** (§5.1) | — |
+| arm64 cross build | **Build** — Linux `aarch64`, both components (§5.2) | In review: [installer#9](https://gitea.whitlocktech.com/RunicGateway/installer/pulls/9), [link#26](https://gitea.whitlocktech.com/RunicGateway/link/pulls/26), [installer#10](https://gitea.whitlocktech.com/RunicGateway/installer/pulls/10); step 3 waits on link's first arm64 release |
+| Backup before upgrade | **Build** — on by default, scoped to what a run overwrites (§5.3) | In review: [installer#11](https://gitea.whitlocktech.com/RunicGateway/installer/pulls/11) |
+| Docs the release invalidates | **Do** (§5.4) | Pending |
 
 #### 5.1 What ships is plain binaries: no `.deb`, no MSI
 
@@ -961,6 +962,13 @@ lasts. Hence:
 `bundle.yml` is therefore edited on `main` only and never on `edge`, so the cutover merge has nothing
 to conflict over.
 
+**What building it found.** Neither crate cross-compiles with the arm64 *compiler* alone.
+`gcc-aarch64-linux-gnu` only **recommends** `libc6-dev-arm64-cross`, and both release workflows
+install with `--no-install-recommends` — so the C that each crate pulls in (bundled SQLite under
+`sqlx` for the sidecar, `ring` under `ureq`'s rustls for the installer) dies on a missing
+`bits/libc-header-start.h` while every Rust dependency builds fine. Both halves were reproduced in a
+`rust:1-slim-bookworm` container, failure then fix, before either workflow was written.
+
 #### 5.3 Backup before overwrite
 
 **Scoped by what cannot be fetched again.** Not the sidecar binary or the overlay files — both are
@@ -982,14 +990,28 @@ that is still downloadable, and the noise would bury the two files that matter.
   from, beside a `manifest.json` naming the source path, its SHA256, and the bundle moved from and
   to. In the state directory, not the ServUO tree — the same rule the tier's `patches/originals/`
   follows, and for the same reason: `uninstall` has promised never to clean up in there.
-- **When:** on by default for `update`, and for an `install` over an existing record. A first
-  install overwrites nothing and writes no backup. `--verify` writes none either, for the reason it
-  runs no part of the sidecar half (Phase 2): a dry run must not create state.
+- **When: whenever the run is about to overwrite something**, whichever verb was typed. This
+  section first said "`update`, and `install` over an existing record", justified by a first install
+  overwriting nothing — **which is wrong**, and building it is what showed that. A tree deployed by
+  hand per [`INSTALL.md`](INSTALL.md) Appendix A2 — the path this project recommends while the
+  binary is unreleased — has `.cs` files the first `install` plans as `Change` and overwrites, with
+  no prior record anywhere to notice. The direct test covers that case, and a genuine first install
+  onto a clean tree still writes nothing, because there is nothing to copy. `--verify` writes none
+  either, for the reason it runs no part of the sidecar half (Phase 2): a dry run must not create
+  state.
+- **`sidecar.toml` joins a backup that is already being taken; it is never the reason for one.**
+  Nothing in the installer rewrites it, so treating it as a trigger would leave a dated directory
+  behind after every no-op `update` — the empty-backup problem one step along. It is copied so that
+  a restored set of files arrives with the token that matches it.
 - **`--no-backup`** opts out, for an operator with their own snapshotting.
 - **Retention is three.** Older ones are pruned as new ones are written; an unbounded directory of
   ServUO source copies on a shard host is its own support problem. `uninstall` keeps them and
   `--purge` drops them, alongside the config, the database and the cached patch set — same rule as
   Phase 4, and the same reason: they are the only offline record of what was there before.
+- **The directory is created lazily and the manifest is written last**, so a directory carrying one
+  is a *complete* backup. Listing and pruning consider only those: a run interrupted mid-copy must
+  neither be mistaken for a backup nor be able to evict a good one by being newer than it. It is
+  left on disk for a human to look at rather than silently deleted.
 - **Restore is printed, not done.** Consistent with the uninstall report, and for the identical
   reason: the installer cannot know what has changed since, and a clever automatic restore over a
   newer overlay eats work rather than saving it. `doctor` names the most recent backup and its