.env.example: document MEMPALACE_PALACE_PATH and why nothing exports it

The only MemPalace variable the template never mentioned, and the one that
moves the feeders' stage as a side effect: the palace root resolves as
$MEMPALACE_PALACE_PATH -> $MEMPAL_PALACE_PATH -> ~/.mempalace/config.json ->
~/.mempalace/palace, and the stage is derived from it (<palace-root>/pi-stage).

The comment states that precedence, records why neither the image nor the
entrypoint exports it (pinning the palace without carrying the stage along
re-creates the split a shared root removed, v1.8.2), warns that a stage whose
persistence differs from the palace makes a scoped `mempalace sync` prune
conversation drawers whose dedup key is the staged path, and notes it is a
path INSIDE the container unlike the host-side WORKSPACE_PATH/SSH_KEY_PATH
above it.

Found while auditing a live host whose .env sets it redundantly to the
default value.

.env.example

@@ -18,6 +18,19 @@ SSH_KEY_PATH=~/.ssh
 # the staged files and the palace dedup keys pointing at them cannot be
 # separated.
 #
+# That palace root is resolved with mempalace's own precedence
+# ($MEMPALACE_PALACE_PATH -> $MEMPAL_PALACE_PATH -> ~/.mempalace/config.json ->
+# ~/.mempalace/palace), and the feeders derive their stage FROM it
+# (<palace-root>/pi-stage). Neither the image nor the entrypoint exports it, by
+# design: pinning the palace without carrying the stage along re-creates the
+# very split that a shared root removed. Override it only to move the palace off
+# the default -- e.g. onto a different mount -- and only to a path with the SAME
+# persistence as the palace itself. A stage that outlives its palace (or dies
+# first) makes a scoped `mempalace sync` prune conversation drawers, because
+# their dedup key is the staged path. Setting it to the default buys nothing.
+# Unlike WORKSPACE_PATH/SSH_KEY_PATH above, this is a path INSIDE the container.
+# MEMPALACE_PALACE_PATH=/home/developer/.mempalace/palace
+#
 # To instead share ONE MemPalace across containers/harnesses (pi + opencode
 # + native), set the URL below. When set, the extension connects over HTTP
 # and NO local mempalace-mcp is spawned; the devbox-palace volume is then

CHANGELOG.md

@@ -11,6 +11,25 @@ Pre-v1.0.0 tags followed the pi npm version (`v{pi_version}[letter]`).
 
 ---
 
+## Unreleased
+
+### Documentation
+
+- **`.env.example` documents `MEMPALACE_PALACE_PATH`.** It was the only MemPalace
+  variable the template never mentioned, while being the one that silently moves
+  the feeders' stage: the palace root resolves as `$MEMPALACE_PALACE_PATH` →
+  `$MEMPAL_PALACE_PATH` → `~/.mempalace/config.json` → `~/.mempalace/palace`, and
+  the stage is derived from it (`<palace-root>/pi-stage`). The comment states the
+  precedence, says why neither the image nor the entrypoint exports it (pinning
+  the palace without carrying the stage re-creates the split a shared root
+  removed — see v1.8.2), warns that a stage whose persistence differs from the
+  palace makes a scoped `mempalace sync` prune conversation drawers whose dedup
+  key is the staged path, and notes it is a *container* path unlike the
+  host-side `WORKSPACE_PATH`/`SSH_KEY_PATH` above it. Found while auditing a live
+  host whose `.env` sets the variable redundantly to the default.
+
+---
+
 ## v1.8.5 — 2026-08-23
 
 Patch release with two fixes in the container's skill wiring — one behavioural,