fix(agent): pin nanobot so a restart cannot take the agent off Matrix

stacklets/agent/Dockerfile

@@ -11,7 +11,18 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
     ca-certificates git libolm-dev tzdata \
     && rm -rf /var/lib/apt/lists/*
 
-RUN uv pip install --system --no-cache "nanobot-ai[matrix]"
+# Pinned, and it has to stay pinned. `runtime/sitecustomize.py` patches
+# nanobot's internals (there is no plugin seam), so a release that moves one
+# of those symbols detaches a shim. The shims fail soft on purpose — a broken
+# one must never stop the agent answering — so the container still starts,
+# still reports healthy, and the Matrix channel is simply gone. Unpinned, that
+# arrives on whatever unrelated `stack restart agent` happens to rebuild the
+# image, which is how 0.2.x moving `nanobot.channels.matrix` from a module to
+# a package took a live instance silently off Matrix.
+#
+# Bump this deliberately, in its own change, and re-verify every symbol in
+# sitecustomize.py's PIN / RECHECK list against the new release.
+RUN uv pip install --system --no-cache "nanobot-ai[matrix]==0.2.2"
 
 # Non-root, matching nanobot's own image (uid 1000, HOME=/home/nanobot).
 RUN useradd -m -u 1000 -s /bin/bash nanobot

stacklets/agent/runtime/sitecustomize.py

@@ -62,9 +62,16 @@
                  `MatrixChannel._handle_message(sender_id, chat_id, content, metadata, is_dm)`
 
     `tests/stacklets/test_agent_runtime_shims.py` asserts every one of these is
-    attached against a stub nanobot, so this list is executable rather than
-    aspirational: a moved symbol fails the unit lane instead of silently
-    reaching production as a logged warning nobody reads.
+    attached — but against a *stub* nanobot this repo hand-writes, so read what
+    that does and does not buy. It catches our own mistakes: a shim that stops
+    attaching, or one whose failure takes another down with it. It cannot catch
+    upstream moving a symbol, because the stub still has the old one and the
+    lane stays green while production is broken. The version pin in the
+    Dockerfile is what actually holds this line; the tests guard the shims, the
+    pin guards the assumption underneath them.
+
+    So when bumping `nanobot-ai`, re-verify this list against the installed
+    package, not against a passing unit lane.
 """
 
 import importlib