fix(knowledge): scope pins to sessions

packages/web/server/lib/session-knowledge/DOCUMENTATION.md

@@ -1,6 +1,6 @@
 # Session Knowledge
 
-What a session must be told about the project — the user's pinned notes and
+What a session must be told about the project — that session's pinned notes and
 plans, and the index of what the agent has remembered — and whether it has been
 told yet.
 
@@ -19,6 +19,11 @@ on believing it does and never sends it again.
 
 ## The contract
 
+`session.metadata.openchamber.project_context_pins` owns the note and plan ids
+attached to that session. Pins never come from project-wide note or plan state.
+A new-session draft passes its pins into this metadata when its first message
+creates the session.
+
 `session.metadata.openchamber.knowledge_context_delivered` holds the signature
 of what the session is carrying. It lives with the session, so it survives the
 tab closing and is visible to every sender, including the ones with no tab.
@@ -78,5 +83,5 @@ no session index, no settings row and no panel tab — absent rather than switch
 off, which would invite turning on something never announced. The setting itself
 also defaults to off, so setting the variable does not enable memory by itself.
 
-Pinned notes and plans are unaffected: they ship as normal and travel with every
-message whether or not memory exists.
+Pinned notes and plans are unaffected by the memory switch and remain scoped to
+the session that pinned them.