Merge pull request #1560 from LakshmanTurlapati/fix/session-scoped-workstream-routing

[codex] isolate active workstream state per session

commands/gsd/workstreams.md

@@ -44,7 +44,9 @@ Display detailed phase breakdown and state information.
 
 ### switch
 Run: `node "$GSD_TOOLS" workstream set <name> --raw --cwd "$CWD"`
-Also set `GSD_WORKSTREAM` env var for the current session.
+Also set `GSD_WORKSTREAM` for the current session when the runtime supports it.
+If the runtime exposes a session identifier, GSD also stores the active workstream
+session-locally so concurrent sessions do not overwrite each other.
 
 ### progress
 Run: `node "$GSD_TOOLS" workstream progress --raw --cwd "$CWD"`