fix(party-mode): add return protocol to prevent lost-in-the-middle failures (#1569)

After Party Mode completes within a parent workflow, the LLM fails to
re-present the parent workflow's completion menu due to lost-in-the-middle
effect at 50-100K tokens. The parent workflow instructions get pushed into
mid-context where they are no longer proactively recalled.

Add a Return Protocol section to step-03-graceful-exit.md that instructs
the LLM to:
1. Identify the parent workflow that invoked party-mode
2. Re-read that file to restore context
3. Resume from the invocation point
4. Present required menus/options

This is platform-independent prompt engineering that forces proactive
re-reading rather than relying on mid-context recall.

Fixes #1319

Co-authored-by: Brian <bmadcode@gmail.com>

src/core/workflows/party-mode/steps/step-03-graceful-exit.md

@@ -142,6 +142,17 @@ Thank you for using BMAD Party Mode for collaborative multi-agent discussions!"
 - Express genuine appreciation for user's participation and engagement
 - Leave user with encouragement for future collaborative sessions
 
+## RETURN PROTOCOL:
+
+If this workflow was invoked from within a parent workflow:
+
+1. Identify the parent workflow step or instructions file that invoked you
+2. Re-read that file now to restore context
+3. Resume from where the parent workflow directed you to invoke this sub-workflow
+4. Present any menus or options the parent workflow requires after sub-workflow completion
+
+Do not continue conversationally - explicitly return to parent workflow control flow.
+
 ## WORKFLOW COMPLETION:
 
 After farewell sequence and final closure: