Fix collaborative prompts without explicit AI targets

[Xeelee33]

Summary

After sharing a conversation, additional messages from both inviter and invitee weren't getting sent to the model unless a workspace context or other action was selected. If this is intentional behavior I suggest adding a toggle to explicitly disable model responses for a message. The default user assumption (at least in our org) is that messages get sent to the model listed in the model selector.

Changes:

• Route ordinary non-empty prompts in collaborative conversations through the shared AI streaming workflow.
• Prevent prompts from being saved as human-only messages without a model response.
• Add regression coverage and clarify the original versus follow-up fix timeline.

Linked issue

No associated GitHub issue was identified.

Release Notes & Latest Features

• New Feature
• Bug Fix
• UI Enhancement
• Breaking Change
• Internal only

Is this visible to end users?

• Yes
• No

Is this admin-facing (Admin Settings, governance, deployment, config)?

• Yes
• No

Should this become a Latest Feature card?

• Yes
• No
• Already added

Screenshot needed for the card?

• Yes
• No
• Attached

Version bump

• application/single_app/config.py VERSION third segment bumped to 0.261.040
• deployers/version.txt bumped, or not needed because deployers/ was not changed

Testing / validation

Collaborative messages now sent to the model:

"Add participants" button is now available immediately after the first response from the model is finished generating instead of requiring a page refresh:

• python functional_tests/test_collaboration_shared_ai_workflow.py
• python -m py_compile application/single_app/config.py functional_tests/test_collaboration_shared_ai_workflow.py
• python scripts/check_xss_sinks.py --full-file application/single_app/static/js/chat/chat-messages.js
• git diff --check
• No matching collaboration UI test was available under ui_tests/.

Documentation

• Release notes updated under v0.261.040
• Feature documentation updated, or not needed
• Fix documentation updated

Security checklist

• No new Flask routes were added.
• No settings were sent to frontend routes.
• Browser JavaScript continues to use local SimpleChat static assets only.
• No secrets, keys, connection strings, or local-only artifacts are included.

[Xeelee33]

Reverted to draft PR because I found two more bugs related to shared conversations. Working on fixes, will resubmit for review with those fixes later today or tomorrow.

[Paul Lizer (paullizer)]

Great effort Xeelee33! Thank you for contributing.