fix(bot-mode): bot sessions always follow the profile's current config

[curator8888]

Fixes the #89497 bug class: bot sessions stuck on a stale provider pin after a profile switch.

Summary

Bot-Mode sessions (room plumbing AND the canonical per-bot DM chat) are plugin-owned scratch conversations. They are now created with explicit contracts — room_plumbing for group-chat member sessions, follow_profile_config for the canonical Bot Chat — persisted in the session row's model_config, so session.resume rebuilds from the member profile's CURRENT config instead of restoring the stored model/provider pin from an old row.

That stale pin is what left bots stuck on a dead provider (e.g. "out of Nous credits" after the profile was switched to ollama-cloud) while the same bot worked fine elsewhere. Normal 1:1 user chats keep the stored-runtime restore: opening an older chat must show the model it actually used.

How to Test

1. Configure a bot profile with model A (e.g. a paid Nous model), open its Bot Chat DM, send a message.
2. Switch the profile to model B (e.g. ollama-cloud/glm-5.1).
3. Reopen the DM (and/or the room). Before this fix: resume restores the stored model A pin → "out of Nous credits" / HTTP 404. After: resume uses the profile's current model B.

Verification

• Backend: _stored_session_runtime_overrides returns {} for rows carrying either marker (dict and JSON model_config shapes); unmarked rows still restore stored runtime; _ensure_session_db_row persists each marker only when the contract is set. Legacy hidden + "Group:" title rows keep the room guard.
• Desktop: createCanonicalChat sends follow_profile_config: true; ensureGroupChatSession sends both room_plumbing: true and follow_profile_config: true on session.create.
• Tests: 29/29 test_custom_provider_session_persistence.py + test_session_resume_db_ownership.py, 42/42 desktop group-chat tests.

Type of Change

• Bug fix (non-breaking change which fixes an issue)

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective
• New and existing unit tests pass locally

[Enough1122]

AI code review — automated review for reference; please use your judgment.

Reviewed by reviewer-e (AI automated review).

Right contract design: replacing a presentation heuristic's scope creep with an explicit, persisted follow_profile_config/room_plumbing marker (set by session.create consumers, stamped into model_config by _ensure_session_db_row, honored by _stored_session_runtime_overrides) fixes the "bot DMs stuck on Nous credits" class at the identity level instead of guessing from titles. Keeping the hidden+"Group:" shape as a legacy fallback only, and leaving normal 1:1 stored-runtime restore untouched (including hidden non-room chats), is exactly the narrow behavior you want — and the test matrix covers marker-in-dict/marker-in-JSON/legacy-shape/unmarked-row/stamp-and-omit for both contracts.

Nit (non-blocking): tui_gateway/server.py:4154-4207 — the room_plumbing and follow_profile_config checks are two ~20-line near-identical copies of "parse model_config (dict or JSON string), read flag" plus duplicated comments; a tiny _model_config_flag(row, key) -> bool helper would collapse them, remove the double parse of the same JSON blob, and keep comment drift from reintroducing subtle differences between the two contracts.

[KeyArgo]

Fresh user report validating this exact fix: #94818 (2026-08-25) reports that switching the model for a Bot Chat in settings has no effect — the chat keeps using the model pinned at session creation ("Model used during chat creation is model that is continued to use"). That's precisely the stale model/provider pin your follow_profile_config contract addresses on session.resume. Flagging as corroboration; this fix looks like the right home for that report.

[teknium1]

Merged via PR #97008 (rebase-merge) — both of your commits landed on main with your authorship preserved in git log. We added one follow-up on top: a legacy backfill so canonical Bot Chats created BEFORE the follow_profile_config marker existed (rows titled exactly "Bot Chat") also follow the profile's current config — that covers users already stuck in the field. Thanks for the clean explicit-contract design.