fix(gateway): keep Telegram topic fork on branch

[Qwinty]

Summary

• keep Telegram DM topic bindings on the new branch after /branch / /fork
• rename the Telegram DM topic to the explicit branch name when /fork <name> is used
• add a regression test covering the stale binding rollback and topic rename

Fixes #58850.

Test Plan

• python -m pytest tests/gateway/test_telegram_topic_mode.py::test_branch_inside_telegram_topic_rewrites_binding_and_renames_topic -q -o 'addopts='
• python -m pytest tests/gateway/test_telegram_topic_mode.py tests/gateway/test_session_boundary_security_state.py tests/cli/test_branch_command.py -q -o 'addopts='

[tonydwb]

Code Review Summary

Verdict: Comment (LGTM)

Small fix: keeps Telegram topic fork on branch. The change is 1 file and addresses a specific Telegram topic branching edge case. Well-scoped and appropriate.

[teknium1]

Thanks for the focused regression test. The /fork premise is confirmed on current main: gateway/slash_commands.py:3882 switches the active session, while gateway/run.py:10976-11008 subsequently applies the still-persisted topic binding and can switch the lane back to its parent. The proposed post-switch sync matches the existing helper at gateway/run.py:3672-3696, and placing it before the rename is correct because the rename helper verifies that binding at gateway/run.py:13919-13927.

Problems

• The equivalent /resume path remains vulnerable: gateway/slash_commands.py:3677-3679 switches a session without updating a Telegram topic binding, so the inbound binding lookup at gateway/run.py:10976-11008 can restore the prior topic session.

Suggested changes

• Synchronize the binding after successful /resume in a Telegram topic lane and add a regression test for that route.

This is an automated hermes-sweeper review.

[Qwinty]

Addressed in 703ac27c3 after rebasing onto current upstream/main. A successful /resume now refreshes the Telegram topic binding to the selected session before the next inbound binding lookup can restore the prior lane. Added a persisted-row regression for /resume, and updated the /fork regression to exercise the current async session-store boundary. Local validation: 47 passed for tests/gateway/test_telegram_topic_mode.py, 52 passed for tests/gateway/test_resume_command.py, ruff passed, and git diff --check passed.

[Qwinty]

Rebased onto current upstream/main.

Conflict in /resume was resolved by keeping main's newer conversation-scope clear path and re-applying the Telegram topic-binding sync after switch_session (without restoring the old _clear_session_boundary_security_state call that main replaced).

Local verification:

python -m pytest -q -o 'addopts=' tests/gateway/test_telegram_topic_mode.py
# 47 passed

[Qwinty]

Maintainer review requested: this remains a narrow, mergeable fix with green CI. Prior review confirmed the /fork premise on current main and the branch preserves the Telegram topic binding after switching to the child session.