fix(gateway): honor /model + channel_overrides in /new and /status banner

[dickyudhandika]

What does this PR do?

_format_session_info was reading model.default directly, so the /new auto-reset notice and /status banner advertised the global default even when the thread was pinned via channel_overrides or had a /model session override. The next agent turn ran on the override model, but the banner showed a different one — misleading at best, wrong at worst.

Fix: _format_session_info accepts an optional source and runs the same priority chain as _resolve_session_agent_runtime (/model session override → channel_overrides → global default). _reset_notice_session_info passes its source through. The no-source path is preserved for CLI introspection where no channel context exists.

Related Issue

Reported by a user running a Telegram thread pinned via channel_overrides to a custom provider model. The /new notice kept advertising the global default while the next turn ran on the pinned model. The bug was in the gateway, not the provider config; the per-thread override just made it visible. Any thread using channel_overrides or a /model session override was affected.

Type of Change

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

Changes Made

• gateway/run.py — _format_session_info(source=None) now applies the priority chain (/model → channel_overrides → global) when source is provided. _reset_notice_session_info is updated to pass its source through. Multiplex-profile gating in the reset path is preserved.
• tests/gateway/test_format_session_info_overrides.py — 4 new tests covering: no source (CLI introspection path), channel override applies, no override thread falls back to global, /model session override wins over channel override.

How to Test

1. Apply the patch, run venv/bin/python -m pytest tests/gateway/test_format_session_info_overrides.py -v → 4 passed
2. Run the broader session-info + model-override regression suite: venv/bin/python -m pytest tests/gateway/test_session_info.py tests/gateway/test_session_model_override_persistence.py tests/gateway/test_session_model_override_credential_pool.py tests/gateway/test_session_model_override_routing.py tests/gateway/test_session_model_reset.py tests/gateway/test_session_reset_notify.py tests/gateway/test_format_session_info_overrides.py -q → 50 passed
3. Manual: pin a Telegram thread via channel_overrides, send /new, confirm the banner reports the pinned model rather than the global default

Checklist

Code

• I've read the Contributing Guide
• My commit messages follow Conventional Commits
• I searched for existing PRs to make sure this isn't a duplicate
• My PR contains only changes related to this fix
• I've run the affected tests and all pass
• I've added tests for my changes
• I've tested on my platform: macOS 26.4.1 (Apple Silicon)

Documentation & Housekeeping

• I've updated relevant documentation — N/A, docstring in _format_session_info was updated inline
• I've considered cross-platform impact (Windows, macOS) — N/A, gateway logic is platform-agnostic

[teknium1]

Thanks for isolating the reset-banner mismatch. The current reset path does reproduce the global-model display issue, but this patch needs a broader shared-resolution pass before it matches its stated /new + /status behavior.

Problems

• /status is implemented independently in gateway/slash_commands.py:550-604; it does not call _format_session_info. Its fallback remains global config at gateway/slash_commands.py:565-594, so this diff cannot fix /status for a fresh overridden channel.
• The new formatter branch selects only a model. Runtime resolution also derives provider settings for channel overrides in gateway/run.py:3824-3835 and applies the full session override at gateway/run.py:3837-3840; banner provider/context/endpoint can remain inconsistent.
• /new clears session model overrides before producing its banner (gateway/slash_commands.py:200-215,252-258), so the added direct formatter test for a /model override does not exercise that production path.

Suggested changes

• Share the effective display/runtime resolver and cover real /new and /status handlers, including a fresh channel override and a session /model status case.

Automated hermes-sweeper review.