feat(gateway): display model name and context usage in response footer

[RichardQidian]

📊 Display Model Name & Context Usage

This PR adds an automatic context usage footer to non-streaming gateway responses, helping users monitor their context window usage in real-time.

What it shows

Every non-streaming response now includes a footer like:

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🤖 anthropic/claude-sonnet-4  |  📊 Context: 45,230 / 200,000 (23%)

When context usage reaches 70%+, it also shows a warning:

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🤖 anthropic/claude-sonnet-4  |  📊 Context: 148,500 / 200,000 (74%) ⚠️ 建议 /new 开启新会话

Changes

• Add context usage footer to non-streaming responses
• Track context_length in agent result (previously only last_prompt_tokens was tracked)
• Warning shown when context usage exceeds 70%, suggesting user to start a new session

Why this matters

• Users often lose track of context consumption in long conversations
• When context gets full, model behavior degrades (truncation, lost instructions)
• Gives users visibility and actionable guidance before hitting the wall
• Helps users choose appropriate models for their context needs

[zjy282]

+1 — would love to see this merged. Switching models often via gateway (Discord/Telegram) makes it hard to know which model is replying; a per-response footer with the active model is exactly the visibility that is missing today. Context usage % is a great bonus.

[teknium1]

Thanks for the contribution, @RichardQidian! This feature landed on main via a parallel implementation in PR #17026 and shipped in v2026.4.30.

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This is an automated hermes-sweeper review.

• gateway/runtime_footer.py (commit e123f4ecf) implements build_footer_line() / format_runtime_footer() / resolve_footer_config() — model name, context percentage, and cwd in a compact footer.
• gateway/run.py lines 6283–6302 and 6513–6523 wire the footer into both streaming and non-streaming response paths.
• The shipped version is opt-in (display.runtime_footer.enabled: true) with per-platform overrides, a /footer on|off toggle command, and a configurable fields list — a superset of what this PR added.

Closing as implemented. If you'd like to contribute further (e.g. adjusting the default-on threshold or adding the warning text), feel free to open a new targeted PR against current main.