feat: make context compression trigger ratio configurable - #10728

Context compression and truncation are triggered when context tokens exceed a hard-coded 82% of the model context window (compression_threshold = 0.82 in both compressors). It cannot be changed without editing the source, so large-window models only compress very late, and users cannot compress earlier to save tokens. The only workaround is lowering the provider's context window, which also changes the real window for that provider.

Closes #9252. Partially addresses #8348 (ratio-based only; an absolute token threshold is not included). This is a smaller take on the same need as #9261, which was closed as stale.

Modifications / 改动点

• Add agent_runner.config.compression.trigger_ratio (default 0.82, clamped to 0.1–0.95 during Agent Runner normalization).

• Map it through resolve_context_compression_config → MainAgentBuildConfig.context_compression_threshold → ToolLoopAgentRunner.reset → ContextConfig.compression_threshold, following the existing keep_recent_ratio path. Chat, Cron and background wakeups all use the shared mapping.

• ContextManager clamps the value again and passes it to both LLMSummaryCompressor and TruncateByTurnsCompressor, so both strategies and the post-compression check honor it. A custom_compressor keeps its own threshold.

• Show the setting in WebUI under the context management strategy for the local runner, with en-US / zh-CN / ja-JP / ru-RU translations.

• Update docs/zh and docs/en context-compress.md, which previously stated a fixed ~82%.

• Existing configs pick up the default 0.82 through normalization, so behavior is unchanged unless the setting is modified.

• This is NOT a breaking change. / 这不是一个破坏性变更。

Screenshots or Test Results / 运行截图或测试结果

• New tests: normalization/clamping and mapping of trigger_ratio, the threshold reaching both compressors, a lower ratio compressing at usage where the default does not, and build_main_agent forwarding the value.
• Affected suites: tests/unit/test_agent_runner_config.py, tests/agent/test_context_manager.py, tests/unit/test_astr_main_agent.py, tests/unit/test_cron_context_compression.py, tests/test_tool_loop_agent_runner.py — 351 passed.
• Full suite on the change merged with master: 4742 passed, 79 skipped.
• ruff check and ruff format --check pass on the changed Python files.

Checklist / 检查清单

• 😊 If there are new features added in the PR, I have discussed it with the authors through issues/emails, etc.
  / 如果 PR 中有新加入的功能，已经通过 Issue / 邮件等方式和作者讨论过。

• 👀 My changes have been well-tested, and "Verification Steps" and "Screenshots" have been provided above.
  / 我的更改经过了良好的测试，并已在上方提供了“验证步骤”和“运行截图”。

• 📚 I checked the affected WebUI instructions and screenshots in docs/zh and docs/en against the changed navigation, page structure, and labels, and updated them in this PR (or explained why no documentation update is needed). For renamed, moved, or merged entry points, I included an old entry → new entry mapping in the documentation and changelog.
  / 我已对照变化后的 WebUI 入口、页面结构和术语，核对并在本 PR 中更新 docs/zh 和 docs/en 的相关操作说明与截图（或说明无需更新文档的原因）。入口改名、移动或合并时，已在文档和 changelog 中补充 旧入口 → 新入口 对照。

• 🤓 I have ensured that no new dependencies are introduced, OR if new dependencies are introduced, they have been added to the appropriate locations in requirements.txt and pyproject.toml.
  / 我确保没有引入新依赖库，或者引入了新依赖库的同时将其添加到 requirements.txt 和 pyproject.toml 文件相应位置。

• 😮 My changes do not introduce malicious code.
  / 我的更改没有引入恶意代码。

Summary by Sourcery

Make the context compression trigger ratio configurable so users can control when context compression or truncation begins without changing the provider context window.

New Features:

• Add a configurable context compression trigger ratio for local agent runners, defaulting to 0.82 and supporting values from 0.1 to 0.95.
• Expose the compression trigger ratio in the WebUI and document its configuration and behavior in English and Chinese.

Enhancements:

• Apply the configured ratio consistently to truncation and LLM summarization while preserving custom compressor behavior.
• Propagate and validate the setting across agent runner configuration and shared context management flows.

Documentation:

• Update context compression documentation to describe the configurable trigger ratio and its default behavior.

Tests:

• Add coverage for trigger-ratio defaults, clamping, propagation, and earlier compression behavior.