Summary

Adds summary_base_url config option and moves all compression configuration to config.yaml (removing the env var bridge layer).

Based on PR #1702 by @uzaylisak. Closes #1591.

Changes

New feature: summary_base_url

compression:
  enabled: true
  summary_model: glm-4.7
  summary_provider: zai
  summary_base_url: https://api.z.ai/api/coding/paas/v4

Compression config is now YAML-only

• cli.py: Removed compression env var bridge (CONTEXT_COMPRESSION_* no longer set from config)
• gateway/run.py: Same — removed bridge and env var override check
• run_agent.py: Now reads compression config directly from config.yaml via load_config() instead of env vars

Bug fix: backwards-compat block condition

• auxiliary.compression.provider defaults to "auto" in DEFAULT_CONFIG, which is truthy — this silently prevented the compression.summary_* keys from ever being read
• Fixed condition from not cfg_provider to not cfg_provider or cfg_provider == "auto"

Tests

• Added test_compression_summary_base_url_from_config — verifies the full config → client flow
• Updated bridge tests to remove compression env var assertions
• Updated gateway parity test to assert compression bridge is absent
• Added DEFAULT_CONFIG shape test for summary_base_url

Docs

• Updated environment-variables.md, configuration.md, fallback-providers.md to show compression as config.yaml-only

Backward Compatibility

Fully backward compatible. Existing configs work unchanged. Users who set CONTEXT_COMPRESSION_* env vars directly (not from config bridge) still get them picked up via the generic _get_auxiliary_env_override function.