fix(config): honor model.context_window as context_length alias

[novax635]

PR Description

This PR makes model.context_window work as a compatibility alias for model.context_length in explicit config override paths.

Hermes already accepts context_window in model metadata parsing, but a few manual config-reading paths only checked model.context_length. As a result, users who configured:

model:
  context_window: 1000000

could still see Hermes fall back to the detected/default context value instead of using the configured override.

This caused incorrect context behavior in agent initialization and gateway status/hygiene flows.

What was fixed

The following paths now read model.context_window when model.context_length is not set:

• agent initialization in run_agent.py
• gateway session hygiene context resolution in gateway/run.py
• gateway session info/status formatting in gateway/run.py

model.context_length still takes precedence when both values are present.

Why this matters

Without this alias, users may believe they configured a larger context window, while Hermes silently ignores it in some runtime paths.

That can lead to:

• incorrect context size shown in gateway/session info
• premature context pressure or compression behavior
• hygiene logic making decisions based on the wrong context limit

Behavior

Priority order is now:

model.context_length
model.context_window
detected/default context value

Invalid values continue to use the existing warning/fallback behavior.

Tests

Added regression coverage for the affected paths:

• test_context_window_alias_works
• test_context_window_alias
• test_session_hygiene_honors_context_window_alias

scripts/run_tests.sh tests/run_agent/test_invalid_context_length_warning.py tests/gateway/test_session_info.py tests/gateway/test_session_hygiene.py

Result:

36 passed, 4 warnings

[alt-glitch]

Likely duplicate of #8010 — same fix: honor model.context_window as alias for context_length in config override paths.

[teknium1]

Thanks for tracing the agent and gateway override paths.

Problems

• The requested alias conflicts with the explicit maintainer decision on #28634: Hermes keeps model.context_length as the single canonical config key. Current main still implements that choice at agent/agent_init.py:1632 and gateway/run.py:10600, gateway/run.py:11023, and gateway/run.py:12227.
• Independently, this patch is incomplete against current main: other top-level readers remain in tui_gateway/server.py:2909, hermes_cli/context_switch_guard.py:148, hermes_cli/web_server.py:5140, and model_tools.py:590.
• If an alias were ever adopted, gateway hot reload would also need updating: _CACHE_BUSTING_CONFIG_KEYS contains only model.context_length at gateway/run.py:15624.

Suggested changes

• Please retain the documented model.context_length key unless maintainers choose to change the canonical-key policy.

Automated hermes-sweeper review.