refactor(agent): remove skip_soul context loading path

[GritLs]

Summary

• Remove the skip_soul parameter from build_context_files_prompt().
• Keep SOUL.md loading exclusively in load_soul_md() as the identity layer.
• Update tests and docs so project context assembly no longer suggests a second SOUL.md injection path.

Why

skip_soul was added when SOUL.md moved from the project context block to the primary identity slot in #1922. The main prompt assembly now has load_soul_identity for the real cron use case from #17509, so the helper-level fallback path preserves old mixed context behavior and makes the prompt order harder to understand.

How to test

• .venv/bin/python -m pytest -o addopts='' tests/agent/test_prompt_builder.py::TestBuildContextFilesPrompt tests/run_agent/test_run_agent.py::TestBuildSystemPrompt tests/cron/test_cron_workdir.py::TestRunJobTerminalCwd -q
• .venv/bin/python - <<'PY' ... PY smoke test covering load_soul_md() plus build_context_files_prompt()
• git diff --check

Platforms tested

• macOS 26.4, CPython 3.14.3 via uv-created .venv

Related

• Follow-up cleanup to feat: use SOUL.md as primary agent identity instead of hardcoded default #1922 and fix(cron): keep SOUL.md identity when workdir is unset (#16756) #17509. No separate issue was opened for this refactor.

Cross-platform impact

This is prompt assembly cleanup only. It removes duplicate SOUL.md loading from the context helper and does not add platform-specific behavior.

[teknium1]

Thanks for the focused prompt-assembly cleanup. The duplicate-injection guard is still present on current main, but this branch predates the system-prompt extraction.

Problems

• agent/system_prompt.py:451-453 is now the live call site and still passes skip_soul=_soul_loaded. The PR removes that parameter in agent/prompt_builder.py but changes the former run_agent.py call site instead. Current main moved the implementation in 2d2cd5e904abc11eb6c00e88e2b6d0c8b025a597; applying the signature change without updating agent/system_prompt.py would raise TypeError while building a prompt.
• The changed English prompt-assembly docs would leave the Chinese rendered counterpart stale: website/i18n/zh-Hans/docusaurus-plugin-content-docs/current/developer-guide/prompt-assembly.md:135,155,170-172,225 still documents skip_soul.

Suggested changes

• Port the caller and regression coverage to agent/system_prompt.py / tests/agent/test_system_prompt.py, then remove the obsolete helper fallback.
• Update the matching translated documentation with the English docs.

Automated hermes-sweeper review.

[teknium1]

On current main this call was extracted to agent/system_prompt.py:451-453 by 2d2cd5e904abc11eb6c00e88e2b6d0c8b025a597. Please port this change there as well: that live caller still passes skip_soul=_soul_loaded, which would otherwise become an unexpected keyword after the helper signature is reduced.