fix: harden post-merge cleanup and image loading

[pancacake]

Summary

• Preserve POSIX directory traversal bits when retrying failed knowledge-base cleanup.
• Resolve multimodal clients in dependency order and reuse one LLM client per image batch.
• Make source-contract tests resilient to formatter-only line wrapping.

Why

These are integration findings from the recent A/B PR merge train. The previous chmod retry could leave undeletable pytest/runtime orphans, while text-only embedding setups unnecessarily initialized the LLM and could fail indexing on unrelated LLM configuration.

Verification

• Full Python suite: 4015 passed, 7 skipped.
• Targeted integration suite: 411 passed.
• Ruff full-repository check passed.
• TypeScript no-emit check passed.
• Target ESLint checks passed.
• Node suite: 413 passed.
• Repository and workspace hygiene checks passed.