fix(core): ignore unsafe project provider endpoints

[BunsDev]

Motivation

• Prevent untrusted project settings from causing provider credential or prompt exfiltration by disallowing project-supplied API keys and remote API bases for non-local providers.
• Preserve developer intent to allow local-only provider endpoints (Ollama, LM Studio, llama.cpp) that are safe to configure per-project.
• Ensure merging project settings into the effective Config does not clobber global/trusted credentials or bases.

Description

• Sanitize project-loaded Settings via Settings::sanitize_project_settings: strip top-level config.api_key and remove per-provider api_key values, and clear api_base for any provider not explicitly allowed as local (ollama, lmstudio/lm-studio, llamacpp/llama-cpp/llama-server). (changes in src-rust/crates/core/src/lib.rs)
• Add is_project_api_base_allowed and is_default_provider_config helpers to centralize allowed-local-provider logic and to drop no-op provider entries from project settings. (in core/src/lib.rs)
• Change settings merge behavior to merge provider metadata without overwriting global credentials or trusted API bases by using merge_provider_configs for provider_configs/providers during Settings::merge. (in core/src/lib.rs)
• Make the project-settings discovery/merge helpers accessible to tests (find_project_settings and merge are pub(crate)) and add unit tests exercising sanitization and merge semantics to prevent regressions. (tests added in core/src/lib.rs)

Testing

• Ran cargo test --package claurst-core test_project_settings_strip_remote_provider_credentials_and_api_base and the test passed.
• Ran cargo test --package claurst-core test_project_provider_sanitization_preserves_global_api_base and cargo check --package claurst-core, both succeeded.
• Attempted workspace-wide checks (cargo check --workspace, cargo clippy --workspace --all-targets -- -D warnings, cargo test --workspace) but these are blocked in the current environment due to a missing system dependency (alsa.pc) required by alsa-sys and therefore could not complete here.

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Codex Task

[Copilot]

Pull request overview

This PR hardens hierarchical settings loading to prevent untrusted project-level settings (.coven-code/settings.json{c}) from injecting provider credentials or unsafe endpoints into the effective configuration, while still permitting per-project configuration for known local-only providers.

Changes:

• Sanitize project-loaded Settings to strip top-level config.api_key, remove per-provider api_key, and clear api_base for non-allowed providers.
• Adjust Settings::merge to merge provider configs field-by-field so project settings don’t clobber trusted/global credentials or API bases.
• Add unit tests covering provider sanitization and merge behavior.

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[BunsDev]

Closing this as superseded by #15, merged in 0a96406.

#15 strips project-controlled provider routing, provider endpoint maps, provider configs, and config API keys before merge, while preserving safe project preferences and trusted global provider settings. That covers the remaining concern here: local-provider IDs alone are not enough if the project can still point api_base at a non-local endpoint.

Thanks @BunsDev