fix(query): preserve explicit model selection

[BunsDev]

Motivation

• Prevent project managed_agents.manager_model from silently replacing an explicit caller-selected model/provider (e.g. --model) at query runtime, which could route private prompts to an unexpected provider.
• Centralize model-selection logic so managed-agent overrides still apply by default but can be opt-out when the caller explicitly chose a model/provider.

Description

• Add preserve_selected_model: bool to QueryConfig (default false) to record when a caller explicitly selected model/provider.
• Introduce selected_model_for_query(cfg: &QueryConfig) -> String to centralize selection logic and return the manager model only when preserve_selected_model is false.
• Replace the inline managed-agent override in run_query_loop with selected_model_for_query and make effective_model derived from it.
• Set query_config.preserve_selected_model = cli.model.is_some() || cli.provider.is_some() in the CLI, and ensure sub-agent QueryConfig instances set it to false.
• Add two unit tests covering the default override and explicit-selection preservation and update agent_tool and other call sites to initialize the new flag.

Testing

• Ran cargo test --package claurst-query test_explicit_model_selection_blocks_managed_agent_override and it passed.
• Ran cargo test --package claurst-query test_managed_agent_manager_model_overrides_by_default and it passed.
• Ran cargo check --package claurst-query and it succeeded.
• cargo check --workspace was attempted but blocked by a missing system dependency (alsa.pc / ALSA pkg-config) in the environment, so workspace-wide check could not complete here.

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Codex Task

[Copilot]

Pull request overview

This PR updates the query model-selection flow to ensure that when a caller explicitly selects a model/provider (e.g., via CLI flags), that choice is preserved and not silently overridden by managed_agents.manager_model at query runtime—reducing the risk of prompts being routed to an unexpected provider.

Changes:

• Add preserve_selected_model: bool to QueryConfig (default false) to record explicit caller selection intent.
• Centralize model selection in selected_model_for_query(&QueryConfig) -> String, applying managed_agents.manager_model only when preserve_selected_model == false.
• Wire the flag from the CLI (--model/--provider) and update AgentTool / tests to initialize the new field.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src-rust/crates/query/src/lib.rs	Adds the new config flag, centralizes model selection logic, and adds unit tests for override vs preservation behavior.
src-rust/crates/query/src/agent_tool.rs	Updates QueryConfig construction to initialize preserve_selected_model for agent tool invocations.
src-rust/crates/cli/src/main.rs	Sets preserve_selected_model when --model or --provider is explicitly provided.

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