Greptile Summary

This PR improves the LLM-facing tool descriptions for file_search, web_search, web_fetch, and the Vega-Lite chart tool, refactors the system prompt to drop the model-name identity in favour of instanceLabel, and introduces a generic agentic guidance block (getAgenticGuidance) that is now prepended alongside per-tool systemGuidance whenever any tool is enabled.

• Tool descriptions: All updated descriptions follow the new "what / when / when-not / caveats" shape and replace all-caps directives with explanatory prose; the Rust backend and TypeScript frontend descriptions were kept in sync.
• System prompt / agentic guidance: getDefaultSystemPrompt drops the modelId parameter (intentional — bare model names can mislead cross-provider routing), and getAppendedSystemGuidance is the new single entry point that combines agentic and per-tool guidance, ensuring the settings modal preview matches what is actually sent.
• Reranker prompt: Compacted from six explicit score bands to three approximate ranges; deliberate prompt-engineering trade-off.

Confidence Score: 4/5

Safe to merge; all changes are prompt-text and light refactoring with no data-path mutations.

The changes are confined to string descriptions and a thin wrapper function. The getDefaultSystemPrompt signature change has no remaining callers passing modelId, and both call sites were updated correctly. The one structural concern is that file_search_tool.rs still duplicates the description literal rather than delegating to Self::function_description(), leaving a future drift risk — but both strings were kept in sync in this PR.

src/services/file_search_tool.rs — the description literal duplication between function_tool_definition() and function_description() is worth tidying before the next description update.

Important Files Changed

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[useChat: build request] --> B{hasSystemMessage?}
    B -- No --> C[getDefaultSystemPrompt]
    C --> D[getAppendedSystemGuidance]
    D --> E[getAgenticGuidance]
    D --> F[getEnabledToolsSystemGuidance]
    E --> G[Combine: basePrompt + guidance]
    F --> G
    G --> H[system message added to input]
    B -- Yes --> H
    I[ConversationSettingsModal] --> J[getDefaultSystemPrompt]
    I --> K[getAppendedSystemGuidance]
    J --> L[Read-only effective prompt preview]
    K --> L

Fix the following 2 code review issues. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 2
src/services/file_search_tool.rs:200-205
The description string is duplicated as a literal in both `function_tool_definition()` and `function_description()`. If one is updated without the other they silently diverge — exactly the drift risk the new documentation section warns about. `web_search_tool.rs` already avoids this by writing `"description": Self::function_description()` in its tool definition; the same pattern works here.

```suggestion
        serde_json::json!({
            "type": "function",
            "name": "file_search",
            "description": Self::function_description(),
            "parameters": Self::function_parameters_schema()
        })
```

### Issue 2 of 2
ui/src/pages/chat/utils/toolExecutors.ts:2738
`getEnabledToolsSystemGuidance` is now only called by `getAppendedSystemGuidance` within the same file — no external callers remain after this PR. Keeping it `export`ed widens the public API surface unnecessarily and may invite callers that bypass the agentic-guidance block. Removing the export clarifies that `getAppendedSystemGuidance` is the intended entry point.

```suggestion
function getEnabledToolsSystemGuidance(enabledToolIds: string[]): string {
```

_{Reviews (1): Last reviewed commit: "Improve prompts and tool descriptions" | Re-trigger Greptile}