feat: system prompt and persona

.living_spec/specs/functional/PERSONA.md

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+# Functional Spec: Agent Persona & System Prompt
+
+## 1. Role Definition
+The Agent acts as a **Senior Software Engineer** embedded within the user's local environment.
+
+## 2. Directives
+The System Prompt must enforce the following behaviors:
+1.  **Tool First:** Do not guess code. Read files first.
+2.  **Conciseness:** Do not explain "I will now do X". Just do X (call the tool).
+3.  **Safety:** Never modify files outside the scope (though backend enforces this, the LLM should know).
+4.  **Format:** When writing code, write the *whole* file if the tool requires it, or handle partials if we upgrade the tool (currently `write_file` is overwrite).
+
+## 3. Implementation
+*   **Location:** `src-tauri/src/llm/prompts.rs`
+*   **Injection:** The system message is prepended to the `messages` vector in `chat::chat` before sending to the Provider.
+*   **Deduplication:** Ensure we don't stack multiple system messages if the loop runs long (though currently we reconstruct history per turn).
+
+## 4. The Prompt Text (Draft)
+"You are a Senior Software Engineer Agent running in a local Tauri environment.
+You have access to the user's filesystem via tools.
+- ALWAYS read files before modifying them to understand context.
+- When asked to create or edit, use 'write_file'.
+- 'write_file' overwrites the ENTIRE content. Do not write partial diffs.
+- Be concise. Use tools immediately."

.living_spec/stories/07_ui_polish_sticky_header.md

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-# Story: UI Polish - Sticky Header & Compact Layout
-
-## User Story
-**As a** User
-**I want** key controls (Model Selection, Tool Toggle, Project Path) to be visible at all times
-**So that** I don't have to scroll up to check my configuration or change settings.
-
-## Acceptance Criteria
-*   [ ] Frontend: Create a fixed `<Header />` component at the top of the viewport.
-*   [ ] Frontend: Move "Active Project" display into this header (make it compact/truncated if long).
-*   [ ] Frontend: Move "Ollama Model" and "Enable Tools" controls into this header.
-*   [ ] Frontend: Ensure the Chat message list scrolls *under* the header (taking up remaining height).
-*   [ ] Frontend: Remove the redundant "Active Project" bar from the main workspace area.
-
-## Out of Scope
-*   Full visual redesign (just layout fixing).
-*   Settings modal (keep controls inline for now).

.living_spec/stories/08_collapsible_tool_outputs.md

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+# Story: Collapsible Tool Outputs
+
+## User Story
+**As a** User
+**I want** tool outputs (like long file contents or search results) to be collapsed by default
+**So that** the chat history remains readable and I can focus on the Agent's reasoning.
+
+## Acceptance Criteria
+*   [ ] Frontend: Render tool outputs inside a `<details>` / `<summary>` component (or custom equivalent).
+*   [ ] Frontend: Default state should be **Closed/Collapsed**.
+*   [ ] Frontend: The summary line should show the Tool Name + minimal args (e.g., "▶ read_file(src/main.rs)").
+*   [ ] Frontend: Clicking the arrow/summary expands to show the full output.
+
+## Out of Scope
+*   Complex syntax highlighting for tool outputs (plain text/pre is fine).

.living_spec/stories/09_system_prompt_persona.md

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+# Story: System Prompt & Persona
+
+## User Story
+**As a** User
+**I want** the Agent to behave like a Senior Engineer and know exactly how to use its tools
+**So that** it writes high-quality code and doesn't hallucinate capabilities or refuse to edit files.
+
+## Acceptance Criteria
+*   [ ] Backend: Define a robust System Prompt constant (likely in `src-tauri/src/llm/prompts.rs`).
+*   [ ] Content: The prompt should define:
+    *   Role: "Senior Software Engineer / Agent".
+    *   Tone: Professional, direct, no fluff.
+    *   Tool usage instructions: "You have access to the local filesystem. Use `read_file` to inspect context before editing."
+    *   Workflow: "When asked to implement a feature, read relevant files first, then write."
+*   [ ] Backend: Inject this system message at the *start* of every `chat` session sent to the Provider.
+
+## Out of Scope
+*   User-editable system prompts (future story).

.living_spec/stories/10_persist_model_selection.md

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+# Story: Persist Model Selection
+
+## User Story
+**As a** User
+**I want** the application to remember which LLM model I selected
+**So that** I don't have to switch from "llama3" to "deepseek" every time I launch the app.
+
+## Acceptance Criteria
+*   [ ] Backend/Frontend: Use `tauri-plugin-store` to save the `selected_model` string.
+*   [ ] Frontend: On mount (after fetching available models), check the store.
+*   [ ] Frontend: If the stored model exists in the available list, select it.
+*   [ ] Frontend: When the user changes the dropdown, update the store.
+
+## Out of Scope
+*   Persisting per-project model settings (global setting is fine for now).