feat(tui): introduce comprehensive state management for TUI interface

- Add AppStateRest as the central state struct for managing TUI state.
- Implement InputState for handling user input, autocomplete, and history.
- Create MiscState to manage overlays, notifications, and editor state.
- Introduce ScrollState for viewport scrolling functionality.
- Develop TranscriptCache for efficient message rendering in the chat pane.
- Implement SimpleAgent and SimpleWorkflowEngine for agent lifecycle management.
- Add helper functions for managing effort levels and token counting.
- Organize state-related modules for better maintainability and clarity.

apps/domain/src/agent/prompt.rs

@@ -0,0 +1,92 @@
+//! System prompts and directive templates for agent and subagent turns.
+//!
+//! Centralising all prompt text here keeps the core turn logic free of
+//! hardcoded prose, making prompts easier to maintain, review, and localise.
+//!
+//! # Flow
+//! The application layer's `AgentTurnServiceImpl` calls `main_agent_prompt()`
+//! to construct the system message at the start of each turn. Subagent and
+//! review prompts are provided by their respective modules.
+
+/// Build the main-agent system prompt.
+///
+/// The prompt establishes the agent's identity as Zesdex, an AI coding
+/// assistant, and defines the priority hierarchy that governs tool selection:
+///
+/// 1. **Workflow first** — `workflow_run` / `hive_mind` for complex tasks
+/// 2. **Planning & TODOs** — `plan_enter` / `todowrite` for structural work
+/// 3. **Reasoning** — `seq_think` for deep analysis
+/// 4. **Tool execution** — direct tools for simple actions
+pub fn main_agent_prompt() -> String {
+    "\
+You are Zesdex, an AI coding assistant. You have access to various tools \
+via native function calling to help the user.
+
+CRITICAL DIRECTIVES & PRIORITY HIERARCHY:
+1. WORKFLOW FIRST: For any multi-step, complex, or non-trivial task, \
+you MUST prioritise using `workflow_run` (to construct and execute a \
+multi-phase YAML workflow) or `hive_mind` (to orchestrate parallel \
+autonomous agents). Workflows are your primary strategy.
+2. PLANNING & TODOS: Use `plan_enter` to establish high-level \
+architectural plans and `todowrite` to maintain granular task checklists.
+3. REASONING: Use `seq_think` for deep step-by-step analysis.
+4. TOOL EXECUTION: Execute individual tools (file edits, terminal commands) \
+within or guided by your workflows. If an error occurs, analyse and fix it.
+
+Respond conversationally, concisely, and helpfully."
+        .to_string()
+}
+
+/// Build a subagent directive prompt.
+///
+/// The directive is embedded in a system message that also communicates the
+/// current working directory and workspace root so the subagent can resolve
+/// paths correctly.
+pub fn subagent_directive(directive: &str, cwd: &str, ws_root: &str) -> String {
+    format!(
+        "\
+You are a focused subagent.
+
+Current directory (PWD): {cwd}
+Workspace root: {ws_root}
+
+Your directive:
+{directive}
+
+Complete the directive autonomously using the tools available to you. \
+Return your final answer when done."
+    )
+}
+
+/// Build a conversation-compaction prompt.
+///
+/// The LLM is asked to produce a concise bulleted summary of the key
+/// requests, decisions, tools executed, and files modified.
+pub fn compaction_prompt() -> String {
+    "\
+You are a helpful assistant summarising conversation history. \
+Provide a concise summary of the key user requests, decisions, tools \
+executed, and modified files. Format as a clear bulleted list."
+        .to_string()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn main_prompt_is_non_empty() {
+        let prompt = main_agent_prompt();
+        assert!(!prompt.is_empty());
+        assert!(prompt.contains("Zesdex"));
+        assert!(prompt.contains("WORKFLOW FIRST"));
+    }
+
+    #[test]
+    fn subagent_directive_includes_directive_text() {
+        let prompt = subagent_directive("test directive", "/home", "/home/project");
+        assert!(prompt.contains("test directive"));
+        assert!(prompt.contains("/home"));
+        assert!(prompt.contains("/home/project"));
+    }
+}