feat: centralize default constants and refactor overlay enter handling in TUI

apps/domain/src/agent/defaults.rs

@@ -0,0 +1,34 @@
+//! Shared default constants used across the application.
+//!
+//! Centralising these values eliminates the hardcoded-string duplication
+//! that existed when every call site provided its own inline fallback.
+//! Consumers should reference these constants rather than repeating
+//! the string literals.
+
+/// Default LLM provider API base URL.
+pub const DEFAULT_API_BASE: &str = "https://opencode.ai/zen/v1";
+
+/// Default LLM model identifier.
+pub const DEFAULT_MODEL: &str = "deepseek-v4-flash-free";
+
+/// Fallback JWT secret used only when `JWT_SECRET` env var is unset.
+/// In production this MUST be configured via environment variable.
+pub const FALLBACK_JWT_SECRET: &str = "dev-secret";
+
+/// Default context window size (128k tokens).
+pub const DEFAULT_CONTEXT_WINDOW: usize = 256_000;
+
+/// Maximum tool-call iterations per agent turn.
+pub const MAX_TOOL_ITERATIONS: u32 = 50;
+
+/// Maximum subagent tool-call iterations.
+pub const MAX_SUBAGENT_ITERATIONS: u32 = 25;
+
+/// Default LLM request max tokens.
+pub const DEFAULT_MAX_TOKENS: u32 = 4096;
+
+/// Default temperature for the main agent.
+pub const DEFAULT_TEMPERATURE: f64 = 0.7;
+
+/// Default temperature for compaction / summary calls.
+pub const DEFAULT_COMPACT_TEMPERATURE: f64 = 0.3;