[bugfix] align countdown snapshot timing with tokio instants

- switch ClockAnchor to tokio::time::Instant
- remove flawed epoch conversion helpers from Countdown
- expose countdown getters for id/label/start/target instants
- update service snapshot to compute remaining_at(now) and return instants directly
- add core extern declaration in lib.rs

src-tauri/src/countdown/commands.rs

@@ -0,0 +1,66 @@
+use crate::countdown::dto::CountdownSnapshotDto;
+use crate::countdown::errors::CountdownError;
+use crate::AppState;
+use tauri::{command, State};
+use tokio::time::Instant;
+
+type CmdResult<T> = Result<T, String>;
+
+#[command]
+pub async fn countdown_start(state: State<'_, AppState>) -> Result<(), String> {
+    state
+        .countdown_service
+        .start(Instant::now())
+        .await
+        .map_err(|e: CountdownError| format!("{e:?}"))?;
+    Ok(())
+}
+
+#[command]
+pub async fn countdown_reset(state: State<'_, AppState>) -> Result<(), String> {
+    state.countdown_service.reset().await;
+    Ok(())
+}
+
+#[command]
+pub async fn countdown_pause(state: State<'_, AppState>) -> Result<(), String> {
+    state
+        .countdown_service
+        .pause(Instant::now())
+        .await
+        .map_err(|e: CountdownError| format!("{e:?}"))?;
+    Ok(())
+}
+
+#[command]
+pub async fn countdown_resume(state: State<'_, AppState>) -> Result<(), String> {
+    state
+        .countdown_service
+        .resume(Instant::now())
+        .await
+        .map_err(|e: CountdownError| format!("{e:?}"))?;
+    Ok(())
+}
+
+#[command]
+pub async fn countdown_snapshot(
+    state: State<'_, AppState>,
+) -> Result<CountdownSnapshotDto, String> {
+    let countdown_snapshot = state.countdown_service.snapshot(Instant::now()).await;
+    let start = match countdown_snapshot.start_instant {
+        Some(instant) => Some(state.clock_anchor.instant_to_epoch_ms(instant)),
+        None => None,
+    };
+    let target = match countdown_snapshot.target_instant {
+        Some(instant) => Some(state.clock_anchor.instant_to_epoch_ms(instant)),
+        None => None,
+    };
+    Ok(CountdownSnapshotDto {
+        id: countdown_snapshot.id,
+        label: countdown_snapshot.label,
+        duration: countdown_snapshot.duration,
+        state: countdown_snapshot.state,
+        start_epoch_ms: start,
+        target_epoch_ms: target,
+    })
+}

src-tauri/src/countdown/errors.rs

@@ -0,0 +1,10 @@
+use crate::countdown::model::CountdownState;
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum CountdownError {
+    InvalidTransition {
+        from: CountdownState,
+        action: &'static str,
+    },
+    TimeOverflow,
+}

src-tauri/src/countdown/mod.rs

@@ -1,3 +1,5 @@
+pub mod commands;
 pub mod dto;
+pub mod errors;
 pub mod model;
 pub mod service;

src-tauri/src/countdown/model.rs

@@ -1,3 +1,4 @@
+use crate::countdown::errors::CountdownError;
 use serde::{Deserialize, Serialize};
 use tokio::time::{Duration, Instant};
 
@@ -9,15 +10,6 @@ pub enum CountdownState {
     Finished,
 }
 
-#[derive(Debug, Clone, PartialEq, Eq)]
-pub enum CountdownError {
-    InvalidTransition {
-        from: CountdownState,
-        action: &'static str,
-    },
-    TimeOverflow,
-}
-
 #[derive(Debug, Clone)]
 pub struct Countdown {
     pub id: u64,

src-tauri/src/countdown/service.rs

@@ -1,4 +1,5 @@
-use crate::countdown::model::{Countdown, CountdownError, CountdownState};
+use crate::countdown::errors::CountdownError;
+use crate::countdown::model::{Countdown, CountdownState};
 use tokio::sync::Mutex;
 use tokio::time::{Duration, Instant};
 
@@ -32,7 +33,7 @@ impl CountdownService {
         let countdown = self.countdown.lock().await.clone();
         CountdownSnapshot {
             id: countdown.id(),
-            label: countdown.label().parse().unwrap(),
+            label: countdown.label().to_string(),
             state: countdown.state(),
             duration: countdown.remaining_at(now),
             start_instant: countdown.start_timestamp(),

src-tauri/src/lib.rs

@@ -3,6 +3,9 @@ extern crate core;
 mod app_state;
 mod countdown;
 
+use crate::countdown::commands::{
+    countdown_pause, countdown_reset, countdown_resume, countdown_snapshot, countdown_start,
+};
 pub use app_state::AppState;
 
 // Learn more about Tauri commands at https://tauri.app/develop/calling-rust/
@@ -17,7 +20,14 @@ pub fn run() {
     tauri::Builder::default()
         .manage(app_state)
         .plugin(tauri_plugin_opener::init())
-        .invoke_handler(tauri::generate_handler![greet])
+        .invoke_handler(tauri::generate_handler![
+            greet,
+            countdown_start,
+            countdown_reset,
+            countdown_pause,
+            countdown_resume,
+            countdown_snapshot,
+        ])
         .run(tauri::generate_context!())
         .expect("error while running tauri application");
 }