refactor(data,core): consolidate APP_DIR_NAME and add #[must_use] on pure fns

- Hoist APP_DIR_NAME = "ferrous_solitaire" to solitaire_data crate root
  as pub(crate); remove 5 duplicate local definitions across achievements,
  progress, settings, storage, replay modules (L-9)
- Add #[must_use] to can_place_on_foundation, can_place_on_tableau, and
  is_valid_tableau_sequence in solitaire_core::rules so callers that
  accidentally discard the result get a compile-time warning (L-6)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

solitaire_data/src/achievements.rs

@@ -10,12 +10,11 @@ use std::path::{Path, PathBuf};
 
 pub use solitaire_sync::AchievementRecord;
 
-const APP_DIR_NAME: &str = "ferrous_solitaire";
 const FILE_NAME: &str = "achievements.json";
 
 /// Platform-specific default path for `achievements.json`.
 pub fn achievements_file_path() -> Option<PathBuf> {
-    crate::data_dir().map(|d| d.join(APP_DIR_NAME).join(FILE_NAME))
+    crate::data_dir().map(|d| d.join(crate::APP_DIR_NAME).join(FILE_NAME))
 }
 
 /// Load achievements from an explicit path. Returns `Vec::new()` if the file

solitaire_data/src/lib.rs

@@ -168,3 +168,6 @@ pub use matomo_client::MatomoClient;
 
 pub mod platform;
 pub use platform::data_dir;
+
+/// Application data subdirectory name, shared by all persistence modules.
+pub(crate) const APP_DIR_NAME: &str = "ferrous_solitaire";

solitaire_data/src/progress.rs

@@ -14,7 +14,6 @@ use chrono::{Datelike, NaiveDate};
 pub use solitaire_sync::progress::level_for_xp;
 pub use solitaire_sync::PlayerProgress;
 
-const APP_DIR_NAME: &str = "ferrous_solitaire";
 const FILE_NAME: &str = "progress.json";
 
 /// Deterministic seed derived from a date, identical for all players globally.
@@ -46,7 +45,7 @@ pub fn xp_for_win(time_seconds: u64, used_undo: bool) -> u64 {
 
 /// Platform-specific default path for `progress.json`.
 pub fn progress_file_path() -> Option<PathBuf> {
-    crate::data_dir().map(|d| d.join(APP_DIR_NAME).join(FILE_NAME))
+    crate::data_dir().map(|d| d.join(crate::APP_DIR_NAME).join(FILE_NAME))
 }
 
 /// Load progress from an explicit path. Returns `default()` if missing/corrupt.

solitaire_data/src/replay.rs

@@ -29,7 +29,6 @@ use serde::{Deserialize, Serialize};
 use solitaire_core::game_state::{DrawMode, GameMode};
 use solitaire_core::pile::PileType;
 
-const APP_DIR_NAME: &str = "ferrous_solitaire";
 const LATEST_REPLAY_FILE_NAME: &str = "latest_replay.json";
 const REPLAY_HISTORY_FILE_NAME: &str = "replays.json";
 
@@ -279,14 +278,14 @@ impl ReplayHistory {
             in migrate_legacy_latest_replay"
 )]
 pub fn latest_replay_path() -> Option<PathBuf> {
-    crate::data_dir().map(|d| d.join(APP_DIR_NAME).join(LATEST_REPLAY_FILE_NAME))
+    crate::data_dir().map(|d| d.join(crate::APP_DIR_NAME).join(LATEST_REPLAY_FILE_NAME))
 }
 
 /// Returns the platform-specific path to `replays.json`, the rolling
 /// history file, or `None` if `crate::data_dir()` is unavailable (e.g.
 /// minimal Linux containers).
 pub fn replay_history_path() -> Option<PathBuf> {
-    crate::data_dir().map(|d| d.join(APP_DIR_NAME).join(REPLAY_HISTORY_FILE_NAME))
+    crate::data_dir().map(|d| d.join(crate::APP_DIR_NAME).join(REPLAY_HISTORY_FILE_NAME))
 }
 
 /// Save a [`Replay`] atomically to `path` using the standard `.tmp` →

solitaire_data/src/settings.rs

@@ -11,7 +11,6 @@ use std::path::{Path, PathBuf};
 use serde::{Deserialize, Serialize};
 use solitaire_core::game_state::{DifficultyLevel, DrawMode};
 
-const APP_DIR_NAME: &str = "ferrous_solitaire";
 const SETTINGS_FILE_NAME: &str = "settings.json";
 
 /// Animation playback speed for card transitions.
@@ -479,7 +478,7 @@ impl Settings {
 /// Returns the platform-specific path to `settings.json`, or `None` if
 /// the platform's data directory is unavailable.
 pub fn settings_file_path() -> Option<PathBuf> {
-    crate::data_dir().map(|d| d.join(APP_DIR_NAME).join(SETTINGS_FILE_NAME))
+    crate::data_dir().map(|d| d.join(crate::APP_DIR_NAME).join(SETTINGS_FILE_NAME))
 }
 
 /// Load settings from an explicit path. Returns `Settings::default()` if the

solitaire_data/src/storage.rs

@@ -13,7 +13,6 @@ use solitaire_core::game_state::{GameState, GAME_STATE_SCHEMA_VERSION};
 
 use crate::stats::StatsSnapshot;
 
-const APP_DIR_NAME: &str = "ferrous_solitaire";
 const STATS_FILE_NAME: &str = "stats.json";
 const GAME_STATE_FILE_NAME: &str = "game_state.json";
 const TIME_ATTACK_SESSION_FILE_NAME: &str = "time_attack_session.json";
@@ -21,7 +20,7 @@ const TIME_ATTACK_SESSION_FILE_NAME: &str = "time_attack_session.json";
 /// Returns the platform-specific path to `stats.json`, or `None` if
 /// `crate::data_dir()` is unavailable (e.g. minimal Linux containers).
 pub fn stats_file_path() -> Option<PathBuf> {
-    crate::data_dir().map(|d| d.join(APP_DIR_NAME).join(STATS_FILE_NAME))
+    crate::data_dir().map(|d| d.join(crate::APP_DIR_NAME).join(STATS_FILE_NAME))
 }
 
 /// Load stats from an explicit path. Returns `StatsSnapshot::default()` if
@@ -71,7 +70,7 @@ pub fn save_stats(stats: &StatsSnapshot) -> io::Result<()> {
 /// Returns the platform-specific path to `game_state.json`, or `None` if
 /// `crate::data_dir()` is unavailable.
 pub fn game_state_file_path() -> Option<PathBuf> {
-    crate::data_dir().map(|d| d.join(APP_DIR_NAME).join(GAME_STATE_FILE_NAME))
+    crate::data_dir().map(|d| d.join(crate::APP_DIR_NAME).join(GAME_STATE_FILE_NAME))
 }
 
 /// Load an in-progress `GameState` from `path`. Returns `None` if the file is
@@ -130,7 +129,7 @@ pub fn delete_game_state_at(path: &Path) -> io::Result<()> {
 /// are silently skipped.
 pub fn cleanup_orphaned_tmp_files() -> io::Result<()> {
     let dir = match crate::data_dir() {
-        Some(d) => d.join(APP_DIR_NAME),
+        Some(d) => d.join(crate::APP_DIR_NAME),
         None => return Ok(()),
     };
 
@@ -181,7 +180,7 @@ pub struct TimeAttackSession {
 /// Returns the platform-specific path to `time_attack_session.json`, or
 /// `None` if `crate::data_dir()` is unavailable.
 pub fn time_attack_session_path() -> Option<PathBuf> {
-    crate::data_dir().map(|d| d.join(APP_DIR_NAME).join(TIME_ATTACK_SESSION_FILE_NAME))
+    crate::data_dir().map(|d| d.join(crate::APP_DIR_NAME).join(TIME_ATTACK_SESSION_FILE_NAME))
 }
 
 /// Save a Time Attack session atomically. Mirrors `save_game_state_to`'s