refactor: drop the Alchementary Link data migration

Startup no longer looks for an AlchementaryLink data directory to copy
into NexusTerminal, and the 'Imported your Alchementary Link data' toast
and the migration docs are gone. Existing Alchementary Link installs are
no longer picked up automatically.

rust/core/src/config.rs

@@ -1,9 +1,8 @@
-//! Data directories, and the one-time move of Alchementary Link data into Nexus Terminal's.
+//! Data directories.
 
 use std::path::{Path, PathBuf};
 
 pub const APP_DIR: &str = "NexusTerminal";
-pub const LEGACY_APP_DIR: &str = "AlchementaryLink";
 
 #[derive(Clone, Debug)]
 pub struct AppConfig {
@@ -11,12 +10,10 @@ pub struct AppConfig {
     pub db_path: PathBuf,
     pub vault_dir: PathBuf,
     pub recordings_dir: PathBuf,
-    /// Set when this run copied data across from Alchementary Link.
-    pub migrated_from: Option<PathBuf>,
 }
 
 /// `~/Library/Application Support` on macOS, `%APPDATA%` on Windows, `$XDG_CONFIG_HOME` or
-/// `~/.config` elsewhere — the same bases the Go app used.
+/// `~/.config` elsewhere.
 pub fn base_dir() -> PathBuf {
     let home = || std::env::var_os(if cfg!(windows) { "USERPROFILE" } else { "HOME" }).map(PathBuf::from).unwrap_or_default();
     if cfg!(target_os = "macos") {
@@ -30,20 +27,12 @@ pub fn base_dir() -> PathBuf {
 
 impl AppConfig {
     pub fn in_dir(data_dir: PathBuf) -> AppConfig {
-        AppConfig {
-            db_path: data_dir.join("nexus.db"),
-            vault_dir: data_dir.join("vault"),
-            recordings_dir: data_dir.join("recordings"),
-            data_dir,
-            migrated_from: None,
-        }
+        AppConfig { db_path: data_dir.join("nexus.db"), vault_dir: data_dir.join("vault"), recordings_dir: data_dir.join("recordings"), data_dir }
     }
 
-    /// Resolves the data directory, migrating legacy data first, and creates the directories.
+    /// Resolves the data directory and creates it.
     pub fn load() -> std::io::Result<AppConfig> {
-        let base = base_dir();
-        let mut cfg = AppConfig::in_dir(base.join(APP_DIR));
-        cfg.migrated_from = migrate_legacy(&base.join(LEGACY_APP_DIR), &cfg)?;
+        let cfg = AppConfig::in_dir(base_dir().join(APP_DIR));
         for d in [&cfg.data_dir, &cfg.vault_dir] {
             create_private_dir(d)?;
         }
@@ -58,70 +47,3 @@ pub fn create_private_dir(d: &Path) -> std::io::Result<()> {
     std::fs::set_permissions(d, std::os::unix::fs::PermissionsExt::from_mode(0o700))?;
     Ok(())
 }
-
-/// Copies (never moves) `AlchementaryLink/{link.db, vault/, recordings/}` into the Nexus
-/// directory when Nexus has no database yet. A pre-rebrand `NexusTerminal/nexus.db` wins as-is.
-pub fn migrate_legacy(legacy: &Path, cfg: &AppConfig) -> std::io::Result<Option<PathBuf>> {
-    let legacy_db = legacy.join("link.db");
-    if cfg.db_path.exists() || !legacy_db.exists() {
-        return Ok(None);
-    }
-    create_private_dir(&cfg.data_dir)?;
-    // Fold the WAL into the main file so the copy is complete.
-    if let Ok(c) = rusqlite::Connection::open(&legacy_db) {
-        let _ = c.pragma_update(None, "wal_checkpoint", "TRUNCATE");
-    }
-    std::fs::copy(&legacy_db, &cfg.db_path)?;
-    copy_dir(&legacy.join("vault"), &cfg.vault_dir)?;
-    copy_dir(&legacy.join("recordings"), &cfg.recordings_dir)?;
-    std::fs::write(cfg.data_dir.join("migrated-from"), legacy.to_string_lossy().as_bytes())?;
-    Ok(Some(legacy.to_path_buf()))
-}
-
-fn copy_dir(from: &Path, to: &Path) -> std::io::Result<()> {
-    let Ok(rd) = std::fs::read_dir(from) else { return Ok(()) };
-    create_private_dir(to)?;
-    for e in rd.flatten() {
-        if e.file_type()?.is_file() && !to.join(e.file_name()).exists() {
-            std::fs::copy(e.path(), to.join(e.file_name()))?;
-        }
-    }
-    Ok(())
-}
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    fn tmp(name: &str) -> PathBuf {
-        let d = std::env::temp_dir().join(format!("nexus-cfg-{name}-{}", std::process::id()));
-        let _ = std::fs::remove_dir_all(&d);
-        d
-    }
-
-    #[test]
-    fn migrates_legacy_once_and_keeps_source() {
-        let base = tmp("mig");
-        let legacy = base.join(LEGACY_APP_DIR);
-        std::fs::create_dir_all(legacy.join("vault")).unwrap();
-        std::fs::write(legacy.join("link.db"), b"db").unwrap();
-        std::fs::write(legacy.join("vault/vault.json"), b"{}").unwrap();
-        let cfg = AppConfig::in_dir(base.join(APP_DIR));
-        assert_eq!(migrate_legacy(&legacy, &cfg).unwrap(), Some(legacy.clone()));
-        assert_eq!(std::fs::read(&cfg.db_path).unwrap(), b"db");
-        assert!(cfg.vault_dir.join("vault.json").exists());
-        assert!(legacy.join("link.db").exists());
-        // Second run: Nexus already has a database, nothing happens.
-        std::fs::write(legacy.join("link.db"), b"newer").unwrap();
-        assert_eq!(migrate_legacy(&legacy, &cfg).unwrap(), None);
-        assert_eq!(std::fs::read(&cfg.db_path).unwrap(), b"db");
-        std::fs::remove_dir_all(base).unwrap();
-    }
-
-    #[test]
-    fn no_legacy_no_migration() {
-        let base = tmp("none");
-        let cfg = AppConfig::in_dir(base.join(APP_DIR));
-        assert_eq!(migrate_legacy(&base.join(LEGACY_APP_DIR), &cfg).unwrap(), None);
-    }
-}