diff --git a/rust/Cargo.lock b/rust/Cargo.lock
index cb8cc7d..817de8b 100644
--- a/rust/Cargo.lock
+++ b/rust/Cargo.lock
@@ -2,6 +2,12 @@
 # It is not intended for manual editing.
 version = 4
 
+[[package]]
+name = "adler2"
+version = "2.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "320119579fcad9c21884f5c4861d16174d0e06250625266f50fe6898340abefa"
+
 [[package]]
 name = "aead"
 version = "0.5.2"
@@ -218,6 +224,12 @@ version = "0.22.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "72b3254f16251a8381aa12e40e3c4d2f0199f8c6508fbecb9d91f575e0fbb8c6"
 
+[[package]]
+name = "base64"
+version = "0.23.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ac07cdecf99051d9a5238b80f35af32cdeba5b336e55d957b318b50137e18da5"
+
 [[package]]
 name = "base64ct"
 version = "1.8.3"
@@ -387,6 +399,15 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "crc32fast"
+version = "1.5.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "01a7799fd6b852db0e61728dde9a204c423b44d689dbd432522543614b490e78"
+dependencies = [
+ "cfg-if",
+]
+
 [[package]]
 name = "crossbeam-utils"
 version = "0.8.23"
@@ -540,6 +561,17 @@ version = "0.1.14"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "aedcfb3409746eddb02b9e19ebda1c3394f759a152e48ee875a0844d1b955484"
 
+[[package]]
+name = "flate2"
+version = "1.1.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6e634e2e0ebac1ee034020da1ca582e17ffe4e0f5e985823721e168928136dcb"
+dependencies = [
+ "crc32fast",
+ "miniz_oxide",
+ "zlib-rs",
+]
+
 [[package]]
 name = "foldhash"
 version = "0.1.5"
@@ -706,6 +738,22 @@ dependencies = [
  "digest",
 ]
 
+[[package]]
+name = "http"
+version = "1.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "918d3568bebf352712bc2ef3d46a8bcf1a75b373be6539de198e9105cbbf9ce0"
+dependencies = [
+ "bytes",
+ "itoa",
+]
+
+[[package]]
+name = "httparse"
+version = "1.10.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6dbf3de79e51f3d586ab4cb9d5c3e2c14aa28ed23d180cf89b4df0454a69cc87"
+
 [[package]]
 name = "iana-time-zone"
 version = "0.1.65"
@@ -837,6 +885,16 @@ dependencies = [
  "autocfg",
 ]
 
+[[package]]
+name = "miniz_oxide"
+version = "0.9.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b63fbc4a50860e98e7b2aa7804ded1db5cbc3aff9193adaff57a6931bf7c4b4c"
+dependencies = [
+ "adler2",
+ "simd-adler32",
+]
+
 [[package]]
 name = "mio"
 version = "1.2.4"
@@ -861,13 +919,14 @@ version = "0.1.0"
 dependencies = [
  "aes-gcm",
  "argon2",
- "base64",
+ "base64 0.22.1",
  "chrono",
  "keyring",
  "rand",
  "rusqlite",
  "serde",
  "serde_json",
+ "ureq",
  "uuid",
 ]
 
@@ -995,6 +1054,12 @@ dependencies = [
  "subtle",
 ]
 
+[[package]]
+name = "percent-encoding"
+version = "2.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9b4f627cb1b25917193a259e49bdad08f671f8d9708acfd5fe0a8c1455d87220"
+
 [[package]]
 name = "pin-project-lite"
 version = "0.2.17"
@@ -1116,6 +1181,20 @@ dependencies = [
  "getrandom 0.2.17",
 ]
 
+[[package]]
+name = "ring"
+version = "0.17.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a4689e6c2294d81e88dc6261c768b63bc4fcdb852be6d1352498b114f61383b7"
+dependencies = [
+ "cc",
+ "cfg-if",
+ "getrandom 0.2.17",
+ "libc",
+ "untrusted",
+ "windows-sys 0.52.0",
+]
+
 [[package]]
 name = "rusqlite"
 version = "0.37.0"
@@ -1143,6 +1222,41 @@ dependencies = [
  "windows-sys 0.61.2",
 ]
 
+[[package]]
+name = "rustls"
+version = "0.23.45"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0d41d731c7d2f962d1ccc364cec258de3c0e93b38c2fb3ba97ac74513048d634"
+dependencies = [
+ "log",
+ "once_cell",
+ "ring",
+ "rustls-pki-types",
+ "rustls-webpki",
+ "subtle",
+ "zeroize",
+]
+
+[[package]]
+name = "rustls-pki-types"
+version = "1.15.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2f4925028c7eb5d1fcdaf196971378ed9d2c1c4efc7dc5d011256f76c99c0a96"
+dependencies = [
+ "zeroize",
+]
+
+[[package]]
+name = "rustls-webpki"
+version = "0.103.15"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f3c3cf1d8b1e7d4927e2d154c3fcb02979afb9939629c62cd9048d4f07b60ac2"
+dependencies = [
+ "ring",
+ "rustls-pki-types",
+ "untrusted",
+]
+
 [[package]]
 name = "rustversion"
 version = "1.0.23"
@@ -1296,6 +1410,12 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "simd-adler32"
+version = "0.3.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3a219298ac11a56ea9a6d2120044824d6f01aeb034955e7af7bc16858527deea"
+
 [[package]]
 name = "slab"
 version = "0.4.12"
@@ -1315,7 +1435,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "c3d1e2c7f27f8d4cb10542a02c49005dbd6e93095799d6f3be745fae9f8fedd4"
 dependencies = [
  "libc",
- "windows-sys 0.60.2",
+ "windows-sys 0.61.2",
 ]
 
 [[package]]
@@ -1475,6 +1595,47 @@ dependencies = [
  "subtle",
 ]
 
+[[package]]
+name = "untrusted"
+version = "0.9.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8ecb6da28b8a351d773b68d5825ac39017e680750f980f3a1a85cd8dd28a47c1"
+
+[[package]]
+name = "ureq"
+version = "3.4.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9a7ac20be9b7726e0bbdbf974c059676d9acb1cd414961f570a4e8231cacd7fc"
+dependencies = [
+ "base64 0.23.1",
+ "flate2",
+ "log",
+ "percent-encoding",
+ "rustls",
+ "rustls-pki-types",
+ "ureq-proto",
+ "utf8-zero",
+ "webpki-roots",
+]
+
+[[package]]
+name = "ureq-proto"
+version = "0.6.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f86fd172ccca569e458f61b6bdd6220965a9ef36e672a6852953b51a0e1583be"
+dependencies = [
+ "base64 0.23.1",
+ "http",
+ "httparse",
+ "log",
+]
+
+[[package]]
+name = "utf8-zero"
+version = "0.8.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b8c0a043c9540bae7c578c88f91dda8bd82e59ae27c21baca69c8b191aaf5a6e"
+
 [[package]]
 name = "uuid"
 version = "1.28.0"
@@ -1549,6 +1710,15 @@ dependencies = [
  "unicode-ident",
 ]
 
+[[package]]
+name = "webpki-roots"
+version = "1.0.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7dcd9d09a39985f5344844e66b0c530a33843579125f23e21e9f0f220850f22a"
+dependencies = [
+ "rustls-pki-types",
+]
+
 [[package]]
 name = "windows-core"
 version = "0.62.2"
@@ -1895,6 +2065,12 @@ dependencies = [
  "syn 2.0.119",
 ]
 
+[[package]]
+name = "zlib-rs"
+version = "0.6.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b268e58e7c693d7c271f93ffc4ba3b380412554231c85bf61ca7af91042a4112"
+
 [[package]]
 name = "zmij"
 version = "1.0.23"
diff --git a/rust/core/Cargo.toml b/rust/core/Cargo.toml
index a3c8903..b4afc9e 100644
--- a/rust/core/Cargo.toml
+++ b/rust/core/Cargo.toml
@@ -13,4 +13,5 @@ argon2 = "0.5"
 aes-gcm = "0.10"
 rand = "0.8"
 base64 = "0.22"
+ureq = "3"
 keyring = { version = "3", features = ["apple-native", "windows-native", "async-secret-service", "tokio", "crypto-rust"] }
diff --git a/rust/core/src/keyfiles.rs b/rust/core/src/keyfiles.rs
new file mode 100644
index 0000000..fbe191f
--- /dev/null
+++ b/rust/core/src/keyfiles.rs
@@ -0,0 +1,145 @@
+//! SSH key file helpers that need no SSH crypto: spotting private keys, listing `~/.ssh`, and
+//! sanitising key and upload file names.
+
+use crate::Result;
+use std::io::Read;
+use std::path::{Path, PathBuf};
+
+const PRIVATE_KEY_MARKERS: [&str; 6] = [
+    "BEGIN OPENSSH PRIVATE KEY",
+    "BEGIN RSA PRIVATE KEY",
+    "BEGIN DSA PRIVATE KEY",
+    "BEGIN EC PRIVATE KEY",
+    "BEGIN ED25519 PRIVATE KEY",
+    "BEGIN PRIVATE KEY",
+];
+
+const IGNORED: [&str; 8] = [
+    "authorized_keys",
+    "authorized_keys2",
+    "config",
+    "known_hosts",
+    "known_hosts.old",
+    "ssh_config",
+    "ssh_known_hosts",
+    "ssh_known_hosts2",
+];
+
+/// Whether the first 512 bytes look like a private key. Unreadable or empty paths are `false`
+/// (this is also Go's `FileIsPrivateKey`).
+pub fn is_likely_private_key(path: &Path) -> bool {
+    let mut head = Vec::with_capacity(512);
+    let Ok(f) = std::fs::File::open(path) else { return false };
+    if f.take(512).read_to_end(&mut head).is_err() || head.is_empty() {
+        return false;
+    }
+    head.starts_with(b"openssh-key-v1")
+        || PRIVATE_KEY_MARKERS.iter().any(|m| head.windows(m.len()).any(|w| w == m.as_bytes()))
+}
+
+/// Candidate private keys in `~/.ssh`, sorted. A missing home or `.ssh` gives an empty list.
+pub fn list_ssh_keys() -> Result<Vec<PathBuf>> {
+    match std::env::home_dir() {
+        Some(home) => list_ssh_keys_in(&home.join(".ssh")),
+        None => Ok(vec![]),
+    }
+}
+
+pub fn list_ssh_keys_in(dir: &Path) -> Result<Vec<PathBuf>> {
+    let entries = match std::fs::read_dir(dir) {
+        Ok(e) => e,
+        Err(e) if e.kind() == std::io::ErrorKind::NotFound => return Ok(vec![]),
+        Err(e) => return Err(e.into()),
+    };
+    let mut keys = Vec::new();
+    for entry in entries {
+        let entry = entry?;
+        if entry.file_type()?.is_dir() {
+            continue;
+        }
+        let name = entry.file_name().to_string_lossy().into_owned();
+        if IGNORED.contains(&name.as_str()) || name.ends_with(".pub") || name.ends_with(".old") {
+            continue;
+        }
+        let path = dir.join(&name);
+        if is_likely_private_key(&path) {
+            keys.push(path);
+        }
+    }
+    keys.sort();
+    Ok(keys)
+}
+
+/// Trimmed name of ASCII letters, digits, `-` and `_`.
+pub fn validate_ssh_key_name(name: &str) -> Result<String> {
+    let name = name.trim();
+    if name.is_empty() {
+        return Err("key name is required".into());
+    }
+    if !name.chars().all(|c| c.is_ascii_alphanumeric() || c == '-' || c == '_') {
+        return Err("key name contains invalid characters (use alphanumeric, hyphens, underscores)".into());
+    }
+    Ok(name.into())
+}
+
+/// The base name of an uploaded file (either slash style), rejecting `.`, `..` and NULs.
+pub fn safe_sftp_upload_name(file_name: &str) -> Result<String> {
+    let name = file_name.trim().replace('\\', "/");
+    if name.is_empty() {
+        return Err("invalid file name".into());
+    }
+    // Go's path.Base: trailing slashes dropped; all slashes gives "/".
+    let trimmed = name.trim_end_matches('/');
+    let base = if trimmed.is_empty() { "/" } else { trimmed.rsplit('/').next().unwrap_or(trimmed) };
+    if matches!(base, "" | "." | ".." | "/") || base.contains('\0') {
+        return Err("invalid file name".into());
+    }
+    Ok(base.into())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn upload_names() {
+        assert_eq!(safe_sftp_upload_name("../report <final>.txt").unwrap(), "report <final>.txt");
+        assert_eq!(safe_sftp_upload_name(r"C:\Users\me\a.txt").unwrap(), "a.txt");
+        assert_eq!(safe_sftp_upload_name("dir/b.txt/").unwrap(), "b.txt");
+        for bad in ["..", "folder/..", r"folder\..", "", "  ", "///", ".", "a\0b"] {
+            assert!(safe_sftp_upload_name(bad).is_err(), "{bad:?}");
+        }
+    }
+
+    #[test]
+    fn key_names() {
+        assert_eq!(validate_ssh_key_name(" id_ed25519-work ").unwrap(), "id_ed25519-work");
+        for bad in ["", "   ", "a/b", "../x", "a b", "kéy"] {
+            assert!(validate_ssh_key_name(bad).is_err(), "{bad:?}");
+        }
+    }
+
+    #[test]
+    fn lists_private_keys() {
+        let dir = std::env::temp_dir().join(format!("nexus-keys-{}", std::process::id()));
+        let _ = std::fs::remove_dir_all(&dir);
+        std::fs::create_dir_all(dir.join("subdir")).unwrap();
+        let key = "-----BEGIN OPENSSH PRIVATE KEY-----\nabc\n";
+        for (name, body) in [
+            ("id_ed25519", key),
+            ("id_rsa", "-----BEGIN RSA PRIVATE KEY-----\n"),
+            ("id_ed25519.pub", key),
+            ("config", key),
+            ("key.old", key),
+            ("notes.txt", "hello"),
+            ("empty", ""),
+        ] {
+            std::fs::write(dir.join(name), body).unwrap();
+        }
+        let keys = list_ssh_keys_in(&dir).unwrap();
+        assert_eq!(keys, vec![dir.join("id_ed25519"), dir.join("id_rsa")]);
+        assert!(!is_likely_private_key(Path::new("")));
+        assert!(list_ssh_keys_in(&dir.join("missing")).unwrap().is_empty());
+        std::fs::remove_dir_all(dir).unwrap();
+    }
+}
diff --git a/rust/core/src/lib.rs b/rust/core/src/lib.rs
index 5eaec28..59c0dd7 100644
--- a/rust/core/src/lib.rs
+++ b/rust/core/src/lib.rs
@@ -4,9 +4,15 @@
 pub mod clients;
 pub mod config;
 pub mod exportimport;
+pub mod keyfiles;
 pub mod models;
+pub mod recording;
 pub mod secrets;
+pub mod sshconfig;
 pub mod storage;
+pub mod terminalenv;
+pub mod updater;
+pub mod validation;
 
 pub type Error = Box<dyn std::error::Error + Send + Sync>;
 pub type Result<T> = std::result::Result<T, Error>;
diff --git a/rust/core/src/recording.rs b/rust/core/src/recording.rs
new file mode 100644
index 0000000..29cc485
--- /dev/null
+++ b/rust/core/src/recording.rs
@@ -0,0 +1,477 @@
+//! Session recording in asciicast v2 (https://docs.asciinema.org/manual/asciicast/v2/): a JSON
+//! header line, then one `[elapsed_secs, type, data]` array per line. Same files as the Go app.
+
+use crate::Result;
+use crate::models::Time;
+use serde::{Deserialize, Serialize};
+use std::collections::BTreeMap;
+use std::fs::File;
+use std::io::{Read, Write};
+use std::path::{Path, PathBuf};
+use std::sync::Mutex;
+use std::time::Instant;
+
+pub const EVENT_OUTPUT: &str = "o";
+pub const EVENT_INPUT: &str = "i";
+/// Bounds a single active recording file.
+pub const MAX_RECORDING_BYTES: u64 = 250 * 1024 * 1024;
+/// Bounds the file size loaded for playback.
+pub const MAX_PLAYBACK_BYTES: u64 = 100 * 1024 * 1024;
+/// Bounds one asciicast line during playback parsing.
+pub const MAX_PLAYBACK_LINE_BYTES: usize = 8 * 1024 * 1024;
+
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize, Default)]
+#[serde(default)]
+pub struct Header {
+    pub version: i64,
+    pub width: i64,
+    pub height: i64,
+    pub timestamp: i64,
+    #[serde(skip_serializing_if = "String::is_empty")]
+    pub title: String,
+    #[serde(skip_serializing_if = "BTreeMap::is_empty")]
+    pub env: BTreeMap<String, String>,
+}
+
+/// One recorded I/O event; `kind` is `"o"` or `"i"` (other types are kept as read).
+#[derive(Clone, Debug, PartialEq)]
+pub struct Event {
+    pub elapsed: f64,
+    pub kind: String,
+    pub data: String,
+}
+
+#[derive(Clone, Debug, PartialEq, Serialize)]
+#[serde(rename_all = "camelCase")]
+pub struct RecordingMeta {
+    pub id: String,
+    pub session_id: String,
+    pub title: String,
+    pub width: i64,
+    pub height: i64,
+    /// seconds
+    pub duration: f64,
+    /// file size in bytes
+    pub size: u64,
+    pub created_at: Time,
+    pub file_path: PathBuf,
+}
+
+#[derive(Clone, Debug, PartialEq, Serialize)]
+#[serde(rename_all = "camelCase")]
+pub struct StorageInfo {
+    pub count: usize,
+    pub total_bytes: u64,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub oldest_created_at: Option<Time>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub newest_created_at: Option<Time>,
+    pub max_recording_bytes: u64,
+    pub max_playback_bytes: u64,
+}
+
+#[derive(Clone, Debug, PartialEq, Default, Serialize)]
+#[serde(rename_all = "camelCase")]
+pub struct CleanupResult {
+    pub deleted: usize,
+    pub freed_bytes: u64,
+}
+
+struct Inner {
+    file: Option<File>,
+    closed: bool,
+    event_count: usize,
+    bytes_written: u64,
+}
+
+/// Captures terminal I/O for one session. Writes are best-effort: errors are dropped and the
+/// recording stops (file closed) once it would exceed its size limit.
+pub struct Recorder {
+    inner: Mutex<Inner>,
+    start: Instant,
+    file_path: PathBuf,
+    max_bytes: u64,
+}
+
+fn mkdir_private(dir: &Path) -> std::io::Result<()> {
+    let mut b = std::fs::DirBuilder::new();
+    b.recursive(true);
+    #[cfg(unix)]
+    std::os::unix::fs::DirBuilderExt::mode(&mut b, 0o700);
+    b.create(dir)
+}
+
+fn json_line<T: Serialize>(v: &T) -> Result<Vec<u8>> {
+    let mut line = serde_json::to_vec(v)?;
+    line.push(b'\n');
+    Ok(line)
+}
+
+impl Recorder {
+    /// Creates `<dir>/<id>.cast` and writes the header.
+    pub fn new(dir: &Path, id: &str, title: &str, cols: i64, rows: i64) -> Result<Recorder> {
+        Self::with_limit(dir, id, title, cols, rows, MAX_RECORDING_BYTES)
+    }
+
+    fn with_limit(dir: &Path, id: &str, title: &str, cols: i64, rows: i64, max_bytes: u64) -> Result<Recorder> {
+        mkdir_private(dir).map_err(|e| format!("recording: failed to create directory: {e}"))?;
+        let path = dir.join(format!("{id}.cast"));
+        let mut f = File::create(&path).map_err(|e| format!("recording: failed to create file: {e}"))?;
+        let start = Instant::now();
+        let hdr = Header {
+            version: 2,
+            width: cols,
+            height: rows,
+            timestamp: chrono::Utc::now().timestamp(),
+            title: title.into(),
+            env: BTreeMap::from([("TERM".into(), "xterm-256color".into())]),
+        };
+        let line = json_line(&hdr)?;
+        if let Err(e) = f.write_all(&line) {
+            drop(f);
+            let _ = std::fs::remove_file(&path);
+            return Err(format!("recording: failed to write header: {e}").into());
+        }
+        Ok(Recorder {
+            inner: Mutex::new(Inner { file: Some(f), closed: false, event_count: 0, bytes_written: line.len() as u64 }),
+            start,
+            file_path: path,
+            max_bytes,
+        })
+    }
+
+    /// Records data from the remote host.
+    pub fn write_output(&self, data: &[u8]) {
+        self.write_event(EVENT_OUTPUT, data)
+    }
+
+    /// Records data from the user.
+    pub fn write_input(&self, data: &[u8]) {
+        self.write_event(EVENT_INPUT, data)
+    }
+
+    fn write_event(&self, kind: &str, data: &[u8]) {
+        let mut g = self.inner.lock().unwrap();
+        if g.closed || g.file.is_none() {
+            return;
+        }
+        let elapsed = self.start.elapsed().as_secs_f64();
+        let Ok(line) = json_line(&(elapsed, kind, String::from_utf8_lossy(data))) else { return };
+        if self.max_bytes > 0 && g.bytes_written + line.len() as u64 > self.max_bytes {
+            g.closed = true;
+            if let Some(f) = g.file.take() {
+                let _ = f.sync_all();
+            }
+            return;
+        }
+        if g.file.as_mut().unwrap().write_all(&line).is_ok() {
+            g.bytes_written += line.len() as u64;
+            g.event_count += 1;
+        }
+    }
+
+    /// Flushes and closes the file. Idempotent.
+    pub fn close(&self) -> Result<()> {
+        let mut g = self.inner.lock().unwrap();
+        if g.closed {
+            return Ok(());
+        }
+        g.closed = true;
+        if let Some(f) = g.file.take() {
+            f.sync_all().map_err(|e| format!("recording: sync failed: {e}"))?;
+        }
+        Ok(())
+    }
+
+    /// Seconds since recording started.
+    pub fn duration(&self) -> f64 {
+        self.start.elapsed().as_secs_f64()
+    }
+
+    pub fn file_path(&self) -> &Path {
+        &self.file_path
+    }
+
+    pub fn event_count(&self) -> usize {
+        self.inner.lock().unwrap().event_count
+    }
+}
+
+/// The recordings directory: listing, playback, deletion and retention.
+#[derive(Clone, Debug)]
+pub struct Store {
+    dir: PathBuf,
+}
+
+impl Store {
+    pub fn new(dir: impl Into<PathBuf>) -> Store {
+        Store { dir: dir.into() }
+    }
+
+    pub fn dir(&self) -> &Path {
+        &self.dir
+    }
+
+    /// Metadata for every readable `.cast` file, newest first.
+    pub fn list(&self) -> Result<Vec<RecordingMeta>> {
+        mkdir_private(&self.dir)?;
+        let entries = std::fs::read_dir(&self.dir).map_err(|e| format!("recording: failed to read directory: {e}"))?;
+        let mut out: Vec<RecordingMeta> = entries
+            .flatten()
+            .filter(|e| !e.file_type().is_ok_and(|t| t.is_dir()))
+            .filter_map(|e| e.file_name().into_string().ok())
+            .filter(|n| n.ends_with(".cast"))
+            .filter_map(|n| self.read_meta(&n).ok()) // skip unreadable files
+            .collect();
+        out.sort_by_key(|m| std::cmp::Reverse(m.created_at));
+        Ok(out)
+    }
+
+    /// Reads the full recording (header + events).
+    pub fn get(&self, id: &str) -> Result<(Header, Vec<Event>)> {
+        self.get_with_limit(id, MAX_PLAYBACK_BYTES)
+    }
+
+    fn get_with_limit(&self, id: &str, max_bytes: u64) -> Result<(Header, Vec<Event>)> {
+        let path = self.recording_path(id)?;
+        let size = std::fs::metadata(&path).map_err(|e| format!("recording: failed to stat file: {e}"))?.len();
+        if max_bytes > 0 && size > max_bytes {
+            return Err(format!("recording: file is too large for playback (max {max_bytes} bytes)").into());
+        }
+        let raw = std::fs::read(&path).map_err(|e| format!("recording: failed to open file: {e}"))?;
+        let text = String::from_utf8_lossy(&raw);
+        let mut lines = text.lines();
+        let Some(first) = lines.next() else { return Err("recording: empty file".into()) };
+        if first.len() > MAX_PLAYBACK_LINE_BYTES {
+            return Err("recording: failed to scan header: token too long".into());
+        }
+        let hdr: Header = serde_json::from_str(first.trim()).map_err(|e| format!("recording: invalid header: {e}"))?;
+        let mut events = Vec::new();
+        for line in lines {
+            if line.len() > MAX_PLAYBACK_LINE_BYTES {
+                return Err("recording: failed to scan events: token too long".into());
+            }
+            let line = line.trim();
+            if line.is_empty() {
+                continue;
+            }
+            if let Ok((elapsed, kind, data)) = serde_json::from_str::<(f64, String, String)>(line) {
+                events.push(Event { elapsed, kind, data });
+            }
+        }
+        Ok((hdr, events))
+    }
+
+    pub fn delete(&self, id: &str) -> Result<()> {
+        let path = self.recording_path(id)?;
+        std::fs::remove_file(path).map_err(|e| format!("recording: failed to delete: {e}"))?;
+        Ok(())
+    }
+
+    pub fn storage_info(&self) -> Result<StorageInfo> {
+        let metas = self.list()?;
+        Ok(StorageInfo {
+            count: metas.len(),
+            total_bytes: metas.iter().map(|m| m.size).sum(),
+            oldest_created_at: metas.iter().map(|m| m.created_at).min(),
+            newest_created_at: metas.iter().map(|m| m.created_at).max(),
+            max_recording_bytes: MAX_RECORDING_BYTES,
+            max_playback_bytes: MAX_PLAYBACK_BYTES,
+        })
+    }
+
+    /// Removes recordings older than `max_age_days`, then the oldest until the total is at most
+    /// `max_total_bytes`. Zero disables either limit.
+    pub fn cleanup(&self, max_age_days: u32, max_total_bytes: u64) -> Result<CleanupResult> {
+        let mut metas = self.list()?;
+        let mut result = CleanupResult::default();
+        let mut deleted = std::collections::HashSet::new();
+        let mut total: u64 = metas.iter().map(|m| m.size).sum();
+        let mut delete = |m: &RecordingMeta, total: &mut u64| {
+            if !deleted.contains(&m.id) && self.delete(&m.id).is_ok() {
+                deleted.insert(m.id.clone());
+                result.deleted += 1;
+                result.freed_bytes += m.size;
+                *total -= m.size;
+            }
+        };
+        if max_age_days > 0 {
+            let cutoff = chrono::Utc::now() - chrono::Duration::days(max_age_days.into());
+            for m in &metas {
+                if m.created_at < cutoff {
+                    delete(m, &mut total);
+                }
+            }
+        }
+        if max_total_bytes > 0 && total > max_total_bytes {
+            metas.sort_by_key(|m| m.created_at);
+            for m in &metas {
+                if total <= max_total_bytes {
+                    break;
+                }
+                delete(m, &mut total);
+            }
+        }
+        Ok(result)
+    }
+
+    fn recording_path(&self, id: &str) -> Result<PathBuf> {
+        let id = id.trim();
+        if id.is_empty() || id == "." || id == ".." || id.contains(['/', '\\']) {
+            return Err("recording: invalid recording ID".into());
+        }
+        Ok(self.dir.join(format!("{id}.cast")))
+    }
+
+    /// Header fields plus the last event's timestamp as the duration.
+    fn read_meta(&self, filename: &str) -> Result<RecordingMeta> {
+        let path = self.dir.join(filename);
+        let mut f = File::open(&path)?;
+        let size = f.metadata()?.len();
+        let mut raw = Vec::new();
+        f.read_to_end(&mut raw)?;
+        let mut values = serde_json::Deserializer::from_slice(&raw).into_iter::<serde_json::Value>();
+        let hdr: Header = serde_json::from_value(values.next().ok_or("recording: empty file")??)?;
+        let mut duration = 0.0;
+        for v in values {
+            let Ok(v) = v else { break };
+            if let Some(e) = v.get(0).and_then(|e| e.as_f64()) {
+                duration = e;
+            }
+        }
+        let id = filename.trim_end_matches(".cast").to_string();
+        let created_at = chrono::DateTime::from_timestamp(hdr.timestamp, 0)
+            .ok_or("recording: invalid timestamp")?
+            .with_timezone(&chrono::Local)
+            .fixed_offset();
+        Ok(RecordingMeta {
+            session_id: id.clone(), // recording ID matches session ID by default
+            id,
+            title: hdr.title,
+            width: hdr.width,
+            height: hdr.height,
+            duration,
+            size,
+            created_at,
+            file_path: path,
+        })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn tmp(name: &str) -> PathBuf {
+        let d = std::env::temp_dir().join(format!("nexus-rec-{name}-{}", std::process::id()));
+        let _ = std::fs::remove_dir_all(&d);
+        d
+    }
+
+    #[test]
+    fn reads_go_fixture() {
+        let store = Store::new(PathBuf::from(env!("CARGO_MANIFEST_DIR")).join("tests/fixtures/recordings"));
+        let (hdr, events) = store.get("rec1").unwrap();
+        assert_eq!((hdr.version, hdr.width, hdr.height, hdr.timestamp), (2, 80, 24, 1791633486));
+        assert_eq!(hdr.title, "Fixture — host");
+        assert_eq!(hdr.env["TERM"], "xterm-256color");
+        assert_eq!(events.len(), 2);
+        assert_eq!((events[0].kind.as_str(), events[0].data.as_str()), ("o", "hello \x1b[1mworld\x1b[0m\r\n"));
+        assert_eq!((events[1].kind.as_str(), events[1].data.as_str()), ("i", "ls\r"));
+        let metas = store.list().unwrap();
+        assert_eq!(metas.len(), 1);
+        assert_eq!(metas[0].duration, 0.000212149);
+    }
+
+    #[test]
+    fn write_and_close() {
+        let dir = tmp("write");
+        let rec = Recorder::new(&dir, "test-session-001", "Test Recording", 80, 24).unwrap();
+        rec.write_output(b"Welcome to the server\r\n");
+        rec.write_output(b"$ ");
+        rec.write_input(b"ls -la\r\n");
+        rec.write_output(b"total 42\r\n");
+        assert_eq!(rec.event_count(), 4);
+        rec.close().unwrap();
+        rec.close().unwrap(); // double close is a no-op
+        let text = std::fs::read_to_string(dir.join("test-session-001.cast")).unwrap();
+        let lines: Vec<&str> = text.trim().lines().collect();
+        assert_eq!(lines.len(), 5);
+        let hdr: Header = serde_json::from_str(lines[0]).unwrap();
+        assert_eq!((hdr.version, hdr.width, hdr.height), (2, 80, 24));
+        let (_, kind, _): (f64, String, String) = serde_json::from_str(lines[1]).unwrap();
+        assert_eq!(kind, "o");
+        std::fs::remove_dir_all(dir).unwrap();
+    }
+
+    #[test]
+    fn list_get_delete() {
+        let dir = tmp("list");
+        let rec = Recorder::new(&dir, "session-abc", "My Session", 120, 40).unwrap();
+        rec.write_output(b"hello world\r\n");
+        rec.write_output(b"done\r\n");
+        rec.close().unwrap();
+        let store = Store::new(&dir);
+        let metas = store.list().unwrap();
+        assert_eq!(metas.len(), 1);
+        assert_eq!((metas[0].id.as_str(), metas[0].width, metas[0].height), ("session-abc", 120, 40));
+        let (hdr, events) = store.get("session-abc").unwrap();
+        assert_eq!(hdr.title, "My Session");
+        assert_eq!(events.len(), 2);
+        store.delete("session-abc").unwrap();
+        assert!(store.list().unwrap().is_empty());
+        assert!(store.delete("../outside").is_err());
+        std::fs::remove_dir_all(dir).unwrap();
+    }
+
+    #[test]
+    fn stops_at_size_limit() {
+        let dir = tmp("limit");
+        let rec = Recorder::with_limit(&dir, "limited", "Limited", 80, 24, 512).unwrap();
+        for _ in 0..50 {
+            rec.write_output("x".repeat(80).as_bytes());
+        }
+        assert!(rec.event_count() < 50);
+        rec.close().unwrap();
+        assert!(std::fs::metadata(dir.join("limited.cast")).unwrap().len() <= 512);
+        std::fs::remove_dir_all(dir).unwrap();
+    }
+
+    #[test]
+    fn rejects_oversized_playback() {
+        let dir = tmp("huge");
+        std::fs::create_dir_all(&dir).unwrap();
+        let body = format!("{{\"version\":2,\"width\":80,\"height\":24,\"timestamp\":1}}\n{}", "x".repeat(256));
+        std::fs::write(dir.join("huge.cast"), body).unwrap();
+        let err = Store::new(&dir).get_with_limit("huge", 128).unwrap_err();
+        assert!(err.to_string().contains("too large"));
+        std::fs::remove_dir_all(dir).unwrap();
+    }
+
+    #[test]
+    fn cleanup_by_age_and_size() {
+        let dir = tmp("cleanup");
+        let make = |id: &str, age_secs: i64, payload: &str| {
+            let rec = Recorder::new(&dir, id, id, 80, 24).unwrap();
+            rec.write_output(payload.as_bytes());
+            rec.close().unwrap();
+            let path = dir.join(format!("{id}.cast"));
+            let text = std::fs::read_to_string(&path).unwrap();
+            let (first, rest) = text.split_once('\n').unwrap();
+            let mut hdr: Header = serde_json::from_str(first).unwrap();
+            hdr.timestamp = chrono::Utc::now().timestamp() - age_secs;
+            let mut out = json_line(&hdr).unwrap();
+            out.extend(rest.as_bytes());
+            std::fs::write(&path, out).unwrap();
+        };
+        make("old", 45 * 86400, "old");
+        make("recent", 2 * 3600, &"recent".repeat(50));
+        let store = Store::new(&dir);
+        assert_eq!(store.cleanup(30, 0).unwrap().deleted, 1);
+        assert!(!dir.join("old.cast").exists());
+        let info = store.storage_info().unwrap();
+        assert_eq!(info.count, 1);
+        assert_eq!(store.cleanup(0, info.total_bytes - 1).unwrap().deleted, 1);
+        std::fs::remove_dir_all(dir).unwrap();
+    }
+}
diff --git a/rust/core/src/sshconfig.rs b/rust/core/src/sshconfig.rs
new file mode 100644
index 0000000..f3cdcfb
--- /dev/null
+++ b/rust/core/src/sshconfig.rs
@@ -0,0 +1,281 @@
+//! Parses OpenSSH `~/.ssh/config` Host blocks into SSH profiles. Supports HostName, Port, User,
+//! IdentityFile, ProxyJump (first hop), ForwardAgent and Compression. Match blocks, wildcard-only
+//! hosts, Include and `%h`-style tokens are ignored, as in the Go app.
+
+use crate::Result;
+use crate::models::{HostKeyPolicy, JumpHost, Profile, Protocol, SecretMode, SshConfig};
+use std::path::{Path, PathBuf};
+
+const MAX_CONFIG_FILE_BYTES: u64 = 5 * 1024 * 1024;
+const MAX_CONFIG_LINE_BYTES: usize = 256 * 1024;
+const MAX_HOST_BLOCKS: usize = 5000;
+
+#[derive(Clone, Debug, PartialEq, Default)]
+pub struct HostBlock {
+    pub aliases: Vec<String>,
+    pub host_name: String,
+    pub port: i64,
+    pub user: String,
+    pub identity_file: String,
+    pub proxy_jump: String,
+    pub forward_agent: bool,
+    pub compression: bool,
+}
+
+pub fn parse_file(path: &Path) -> Result<Vec<HostBlock>> {
+    let p = path.display();
+    let meta = std::fs::metadata(path).map_err(|e| format!("sshconfig: failed to open {p}: {e}"))?;
+    if meta.is_dir() {
+        return Err(format!("sshconfig: {p} is a directory").into());
+    }
+    if meta.len() > MAX_CONFIG_FILE_BYTES {
+        return Err(format!(
+            "sshconfig: config file is too large: {} bytes exceeds {MAX_CONFIG_FILE_BYTES} bytes",
+            meta.len()
+        )
+        .into());
+    }
+    let raw = std::fs::read(path).map_err(|e| format!("sshconfig: failed to open {p}: {e}"))?;
+    parse(&String::from_utf8_lossy(&raw))
+}
+
+fn parse(text: &str) -> Result<Vec<HostBlock>> {
+    let mut blocks = Vec::new();
+    let mut current: Option<HostBlock> = None;
+    let mut commit = |cur: &mut Option<HostBlock>| -> Result<()> {
+        if let Some(b) = cur.take() {
+            if blocks.len() >= MAX_HOST_BLOCKS {
+                return Err(format!("sshconfig: too many Host blocks (max {MAX_HOST_BLOCKS})").into());
+            }
+            blocks.push(b);
+        }
+        Ok(())
+    };
+    for line in text.lines() {
+        if line.len() > MAX_CONFIG_LINE_BYTES {
+            return Err("sshconfig: read error: token too long".into());
+        }
+        let line = line.trim();
+        if line.is_empty() || line.starts_with('#') {
+            continue;
+        }
+        let (key, value) = split_directive(line);
+        match key.to_lowercase().as_str() {
+            "host" => {
+                commit(&mut current)?;
+                let aliases: Vec<String> = value.split_whitespace().map(String::from).collect();
+                // Skip wildcard-only hosts (e.g. "Host *").
+                let wildcard = aliases.iter().any(|a| a.contains(['*', '?']));
+                if !(wildcard && aliases.len() == 1) {
+                    current = Some(HostBlock { aliases, port: 22, ..Default::default() });
+                }
+            }
+            "match" => commit(&mut current)?,
+            key => {
+                let Some(b) = current.as_mut() else { continue };
+                match key {
+                    "hostname" => b.host_name = value.into(),
+                    "port" => {
+                        if let Ok(p) = value.parse() {
+                            b.port = p
+                        }
+                    }
+                    "user" => b.user = value.into(),
+                    "identityfile" => b.identity_file = expand_tilde(value),
+                    "proxyjump" => b.proxy_jump = value.into(),
+                    "forwardagent" => b.forward_agent = is_trueish(value),
+                    "compression" => b.compression = is_trueish(value),
+                    _ => {}
+                }
+            }
+        }
+    }
+    commit(&mut current)?;
+    Ok(blocks)
+}
+
+/// `~/.ssh/config`, if the home directory is known.
+pub fn default_config_path() -> Option<PathBuf> {
+    std::env::home_dir().map(|h| h.join(".ssh").join("config"))
+}
+
+/// One SSH profile per block; the first alias becomes the display name.
+pub fn to_profiles(blocks: &[HostBlock], folder: &str) -> Vec<Profile> {
+    blocks
+        .iter()
+        .filter(|b| !b.aliases.is_empty())
+        .map(|b| {
+            let mut ssh = SshConfig {
+                auth_methods: vec!["publickey".into(), "password".into()],
+                secret_mode: SecretMode::AskEveryTime,
+                host_key_policy: HostKeyPolicy::Ask,
+                terminal_type: "xterm-256color".into(),
+                agent_auth: b.forward_agent,
+                agent_forwarding: b.forward_agent,
+                compression: b.compression,
+                private_key_path: b.identity_file.clone(),
+                ..Default::default()
+            };
+            if !b.proxy_jump.is_empty() && b.proxy_jump != "none" {
+                ssh.jump_hosts = parse_proxy_jump(&b.proxy_jump).into_iter().collect();
+            }
+            let mut p = Profile::new(Protocol::Ssh);
+            p.display_name = b.aliases[0].clone();
+            p.host = if b.host_name.is_empty() { b.aliases[0].clone() } else { b.host_name.clone() };
+            p.port = b.port;
+            p.username = b.user.clone();
+            p.folder = folder.into();
+            p.ssh = Some(ssh);
+            p.tags = vec!["ssh-config-import".into()];
+            p
+        })
+        .collect()
+}
+
+/// `[user@]host[:port]`; only the first hop of a comma-separated chain.
+fn parse_proxy_jump(value: &str) -> Option<JumpHost> {
+    let mut value = value.split(',').next().unwrap_or("").trim();
+    if value.is_empty() || value == "none" {
+        return None;
+    }
+    let mut jh =
+        JumpHost { port: 22, auth_method: "publickey".into(), secret_mode: SecretMode::AskEveryTime, ..Default::default() };
+    if let Some((user, rest)) = value.split_once('@') {
+        jh.username = user.into();
+        value = rest;
+    }
+    if let Some((host, port)) = value.rsplit_once(':')
+        && let Ok(p) = port.parse()
+    {
+        jh.port = p;
+        value = host;
+    }
+    jh.host = value.into();
+    Some(jh)
+}
+
+/// `Key Value` or `Key=Value`.
+fn split_directive(line: &str) -> (&str, &str) {
+    if let Some((k, v)) = line.split_once('=') {
+        return (k.trim(), v.trim());
+    }
+    match line.split_once(' ').or_else(|| line.split_once('\t')) {
+        Some((k, v)) => (k.trim(), v.trim()),
+        None => (line, ""),
+    }
+}
+
+fn expand_tilde(path: &str) -> String {
+    match (path.strip_prefix("~/"), std::env::home_dir()) {
+        (Some(rest), Some(home)) => home.join(rest).to_string_lossy().into_owned(),
+        _ => path.into(),
+    }
+}
+
+fn is_trueish(v: &str) -> bool {
+    matches!(v.to_lowercase().as_str(), "yes" | "true" | "on" | "1")
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const TEST_CONFIG: &str = "# Test SSH config
+
+Host *
+    ServerAliveInterval 60
+
+Host webserver
+    HostName web.example.com
+    Port 2222
+    User deploy
+    IdentityFile ~/.ssh/deploy_key
+    ForwardAgent yes
+    Compression yes
+
+Host dbserver
+    HostName db.internal.example.com
+    User postgres
+    ProxyJump bastion@jump.example.com:2200
+
+Host simple
+    HostName 10.0.0.5
+
+Host wildcard-*
+    User admin
+";
+
+    #[test]
+    fn parses_file() {
+        let path = std::env::temp_dir().join(format!("nexus-sshconfig-{}", std::process::id()));
+        std::fs::write(&path, TEST_CONFIG).unwrap();
+        let blocks = parse_file(&path).unwrap();
+        std::fs::remove_file(&path).unwrap();
+        assert_eq!(blocks.len(), 3);
+        let wb = &blocks[0];
+        assert_eq!(wb.aliases[0], "webserver");
+        assert_eq!((wb.host_name.as_str(), wb.port, wb.user.as_str()), ("web.example.com", 2222, "deploy"));
+        assert!(wb.forward_agent && wb.compression);
+        assert!(wb.identity_file.ends_with(".ssh/deploy_key") && !wb.identity_file.starts_with('~'));
+        assert_eq!(blocks[1].aliases[0], "dbserver");
+        assert_eq!(blocks[1].proxy_jump, "bastion@jump.example.com:2200");
+        assert_eq!((blocks[2].host_name.as_str(), blocks[2].port), ("10.0.0.5", 22));
+    }
+
+    #[test]
+    fn rejects_oversized_file() {
+        let path = std::env::temp_dir().join(format!("nexus-sshconfig-big-{}", std::process::id()));
+        std::fs::File::create(&path).unwrap().set_len(MAX_CONFIG_FILE_BYTES + 1).unwrap();
+        let err = parse_file(&path).unwrap_err();
+        std::fs::remove_file(&path).unwrap();
+        assert!(err.to_string().contains("too large"));
+    }
+
+    #[test]
+    fn rejects_too_many_host_blocks() {
+        let text: String = (0..=MAX_HOST_BLOCKS).map(|i| format!("Host host{i}\n    HostName example.com\n")).collect();
+        assert!(parse(&text).unwrap_err().to_string().contains("too many Host blocks"));
+    }
+
+    #[test]
+    fn converts_to_profiles() {
+        let blocks = vec![
+            HostBlock {
+                aliases: vec!["myserver".into()],
+                host_name: "srv.example.com".into(),
+                port: 22,
+                user: "admin".into(),
+                forward_agent: true,
+                ..Default::default()
+            },
+            HostBlock {
+                aliases: vec!["jumpbox".into()],
+                host_name: "jump.example.com".into(),
+                port: 2200,
+                user: "jumper".into(),
+                proxy_jump: "gateway@gw.example.com".into(),
+                ..Default::default()
+            },
+        ];
+        let ps = to_profiles(&blocks, "Imported");
+        assert_eq!(ps.len(), 2);
+        assert_eq!((ps[0].display_name.as_str(), ps[0].host.as_str()), ("myserver", "srv.example.com"));
+        assert_eq!(ps[0].folder, "Imported");
+        assert!(ps[0].ssh.as_ref().unwrap().agent_auth);
+        let jh = &ps[1].ssh.as_ref().unwrap().jump_hosts[0];
+        assert_eq!((jh.host.as_str(), jh.username.as_str()), ("gw.example.com", "gateway"));
+    }
+
+    #[test]
+    fn parses_proxy_jump() {
+        for (input, host, user, port) in [
+            ("bastion.example.com", "bastion.example.com", "", 22),
+            ("user@bastion.example.com", "bastion.example.com", "user", 22),
+            ("user@bastion.example.com:2200", "bastion.example.com", "user", 2200),
+            ("host:443", "host", "", 443),
+        ] {
+            let jh = parse_proxy_jump(input).unwrap();
+            assert_eq!((jh.host.as_str(), jh.username.as_str(), jh.port), (host, user, port), "{input}");
+        }
+    }
+}
diff --git a/rust/core/src/terminalenv.rs b/rust/core/src/terminalenv.rs
new file mode 100644
index 0000000..b43ee4e
--- /dev/null
+++ b/rust/core/src/terminalenv.rs
@@ -0,0 +1,109 @@
+//! Environment variables for terminal sessions: TERM and a UTF-8 character locale.
+
+use std::collections::BTreeMap;
+
+const LANG: &str = "LANG";
+const LC_ALL: &str = "LC_ALL";
+const LC_CTYPE: &str = "LC_CTYPE";
+const TERM: &str = "TERM";
+const DEFAULT_TERM: &str = "xterm-256color";
+
+/// `KEY=VALUE` entries for a local interactive PTY.
+pub fn local_shell_env(env: Vec<String>) -> Vec<String> {
+    ensure_utf8_character_locale(set_env(env, TERM, DEFAULT_TERM), std::env::consts::OS)
+}
+
+/// Variables to request for an SSH session. A locale set by the profile is kept as is; otherwise
+/// a UTF-8 `LC_CTYPE` is added. Keys are trimmed and empty keys dropped. Iteration order is sorted.
+pub fn ssh_env_vars(profile_env: &BTreeMap<String, String>) -> BTreeMap<String, String> {
+    let mut out: BTreeMap<String, String> = profile_env
+        .iter()
+        .map(|(k, v)| (k.trim().to_string(), v.clone()))
+        .filter(|(k, _)| !k.is_empty())
+        .collect();
+    if ![LC_ALL, LC_CTYPE, LANG].iter().any(|k| out.contains_key(*k)) {
+        out.insert(LC_CTYPE.into(), default_utf8_locale(std::env::consts::OS).into());
+    }
+    out
+}
+
+/// A UTF-8 locale broadly available on `os` (Go's `darwin` or Rust's `macos` get `en_US.UTF-8`).
+pub fn default_utf8_locale(os: &str) -> &'static str {
+    if os == "darwin" || os == "macos" { "en_US.UTF-8" } else { "C.UTF-8" }
+}
+
+fn ensure_utf8_character_locale(env: Vec<String>, os: &str) -> Vec<String> {
+    // The first of LC_ALL, LC_CTYPE, LANG that is set decides the character locale.
+    let effective = [LC_ALL, LC_CTYPE, LANG].iter().find_map(|k| get_env(&env, k));
+    if effective.is_some_and(is_utf8_locale) {
+        return env;
+    }
+    let locale = default_utf8_locale(os);
+    if get_env(&env, LC_ALL).is_some() {
+        set_env(env, LC_ALL, locale)
+    } else if get_env(&env, LC_CTYPE).is_some() || get_env(&env, LANG).is_some() {
+        set_env(env, LC_CTYPE, locale)
+    } else {
+        set_env(env, LANG, locale)
+    }
+}
+
+fn is_utf8_locale(v: &str) -> bool {
+    v.replace('-', "").to_lowercase().contains("utf8")
+}
+
+fn get_env<'a>(env: &'a [String], key: &str) -> Option<&'a str> {
+    env.iter().rev().find_map(|e| e.strip_prefix(key)?.strip_prefix('='))
+}
+
+fn set_env(env: Vec<String>, key: &str, value: &str) -> Vec<String> {
+    let mut out: Vec<String> = env.into_iter().filter(|e| get_env(std::slice::from_ref(e), key).is_none()).collect();
+    out.push(format!("{key}={value}"));
+    out
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn s(v: &[&str]) -> Vec<String> {
+        v.iter().map(|x| x.to_string()).collect()
+    }
+
+    #[test]
+    fn local_env_sets_term_and_utf8_when_missing() {
+        let got = local_shell_env(s(&["SHELL=/bin/zsh"]));
+        assert_eq!(get_env(&got, TERM), Some(DEFAULT_TERM));
+        assert!(get_env(&got, LANG).is_some_and(is_utf8_locale));
+    }
+
+    #[test]
+    fn local_env_uses_lc_ctype_when_lang_is_not_utf8() {
+        let got = ensure_utf8_character_locale(s(&["LANG=C"]), "linux");
+        assert_eq!(get_env(&got, LANG), Some("C"));
+        assert_eq!(get_env(&got, LC_CTYPE), Some("C.UTF-8"));
+    }
+
+    #[test]
+    fn local_env_overrides_non_utf8_lc_all() {
+        let got = ensure_utf8_character_locale(s(&["LC_ALL=C", "LANG=C"]), "darwin");
+        assert_eq!(get_env(&got, LC_ALL), Some("en_US.UTF-8"));
+    }
+
+    #[test]
+    fn ssh_env_preserves_profile_locale() {
+        let got = ssh_env_vars(&BTreeMap::from([("LANG".into(), "de_DE.UTF-8".into()), ("FOO".into(), "bar".into())]));
+        assert_eq!((got["LANG"].as_str(), got["FOO"].as_str()), ("de_DE.UTF-8", "bar"));
+        assert!(!got.contains_key(LC_CTYPE));
+        let got = ssh_env_vars(&BTreeMap::from([("LANG".into(), "C".into())]));
+        assert_eq!(got["LANG"], "C");
+        assert!(!got.contains_key(LC_CTYPE));
+    }
+
+    #[test]
+    fn ssh_env_adds_utf8_lc_ctype_by_default() {
+        let got = ssh_env_vars(&BTreeMap::from([("FOO".into(), "bar".into())]));
+        assert_eq!(got["FOO"], "bar");
+        assert!(is_utf8_locale(&got[LC_CTYPE]));
+    }
+}
diff --git a/rust/core/src/updater.rs b/rust/core/src/updater.rs
new file mode 100644
index 0000000..4e64099
--- /dev/null
+++ b/rust/core/src/updater.rs
@@ -0,0 +1,302 @@
+//! Update checks against a self-hosted manifest (or, as a fallback, GitHub's latest release).
+//! Opt-in and check-only: nothing is downloaded or installed. Calls block; run them off the UI
+//! thread.
+
+use crate::Result;
+use serde::{Deserialize, Serialize};
+use std::io::Read;
+use std::time::Duration;
+
+/// Manifest URL template; expand with [`expand_update_url`].
+pub const DEFAULT_UPDATE_URL: &str = "https://alchementary.co.uk/download/link/manifest-{platform}-{arch}.json";
+const GITHUB_OWNER: &str = "nexus-terminal";
+const GITHUB_REPO: &str = "nexus-terminal";
+const USER_AGENT: &str = "NexusTerminal-UpdateChecker";
+const REQUEST_TIMEOUT: Duration = Duration::from_secs(10);
+const MAX_UPDATE_RESPONSE_BYTES: usize = 1 << 20;
+
+#[derive(Clone, Debug, PartialEq, Default, Serialize)]
+#[serde(rename_all = "camelCase")]
+pub struct UpdateInfo {
+    pub available: bool,
+    pub current_version: String,
+    pub latest_version: String,
+    #[serde(rename = "releaseURL")]
+    pub release_url: String,
+    pub release_name: String,
+    pub release_notes: String,
+    pub published_at: String,
+}
+
+#[derive(Deserialize, Default)]
+#[serde(default)]
+struct Release {
+    tag_name: String,
+    name: String,
+    html_url: String,
+    published_at: String,
+    body: String,
+    prerelease: bool,
+    draft: bool,
+}
+
+#[derive(Deserialize, Default)]
+#[serde(default, rename_all = "camelCase")]
+struct Manifest {
+    latest_version: String,
+    version: String,
+    #[serde(rename = "releaseURL")]
+    release_url: String,
+    release_name: String,
+    release_notes: String,
+    published_at: String,
+}
+
+/// Fills `{platform}`/`{os}` and `{arch}` with Go's GOOS/GOARCH names, which the published
+/// manifest file names use.
+pub fn expand_update_url(template: &str) -> String {
+    let os = match std::env::consts::OS {
+        "macos" => "darwin",
+        o => o,
+    };
+    let arch = match std::env::consts::ARCH {
+        "x86_64" => "amd64",
+        "aarch64" => "arm64",
+        "x86" => "386",
+        a => a,
+    };
+    template.replace("{platform}", os).replace("{os}", os).replace("{arch}", arch)
+}
+
+/// GET with the updater headers; the body is read (bounded) only on 200.
+fn fetch(url: &str, accept: &str) -> Result<(u16, Vec<u8>)> {
+    let agent: ureq::Agent = ureq::Agent::config_builder()
+        .timeout_global(Some(REQUEST_TIMEOUT))
+        .http_status_as_error(false)
+        .build()
+        .into();
+    let resp = agent
+        .get(url)
+        .header("Accept", accept)
+        .header("User-Agent", USER_AGENT)
+        .call()
+        .map_err(|e| format!("updater: request failed: {e}"))?;
+    let status = resp.status().as_u16();
+    if status != 200 {
+        return Ok((status, vec![]));
+    }
+    let mut body = Vec::new();
+    resp.into_body()
+        .into_reader()
+        .take(MAX_UPDATE_RESPONSE_BYTES as u64 + 1)
+        .read_to_end(&mut body)
+        .map_err(|e| format!("updater: failed to read response: {e}"))?;
+    if body.len() > MAX_UPDATE_RESPONSE_BYTES {
+        return Err(format!("updater: failed to read response: response exceeds {MAX_UPDATE_RESPONSE_BYTES} bytes").into());
+    }
+    Ok((status, body))
+}
+
+/// Checks a manifest URL. The body is either a JSON manifest (`latestVersion` or `version`, plus
+/// optional `releaseURL`, `releaseName`, `releaseNotes`, `publishedAt`) or a bare version string.
+pub fn check_url(url: &str, current_version: &str) -> Result<UpdateInfo> {
+    if url.is_empty() {
+        return Err("updater: update manifest URL is empty".into());
+    }
+    let current = normalise_version(current_version);
+    let (status, body) = fetch(url, "application/json, text/plain")?;
+    if status != 200 {
+        return Err(format!("updater: update server returned {status}").into());
+    }
+    if let Some(info) = parse_manifest(&body, &current) {
+        return Ok(info);
+    }
+    let latest = normalise_version(&String::from_utf8_lossy(&body));
+    if latest.is_empty() {
+        return Err("updater: update manifest is empty".into());
+    }
+    Ok(UpdateInfo { available: is_newer(&latest, &current), current_version: current, latest_version: latest, ..Default::default() })
+}
+
+/// Checks the latest GitHub release of `nexus-terminal/nexus-terminal`.
+pub fn check_github(current_version: &str) -> Result<UpdateInfo> {
+    let current = normalise_version(current_version);
+    let url = format!("https://api.github.com/repos/{GITHUB_OWNER}/{GITHUB_REPO}/releases/latest");
+    let (status, body) = fetch(&url, "application/vnd.github+json")?;
+    if status == 404 {
+        // No releases yet.
+        return Ok(UpdateInfo { latest_version: current.clone(), current_version: current, ..Default::default() });
+    }
+    if status != 200 {
+        return Err(format!("updater: GitHub API returned {status}").into());
+    }
+    let release: Release =
+        serde_json::from_slice(&body).map_err(|e| format!("updater: failed to decode response: {e}"))?;
+    let latest = normalise_version(&release.tag_name);
+    if release.draft || release.prerelease {
+        return Ok(UpdateInfo { current_version: current, latest_version: latest, ..Default::default() });
+    }
+    Ok(UpdateInfo {
+        available: is_newer(&latest, &current),
+        current_version: current,
+        latest_version: latest,
+        release_url: release.html_url,
+        release_name: release.name,
+        release_notes: truncate_notes(&release.body, 500),
+        published_at: release.published_at,
+    })
+}
+
+fn normalise_version(v: &str) -> String {
+    let v = v.trim();
+    v.strip_prefix('v').unwrap_or(v).to_string()
+}
+
+fn parse_manifest(body: &[u8], current: &str) -> Option<UpdateInfo> {
+    let m: Manifest = serde_json::from_slice(body).ok()?;
+    let latest = normalise_version(if m.latest_version.is_empty() { &m.version } else { &m.latest_version });
+    if latest.is_empty() {
+        return None;
+    }
+    Some(UpdateInfo {
+        available: is_newer(&latest, current),
+        current_version: current.into(),
+        latest_version: latest,
+        release_url: m.release_url,
+        release_name: m.release_name,
+        release_notes: m.release_notes,
+        published_at: m.published_at,
+    })
+}
+
+/// Compares dot-separated numeric parts (leading integer of each part, else 0). Dev builds and an
+/// empty current version never see updates.
+fn is_newer(latest: &str, current: &str) -> bool {
+    if current.is_empty() || current == "dev" {
+        return false;
+    }
+    let l: Vec<&str> = latest.split('.').collect();
+    let c: Vec<&str> = current.split('.').collect();
+    for i in 0..l.len().max(c.len()) {
+        let (lv, cv) = (leading_int(l.get(i)), leading_int(c.get(i)));
+        if lv != cv {
+            return lv > cv;
+        }
+    }
+    false
+}
+
+/// Go's `fmt.Sscanf(s, "%d")`: optional sign then digits; anything else is 0.
+fn leading_int(s: Option<&&str>) -> i64 {
+    let s = s.map_or("", |s| s.trim_start());
+    let end = s
+        .char_indices()
+        .find(|&(i, c)| !(c.is_ascii_digit() || (i == 0 && (c == '+' || c == '-'))))
+        .map_or(s.len(), |(i, _)| i);
+    s[..end].parse().unwrap_or(0)
+}
+
+/// Cuts at `max` bytes (backing off to a char boundary) and appends "…".
+fn truncate_notes(body: &str, max: usize) -> String {
+    if body.len() <= max {
+        return body.into();
+    }
+    let mut i = max;
+    while !body.is_char_boundary(i) {
+        i -= 1;
+    }
+    format!("{}…", &body[..i])
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::io::Write;
+
+    /// Serves one HTTP response on a random local port; returns its URL.
+    fn serve_once(content_type: &'static str, body: Vec<u8>) -> String {
+        let l = std::net::TcpListener::bind("127.0.0.1:0").unwrap();
+        let url = format!("http://{}/", l.local_addr().unwrap());
+        std::thread::spawn(move || {
+            let (mut s, _) = l.accept().unwrap();
+            let mut req: Vec<u8> = Vec::new();
+            let mut buf = [0u8; 1024];
+            while !req.windows(4).any(|w| w == b"\r\n\r\n") {
+                let n = s.read(&mut buf).unwrap();
+                if n == 0 {
+                    break;
+                }
+                req.extend(&buf[..n]);
+            }
+            let head = format!(
+                "HTTP/1.1 200 OK\r\nContent-Type: {content_type}\r\nContent-Length: {}\r\nConnection: close\r\n\r\n",
+                body.len()
+            );
+            let _ = s.write_all(head.as_bytes());
+            let _ = s.write_all(&body);
+        });
+        url
+    }
+
+    #[test]
+    fn normalises_versions() {
+        for (i, w) in [("v1.2.3", "1.2.3"), ("1.2.3", "1.2.3"), (" v0.5.0 ", "0.5.0"), ("dev", "dev")] {
+            assert_eq!(normalise_version(i), w);
+        }
+    }
+
+    #[test]
+    fn compares_versions() {
+        for (l, c, w) in [
+            ("1.1.0", "1.0.0", true),
+            ("2.0.0", "1.9.9", true),
+            ("1.0.1", "1.0.0", true),
+            ("1.0.0", "1.0.0", false),
+            ("0.9.0", "1.0.0", false),
+            ("1.0.0", "dev", false),
+            ("1.0.0", "", false),
+            ("1.2", "1.1.0", true),
+            ("1.0.0", "1.0.0.1", false),
+            ("1.3.0-beta", "1.2.9", true),
+        ] {
+            assert_eq!(is_newer(l, c), w, "{l} vs {c}");
+        }
+    }
+
+    #[test]
+    fn truncates_notes() {
+        assert_eq!(truncate_notes("Short note", 100), "Short note");
+        let got = truncate_notes(&"x".repeat(600), 500);
+        assert!(got.ends_with('…'));
+        assert_eq!(got.chars().count(), 501);
+        assert_eq!(truncate_notes("aé", 2), "a…");
+    }
+
+    #[test]
+    fn expands_url_template() {
+        let u = expand_update_url(DEFAULT_UPDATE_URL);
+        assert!(!u.contains('{') && !u.contains("macos") && !u.contains("x86_64"), "{u}");
+    }
+
+    #[test]
+    fn url_manifest_json() {
+        let url = serve_once("application/json", br#"{"latestVersion":"1.2.3","releaseURL":"https://example.com/release"}"#.to_vec());
+        let info = check_url(&url, "1.2.0").unwrap();
+        assert!(info.available);
+        assert_eq!(info.latest_version, "1.2.3");
+        assert_eq!(info.release_url, "https://example.com/release");
+    }
+
+    #[test]
+    fn url_plain_text() {
+        let url = serve_once("text/plain", b"2.0.0".to_vec());
+        assert!(check_url(&url, "1.9.0").unwrap().available);
+    }
+
+    #[test]
+    fn url_rejects_oversized_manifest() {
+        let url = serve_once("text/plain", vec![b'x'; MAX_UPDATE_RESPONSE_BYTES + 1]);
+        let err = check_url(&url, "1.9.0").unwrap_err();
+        assert!(err.to_string().contains("response exceeds"), "{err}");
+    }
+}
diff --git a/rust/core/src/validation.rs b/rust/core/src/validation.rs
new file mode 100644
index 0000000..f5866f1
--- /dev/null
+++ b/rust/core/src/validation.rs
@@ -0,0 +1,573 @@
+//! Field-level validation of profiles and their protocol configs. Enum-typed fields (secret modes,
+//! host-key policy, line endings, forward direction, protocol) can't hold invalid values in Rust,
+//! so the Go checks for those are enforced by the types instead.
+
+use crate::models::{GitHubConfig, IrcConfig, Profile, Protocol, RawConfig, SerialConfig, SshConfig, TelnetConfig, VncConfig};
+use serde::Serialize;
+use std::fmt;
+
+#[derive(Clone, Debug, PartialEq, Serialize)]
+pub struct ValidationError {
+    pub field: String,
+    pub message: String,
+}
+
+impl fmt::Display for ValidationError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{}: {}", self.field, self.message)
+    }
+}
+impl std::error::Error for ValidationError {}
+
+#[derive(Clone, Debug, PartialEq, Default, Serialize)]
+pub struct ValidationErrors {
+    pub errors: Vec<ValidationError>,
+}
+
+impl fmt::Display for ValidationErrors {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let msgs: Vec<String> = self.errors.iter().map(|e| e.to_string()).collect();
+        write!(f, "validation failed: {}", msgs.join("; "))
+    }
+}
+impl std::error::Error for ValidationErrors {}
+
+impl ValidationErrors {
+    pub fn add(&mut self, field: impl Into<String>, message: impl Into<String>) {
+        self.errors.push(ValidationError { field: field.into(), message: message.into() });
+    }
+    fn into_result(self) -> Result<(), ValidationErrors> {
+        if self.errors.is_empty() { Ok(()) } else { Err(self) }
+    }
+    fn merge(&mut self, r: Result<(), ValidationErrors>) {
+        if let Err(e) = r {
+            self.errors.extend(e.errors);
+        }
+    }
+    /// Adds `r`'s message (if any) under `field`.
+    fn check(&mut self, field: &str, r: Result<(), ValidationError>) {
+        if let Err(e) = r {
+            self.add(field, e.message);
+        }
+    }
+}
+
+fn err(field: &str, message: &str) -> Result<(), ValidationError> {
+    Err(ValidationError { field: field.into(), message: message.into() })
+}
+
+pub fn validate_profile(p: &Profile) -> Result<(), ValidationErrors> {
+    let mut errs = ValidationErrors::default();
+    if p.id.trim().is_empty() {
+        errs.add("id", "profile ID must not be empty");
+    }
+    if p.display_name.trim().is_empty() {
+        errs.add("displayName", "display name must not be empty");
+    }
+
+    match p.protocol {
+        Protocol::Ssh => {
+            host_port(&mut errs, &p.host, p.port);
+            if p.username.trim().is_empty() {
+                errs.add("username", "username is required for SSH connections");
+            } else {
+                errs.check("username", validate_username(&p.username));
+            }
+            match &p.ssh {
+                None => errs.add("ssh", "SSH configuration is required for SSH protocol"),
+                Some(c) => errs.merge(validate_ssh_config(c)),
+            }
+        }
+        Protocol::Telnet => {
+            host_port(&mut errs, &p.host, p.port);
+            match &p.telnet {
+                None => errs.add("telnet", "Telnet configuration is required for Telnet protocol"),
+                Some(c) => errs.merge(validate_telnet_config(c)),
+            }
+        }
+        Protocol::Raw => {
+            host_port(&mut errs, &p.host, p.port);
+            match &p.raw {
+                None => errs.add("raw", "RAW configuration is required for RAW protocol"),
+                Some(c) => errs.merge(validate_raw_config(c)),
+            }
+        }
+        Protocol::Github => match &p.github {
+            None => errs.add("github", "GitHub configuration is required for GitHub protocol"),
+            Some(c) => errs.merge(validate_github_config(c)),
+        },
+        Protocol::Vnc => match &p.vnc {
+            None => errs.add("vnc", "VNC configuration is required for VNC protocol"),
+            Some(c) => errs.merge(validate_vnc_config(&p.host, c)),
+        },
+        Protocol::Irc => {
+            host_port(&mut errs, &p.host, p.port);
+            match &p.irc {
+                None => errs.add("irc", "IRC configuration is required for IRC protocol"),
+                Some(c) => errs.merge(validate_irc_config(c)),
+            }
+        }
+        Protocol::Serial => {
+            if p.host.trim().is_empty() {
+                errs.add("host", "serial device path must not be empty");
+            }
+            match &p.serial {
+                None => errs.add("serial", "Serial configuration is required for Serial protocol"),
+                Some(c) => errs.merge(validate_serial_config(c)),
+            }
+        }
+        Protocol::Local => errs.add("protocol", format!("unsupported protocol {:?}", p.protocol.id())),
+    }
+
+    if p.connect_timeout < 0 {
+        errs.add("connectTimeout", "connect timeout must not be negative");
+    }
+    if p.read_timeout < 0 {
+        errs.add("readTimeout", "read timeout must not be negative");
+    }
+    if !(1..=72).contains(&p.terminal_font_size) {
+        errs.add("terminalFontSize", "font size must be between 1 and 72");
+    }
+    if p.terminal_scrollback < 0 {
+        errs.add("terminalScrollback", "scrollback must not be negative");
+    }
+    errs.into_result()
+}
+
+fn host_port(errs: &mut ValidationErrors, host: &str, port: i64) {
+    errs.check("host", validate_host(host));
+    errs.check("port", validate_port(port));
+}
+
+/// Non-empty, no whitespace, no URI scheme, no leading hyphen.
+pub fn validate_host(host: &str) -> Result<(), ValidationError> {
+    let h = host.trim();
+    if h.is_empty() {
+        return err("host", "host must not be empty");
+    }
+    if h.contains([' ', '\t', '\n', '\r']) {
+        return err("host", "host must not contain whitespace");
+    }
+    if h.contains("://") {
+        return err("host", "host must not include a URI scheme");
+    }
+    // An IP address never starts with '-', so this only rejects hostnames (as in Go).
+    if h.starts_with('-') {
+        return err("host", "host must not begin with a hyphen");
+    }
+    Ok(())
+}
+
+pub fn validate_port(port: i64) -> Result<(), ValidationError> {
+    if !(1..=65535).contains(&port) {
+        return err("port", "port must be between 1 and 65535");
+    }
+    Ok(())
+}
+
+/// Non-empty and free of control characters.
+pub fn validate_username(username: &str) -> Result<(), ValidationError> {
+    let u = username.trim();
+    if u.is_empty() {
+        return err("username", "username must not be empty");
+    }
+    if u.chars().any(is_control) {
+        return err("username", "username must not contain control characters");
+    }
+    Ok(())
+}
+
+fn is_control(c: char) -> bool {
+    c < '\x20' || c == '\x7f'
+}
+
+pub fn validate_ssh_config(cfg: &SshConfig) -> Result<(), ValidationErrors> {
+    let mut errs = ValidationErrors::default();
+    if cfg.auth_methods.is_empty() {
+        errs.add("ssh.authMethods", "at least one authentication method is required");
+    }
+    for m in &cfg.auth_methods {
+        if !matches!(m.as_str(), "password" | "publickey" | "keyboard-interactive") {
+            errs.add("ssh.authMethods", format!("unsupported authentication method {m:?}"));
+        }
+    }
+    if cfg.keepalive_interval < 0 {
+        errs.add("ssh.keepaliveInterval", "keepalive interval must not be negative");
+    }
+    if cfg.keepalive_count_max < 0 {
+        errs.add("ssh.keepaliveCountMax", "keepalive count max must not be negative");
+    }
+    for (i, jh) in cfg.jump_hosts.iter().enumerate() {
+        let prefix = format!("ssh.jumpHosts[{i}]");
+        if jh.host.trim().is_empty() {
+            errs.add(format!("{prefix}.host"), "jump host address must not be empty");
+        }
+        if !(1..=65535).contains(&jh.port) {
+            errs.add(format!("{prefix}.port"), "jump host port must be between 1 and 65535");
+        }
+        if jh.username.trim().is_empty() {
+            errs.add(format!("{prefix}.username"), "jump host username must not be empty");
+        }
+    }
+    for (i, pf) in cfg.port_forwards.iter().enumerate() {
+        let prefix = format!("ssh.portForwards[{i}]");
+        if !(1..=65535).contains(&pf.bind_port) {
+            errs.add(format!("{prefix}.bindPort"), "bind port must be between 1 and 65535");
+        }
+        if !(1..=65535).contains(&pf.dest_port) {
+            errs.add(format!("{prefix}.destPort"), "destination port must be between 1 and 65535");
+        }
+        if pf.dest_host.trim().is_empty() {
+            errs.add(format!("{prefix}.destHost"), "destination host must not be empty");
+        }
+    }
+    errs.into_result()
+}
+
+pub fn validate_telnet_config(cfg: &TelnetConfig) -> Result<(), ValidationErrors> {
+    let mut errs = ValidationErrors::default();
+    if cfg.encoding.trim().is_empty() {
+        errs.add("telnet.encoding", "encoding must not be empty");
+    }
+    errs.into_result()
+}
+
+pub fn validate_raw_config(cfg: &RawConfig) -> Result<(), ValidationErrors> {
+    let mut errs = ValidationErrors::default();
+    if cfg.encoding.trim().is_empty() {
+        errs.add("raw.encoding", "encoding must not be empty");
+    }
+    for (i, preset) in cfg.payload_presets.iter().enumerate() {
+        let prefix = format!("raw.payloadPresets[{i}]");
+        if preset.name.trim().is_empty() {
+            errs.add(format!("{prefix}.name"), "payload preset name must not be empty");
+        }
+        if !matches!(preset.format.as_str(), "text" | "hex" | "escaped") {
+            errs.add(format!("{prefix}.format"), format!("unsupported payload format {:?}", preset.format));
+        }
+    }
+    errs.into_result()
+}
+
+/// The API base URL must be absolute HTTPS (HTTP only to loopback) without credentials.
+pub fn validate_github_config(cfg: &GitHubConfig) -> Result<(), ValidationErrors> {
+    let mut errs = ValidationErrors::default();
+    match split_url(cfg.base_url.trim()) {
+        None => errs.add("github.baseURL", "API base URL must be an absolute HTTPS URL"),
+        Some((scheme, has_user, hostname)) => {
+            if has_user {
+                errs.add("github.baseURL", "API base URL must not include credentials");
+            }
+            if scheme != "https" && !(scheme == "http" && is_loopback_host(hostname)) {
+                errs.add("github.baseURL", "API base URL must use HTTPS unless it points to loopback");
+            }
+        }
+    }
+    if cfg.refresh_interval_secs != 0 && cfg.refresh_interval_secs < 60 {
+        errs.add("github.refreshIntervalSecs", "refresh interval must be at least 60 seconds");
+    }
+    errs.into_result()
+}
+
+/// (lowercased scheme, has userinfo, hostname without port/brackets) of an absolute URL.
+fn split_url(s: &str) -> Option<(String, bool, &str)> {
+    let (scheme, rest) = s.split_once("://")?;
+    if scheme.is_empty() {
+        return None;
+    }
+    let authority = &rest[..rest.find(['/', '?', '#']).unwrap_or(rest.len())];
+    let (has_user, host) = match authority.rsplit_once('@') {
+        Some((_, h)) => (true, h),
+        None => (false, authority),
+    };
+    if host.is_empty() {
+        return None;
+    }
+    let hostname = match host.strip_prefix('[') {
+        Some(h) => h.split(']').next().unwrap_or(h),
+        None => host.rsplit_once(':').map_or(host, |(h, _)| h),
+    };
+    Some((scheme.to_ascii_lowercase(), has_user, hostname))
+}
+
+fn is_loopback_host(host: &str) -> bool {
+    let h = host.trim().to_lowercase();
+    h == "localhost" || h.parse::<std::net::IpAddr>().is_ok_and(|ip| ip.to_canonical().is_loopback())
+}
+
+/// The VNC host falls back to the profile host.
+pub fn validate_vnc_config(profile_host: &str, cfg: &VncConfig) -> Result<(), ValidationErrors> {
+    let mut errs = ValidationErrors::default();
+    let host = if cfg.vnc_host.trim().is_empty() { profile_host } else { &cfg.vnc_host };
+    errs.check("vnc.vncHost", validate_host(host));
+    errs.check("vnc.vncPort", validate_port(cfg.vnc_port));
+    if !(0..=9).contains(&cfg.quality) {
+        errs.add("vnc.quality", "quality must be between 0 and 9");
+    }
+    if cfg.ssh_tunnel {
+        ssh_tunnel(&mut errs, "vnc", &cfg.ssh_host, cfg.ssh_port, &cfg.ssh_username, &cfg.ssh_auth_method);
+    }
+    errs.into_result()
+}
+
+fn ssh_tunnel(errs: &mut ValidationErrors, p: &str, host: &str, port: i64, user: &str, auth: &str) {
+    errs.check(&format!("{p}.sshHost"), validate_host(host));
+    errs.check(&format!("{p}.sshPort"), validate_port(port));
+    if user.trim().is_empty() {
+        errs.add(format!("{p}.sshUsername"), "SSH username is required when tunnelling");
+    } else {
+        errs.check(&format!("{p}.sshUsername"), validate_username(user));
+    }
+    if auth != "password" && auth != "publickey" {
+        errs.add(format!("{p}.sshAuthMethod"), format!("unsupported SSH auth method {auth:?}"));
+    }
+}
+
+pub fn validate_irc_config(cfg: &IrcConfig) -> Result<(), ValidationErrors> {
+    let mut errs = ValidationErrors::default();
+    let nick = cfg.nick.trim();
+    if nick.is_empty() {
+        errs.add("irc.nick", "nickname is required");
+    } else if !is_valid_nick(nick) {
+        errs.add("irc.nick", "nickname is not valid for IRC");
+    }
+    if cfg.real_name.contains(['\r', '\n', '\0']) {
+        errs.add("irc.realName", "real name must not contain control characters");
+    }
+    if cfg.nick_serv_identify && cfg.nick_serv_account.chars().any(is_control) {
+        errs.add("irc.nickServAccount", "NickServ account must not contain control characters");
+    }
+    let mut seen = std::collections::HashSet::new();
+    for (i, room) in cfg.auto_join_rooms.iter().enumerate() {
+        let field = format!("irc.autoJoinRooms[{i}]");
+        let name = room.trim();
+        if name.is_empty() {
+            errs.add(field, "room name must not be empty");
+            continue;
+        }
+        if !is_valid_channel(name) {
+            errs.add(field.clone(), "room name must start with a valid IRC channel prefix");
+        }
+        if !seen.insert(name.to_lowercase()) {
+            errs.add(field, "room is listed more than once");
+        }
+    }
+    if cfg.ssh_tunnel {
+        ssh_tunnel(&mut errs, "irc", &cfg.ssh_host, cfg.ssh_port, &cfg.ssh_username, &cfg.ssh_auth_method);
+    }
+    if cfg.max_reconnect_tries < 0 {
+        errs.add("irc.maxReconnectTries", "max reconnect attempts must not be negative");
+    }
+    errs.into_result()
+}
+
+/// Device path lives in `Profile::host` and is checked by `validate_profile`.
+pub fn validate_serial_config(cfg: &SerialConfig) -> Result<(), ValidationErrors> {
+    let mut errs = ValidationErrors::default();
+    if cfg.baud_rate == 0 {
+        errs.add("serial.baudRate", "baud rate must be greater than 0");
+    }
+    if !(5..=8).contains(&cfg.data_bits) {
+        errs.add("serial.dataBits", "data bits must be between 5 and 8");
+    }
+    if cfg.stop_bits != 1 && cfg.stop_bits != 2 {
+        errs.add("serial.stopBits", "stop bits must be 1 or 2");
+    }
+    errs.into_result()
+}
+
+/// girc's IsValidNick: first byte in 'A'..='}' or '?', the rest also digits or '-'.
+fn is_valid_nick(nick: &str) -> bool {
+    let b = nick.as_bytes();
+    let Some((&first, rest)) = b.split_first() else { return false };
+    ((b'A'..=b'}').contains(&first) || first == b'?')
+        && rest.iter().all(|c| (b'A'..=b'}').contains(c) || c.is_ascii_digit() || *c == b'-')
+}
+
+/// girc's IsValidChannel.
+fn is_valid_channel(ch: &str) -> bool {
+    let b = ch.as_bytes();
+    if b.len() <= 1 || b.len() > 50 || !b"!#&*~+".contains(&b[0]) {
+        return false;
+    }
+    // !<5-char ID><name>
+    if b[0] == b'!' && (b.len() < 7 || !b[1..6].iter().all(|c| c.is_ascii_digit() || c.is_ascii_uppercase())) {
+        return false;
+    }
+    !b[1..].iter().any(|c| [0x00, 0x07, 0x0d, 0x0a, 0x20, 0x2c, 0x3a].contains(c))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::models::{JumpHost, PayloadPreset};
+
+    #[test]
+    fn hosts() {
+        for (h, ok) in [
+            ("example.com", true),
+            ("192.168.1.1", true),
+            ("::1", true),
+            ("", false),
+            ("   ", false),
+            ("host name", false),
+            ("host\tname", false),
+            ("ssh://example.com", false),
+            ("-bad-host", false),
+            ("server.internal.corp", true),
+        ] {
+            assert_eq!(validate_host(h).is_ok(), ok, "{h:?}");
+        }
+    }
+
+    #[test]
+    fn ports() {
+        for (p, ok) in [(1, true), (22, true), (443, true), (65535, true), (0, false), (-1, false), (65536, false), (99999, false)] {
+            assert_eq!(validate_port(p).is_ok(), ok, "{p}");
+        }
+    }
+
+    #[test]
+    fn usernames() {
+        for (u, ok) in [
+            ("admin", true),
+            ("", false),
+            ("   ", false),
+            ("my user", true),
+            ("abcdefghijklmnopqrstuvwxyz0123456789abcdefghijklmnopqrstuvwxyz0123456789", true),
+            ("bad\x01user", false),
+            ("bad\x7fuser", false),
+        ] {
+            assert_eq!(validate_username(u).is_ok(), ok, "{u:?}");
+        }
+    }
+
+    fn ssh() -> Profile {
+        let mut p = Profile::new(Protocol::Ssh);
+        p.display_name = "Test SSH".into();
+        p.host = "example.com".into();
+        p.username = "root".into();
+        p
+    }
+
+    #[test]
+    fn profiles() {
+        let mut telnet = Profile::new(Protocol::Telnet);
+        telnet.display_name = "Test Telnet".into();
+        telnet.host = "switch.local".into();
+        let mut raw = Profile::new(Protocol::Raw);
+        raw.display_name = "Test RAW".into();
+        raw.host = "device.local".into();
+        let mut vnc = Profile::new(Protocol::Vnc);
+        vnc.display_name = "Test VNC".into();
+        vnc.vnc.as_mut().unwrap().vnc_host = "desktop.local".into();
+        for p in [ssh(), telnet, raw, vnc] {
+            assert!(validate_profile(&p).is_ok(), "{:?}", validate_profile(&p));
+        }
+
+        let bad: [fn(&mut Profile); 7] = [
+            |p| p.host.clear(),
+            |p| p.port = 0,
+            |p| p.protocol = Protocol::Local,
+            |p| p.username.clear(),
+            |p| p.ssh = None,
+            |p| p.connect_timeout = -1,
+            |p| p.terminal_font_size = 0,
+        ];
+        for (i, f) in bad.iter().enumerate() {
+            let mut p = ssh();
+            f(&mut p);
+            assert!(validate_profile(&p).is_err(), "case {i}");
+        }
+    }
+
+    #[test]
+    fn serial_profiles() {
+        let mut p = Profile::new(Protocol::Serial);
+        p.display_name = "Console".into();
+        p.host = "/dev/ttyUSB0".into();
+        assert!(validate_profile(&p).is_ok());
+        let bad: [fn(&mut Profile); 6] = [
+            |p| p.host = "  ".into(),
+            |p| p.serial = None,
+            |p| p.serial.as_mut().unwrap().baud_rate = 0,
+            |p| p.serial.as_mut().unwrap().data_bits = 4,
+            |p| p.serial.as_mut().unwrap().data_bits = 9,
+            |p| p.serial.as_mut().unwrap().stop_bits = 3,
+        ];
+        for (i, f) in bad.iter().enumerate() {
+            let mut q = p.clone();
+            f(&mut q);
+            assert!(validate_profile(&q).is_err(), "case {i}");
+        }
+    }
+
+    #[test]
+    fn github() {
+        let cfg = |url: &str, secs| GitHubConfig { base_url: url.into(), refresh_interval_secs: secs, ..Default::default() };
+        for (c, ok) in [
+            (cfg("https://api.github.com", 300), true),
+            (cfg("http://localhost:3000/api/v3", 60), true),
+            (cfg("http://[::1]:3000/api/v3", 60), true),
+            (cfg("http://127.0.0.1/api/v3", 0), true),
+            (cfg("http://evil.example/api/v3", 300), false),
+            (cfg("https://token@example.com/api/v3", 300), false),
+            (cfg("https://api.github.com", 1), false),
+            (cfg("api.github.com", 300), false),
+        ] {
+            assert_eq!(validate_github_config(&c).is_ok(), ok, "{c:?}");
+        }
+    }
+
+    #[test]
+    fn vnc() {
+        let base = VncConfig { vnc_port: 5900, quality: 6, ..Default::default() };
+        let named = VncConfig { vnc_host: "desktop.local".into(), ..base.clone() };
+        assert!(validate_vnc_config("", &named).is_ok());
+        assert!(validate_vnc_config("desktop.local", &base).is_ok());
+        assert!(validate_vnc_config("", &base).is_err());
+        let tunnel = VncConfig {
+            ssh_tunnel: true,
+            ssh_host: "jump.local".into(),
+            ssh_port: 22,
+            ssh_username: "admin".into(),
+            ssh_auth_method: "token".into(),
+            ..base
+        };
+        assert!(validate_vnc_config("desktop.local", &tunnel).is_err());
+    }
+
+    #[test]
+    fn ssh_configs() {
+        let valid = || SshConfig { auth_methods: vec!["password".into()], keepalive_interval: 30, keepalive_count_max: 3, ..Default::default() };
+        assert!(validate_ssh_config(&valid()).is_ok());
+        assert!(validate_ssh_config(&SshConfig { auth_methods: vec![], ..valid() }).is_err());
+        assert!(validate_ssh_config(&SshConfig { auth_methods: vec!["oauth".into()], ..valid() }).is_err());
+        assert!(validate_ssh_config(&SshConfig { jump_hosts: vec![JumpHost::default()], ..valid() }).is_err());
+    }
+
+    #[test]
+    fn telnet_and_raw() {
+        assert!(validate_telnet_config(&TelnetConfig { encoding: "utf-8".into(), ..Default::default() }).is_ok());
+        assert!(validate_telnet_config(&TelnetConfig::default()).is_err());
+        let raw = |presets| RawConfig { encoding: "utf-8".into(), payload_presets: presets, ..Default::default() };
+        let preset = |n: &str, f: &str| PayloadPreset { name: n.into(), format: f.into(), ..Default::default() };
+        assert!(validate_raw_config(&raw(vec![])).is_ok());
+        assert!(validate_raw_config(&RawConfig::default()).is_err());
+        assert!(validate_raw_config(&raw(vec![preset("ping", "binary")])).is_err());
+        assert!(validate_raw_config(&raw(vec![preset("", "text")])).is_err());
+    }
+
+    #[test]
+    fn irc() {
+        let ok = IrcConfig { nick: "nexus".into(), auto_join_rooms: vec!["#rust".into(), "&local".into()], ..Default::default() };
+        assert!(validate_irc_config(&ok).is_ok());
+        for nick in ["", "1abc", "bad nick"] {
+            assert!(validate_irc_config(&IrcConfig { nick: nick.into(), ..ok.clone() }).is_err(), "{nick:?}");
+        }
+        for rooms in [vec!["rust"], vec!["#"], vec!["#a,b"], vec!["#rust", "#RUST"], vec![" "]] {
+            let c = IrcConfig { auto_join_rooms: rooms.iter().map(|r| r.to_string()).collect(), ..ok.clone() };
+            assert!(validate_irc_config(&c).is_err(), "{rooms:?}");
+        }
+    }
+}