diff --git a/crates/relicario-cli/src/main.rs b/crates/relicario-cli/src/main.rs
index a613c66..a1d056b 100644
--- a/crates/relicario-cli/src/main.rs
+++ b/crates/relicario-cli/src/main.rs
@@ -38,6 +38,7 @@
 //! creates a git commit, preserving an audit log of all vault changes.
 
 mod helpers;
+mod session;
 
 use anyhow::{bail, Context, Result};
 use clap::{Parser, Subcommand};
diff --git a/crates/relicario-cli/src/session.rs b/crates/relicario-cli/src/session.rs
new file mode 100644
index 0000000..672b81f
--- /dev/null
+++ b/crates/relicario-cli/src/session.rs
@@ -0,0 +1,139 @@
+//! Unlocked-vault session: the shape every vault-mutating command works with.
+//!
+//! Holds the derived master key in `Zeroizing<[u8; 32]>` for the lifetime of a
+//! CLI invocation. Drops it (via Zeroize) when the struct goes out of scope.
+
+use std::fs;
+use std::path::{Path, PathBuf};
+
+use anyhow::{bail, Context, Result};
+use zeroize::Zeroizing;
+
+use relicario_core::{
+    decrypt_item, decrypt_manifest, decrypt_settings,
+    derive_master_key, encrypt_item, encrypt_manifest, encrypt_settings,
+    imgsecret, Item, ItemId, KdfParams, Manifest, VaultSettings,
+};
+
+use crate::helpers::vault_dir;
+
+/// A vault whose master key has been derived and is held in memory.
+/// The key is wiped via `Zeroize` when this struct drops.
+pub struct UnlockedVault {
+    root: PathBuf,
+    master_key: Zeroizing<[u8; 32]>,
+}
+
+impl UnlockedVault {
+    pub fn root(&self) -> &Path { &self.root }
+    pub fn key(&self) -> &Zeroizing<[u8; 32]> { &self.master_key }
+
+    /// Full interactive unlock flow: locate vault, prompt passphrase, locate
+    /// reference image, derive master key.
+    pub fn unlock_interactive() -> Result<Self> {
+        let root = vault_dir()?;
+        let salt = read_salt(&root)?;
+        let params = read_params(&root)?;
+        let image_path = get_image_path()?;
+        let image_bytes = fs::read(&image_path)
+            .with_context(|| format!("failed to read reference image {}", image_path.display()))?;
+        let image_secret = imgsecret::extract(&image_bytes)?;
+
+        let passphrase = Zeroizing::new(
+            rpassword::prompt_password("Passphrase: ")
+                .context("failed to read passphrase")?
+        );
+
+        let master_key = derive_master_key(
+            passphrase.as_bytes(),
+            &image_secret,
+            &salt,
+            &params,
+        )?;
+
+        Ok(Self { root, master_key })
+    }
+
+    pub fn manifest_path(&self) -> PathBuf { self.root.join("manifest.enc") }
+    pub fn settings_path(&self) -> PathBuf { self.root.join("settings.enc") }
+    pub fn item_path(&self, id: &ItemId) -> PathBuf {
+        self.root.join("items").join(format!("{}.enc", id.as_str()))
+    }
+
+    pub fn load_manifest(&self) -> Result<Manifest> {
+        let bytes = fs::read(self.manifest_path()).context("failed to read manifest.enc")?;
+        Ok(decrypt_manifest(&bytes, &self.master_key)?)
+    }
+
+    pub fn save_manifest(&self, manifest: &Manifest) -> Result<()> {
+        let bytes = encrypt_manifest(manifest, &self.master_key)?;
+        atomic_write(&self.manifest_path(), &bytes)
+    }
+
+    pub fn load_settings(&self) -> Result<VaultSettings> {
+        let bytes = fs::read(self.settings_path()).context("failed to read settings.enc")?;
+        Ok(decrypt_settings(&bytes, &self.master_key)?)
+    }
+
+    pub fn save_settings(&self, settings: &VaultSettings) -> Result<()> {
+        let bytes = encrypt_settings(settings, &self.master_key)?;
+        atomic_write(&self.settings_path(), &bytes)
+    }
+
+    pub fn load_item(&self, id: &ItemId) -> Result<Item> {
+        let bytes = fs::read(self.item_path(id))
+            .with_context(|| format!("failed to read item {}", id.as_str()))?;
+        Ok(decrypt_item(&bytes, &self.master_key)?)
+    }
+
+    pub fn save_item(&self, item: &Item) -> Result<()> {
+        let path = self.item_path(&item.id);
+        if let Some(parent) = path.parent() { fs::create_dir_all(parent)?; }
+        let bytes = encrypt_item(item, &self.master_key)?;
+        atomic_write(&path, &bytes)
+    }
+}
+
+fn read_salt(root: &Path) -> Result<[u8; 32]> {
+    let data = fs::read(root.join(".relicario").join("salt"))
+        .context("failed to read .relicario/salt")?;
+    if data.len() != 32 { bail!("invalid salt length: {}", data.len()); }
+    let mut salt = [0u8; 32];
+    salt.copy_from_slice(&data);
+    Ok(salt)
+}
+
+fn read_params(root: &Path) -> Result<KdfParams> {
+    let s = fs::read_to_string(root.join(".relicario").join("params.json"))
+        .context("failed to read .relicario/params.json")?;
+    let params: KdfParams = serde_json::from_str(&s).context("failed to parse params.json")?;
+    Ok(params)
+}
+
+/// Locate the reference image path via `RELICARIO_IMAGE` env var or interactive prompt.
+pub fn get_image_path() -> Result<PathBuf> {
+    if let Ok(path) = std::env::var("RELICARIO_IMAGE") {
+        return Ok(PathBuf::from(path));
+    }
+    // Also accept <vault_root>/reference.jpg as a convention.
+    if let Ok(root) = vault_dir() {
+        let default = root.join("reference.jpg");
+        if default.exists() { return Ok(default); }
+    }
+    eprint!("Reference image path: ");
+    std::io::Write::flush(&mut std::io::stderr())?;
+    let mut line = String::new();
+    std::io::stdin().read_line(&mut line)?;
+    let trimmed = line.trim();
+    if trimmed.is_empty() { bail!("no reference image path provided"); }
+    Ok(PathBuf::from(trimmed))
+}
+
+/// Atomic write: write to <path>.tmp, then rename over <path>. Keeps the
+/// vault file consistent if we crash mid-write.
+fn atomic_write(path: &Path, data: &[u8]) -> Result<()> {
+    let tmp = path.with_extension("tmp");
+    fs::write(&tmp, data).with_context(|| format!("failed to write {}", tmp.display()))?;
+    fs::rename(&tmp, path).with_context(|| format!("failed to rename {}", path.display()))?;
+    Ok(())
+}