diff --git a/DEPENDENCIES.md b/DEPENDENCIES.md
index b2c9a7b..6800f6f 100644
--- a/DEPENDENCIES.md
+++ b/DEPENDENCIES.md
@@ -21,6 +21,7 @@ The current direct dependencies are:
 | [pgp 0.20](https://crates.io/crates/pgp/0.20.0) | Embedded OpenPGP key import, encryption, decryption, and signatures | MIT OR Apache-2.0 |
 | [rand 0.8](https://crates.io/crates/rand/0.8.7) | Operating-system-backed cryptographic randomness for OpenPGP operations | MIT OR Apache-2.0 |
 | [regex 1.13](https://crates.io/crates/regex/1.13.1) | Linear-time byte-oriented decrypted grep matching | MIT OR Apache-2.0 |
+| [tempfile 3](https://crates.io/crates/tempfile) | Permission-restricted CLI editor session directories and cleanup | MIT OR Apache-2.0 |
 | [Serde 1](https://crates.io/crates/serde), [TOML 0.9](https://crates.io/crates/toml), [shlex 1.3](https://crates.io/crates/shlex), [url 2.5](https://crates.io/crates/url) | Strict configuration and command values | MIT OR Apache-2.0 |
 | [UniFFI 0.32](https://crates.io/crates/uniffi/0.32.0) | Swift bridge | MPL-2.0 |
 | [zeroize 1.9](https://crates.io/crates/zeroize/1.9.0) | Clear decrypted bytes on drop | MIT OR Apache-2.0 |
diff --git a/README.md b/README.md
index 60d3ffa..bc9d56e 100644
--- a/README.md
+++ b/README.md
@@ -36,6 +36,8 @@ the rollback/commit contract are documented in
 [`docs/recipient-policies.md`](docs/recipient-policies.md).
 Typed list/show/find/decrypted-grep models and secret presentation selection are
 documented in [`docs/read-domains.md`](docs/read-domains.md).
+Insert modes, concurrency-safe edit sessions, and the secure CLI editor-file
+boundary are documented in [`docs/write-domains.md`](docs/write-domains.md).
 
 ## Project layout
 
diff --git a/apps/cli/Cargo.toml b/apps/cli/Cargo.toml
index 8af4c86..365ef4f 100644
--- a/apps/cli/Cargo.toml
+++ b/apps/cli/Cargo.toml
@@ -12,6 +12,6 @@ path = "src/main.rs"
 
 [dependencies]
 ironstorage.workspace = true
+tempfile = "3"
 
 [dev-dependencies]
-tempfile = "3"
diff --git a/apps/cli/src/editor.rs b/apps/cli/src/editor.rs
new file mode 100644
index 0000000..cd6f247
--- /dev/null
+++ b/apps/cli/src/editor.rs
@@ -0,0 +1,308 @@
+use std::{
+    error::Error,
+    ffi::OsString,
+    fmt, fs,
+    io::{self, Read as _, Seek as _, SeekFrom, Write as _},
+    path::{Path, PathBuf},
+};
+
+use ironstorage::{config::ResolvedEditor, repository::SecretBytes};
+
+const MAX_EDIT_BYTES: u64 = 16 * 1024 * 1024;
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub(crate) struct EditorInvocation {
+    program: String,
+    arguments: Vec<OsString>,
+    plaintext_path: PathBuf,
+}
+
+impl EditorInvocation {
+    pub(crate) fn program(&self) -> &str {
+        &self.program
+    }
+
+    pub(crate) fn arguments(&self) -> &[OsString] {
+        &self.arguments
+    }
+
+    pub(crate) fn plaintext_path(&self) -> &Path {
+        &self.plaintext_path
+    }
+}
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub(crate) enum EditorStatus {
+    Saved,
+    Cancelled,
+    Failed(i32),
+}
+
+/// Host boundary for the one CLI-only editor exception. Storage and other applications never
+/// receive an executable and tests can exercise the complete session without spawning a process.
+pub(crate) trait EditorHost {
+    fn edit(&mut self, invocation: &EditorInvocation) -> Result<EditorStatus, EditorHostError>;
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub(crate) struct EditorHostError;
+
+impl fmt::Display for EditorHostError {
+    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
+        formatter.write_str("editor host failed")
+    }
+}
+
+impl Error for EditorHostError {}
+
+pub(crate) fn edit_replacement(
+    plaintext: &SecretBytes,
+    editor: &ResolvedEditor,
+    host: &mut impl EditorHost,
+) -> Result<SecretBytes, CliEditorError> {
+    let temporary = create_secure_directory()?;
+    let path = temporary.path().join("entry.txt");
+    let mut file = create_private_file(&path)?;
+    let prepared = file
+        .write_all(plaintext.expose())
+        .and_then(|()| file.sync_all());
+    drop(file);
+    if prepared.is_err() {
+        let _ = wipe_and_remove(&path);
+        return Err(CliEditorError::TemporaryFile);
+    }
+
+    let command = editor.command();
+    let mut arguments = command
+        .arguments()
+        .iter()
+        .map(OsString::from)
+        .collect::<Vec<_>>();
+    arguments.push(path.clone().into_os_string());
+    let invocation = EditorInvocation {
+        program: command.program().to_owned(),
+        arguments,
+        plaintext_path: path.clone(),
+    };
+    let result = match host.edit(&invocation) {
+        Ok(EditorStatus::Saved) => {
+            restrict_file_permissions(&path).and_then(|()| read_replacement(&path))
+        }
+        Ok(EditorStatus::Cancelled) => Err(CliEditorError::Cancelled),
+        Ok(EditorStatus::Failed(code)) => Err(CliEditorError::Failed(code)),
+        Err(error) => Err(CliEditorError::Host(error)),
+    };
+    wipe_and_remove(&path)?;
+    result
+}
+
+fn create_secure_directory() -> Result<tempfile::TempDir, CliEditorError> {
+    #[cfg(target_os = "linux")]
+    if Path::new("/dev/shm").is_dir()
+        && let Ok(directory) = tempfile::Builder::new()
+            .prefix("ironstorage-edit-")
+            .tempdir_in("/dev/shm")
+    {
+        return Ok(directory);
+    }
+    tempfile::Builder::new()
+        .prefix("ironstorage-edit-")
+        .tempdir()
+        .map_err(|_| CliEditorError::TemporaryDirectory)
+}
+
+#[cfg(unix)]
+fn create_private_file(path: &Path) -> Result<fs::File, CliEditorError> {
+    use std::os::unix::fs::OpenOptionsExt as _;
+
+    fs::OpenOptions::new()
+        .create_new(true)
+        .read(true)
+        .write(true)
+        .mode(0o600)
+        .open(path)
+        .map_err(|_| CliEditorError::TemporaryFile)
+}
+
+#[cfg(not(unix))]
+fn create_private_file(path: &Path) -> Result<fs::File, CliEditorError> {
+    fs::OpenOptions::new()
+        .create_new(true)
+        .read(true)
+        .write(true)
+        .open(path)
+        .map_err(|_| CliEditorError::TemporaryFile)
+}
+
+fn read_replacement(path: &Path) -> Result<SecretBytes, CliEditorError> {
+    let metadata = fs::metadata(path).map_err(|_| CliEditorError::TemporaryFile)?;
+    if !metadata.is_file() || metadata.len() > MAX_EDIT_BYTES {
+        return Err(CliEditorError::ReplacementTooLarge);
+    }
+    let mut file = fs::File::open(path).map_err(|_| CliEditorError::TemporaryFile)?;
+    let mut bytes = Vec::with_capacity(metadata.len() as usize);
+    file.read_to_end(&mut bytes)
+        .map_err(|_| CliEditorError::TemporaryFile)?;
+    Ok(SecretBytes::new(bytes))
+}
+
+#[cfg(unix)]
+fn restrict_file_permissions(path: &Path) -> Result<(), CliEditorError> {
+    use std::os::unix::fs::PermissionsExt as _;
+
+    fs::set_permissions(path, fs::Permissions::from_mode(0o600))
+        .map_err(|_| CliEditorError::TemporaryFile)
+}
+
+#[cfg(not(unix))]
+fn restrict_file_permissions(_path: &Path) -> Result<(), CliEditorError> {
+    Ok(())
+}
+
+fn wipe_and_remove(path: &Path) -> Result<(), CliEditorError> {
+    let mut file = match fs::OpenOptions::new().read(true).write(true).open(path) {
+        Ok(file) => file,
+        Err(error) if error.kind() == io::ErrorKind::NotFound => return Ok(()),
+        Err(_) => return Err(CliEditorError::Cleanup),
+    };
+    let length = file.metadata().map_err(|_| CliEditorError::Cleanup)?.len();
+    file.seek(SeekFrom::Start(0))
+        .map_err(|_| CliEditorError::Cleanup)?;
+    let zeros = [0_u8; 8192];
+    let mut remaining = length;
+    while remaining > 0 {
+        let count = remaining.min(zeros.len() as u64) as usize;
+        file.write_all(&zeros[..count])
+            .map_err(|_| CliEditorError::Cleanup)?;
+        remaining -= count as u64;
+    }
+    file.set_len(0).map_err(|_| CliEditorError::Cleanup)?;
+    file.sync_all().map_err(|_| CliEditorError::Cleanup)?;
+    drop(file);
+    fs::remove_file(path).map_err(|_| CliEditorError::Cleanup)
+}
+
+#[derive(Debug)]
+pub(crate) enum CliEditorError {
+    TemporaryDirectory,
+    TemporaryFile,
+    ReplacementTooLarge,
+    Host(EditorHostError),
+    Cancelled,
+    Failed(i32),
+    Cleanup,
+}
+
+impl fmt::Display for CliEditorError {
+    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::TemporaryDirectory => formatter.write_str("cannot create secure edit directory"),
+            Self::TemporaryFile => formatter.write_str("cannot use secure edit file"),
+            Self::ReplacementTooLarge => formatter.write_str("edited entry is too large"),
+            Self::Host(error) => error.fmt(formatter),
+            Self::Cancelled => formatter.write_str("editor cancelled"),
+            Self::Failed(code) => write!(formatter, "editor exited unsuccessfully ({code})"),
+            Self::Cleanup => formatter.write_str("cannot securely clean up edit file"),
+        }
+    }
+}
+
+impl Error for CliEditorError {}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use ironstorage::{config::ConfigLoader, repository::SecretBytes};
+
+    #[derive(Default)]
+    struct RecordingHost {
+        replacement: Vec<u8>,
+        status: Option<EditorStatus>,
+        invocation: Option<EditorInvocation>,
+        mode: Option<u32>,
+    }
+
+    impl EditorHost for RecordingHost {
+        fn edit(&mut self, invocation: &EditorInvocation) -> Result<EditorStatus, EditorHostError> {
+            self.invocation = Some(invocation.clone());
+            #[cfg(unix)]
+            {
+                use std::os::unix::fs::PermissionsExt as _;
+                self.mode = Some(
+                    fs::metadata(invocation.plaintext_path())
+                        .unwrap()
+                        .permissions()
+                        .mode()
+                        & 0o777,
+                );
+            }
+            if self.status.unwrap_or(EditorStatus::Saved) == EditorStatus::Saved {
+                fs::write(invocation.plaintext_path(), &self.replacement).unwrap();
+            }
+            Ok(self.status.unwrap_or(EditorStatus::Saved))
+        }
+    }
+
+    #[test]
+    fn secure_editor_file_uses_resolved_arguments_permissions_and_cleanup()
+    -> Result<(), Box<dyn Error>> {
+        let temporary = tempfile::tempdir()?;
+        fs::create_dir(temporary.path().join("vault"))?;
+        fs::create_dir(temporary.path().join("keys"))?;
+        let config_path = temporary.path().join("config.toml");
+        fs::write(
+            &config_path,
+            "vault='vault'\ndefault_key='alice'\nkey_material='keys'\neditor=['fixture-editor','--wait','--clean']\n",
+        )?;
+        let config = ConfigLoader::new(temporary.path().to_owned(), temporary.path().to_owned())
+            .load(Some(&config_path))?;
+        let editor = config.resolve_editor_from(None, None)?;
+
+        let plaintext = SecretBytes::new(b"original\n".to_vec());
+        let mut host = RecordingHost {
+            replacement: b"replacement\n".to_vec(),
+            ..RecordingHost::default()
+        };
+        let replacement = edit_replacement(&plaintext, &editor, &mut host)?;
+        assert_eq!(replacement.expose(), b"replacement\n");
+        let invocation = host.invocation.expect("invocation");
+        assert_eq!(invocation.program(), "fixture-editor");
+        assert_eq!(invocation.arguments()[0].to_str(), Some("--wait"));
+        assert_eq!(invocation.arguments()[1].to_str(), Some("--clean"));
+        assert_eq!(
+            invocation.arguments().last().unwrap(),
+            invocation.plaintext_path().as_os_str()
+        );
+        #[cfg(unix)]
+        assert_eq!(host.mode, Some(0o600));
+        assert!(!invocation.plaintext_path().exists());
+        Ok(())
+    }
+
+    #[test]
+    fn failure_and_cancellation_clean_up_without_returning_plaintext() -> Result<(), Box<dyn Error>>
+    {
+        let temporary = tempfile::tempdir()?;
+        fs::create_dir(temporary.path().join("vault"))?;
+        fs::create_dir(temporary.path().join("keys"))?;
+        let config_path = temporary.path().join("config.toml");
+        fs::write(
+            &config_path,
+            "vault='vault'\ndefault_key='alice'\nkey_material='keys'\n",
+        )?;
+        let config = ConfigLoader::new(temporary.path().to_owned(), temporary.path().to_owned())
+            .load(Some(&config_path))?;
+        let editor =
+            config.resolve_editor_from(Some(std::ffi::OsStr::new("visual --flag")), None)?;
+        let plaintext = SecretBytes::new(b"secret".to_vec());
+        for status in [EditorStatus::Failed(42), EditorStatus::Cancelled] {
+            let mut host = RecordingHost {
+                status: Some(status),
+                ..RecordingHost::default()
+            };
+            assert!(edit_replacement(&plaintext, &editor, &mut host).is_err());
+            assert!(!host.invocation.unwrap().plaintext_path().exists());
+        }
+        Ok(())
+    }
+}
diff --git a/apps/cli/src/main.rs b/apps/cli/src/main.rs
index 7f9e2a6..04a3b35 100644
--- a/apps/cli/src/main.rs
+++ b/apps/cli/src/main.rs
@@ -11,6 +11,9 @@ use ironstorage::{
     config::Config,
 };
 
+#[allow(dead_code)]
+mod editor;
+
 fn main() -> ExitCode {
     match run() {
         Ok(code) => ExitCode::from(code),
diff --git a/crates/storage/src/lib.rs b/crates/storage/src/lib.rs
index 2142086..4185f5b 100644
--- a/crates/storage/src/lib.rs
+++ b/crates/storage/src/lib.rs
@@ -11,6 +11,7 @@ pub mod crypto;
 pub mod read;
 pub mod recipient;
 pub mod repository;
+pub mod write;
 
 /// Product name shared by the presentation adapters.
 pub const PRODUCT_NAME: &str = "IronStorage";
diff --git a/crates/storage/src/repository.rs b/crates/storage/src/repository.rs
index c6a8431..f54001e 100644
--- a/crates/storage/src/repository.rs
+++ b/crates/storage/src/repository.rs
@@ -37,6 +37,10 @@ impl EntryPath {
         &self.0
     }
 
+    pub fn parent_directory(&self) -> DirectoryPath {
+        self.parent()
+    }
+
     fn parent(&self) -> DirectoryPath {
         DirectoryPath(self.0.parent().map_or_else(PathBuf::new, Path::to_path_buf))
     }
@@ -511,6 +515,20 @@ impl Repository {
         self.write_entry_with_checkpoint(path, ciphertext, |_| Ok(()))
     }
 
+    pub fn remove_entry(&self, path: &EntryPath) -> Result<EncryptedEntry, RepositoryError> {
+        let original = self.read_entry(path)?;
+        let (parent, file_name) = self.open_entry_parent(path)?;
+        parent
+            .remove_file(&file_name)
+            .map_err(|error| io_error("remove encrypted entry", &path.0, error))?;
+        sync_directory(&parent, &path.parent().0).map_err(|_| {
+            RepositoryError::DurabilityUncertain {
+                path: path.0.clone(),
+            }
+        })?;
+        Ok(original)
+    }
+
     fn write_entry_with_checkpoint<F>(
         &self,
         path: &EntryPath,
diff --git a/crates/storage/src/write.rs b/crates/storage/src/write.rs
new file mode 100644
index 0000000..2996f6e
--- /dev/null
+++ b/crates/storage/src/write.rs
@@ -0,0 +1,398 @@
+//! Insert and concurrency-safe in-process edit sessions.
+
+use std::{error::Error, fmt};
+
+use crate::{
+    command::{EditRequest, InsertInput, InsertRequest},
+    crypto::{CryptoError, KeyStore, SecretProvider},
+    recipient::{RecipientPolicyError, RecipientPolicyManager, SigningPolicy},
+    repository::{EncryptedEntry, EntryPath, Repository, RepositoryError, SecretBytes},
+};
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub enum OverwriteDecision {
+    Allow,
+    Decline,
+}
+
+pub struct InsertContent {
+    mode: InsertInput,
+    secret: SecretBytes,
+}
+
+impl InsertContent {
+    pub fn hidden(first: Vec<u8>, confirmation: Vec<u8>) -> Result<Self, WriteError> {
+        validate_single_line(&first)?;
+        validate_single_line(&confirmation)?;
+        if first != confirmation {
+            return Err(WriteError::ConfirmationMismatch);
+        }
+        if first.is_empty() {
+            return Err(WriteError::EmptySingleLine);
+        }
+        Ok(Self {
+            mode: InsertInput::HiddenConfirmed,
+            secret: SecretBytes::new(first),
+        })
+    }
+
+    pub fn echoed(line: Vec<u8>) -> Result<Self, WriteError> {
+        validate_single_line(&line)?;
+        if line.is_empty() {
+            return Err(WriteError::EmptySingleLine);
+        }
+        Ok(Self {
+            mode: InsertInput::EchoedLine,
+            secret: SecretBytes::new(line),
+        })
+    }
+
+    pub fn multiline(contents: Vec<u8>) -> Self {
+        Self {
+            mode: InsertInput::Multiline,
+            secret: SecretBytes::new(contents),
+        }
+    }
+
+    pub fn expose(&self) -> &[u8] {
+        self.secret.expose()
+    }
+
+    fn into_secret(self) -> SecretBytes {
+        self.secret
+    }
+}
+
+impl fmt::Debug for InsertContent {
+    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
+        formatter.write_str("InsertContent([REDACTED])")
+    }
+}
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub enum EntryAction {
+    Insert,
+    Edit,
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct EntryCommit {
+    path: EntryPath,
+    action: EntryAction,
+    message: String,
+}
+
+impl EntryCommit {
+    pub fn path(&self) -> &EntryPath {
+        &self.path
+    }
+
+    pub fn action(&self) -> EntryAction {
+        self.action
+    }
+
+    pub fn message(&self) -> &str {
+        &self.message
+    }
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct EntryCommitError(String);
+
+impl EntryCommitError {
+    pub fn new(message: impl Into<String>) -> Self {
+        Self(message.into())
+    }
+}
+
+impl fmt::Display for EntryCommitError {
+    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
+        formatter.write_str(&self.0)
+    }
+}
+
+impl Error for EntryCommitError {}
+
+pub trait EntryCommitter {
+    fn commit(&mut self, change: &EntryCommit) -> Result<(), EntryCommitError>;
+}
+
+#[derive(Default)]
+pub struct NoGitEntryCommitter;
+
+impl EntryCommitter for NoGitEntryCommitter {
+    fn commit(&mut self, _change: &EntryCommit) -> Result<(), EntryCommitError> {
+        Ok(())
+    }
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct WriteOutcome {
+    path: EntryPath,
+    action: EntryAction,
+}
+
+impl WriteOutcome {
+    pub fn path(&self) -> &EntryPath {
+        &self.path
+    }
+
+    pub fn action(&self) -> EntryAction {
+        self.action
+    }
+}
+
+pub struct EditSession {
+    path: EntryPath,
+    original_ciphertext: Option<EncryptedEntry>,
+    plaintext: SecretBytes,
+}
+
+impl EditSession {
+    pub fn path(&self) -> &EntryPath {
+        &self.path
+    }
+
+    pub fn plaintext(&self) -> &SecretBytes {
+        &self.plaintext
+    }
+}
+
+impl fmt::Debug for EditSession {
+    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
+        formatter
+            .debug_struct("EditSession")
+            .field("path", &self.path)
+            .field("plaintext", &self.plaintext)
+            .finish_non_exhaustive()
+    }
+}
+
+pub struct VaultWriter<'a> {
+    repository: &'a Repository,
+    keys: &'a KeyStore,
+}
+
+impl<'a> VaultWriter<'a> {
+    pub fn new(repository: &'a Repository, keys: &'a KeyStore) -> Self {
+        Self { repository, keys }
+    }
+
+    #[allow(clippy::too_many_arguments)]
+    pub fn insert(
+        &self,
+        request: &InsertRequest,
+        contents: InsertContent,
+        overwrite: OverwriteDecision,
+        signing: Option<&SigningPolicy>,
+        committer: &mut impl EntryCommitter,
+    ) -> Result<WriteOutcome, WriteError> {
+        let path = EntryPath::parse(&request.entry)?;
+        if contents.mode != request.input {
+            return Err(WriteError::InputModeMismatch);
+        }
+        let original = match self.repository.read_entry(&path) {
+            Ok(original) => Some(original),
+            Err(RepositoryError::NotFound { .. }) => None,
+            Err(error) => return Err(error.into()),
+        };
+        if original.is_some() && !request.force && overwrite == OverwriteDecision::Decline {
+            return Err(WriteError::Cancelled);
+        }
+        let recipients = RecipientPolicyManager::new(self.repository, self.keys)
+            .resolve_for_entry(&path, signing)?;
+        let ciphertext = self
+            .keys
+            .encrypt(contents.into_secret(), recipients.recipients())?;
+        self.repository.write_entry(&path, &ciphertext)?;
+        let change = EntryCommit {
+            path: path.clone(),
+            action: EntryAction::Insert,
+            message: format!("Add given password for {path} to store."),
+        };
+        if let Err(error) = committer.commit(&change) {
+            if let Err(rollback) = self.restore(&path, original.as_ref()) {
+                return Err(WriteError::RollbackFailed {
+                    operation: error,
+                    rollback,
+                });
+            }
+            return Err(WriteError::Commit(error));
+        }
+        Ok(WriteOutcome {
+            path,
+            action: EntryAction::Insert,
+        })
+    }
+
+    pub fn begin_edit(
+        &self,
+        request: &EditRequest,
+        provider: &mut impl SecretProvider,
+    ) -> Result<EditSession, WriteError> {
+        let path = EntryPath::parse(&request.entry)?;
+        let original_ciphertext = match self.repository.read_entry(&path) {
+            Ok(ciphertext) => Some(ciphertext),
+            Err(RepositoryError::NotFound { .. }) => None,
+            Err(error) => return Err(error.into()),
+        };
+        let plaintext = if let Some(ciphertext) = &original_ciphertext {
+            self.keys.decrypt(ciphertext, provider)?
+        } else {
+            SecretBytes::new(Vec::new())
+        };
+        Ok(EditSession {
+            path,
+            original_ciphertext,
+            plaintext,
+        })
+    }
+
+    #[allow(clippy::too_many_arguments)]
+    pub fn finish_edit(
+        &self,
+        session: EditSession,
+        replacement: SecretBytes,
+        editor_name: &str,
+        signing: Option<&SigningPolicy>,
+        committer: &mut impl EntryCommitter,
+    ) -> Result<WriteOutcome, WriteError> {
+        if replacement.expose() == session.plaintext.expose() {
+            return Err(WriteError::Unchanged);
+        }
+        let concurrent = match (
+            session.original_ciphertext.as_ref(),
+            self.repository.read_entry(&session.path),
+        ) {
+            (Some(original), Ok(current)) => &current != original,
+            (None, Err(RepositoryError::NotFound { .. })) => false,
+            (Some(_), Err(RepositoryError::NotFound { .. })) | (None, Ok(_)) => true,
+            (_, Err(error)) => return Err(error.into()),
+        };
+        if concurrent {
+            return Err(WriteError::ConcurrentModification {
+                path: session.path.clone(),
+            });
+        }
+        let recipients = RecipientPolicyManager::new(self.repository, self.keys)
+            .resolve_for_entry(&session.path, signing)?;
+        let ciphertext = self.keys.encrypt(replacement, recipients.recipients())?;
+        self.repository.write_entry(&session.path, &ciphertext)?;
+        let change = EntryCommit {
+            path: session.path.clone(),
+            action: EntryAction::Edit,
+            message: format!("Edit password for {} using {}.", session.path, editor_name),
+        };
+        if let Err(error) = committer.commit(&change) {
+            if let Err(rollback) = self.restore(&session.path, session.original_ciphertext.as_ref())
+            {
+                return Err(WriteError::RollbackFailed {
+                    operation: error,
+                    rollback,
+                });
+            }
+            return Err(WriteError::Commit(error));
+        }
+        Ok(WriteOutcome {
+            path: session.path,
+            action: EntryAction::Edit,
+        })
+    }
+
+    fn restore(
+        &self,
+        path: &EntryPath,
+        original: Option<&EncryptedEntry>,
+    ) -> Result<(), RepositoryError> {
+        if let Some(original) = original {
+            self.repository.write_entry(path, original)?;
+        } else {
+            self.repository.remove_entry(path)?;
+            self.repository
+                .cleanup_empty_directories(&path.parent_directory())?;
+        }
+        Ok(())
+    }
+}
+
+fn validate_single_line(line: &[u8]) -> Result<(), WriteError> {
+    if line.iter().any(|byte| matches!(byte, b'\n' | b'\r')) {
+        Err(WriteError::InvalidSingleLine)
+    } else {
+        Ok(())
+    }
+}
+
+#[derive(Debug)]
+pub enum WriteError {
+    Repository(RepositoryError),
+    Crypto(CryptoError),
+    RecipientPolicy(RecipientPolicyError),
+    ConfirmationMismatch,
+    EmptySingleLine,
+    InvalidSingleLine,
+    InputModeMismatch,
+    Cancelled,
+    Unchanged,
+    ConcurrentModification {
+        path: EntryPath,
+    },
+    Commit(EntryCommitError),
+    RollbackFailed {
+        operation: EntryCommitError,
+        rollback: RepositoryError,
+    },
+}
+
+impl fmt::Display for WriteError {
+    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::Repository(error) => error.fmt(formatter),
+            Self::Crypto(error) => error.fmt(formatter),
+            Self::RecipientPolicy(error) => error.fmt(formatter),
+            Self::ConfirmationMismatch => {
+                formatter.write_str("password confirmation does not match")
+            }
+            Self::EmptySingleLine => formatter.write_str("password may not be empty"),
+            Self::InvalidSingleLine => {
+                formatter.write_str("single-line input contains a line break")
+            }
+            Self::InputModeMismatch => {
+                formatter.write_str("insert content does not match the requested input mode")
+            }
+            Self::Cancelled => formatter.write_str("entry overwrite was declined"),
+            Self::Unchanged => formatter.write_str("entry was not changed"),
+            Self::ConcurrentModification { path } => {
+                write!(formatter, "entry changed during editing: {path}")
+            }
+            Self::Commit(error) => write!(formatter, "cannot commit entry mutation: {error}"),
+            Self::RollbackFailed {
+                operation,
+                rollback,
+            } => write!(
+                formatter,
+                "entry commit failed ({operation}) and repository rollback failed ({rollback})"
+            ),
+        }
+    }
+}
+
+impl Error for WriteError {}
+
+impl From<RepositoryError> for WriteError {
+    fn from(error: RepositoryError) -> Self {
+        Self::Repository(error)
+    }
+}
+
+impl From<CryptoError> for WriteError {
+    fn from(error: CryptoError) -> Self {
+        Self::Crypto(error)
+    }
+}
+
+impl From<RecipientPolicyError> for WriteError {
+    fn from(error: RecipientPolicyError) -> Self {
+        Self::RecipientPolicy(error)
+    }
+}
diff --git a/crates/storage/tests/write_domains.rs b/crates/storage/tests/write_domains.rs
new file mode 100644
index 0000000..fd28a68
--- /dev/null
+++ b/crates/storage/tests/write_domains.rs
@@ -0,0 +1,374 @@
+#![forbid(unsafe_code)]
+
+mod support;
+
+use std::{collections::BTreeMap, fs};
+
+use ironstorage::{
+    command::{EditRequest, InsertInput, InsertRequest},
+    crypto::{CryptoError, KeyInfo, KeyStore, SecretProvider, SecretProviderError},
+    repository::{EntryPath, Repository, SecretBytes},
+    write::{
+        EntryCommit, EntryCommitError, EntryCommitter, InsertContent, OverwriteDecision,
+        VaultWriter, WriteError,
+    },
+};
+use support::compatibility::{FixtureSet, TestResult};
+
+struct FixtureSecrets(BTreeMap<String, Vec<u8>>);
+
+impl FixtureSecrets {
+    fn all(fixture: &FixtureSet) -> Self {
+        Self(
+            fixture
+                .generated
+                .keys
+                .iter()
+                .map(|key| {
+                    (
+                        key.primary_fingerprint.clone(),
+                        key.passphrase.as_bytes().to_vec(),
+                    )
+                })
+                .collect(),
+        )
+    }
+}
+
+impl SecretProvider for FixtureSecrets {
+    fn secret_for(&mut self, key: &KeyInfo) -> Result<SecretBytes, SecretProviderError> {
+        self.0
+            .get(key.fingerprint().as_str())
+            .cloned()
+            .map(SecretBytes::new)
+            .ok_or(SecretProviderError::Unavailable)
+    }
+}
+
+#[derive(Default)]
+struct RecordingCommitter {
+    changes: Vec<EntryCommit>,
+    fail: bool,
+}
+
+impl EntryCommitter for RecordingCommitter {
+    fn commit(&mut self, change: &EntryCommit) -> Result<(), EntryCommitError> {
+        self.changes.push(change.clone());
+        if self.fail {
+            Err(EntryCommitError::new("simulated Git failure"))
+        } else {
+            Ok(())
+        }
+    }
+}
+
+#[test]
+fn insert_content_modes_validate_and_redact_input() -> TestResult {
+    let hidden = InsertContent::hidden(b"secret".to_vec(), b"secret".to_vec())?;
+    assert_eq!(hidden.expose(), b"secret");
+    assert!(!format!("{hidden:?}").contains("secret"));
+    assert!(matches!(
+        InsertContent::hidden(b"first".to_vec(), b"second".to_vec()),
+        Err(WriteError::ConfirmationMismatch)
+    ));
+    assert!(matches!(
+        InsertContent::echoed(Vec::new()),
+        Err(WriteError::EmptySingleLine)
+    ));
+    assert!(matches!(
+        InsertContent::echoed(b"two\nlines".to_vec()),
+        Err(WriteError::InvalidSingleLine)
+    ));
+    assert!(InsertContent::multiline(Vec::new()).expose().is_empty());
+    Ok(())
+}
+
+#[test]
+fn insert_hidden_echoed_and_multiline_use_inherited_recipients() -> TestResult {
+    let fixture = FixtureSet::load()?;
+    let store = fixture.materialize_store("basic")?;
+    let repository = Repository::open(store.path())?;
+    let keys = KeyStore::load(fixture.path("keys"))?;
+    let writer = VaultWriter::new(&repository, &keys);
+    let mut committer = RecordingCommitter::default();
+
+    for (path, input, contents) in [
+        (
+            "new/hidden",
+            InsertInput::HiddenConfirmed,
+            InsertContent::hidden(b"hidden".to_vec(), b"hidden".to_vec())?,
+        ),
+        (
+            "new/echoed",
+            InsertInput::EchoedLine,
+            InsertContent::echoed(b"echoed".to_vec())?,
+        ),
+        (
+            "new/multiline",
+            InsertInput::Multiline,
+            InsertContent::multiline(b"first\nsecond\n".to_vec()),
+        ),
+    ] {
+        writer.insert(
+            &insert(path, false, input),
+            contents,
+            OverwriteDecision::Decline,
+            None,
+            &mut committer,
+        )?;
+    }
+    assert_eq!(committer.changes.len(), 3);
+    assert_eq!(
+        committer.changes[2].message(),
+        "Add given password for new/multiline to store."
+    );
+    let mut provider = FixtureSecrets::all(&fixture);
+    let plaintext = keys.decrypt(
+        &repository.read_entry(&EntryPath::parse("new/multiline")?)?,
+        &mut provider,
+    )?;
+    assert_eq!(plaintext.expose(), b"first\nsecond\n");
+    let alice = fixture.key("alice")?;
+    assert!(keys.is_encrypted_for(
+        &repository.read_entry(&EntryPath::parse("new/hidden")?)?,
+        &[keys.resolve(&alice.primary_fingerprint)?]
+    )?);
+    Ok(())
+}
+
+#[test]
+fn overwrite_decision_force_and_commit_failure_are_transactional() -> TestResult {
+    let fixture = FixtureSet::load()?;
+    let store = fixture.materialize_store("basic")?;
+    let repository = Repository::open(store.path())?;
+    let keys = KeyStore::load(fixture.path("keys"))?;
+    let writer = VaultWriter::new(&repository, &keys);
+    let path = EntryPath::parse("email/personal")?;
+    let original = repository.read_entry(&path)?;
+    let mut committer = RecordingCommitter::default();
+
+    assert!(matches!(
+        writer.insert(
+            &insert("email/personal", false, InsertInput::EchoedLine),
+            InsertContent::echoed(b"declined".to_vec())?,
+            OverwriteDecision::Decline,
+            None,
+            &mut committer,
+        ),
+        Err(WriteError::Cancelled)
+    ));
+    assert_eq!(repository.read_entry(&path)?, original);
+
+    writer.insert(
+        &insert("email/personal", true, InsertInput::EchoedLine),
+        InsertContent::echoed(b"forced".to_vec())?,
+        OverwriteDecision::Decline,
+        None,
+        &mut committer,
+    )?;
+    let forced = repository.read_entry(&path)?;
+    assert_ne!(forced, original);
+
+    committer.fail = true;
+    assert!(matches!(
+        writer.insert(
+            &insert("email/personal", true, InsertInput::EchoedLine),
+            InsertContent::echoed(b"rollback".to_vec())?,
+            OverwriteDecision::Allow,
+            None,
+            &mut committer,
+        ),
+        Err(WriteError::Commit(_))
+    ));
+    assert_eq!(repository.read_entry(&path)?, forced);
+
+    assert!(matches!(
+        writer.insert(
+            &insert("temporary/deep/entry", false, InsertInput::Multiline),
+            InsertContent::multiline(b"new".to_vec()),
+            OverwriteDecision::Allow,
+            None,
+            &mut committer,
+        ),
+        Err(WriteError::Commit(_))
+    ));
+    assert!(!store.path().join("temporary").exists());
+    Ok(())
+}
+
+#[test]
+fn edit_session_handles_replacement_unchanged_and_commit_failure() -> TestResult {
+    let fixture = FixtureSet::load()?;
+    let store = fixture.materialize_store("basic")?;
+    let repository = Repository::open(store.path())?;
+    let keys = KeyStore::load(fixture.path("keys"))?;
+    let writer = VaultWriter::new(&repository, &keys);
+    let request = EditRequest {
+        entry: "email/personal".to_owned(),
+    };
+    let path = EntryPath::parse("email/personal")?;
+    let mut provider = FixtureSecrets::all(&fixture);
+    let mut committer = RecordingCommitter::default();
+
+    let unchanged = writer.begin_edit(&request, &mut provider)?;
+    let same = SecretBytes::new(unchanged.plaintext().expose().to_vec());
+    assert!(matches!(
+        writer.finish_edit(unchanged, same, "fixture-editor", None, &mut committer),
+        Err(WriteError::Unchanged)
+    ));
+    assert!(committer.changes.is_empty());
+
+    let session = writer.begin_edit(&request, &mut provider)?;
+    writer.finish_edit(
+        session,
+        SecretBytes::new(b"edited\nlogin: replacement\n".to_vec()),
+        "fixture-editor",
+        None,
+        &mut committer,
+    )?;
+    assert_eq!(
+        committer.changes[0].message(),
+        "Edit password for email/personal using fixture-editor."
+    );
+    let edited = repository.read_entry(&path)?;
+    let plaintext = keys.decrypt(&edited, &mut provider)?;
+    assert_eq!(plaintext.expose(), b"edited\nlogin: replacement\n");
+
+    let session = writer.begin_edit(&request, &mut provider)?;
+    committer.fail = true;
+    assert!(matches!(
+        writer.finish_edit(
+            session,
+            SecretBytes::new(b"must roll back".to_vec()),
+            "fixture-editor",
+            None,
+            &mut committer,
+        ),
+        Err(WriteError::Commit(_))
+    ));
+    assert_eq!(repository.read_entry(&path)?, edited);
+    Ok(())
+}
+
+#[test]
+fn edit_detects_concurrent_ciphertext_change_before_writing() -> TestResult {
+    let fixture = FixtureSet::load()?;
+    let store = fixture.materialize_store("basic")?;
+    let repository = Repository::open(store.path())?;
+    let keys = KeyStore::load(fixture.path("keys"))?;
+    let writer = VaultWriter::new(&repository, &keys);
+    let request = EditRequest {
+        entry: "email/personal".to_owned(),
+    };
+    let path = EntryPath::parse("email/personal")?;
+    let mut provider = FixtureSecrets::all(&fixture);
+    let session = writer.begin_edit(&request, &mut provider)?;
+    let mut committer = RecordingCommitter::default();
+    writer.insert(
+        &insert("email/personal", true, InsertInput::EchoedLine),
+        InsertContent::echoed(b"concurrent".to_vec())?,
+        OverwriteDecision::Allow,
+        None,
+        &mut committer,
+    )?;
+    let concurrent = repository.read_entry(&path)?;
+
+    assert!(matches!(
+        writer.finish_edit(
+            session,
+            SecretBytes::new(b"stale editor".to_vec()),
+            "fixture-editor",
+            None,
+            &mut committer,
+        ),
+        Err(WriteError::ConcurrentModification { .. })
+    ));
+    assert_eq!(repository.read_entry(&path)?, concurrent);
+    Ok(())
+}
+
+#[test]
+fn edit_session_can_create_a_new_entry_and_detect_one_appearing_concurrently() -> TestResult {
+    let fixture = FixtureSet::load()?;
+    let store = fixture.materialize_store("basic")?;
+    let repository = Repository::open(store.path())?;
+    let keys = KeyStore::load(fixture.path("keys"))?;
+    let writer = VaultWriter::new(&repository, &keys);
+    let request = EditRequest {
+        entry: "new/from-editor".to_owned(),
+    };
+    let mut provider = FixtureSecrets::all(&fixture);
+    let session = writer.begin_edit(&request, &mut provider)?;
+    assert!(session.plaintext().expose().is_empty());
+    let mut committer = RecordingCommitter::default();
+    writer.finish_edit(
+        session,
+        SecretBytes::new(b"created by editor\n".to_vec()),
+        "fixture-editor",
+        None,
+        &mut committer,
+    )?;
+    assert!(store.path().join("new/from-editor.gpg").is_file());
+
+    let concurrent_request = EditRequest {
+        entry: "new/concurrent-editor".to_owned(),
+    };
+    let session = writer.begin_edit(&concurrent_request, &mut provider)?;
+    writer.insert(
+        &insert("new/concurrent-editor", false, InsertInput::EchoedLine),
+        InsertContent::echoed(b"appeared".to_vec())?,
+        OverwriteDecision::Allow,
+        None,
+        &mut committer,
+    )?;
+    assert!(matches!(
+        writer.finish_edit(
+            session,
+            SecretBytes::new(b"stale".to_vec()),
+            "fixture-editor",
+            None,
+            &mut committer,
+        ),
+        Err(WriteError::ConcurrentModification { .. })
+    ));
+    Ok(())
+}
+
+#[test]
+fn invalid_recipient_policy_fails_before_entry_creation() -> TestResult {
+    let fixture = FixtureSet::load()?;
+    let store = fixture.materialize_store("basic")?;
+    fs::create_dir(store.path().join("invalid"))?;
+    fs::write(
+        store.path().join("invalid/.gpg-id"),
+        b"missing@ironstorage.invalid\n",
+    )?;
+    let repository = Repository::open(store.path())?;
+    let keys = KeyStore::load(fixture.path("keys"))?;
+    let writer = VaultWriter::new(&repository, &keys);
+
+    assert!(matches!(
+        writer.insert(
+            &insert("invalid/entry", false, InsertInput::Multiline),
+            InsertContent::multiline(b"secret".to_vec()),
+            OverwriteDecision::Allow,
+            None,
+            &mut RecordingCommitter::default(),
+        ),
+        Err(WriteError::RecipientPolicy(
+            ironstorage::recipient::RecipientPolicyError::Crypto(
+                CryptoError::MissingIdentity { .. }
+            )
+        ))
+    ));
+    assert!(!store.path().join("invalid/entry.gpg").exists());
+    Ok(())
+}
+
+fn insert(entry: &str, force: bool, input: InsertInput) -> InsertRequest {
+    InsertRequest {
+        entry: entry.to_owned(),
+        input,
+        force,
+    }
+}
diff --git a/docs/write-domains.md b/docs/write-domains.md
new file mode 100644
index 0000000..90cd5dc
--- /dev/null
+++ b/docs/write-domains.md
@@ -0,0 +1,52 @@
+# Insert and edit domains
+
+`VaultWriter` in `crates/storage` owns insertion, edit concurrency, recipient
+selection, encryption, repository mutation, rollback, and commit intent.
+Frontends collect input and overwrite decisions but cannot write an encrypted
+entry directly.
+
+## Insert
+
+`InsertContent` has distinct constructors for hidden confirmed input, echoed
+single-line input, and exact multiline bytes. Hidden values must match their
+confirmation; both single-line modes reject empty values and embedded line
+breaks. Multiline input preserves every byte and may be empty. The content mode
+must equal the parsed `InsertRequest`, preventing an adapter from silently
+changing stdin semantics.
+
+An existing entry requires either `--force` or an explicit allow decision. A
+decline returns before recipient resolution or encryption. The nearest signed
+or unsigned recipient policy is resolved for the destination, plaintext is
+consumed by embedded OpenPGP encryption, and repository replacement is atomic.
+The storage commit boundary is invoked only afterward with the compatible
+`Add given password ...` intent. Commit failure restores the exact old
+ciphertext or removes a newly created entry and its empty parent directories.
+
+## Edit sessions
+
+Beginning a session snapshots the original encrypted bytes and decrypts an
+existing entry into redacted `SecretBytes`; a missing entry starts with empty
+contents so `pass edit` can create it. Finishing consumes replacement
+`SecretBytes`. Unchanged content returns without encryption or commit. Before
+writing, storage compares current encrypted bytes with the snapshot (or checks
+that a new path is still absent), so concurrent replacement, removal, or
+creation is rejected without overwriting the other writer.
+
+Successful replacement uses the destination's current recipient policy and
+records compatible editor commit intent. A commit error restores the prior
+state. Rollback failure retains both the commit and repository errors.
+
+## CLI editor boundary
+
+Editor precedence remains TOML configuration, `VISUAL`, `EDITOR`, then `vim`,
+with the program and arguments parsed without a shell. The CLI adapter converts
+that value to one `EditorInvocation` for a narrowly injected `EditorHost`;
+storage, TUI, GUI, iOS, and watchOS never receive executable information and
+continue to use the in-process replacement API.
+
+Before invoking the host, the CLI creates a mode-0600 plaintext file inside a
+private temporary directory. Linux prefers `/dev/shm` when available; native
+temporary storage is the fallback. The file is never inside the vault. A saved
+file is bounded before reading. Saved, cancelled, failed, and host-error paths
+all overwrite the file with zeros, truncate and sync it, remove it, and finally
+drop the private directory. Returned replacement bytes remain zeroizing.