diff --git a/crates/idfoto-core/src/lib.rs b/crates/idfoto-core/src/lib.rs
index 9cbb180..0e3d512 100644
--- a/crates/idfoto-core/src/lib.rs
+++ b/crates/idfoto-core/src/lib.rs
@@ -53,6 +53,12 @@ pub use attachment::{AttachmentRef, AttachmentSummary};
 pub mod manifest;
 pub use manifest::{Manifest, ManifestEntry, MANIFEST_SCHEMA_VERSION};
 
+pub mod settings;
+pub use settings::{
+    AttachmentCaps, Capitalization, CharClasses, GeneratorRequest, HistoryRetention,
+    SymbolCharset, TrashRetention, VaultSettings,
+};
+
 pub mod crypto;
 pub use crypto::{decrypt, derive_master_key, encrypt, KdfParams};
 
diff --git a/crates/idfoto-core/src/settings.rs b/crates/idfoto-core/src/settings.rs
new file mode 100644
index 0000000..7557252
--- /dev/null
+++ b/crates/idfoto-core/src/settings.rs
@@ -0,0 +1,173 @@
+//! Vault-level settings: trash retention, history retention, generator
+//! defaults, attachment caps, autofill TOFU acks.
+
+use serde::{Deserialize, Serialize};
+use std::collections::HashMap;
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct VaultSettings {
+    pub trash_retention: TrashRetention,
+    pub field_history_retention: HistoryRetention,
+    pub generator_defaults: GeneratorRequest,
+    pub attachment_caps: AttachmentCaps,
+    /// hostname → unix-seconds first-acked
+    #[serde(default)]
+    pub autofill_origin_acks: HashMap<String, i64>,
+}
+
+impl Default for VaultSettings {
+    fn default() -> Self {
+        Self {
+            trash_retention: TrashRetention::Days(30),
+            field_history_retention: HistoryRetention::Forever,
+            generator_defaults: GeneratorRequest::default(),
+            attachment_caps: AttachmentCaps::default(),
+            autofill_origin_acks: HashMap::new(),
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(tag = "kind", content = "value", rename_all = "snake_case")]
+pub enum TrashRetention {
+    Days(u32),
+    Forever,
+}
+
+impl TrashRetention {
+    pub fn should_purge(&self, trashed_at: i64, now: i64) -> bool {
+        match self {
+            TrashRetention::Forever => false,
+            TrashRetention::Days(d) => now - trashed_at > (*d as i64) * 86_400,
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(tag = "kind", content = "value", rename_all = "snake_case")]
+pub enum HistoryRetention {
+    LastN(u32),
+    Days(u32),
+    Forever,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(tag = "kind", rename_all = "snake_case")]
+pub enum GeneratorRequest {
+    Bip39 {
+        word_count: u32,
+        separator: String,
+        capitalization: Capitalization,
+    },
+    Random {
+        length: u32,
+        classes: CharClasses,
+        symbol_charset: SymbolCharset,
+    },
+}
+
+impl Default for GeneratorRequest {
+    fn default() -> Self {
+        GeneratorRequest::Random {
+            length: 20,
+            classes: CharClasses { lower: true, upper: true, digits: true, symbols: true },
+            symbol_charset: SymbolCharset::SafeOnly,
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum Capitalization {
+    Lower,
+    Upper,
+    FirstOfEach,
+    Title,
+    Mixed,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
+pub struct CharClasses {
+    pub lower: bool,
+    pub upper: bool,
+    pub digits: bool,
+    pub symbols: bool,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(tag = "kind", rename_all = "snake_case")]
+pub enum SymbolCharset {
+    SafeOnly,
+    Extended,
+    Custom(String),
+}
+
+#[derive(Debug, Clone, Copy, Serialize, Deserialize)]
+pub struct AttachmentCaps {
+    pub per_attachment_max_bytes: u64,
+    pub per_item_max_count: u32,
+    pub per_vault_soft_cap_bytes: u64,
+    pub per_vault_hard_cap_bytes: u64,
+}
+
+impl Default for AttachmentCaps {
+    fn default() -> Self {
+        Self {
+            per_attachment_max_bytes: 10 * 1024 * 1024,
+            per_item_max_count: 20,
+            per_vault_soft_cap_bytes: 100 * 1024 * 1024,
+            per_vault_hard_cap_bytes: 500 * 1024 * 1024,
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn defaults_match_spec() {
+        let s = VaultSettings::default();
+        assert!(matches!(s.trash_retention, TrashRetention::Days(30)));
+        assert!(matches!(s.field_history_retention, HistoryRetention::Forever));
+        assert_eq!(s.attachment_caps.per_attachment_max_bytes, 10 * 1024 * 1024);
+        assert_eq!(s.attachment_caps.per_item_max_count, 20);
+    }
+
+    #[test]
+    fn trash_retention_purges_after_days() {
+        let r = TrashRetention::Days(30);
+        let now = 1_000_000_000;
+        let recently_trashed = now - 29 * 86_400;
+        let long_trashed = now - 31 * 86_400;
+        assert!(!r.should_purge(recently_trashed, now));
+        assert!(r.should_purge(long_trashed, now));
+    }
+
+    #[test]
+    fn trash_retention_forever_never_purges() {
+        let r = TrashRetention::Forever;
+        assert!(!r.should_purge(0, 1_000_000_000));
+    }
+
+    #[test]
+    fn settings_round_trip() {
+        let s = VaultSettings::default();
+        let json = serde_json::to_string(&s).unwrap();
+        let parsed: VaultSettings = serde_json::from_str(&json).unwrap();
+        assert_eq!(parsed.attachment_caps.per_attachment_max_bytes,
+                   s.attachment_caps.per_attachment_max_bytes);
+    }
+
+    #[test]
+    fn random_generator_default_is_20_safe() {
+        match VaultSettings::default().generator_defaults {
+            GeneratorRequest::Random { length, classes, symbol_charset } => {
+                assert_eq!(length, 20);
+                assert!(classes.lower && classes.upper && classes.digits && classes.symbols);
+                assert!(matches!(symbol_charset, SymbolCharset::SafeOnly));
+            }
+            _ => panic!("expected Random default"),
+        }
+    }
+}