feat(core): add csv dep + import error variants

Adds csv = "1" to relicario-core; introduces
ImportCsvHeader and ImportCsvFormat. Foundation for the
import_lastpass module landing in Task 2.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Cargo.lock

@@ -437,6 +437,27 @@ dependencies = [
  "typenum",
 ]
 
+[[package]]
+name = "csv"
+version = "1.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "52cd9d68cf7efc6ddfaaee42e7288d3a99d613d4b50f76ce9827ae0c6e14f938"
+dependencies = [
+ "csv-core",
+ "itoa",
+ "ryu",
+ "serde_core",
+]
+
+[[package]]
+name = "csv-core"
+version = "0.1.13"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "704a3c26996a80471189265814dbc2c257598b96b8a7feae2d31ace646bb9782"
+dependencies = [
+ "memchr",
+]
+
 [[package]]
 name = "curve25519-dalek"
 version = "4.1.3"
@@ -1609,6 +1630,7 @@ dependencies = [
  "bip39",
  "chacha20poly1305",
  "chrono",
+ "csv",
  "ed25519-dalek",
  "getrandom 0.2.17",
  "hex",
@@ -1696,6 +1718,12 @@ version = "1.0.22"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b39cdef0fa800fc44525c84ccb54a029961a8215f9619753635a9c0d2538d46d"
 
+[[package]]
+name = "ryu"
+version = "1.0.23"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9774ba4a74de5f7b1c1451ed6cd5285a32eddb5cccb8cc655a4e50009e06477f"
+
 [[package]]
 name = "same-file"
 version = "1.0.6"

crates/relicario-core/Cargo.toml

@@ -29,5 +29,6 @@ getrandom = "0.2"
 zstd = { version = "0.13", default-features = false }
 tar = { version = "0.4", default-features = false }
 base64 = "0.22"
+csv = "1"
 
 [dev-dependencies]

crates/relicario-core/src/error.rs

@@ -51,6 +51,17 @@ pub enum RelicarioError {
     #[error("backup envelope schema v{found}; this relicario reads v{expected}")]
     BackupSchemaMismatch { found: u32, expected: u32 },
 
+    /// CSV header doesn't match the LastPass column layout.
+    #[error("unrecognized CSV header — expected LastPass export format ({0})")]
+    ImportCsvHeader(String),
+
+    /// CSV body could not be parsed (mismatched quoting, encoding, etc.).
+    /// Per-row record errors that the importer recovers from become
+    /// `ImportWarning` entries — this variant is reserved for failures
+    /// that abort the whole import.
+    #[error("CSV parse failed: {0}")]
+    ImportCsvFormat(String),
+
     /// An item was looked up by ID but does not exist in the manifest.
     #[error("item not found: {0}")]
     ItemNotFound(String),
@@ -156,4 +167,15 @@ mod tests {
         let s = format!("{}", schema);
         assert!(s.contains("v2") && s.contains("v1"));
     }
+
+    #[test]
+    fn import_errors_carry_useful_messages() {
+        let h = RelicarioError::ImportCsvHeader("missing 'name' column".into());
+        assert!(format!("{}", h).contains("LastPass"));
+        assert!(format!("{}", h).contains("missing 'name'"));
+
+        let f = RelicarioError::ImportCsvFormat("unterminated quote at line 12".into());
+        assert!(format!("{}", f).contains("CSV parse failed"));
+        assert!(format!("{}", f).contains("unterminated quote"));
+    }
 }