First slice: ledger-store (journal+blobs+sqlite) and ledger-mcp (18 tools, receipt policy)

crates/ledger-store/src/blob.rs

@@ -0,0 +1,78 @@
+//! The blob store: content-addressed, immutable bytes.
+//!
+//! Files are keyed by the SHA-256 of their exact bytes and laid out sharded
+//! by hash prefix: `<root>/<aa>/<bb>/<full-hex>`. Reads re-hash and compare,
+//! so corruption is detected, never served. Writes are atomic (temp file +
+//! rename) and fsync'd. Blobs are never modified or deleted by the
+//! application.
+
+use crate::error::StoreError;
+use crate::journal::sha256_hex;
+use std::fs;
+use std::path::{Path, PathBuf};
+
+/// Content-addressed file store rooted at `root`.
+pub struct BlobStore {
+    root: PathBuf,
+}
+
+impl BlobStore {
+    /// Open (creating) the blob store at `root`.
+    pub fn open(root: &Path) -> Result<Self, StoreError> {
+        fs::create_dir_all(root)?;
+        Ok(Self {
+            root: root.to_path_buf(),
+        })
+    }
+
+    fn path_for(&self, sha_hex: &str) -> PathBuf {
+        self.root
+            .join(&sha_hex[0..2])
+            .join(&sha_hex[2..4])
+            .join(sha_hex)
+    }
+
+    /// Store bytes. Returns `(sha256_hex, deduplicated)`. Identical bytes
+    /// store once: the second put is a no-op that reports `deduplicated`.
+    pub fn put(&self, bytes: &[u8]) -> Result<(String, bool), StoreError> {
+        let sha = sha256_hex(bytes);
+        let path = self.path_for(&sha);
+        if path.exists() {
+            return Ok((sha, true));
+        }
+        if let Some(parent) = path.parent() {
+            fs::create_dir_all(parent)?;
+        }
+        // Atomic write: temp file in the same directory, fsync, rename.
+        let tmp = path.with_extension("tmp");
+        {
+            let mut f = fs::File::create(&tmp)?;
+            use std::io::Write;
+            f.write_all(bytes)?;
+            f.sync_all()?;
+        }
+        fs::rename(&tmp, &path)?;
+        // Fsync the directory so the rename itself is durable.
+        let dir = fs::File::open(path.parent().unwrap())?;
+        dir.sync_all()?;
+        Ok((sha, false))
+    }
+
+    /// Read bytes, verifying the SHA-256. A mismatch is corruption, and it
+    /// is reported — never served.
+    pub fn get(&self, sha_hex: &str) -> Result<Vec<u8>, StoreError> {
+        let sha_hex = sha_hex.to_lowercase();
+        let bytes = fs::read(self.path_for(&sha_hex))?;
+        let actual = sha256_hex(&bytes);
+        if actual != sha_hex {
+            return Err(StoreError::CorruptBlob(sha_hex));
+        }
+        Ok(bytes)
+    }
+
+    /// True when the blob exists (content not verified; use [`Self::get`]
+    /// for a verifying read).
+    pub fn exists(&self, sha_hex: &str) -> bool {
+        self.path_for(&sha_hex.to_lowercase()).exists()
+    }
+}