mcp: Implement Smart Cache Engine stdio server

Replace the placeholder `sce mcp` implementation with a full MCP stdio
server providing cache-aware file reads. The server persists per-repo
cache state under <state_root>/sce/cache/ and tracks file visibility
across sessions.

Author: davidabram

cli/Cargo.lock

@@ -23,8 +23,10 @@ reqwest = { version = "0.12", default-features = false, features = ["json", "rus
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"
 sha2 = "0.10"
-tokio = { version = "1", default-features = false, features = ["rt"] }
+tokio = { version = "1", default-features = false, features = ["rt", "io-util"] }
 tracing = "0.1"
+rmcp = { version = "1", features = ["server", "transport-io"] }
+schemars = "1"
 tracing-opentelemetry = "0.29"
 tracing-subscriber = { version = "0.3", features = ["registry"] }
 turso = "0"

cli/Cargo.toml

@@ -4,6 +4,7 @@ use std::{
     fs,
     io::{self, Write as IoWrite},
     path::{Path, PathBuf},
+    process::Command,
 };
 
 const TARGETS: &[TargetSpec] = &[
@@ -34,6 +35,59 @@ fn main() {
     if let Err(error) = generate_embedded_asset_manifest() {
         panic!("failed to generate setup embedded asset manifest: {error}");
     }
+
+    emit_git_commit();
+}
+
+fn emit_git_commit() {
+    println!("cargo:rerun-if-env-changed=SCE_GIT_COMMIT");
+
+    if let Ok(commit) = env::var("SCE_GIT_COMMIT") {
+        let commit = commit.trim();
+        if !commit.is_empty() {
+            println!("cargo:rustc-env=SCE_GIT_COMMIT={commit}");
+            return;
+        }
+    }
+
+    let manifest_dir = match env::var("CARGO_MANIFEST_DIR") {
+        Ok(value) => PathBuf::from(value),
+        Err(_) => return,
+    };
+
+    let repository_root = match manifest_dir.parent() {
+        Some(path) => path.to_path_buf(),
+        None => return,
+    };
+
+    let git_dir = repository_root.join(".git");
+    println!("cargo:rerun-if-changed={}", git_dir.join("HEAD").display());
+    println!(
+        "cargo:rerun-if-changed={}",
+        git_dir.join("packed-refs").display()
+    );
+
+    let output = Command::new("git")
+        .args(["rev-parse", "--short=12", "HEAD"])
+        .current_dir(&repository_root)
+        .output();
+
+    let Ok(output) = output else {
+        return;
+    };
+
+    if !output.status.success() {
+        return;
+    }
+
+    let Ok(commit) = String::from_utf8(output.stdout) else {
+        return;
+    };
+
+    let commit = commit.trim();
+    if !commit.is_empty() {
+        println!("cargo:rustc-env=SCE_GIT_COMMIT={commit}");
+    }
 }
 
 fn generate_embedded_asset_manifest() -> io::Result<()> {

cli/build.rs

@@ -29,6 +29,14 @@
         };
 
         version = pkgs.lib.strings.trim (builtins.readFile "${src}/.version");
+        gitCommit =
+          if self ? rev then
+            self.rev
+          else if self ? dirtyRev then
+            self.dirtyRev
+          else
+            "unknown";
+        shortGitCommit = builtins.substring 0 12 gitCommit;
 
         rustToolchain = pkgs.rust-bin.stable.latest.default.override {
           extensions = [
@@ -47,6 +55,7 @@
           inherit version;
           inherit src;
           sourceRoot = "source/cli";
+          SCE_GIT_COMMIT = shortGitCommit;
 
           cargoLock = {
             lockFile = ./Cargo.lock;
@@ -80,6 +89,7 @@
             inherit version;
             inherit src;
             sourceRoot = "source/cli";
+            SCE_GIT_COMMIT = shortGitCommit;
 
             cargoLock = {
               lockFile = ./Cargo.lock;
@@ -111,6 +121,7 @@
             inherit version;
             inherit src;
             sourceRoot = "source/cli";
+            SCE_GIT_COMMIT = shortGitCommit;
 
             cargoLock = {
               lockFile = ./Cargo.lock;