feat(mcp): restore durable checkpoints

apps/server/src/checkpointing/CheckpointStore.test.ts

@@ -114,6 +114,76 @@ it.layer(TestLayer)("CheckpointStore.layer", (it) => {
     );
   });
 
+  describe("readWorkspaceFingerprint", () => {
+    it.effect("tracks the exact tracked and untracked tree affected by restore", () =>
+      Effect.gen(function* () {
+        const tmp = yield* makeTmpDir();
+        yield* initRepoWithCommit(tmp);
+        const checkpointStore = yield* CheckpointStore.CheckpointStore;
+
+        const initial = yield* checkpointStore.readWorkspaceFingerprint(tmp);
+        yield* writeTextFile(NodePath.join(tmp, "README.md"), "# changed\n");
+        const trackedChange = yield* checkpointStore.readWorkspaceFingerprint(tmp);
+        yield* writeTextFile(NodePath.join(tmp, "new-file.txt"), "new\n");
+        const untrackedChange = yield* checkpointStore.readWorkspaceFingerprint(tmp);
+
+        expect(trackedChange).not.toBe(initial);
+        expect(untrackedChange).not.toBe(trackedChange);
+        expect(yield* git(tmp, ["status", "--short"])).toContain("README.md");
+        expect(yield* git(tmp, ["status", "--short"])).toContain("new-file.txt");
+      }),
+    );
+
+    it.effect("tracks staged-only changes without modifying the user's index", () =>
+      Effect.gen(function* () {
+        const tmp = yield* makeTmpDir();
+        yield* initRepoWithCommit(tmp);
+        const checkpointStore = yield* CheckpointStore.CheckpointStore;
+        const readme = NodePath.join(tmp, "README.md");
+
+        const initial = yield* checkpointStore.readWorkspaceFingerprint(tmp);
+        yield* writeTextFile(readme, "# staged\n");
+        yield* git(tmp, ["add", "README.md"]);
+        yield* writeTextFile(readme, "# test\n");
+        const stagedBefore = yield* git(tmp, ["diff", "--cached", "--", "README.md"]);
+        const stagedOnly = yield* checkpointStore.readWorkspaceFingerprint(tmp);
+        const stagedAfter = yield* git(tmp, ["diff", "--cached", "--", "README.md"]);
+
+        expect(stagedOnly).not.toBe(initial);
+        expect(stagedAfter).toBe(stagedBefore);
+        expect(yield* git(tmp, ["diff", "--", "README.md"])).not.toBe("");
+      }),
+    );
+
+    it.effect("limits staged-state fingerprints to a nested restore cwd", () =>
+      Effect.gen(function* () {
+        const tmp = yield* makeTmpDir();
+        yield* initRepoWithCommit(tmp);
+        const nested = NodePath.join(tmp, "packages", "nested");
+        const sibling = NodePath.join(tmp, "sibling.txt");
+        const nestedFile = NodePath.join(nested, "file.txt");
+        const fileSystem = yield* FileSystem.FileSystem;
+        yield* fileSystem.makeDirectory(nested, { recursive: true });
+        yield* writeTextFile(nestedFile, "nested\n");
+        yield* writeTextFile(sibling, "sibling\n");
+        yield* git(tmp, ["add", "."]);
+        yield* git(tmp, ["commit", "-m", "nested files"]);
+        const checkpointStore = yield* CheckpointStore.CheckpointStore;
+
+        const initial = yield* checkpointStore.readWorkspaceFingerprint(nested);
+        yield* writeTextFile(sibling, "sibling staged\n");
+        yield* git(tmp, ["add", "sibling.txt"]);
+        yield* writeTextFile(sibling, "sibling\n");
+        expect(yield* checkpointStore.readWorkspaceFingerprint(nested)).toBe(initial);
+
+        yield* writeTextFile(nestedFile, "nested staged\n");
+        yield* git(tmp, ["add", "packages/nested/file.txt"]);
+        yield* writeTextFile(nestedFile, "nested\n");
+        expect(yield* checkpointStore.readWorkspaceFingerprint(nested)).not.toBe(initial);
+      }),
+    );
+  });
+
   describe("diffCheckpoints", () => {
     it.effect("returns full oversized checkpoint diffs without truncation", () =>
       Effect.gen(function* () {

apps/server/src/checkpointing/CheckpointStore.ts

@@ -53,6 +53,9 @@ export class CheckpointStore extends Context.Service<
     /** Check whether cwd is inside a Git worktree. */
     readonly isGitRepository: (cwd: string) => Effect.Effect<boolean, CheckpointStoreError>;
 
+    /** Hash the tracked and untracked workspace state affected by restore. */
+    readonly readWorkspaceFingerprint: (cwd: string) => Effect.Effect<string, CheckpointStoreError>;
+
     /**
      * Capture a checkpoint commit and store it at the provided checkpoint ref.
      *
@@ -119,6 +122,15 @@ export const make = Effect.gen(function* () {
       .detect({ cwd, requestedKind: "git" })
       .pipe(Effect.map((repository) => repository !== null));
 
+  const readWorkspaceFingerprint: CheckpointStore["Service"]["readWorkspaceFingerprint"] =
+    Effect.fn("readWorkspaceFingerprint")(function* (cwd) {
+      const checkpoints = yield* resolveCheckpoints(
+        "CheckpointStore.readWorkspaceFingerprint",
+        cwd,
+      );
+      return yield* checkpoints.readWorkspaceFingerprint(cwd);
+    });
+
   const captureCheckpoint: CheckpointStore["Service"]["captureCheckpoint"] = Effect.fn(
     "captureCheckpoint",
   )(function* (input) {
@@ -159,6 +171,7 @@ export const make = Effect.gen(function* () {
 
   return CheckpointStore.of({
     isGitRepository,
+    readWorkspaceFingerprint,
     captureCheckpoint,
     hasCheckpointRef,
     restoreCheckpoint,