diff --git a/apps/server/src/vcs/GitVcsDriverCore.ts b/apps/server/src/vcs/GitVcsDriverCore.ts
index 0dd73af687f9..4ce3f7e07866 100644
--- a/apps/server/src/vcs/GitVcsDriverCore.ts
+++ b/apps/server/src/vcs/GitVcsDriverCore.ts
@@ -860,6 +860,9 @@ export const makeGitVcsDriverCore = Effect.fn("makeGitVcsDriverCore")(function*
               cwd: commandInput.cwd,
               env: {
                 ...process.env,
+                // Status polling runs beside the user's own git commands; without this,
+                // `git status` takes index.lock to save its refreshed index.
+                GIT_OPTIONAL_LOCKS: "0",
                 ...input.env,
                 ...trace2Monitor.env,
               },
@@ -1771,10 +1774,12 @@ export const makeGitVcsDriverCore = Effect.fn("makeGitVcsDriverCore")(function*
     const statusCacheKey = repositoryPaths?.gitCommonDir;
     const [numstatStdout, defaultBranch, hasPrimaryRemote] = yield* Effect.all(
       [
+        // Plumbing, because porcelain `git diff` rewrites the index even with
+        // GIT_OPTIONAL_LOCKS=0. -M keeps porcelain's rename detection.
         executeGitWithStableDiagnostics(
           "GitVcsDriver.statusDetails.numstat",
           cwd,
-          ["diff", "HEAD", "--numstat", "--"],
+          ["diff-index", "-M", "--numstat", "HEAD", "--"],
           { allowNonZeroExit: true },
         ).pipe(
           Effect.flatMap((result) => {
@@ -1783,7 +1788,7 @@ export const makeGitVcsDriverCore = Effect.fn("makeGitVcsDriverCore")(function*
               return Effect.map(
                 Effect.all([
                   runGitStdout("GitVcsDriver.statusDetails.numstat.unborn", cwd, [
-                    "diff",
+                    "diff-files",
                     "--numstat",
                   ]),
                   runGitStdout("GitVcsDriver.statusDetails.numstat.unborn.staged", cwd, [
@@ -1816,9 +1821,9 @@ export const makeGitVcsDriverCore = Effect.fn("makeGitVcsDriverCore")(function*
                 ...gitCommandContext({
                   operation: "GitVcsDriver.statusDetails.numstat",
                   cwd,
-                  args: ["diff", "HEAD", "--numstat", "--"],
+                  args: ["diff-index", "-M", "--numstat", "HEAD", "--"],
                 }),
-                detail: "git diff HEAD --numstat failed.",
+                detail: "git diff-index HEAD --numstat failed.",
                 exitCode: result.exitCode,
                 stdoutLength: result.stdout.length,
                 stderrLength: result.stderr.length,