diff --git a/plugins/codex/scripts/lib/git.mjs b/plugins/codex/scripts/lib/git.mjs
index 1749cfc8..98b2e210 100644
--- a/plugins/codex/scripts/lib/git.mjs
+++ b/plugins/codex/scripts/lib/git.mjs
@@ -65,8 +65,8 @@ function measureCombinedGitOutputBytes(cwd, argSets, maxBytes) {
   return totalBytes;
 }
 
-function buildBranchComparison(cwd, baseRef) {
-  const mergeBase = gitChecked(cwd, ["merge-base", "HEAD", baseRef]).stdout.trim();
+function buildBranchComparison(cwd, baseRef, _gitCheckedImpl = gitChecked) {
+  const mergeBase = _gitCheckedImpl(cwd, ["merge-base", "HEAD", "--end-of-options", baseRef]).stdout.trim();
   return {
     mergeBase,
     commitRange: `${mergeBase}..HEAD`,
@@ -101,11 +101,11 @@ export function detectDefaultBranch(cwd) {
 
   const candidates = ["main", "master", "trunk"];
   for (const candidate of candidates) {
-    const local = git(cwd, ["show-ref", "--verify", "--quiet", `refs/heads/${candidate}`]);
+    const local = git(cwd, ["show-ref", "--verify", "--quiet", "--end-of-options", `refs/heads/${candidate}`]);
     if (local.status === 0) {
       return candidate;
     }
-    const remote = git(cwd, ["show-ref", "--verify", "--quiet", `refs/remotes/origin/${candidate}`]);
+    const remote = git(cwd, ["show-ref", "--verify", "--quiet", "--end-of-options", `refs/remotes/origin/${candidate}`]);
     if (remote.status === 0) {
       return `origin/${candidate}`;
     }
@@ -262,9 +262,9 @@ function collectBranchContext(cwd, baseRef, options = {}) {
   const includeDiff = options.includeDiff !== false;
   const comparison = options.comparison ?? buildBranchComparison(cwd, baseRef);
   const currentBranch = getCurrentBranch(cwd);
-  const changedFiles = gitChecked(cwd, ["diff", "--name-only", comparison.commitRange]).stdout.trim().split("\n").filter(Boolean);
-  const logOutput = gitChecked(cwd, ["log", "--oneline", "--decorate", comparison.commitRange]).stdout.trim();
-  const diffStat = gitChecked(cwd, ["diff", "--stat", comparison.commitRange]).stdout.trim();
+  const changedFiles = gitChecked(cwd, ["diff", "--name-only", "--end-of-options", comparison.commitRange]).stdout.trim().split("\n").filter(Boolean);
+  const logOutput = gitChecked(cwd, ["log", "--oneline", "--decorate", "--end-of-options", comparison.commitRange]).stdout.trim();
+  const diffStat = gitChecked(cwd, ["diff", "--stat", "--end-of-options", comparison.commitRange]).stdout.trim();
 
   return {
     mode: "branch",
@@ -275,7 +275,7 @@ function collectBranchContext(cwd, baseRef, options = {}) {
           formatSection("Diff Stat", diffStat),
           formatSection(
             "Branch Diff",
-            gitChecked(cwd, ["diff", "--binary", "--no-ext-diff", "--submodule=diff", comparison.commitRange]).stdout
+            gitChecked(cwd, ["diff", "--binary", "--no-ext-diff", "--submodule=diff", "--end-of-options", comparison.commitRange]).stdout
           )
         ].join("\n")
       : [
@@ -321,11 +321,11 @@ export function collectReviewContext(cwd, target, options = {}) {
         diffBytes <= maxInlineDiffBytes);
     details = collectWorkingTreeContext(repoRoot, state, { includeDiff });
   } else {
-    const comparison = buildBranchComparison(repoRoot, target.baseRef);
-    const fileCount = gitChecked(repoRoot, ["diff", "--name-only", comparison.commitRange]).stdout.trim().split("\n").filter(Boolean).length;
+    const comparison = buildBranchComparison(repoRoot, target.baseRef, options._gitCheckedImpl);
+    const fileCount = gitChecked(repoRoot, ["diff", "--name-only", "--end-of-options", comparison.commitRange]).stdout.trim().split("\n").filter(Boolean).length;
     diffBytes = measureGitOutputBytes(
       repoRoot,
-      ["diff", "--binary", "--no-ext-diff", "--submodule=diff", comparison.commitRange],
+      ["diff", "--binary", "--no-ext-diff", "--submodule=diff", "--end-of-options", comparison.commitRange],
       maxInlineDiffBytes
     );
     includeDiff = options.includeDiff ?? (fileCount <= maxInlineFiles && diffBytes <= maxInlineDiffBytes);
diff --git a/tests/git.test.mjs b/tests/git.test.mjs
index 14ff2576..7e838faa 100644
--- a/tests/git.test.mjs
+++ b/tests/git.test.mjs
@@ -4,6 +4,7 @@ import test from "node:test";
 import assert from "node:assert/strict";
 
 import { collectReviewContext, resolveReviewTarget } from "../plugins/codex/scripts/lib/git.mjs";
+import { runCommandChecked } from "../plugins/codex/scripts/lib/process.mjs";
 import { initGitRepo, makeTempDir, run } from "./helpers.mjs";
 
 test("resolveReviewTarget prefers working tree when repo is dirty", () => {
@@ -181,3 +182,90 @@ test("collectReviewContext keeps untracked file content in lightweight working t
   assert.match(context.content, /## Untracked Files/);
   assert.match(context.content, /UNTRACKED_RISK_MARKER/);
 });
+
+// --- option-injection hardening tests ---
+
+test("resolveReviewTarget with a flag-shaped --base value does not pass it as a git option", () => {
+  const cwd = makeTempDir();
+  initGitRepo(cwd);
+  fs.writeFileSync(path.join(cwd, "app.js"), "console.log('v1');\n");
+  run("git", ["add", "app.js"], { cwd });
+  run("git", ["commit", "-m", "init"], { cwd });
+  run("git", ["checkout", "-b", "feature/test"], { cwd });
+  fs.writeFileSync(path.join(cwd, "app.js"), "console.log('v2');\n");
+  run("git", ["add", "app.js"], { cwd });
+  run("git", ["commit", "-m", "change"], { cwd });
+
+  // Sentinel file that --output= would create if option-parsing succeeded.
+  const sentinel = path.join(cwd, "sentinel-must-not-exist.txt");
+  assert.equal(fs.existsSync(sentinel), false, "sentinel must not exist before the call");
+
+  const target = resolveReviewTarget(cwd, { base: `--output=${sentinel}` });
+
+  // resolveReviewTarget itself just records the baseRef; the hostile value
+  // only reaches git when collectReviewContext calls buildBranchComparison.
+  assert.equal(target.mode, "branch");
+  assert.equal(target.baseRef, `--output=${sentinel}`);
+
+  // collectReviewContext must throw because git rejects the value as a bad ref,
+  // NOT silently succeed (which would indicate option-injection worked).
+  // Note: git merge-base does not support --output, so in practice the current
+  // code also errors — but without --end-of-options the boundary is unguarded
+  // if a future subcommand does accept such an option.
+  assert.throws(
+    () => collectReviewContext(cwd, target),
+    /unknown revision|bad revision|did not match|ambiguous argument|unknown option|not a valid object name/i
+  );
+
+  // The sentinel must still not exist — git did NOT treat the value as --output=<file>.
+  assert.equal(fs.existsSync(sentinel), false, "sentinel must remain absent after the call");
+});
+
+test("resolveReviewTarget accepts refs with embedded dashes", () => {
+  const cwd = makeTempDir();
+  initGitRepo(cwd);
+  fs.writeFileSync(path.join(cwd, "app.js"), "console.log('v1');\n");
+  run("git", ["add", "app.js"], { cwd });
+  run("git", ["commit", "-m", "init"], { cwd });
+  run("git", ["checkout", "-b", "feature/has-dashes-in-name"], { cwd });
+  fs.writeFileSync(path.join(cwd, "app.js"), "console.log('v2');\n");
+  run("git", ["add", "app.js"], { cwd });
+  run("git", ["commit", "-m", "change"], { cwd });
+  run("git", ["checkout", "main"], { cwd });
+
+  const target = resolveReviewTarget(cwd, { base: "feature/has-dashes-in-name" });
+  const context = collectReviewContext(cwd, target);
+
+  assert.equal(target.mode, "branch");
+  assert.equal(target.baseRef, "feature/has-dashes-in-name");
+  assert.match(context.content, /Branch Diff|Diff Stat|Changed Files/);
+});
+
+test("buildBranchComparison passes --end-of-options before user-controlled baseRef in merge-base argv", () => {
+  const cwd = makeTempDir();
+  initGitRepo(cwd);
+  fs.writeFileSync(path.join(cwd, "app.js"), "console.log('v1');\n");
+  run("git", ["add", "app.js"], { cwd });
+  run("git", ["commit", "-m", "init"], { cwd });
+  run("git", ["checkout", "-b", "feature/test"], { cwd });
+  fs.writeFileSync(path.join(cwd, "app.js"), "console.log('v2');\n");
+  run("git", ["add", "app.js"], { cwd });
+  run("git", ["commit", "-m", "change"], { cwd });
+
+  const capturedArgvs = [];
+  const spyGitChecked = (wd, args, opts = {}) => {
+    capturedArgvs.push([...args]);
+    return runCommandChecked("git", args, { cwd: wd, ...opts });
+  };
+
+  const target = resolveReviewTarget(cwd, { base: "main" });
+  collectReviewContext(cwd, target, { _gitCheckedImpl: spyGitChecked });
+
+  const mergeBaseArgv = capturedArgvs.find((args) => args[0] === "merge-base");
+  assert.ok(mergeBaseArgv, "expected a merge-base call to be captured");
+
+  const eooIdx = mergeBaseArgv.indexOf("--end-of-options");
+  const baseRefIdx = mergeBaseArgv.indexOf("main");
+  assert.ok(eooIdx !== -1, `--end-of-options must appear in merge-base argv; got: ${JSON.stringify(mergeBaseArgv)}`);
+  assert.ok(eooIdx < baseRefIdx, `--end-of-options must come before baseRef; got: ${JSON.stringify(mergeBaseArgv)}`);
+});