diff --git a/backend/app/modules/code/code_context_api.py b/backend/app/modules/code/code_context_api.py
index 644c889e..db3cd495 100644
--- a/backend/app/modules/code/code_context_api.py
+++ b/backend/app/modules/code/code_context_api.py
@@ -30,7 +30,7 @@
 
 class BuildContextRequest(BaseModel):
     """Request to build repository context."""
-    repoPath: str = Field(..., description="Absolute path to repository")
+    repoPath: str = Field(..., max_length=1024, description="Absolute path to repository")
     includeGlobs: List[str] = Field(default=["*"], description="Glob patterns to include")
     excludeGlobs: List[str] = Field(default=[], description="Additional glob patterns to exclude")
     maxFileSize: int = Field(default=1024*1024, description="Maximum file size in bytes")
diff --git a/backend/tests/test_pr_16_code_context_validation.py b/backend/tests/test_pr_16_code_context_validation.py
new file mode 100644
index 00000000..5a2cf35e
--- /dev/null
+++ b/backend/tests/test_pr_16_code_context_validation.py
@@ -0,0 +1,35 @@
+"""Tests for code_context_api BuildContextRequest repoPath validation (PR-B16)."""
+import sys
+import os
+import pytest
+
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), ".."))
+
+from app.modules.code.code_context_api import BuildContextRequest
+
+
+class TestBuildContextRequestRepoPathMaxLength:
+    """repoPath must reject values longer than 1024 characters."""
+
+    def test_normal_repopath_accepted(self):
+        req = BuildContextRequest(repoPath="/home/user/repos/project")
+        assert req.repoPath == "/home/user/repos/project"
+
+    def test_repopath_at_max_length_accepted(self):
+        path = "a" * 1024
+        req = BuildContextRequest(repoPath=path)
+        assert len(req.repoPath) == 1024
+
+    def test_repopath_over_max_length_rejected(self):
+        from pydantic import ValidationError
+        path = "a" * 1025
+        with pytest.raises(ValidationError) as exc_info:
+            BuildContextRequest(repoPath=path)
+        errors = exc_info.value.errors()
+        assert any("repoPath" in str(e.get("loc", "")) for e in errors)
+
+    def test_repopath_massively_over_rejected(self):
+        from pydantic import ValidationError
+        path = "z" * 50000
+        with pytest.raises(ValidationError):
+            BuildContextRequest(repoPath=path)