diff --git a/apps/coordinator/pyproject.toml b/apps/coordinator/pyproject.toml
index 2017ffa..c8cd787 100644
--- a/apps/coordinator/pyproject.toml
+++ b/apps/coordinator/pyproject.toml
@@ -10,6 +10,7 @@ dependencies = [
     "pydantic-settings>=2.1.0",
     "python-dotenv>=1.0.0",
     "anthropic>=0.39.0",
+    "slowapi>=0.1.9",
 ]
 
 [project.optional-dependencies]
diff --git a/apps/coordinator/src/gates/build_gate.py b/apps/coordinator/src/gates/build_gate.py
index 4cbb650..64876d3 100644
--- a/apps/coordinator/src/gates/build_gate.py
+++ b/apps/coordinator/src/gates/build_gate.py
@@ -24,6 +24,7 @@ class BuildGate:
                 capture_output=True,
                 text=True,
                 check=False,  # Don't raise on non-zero exit
+                timeout=300,  # 5 minute timeout
             )
 
             if result.returncode == 0:
@@ -54,11 +55,11 @@ class BuildGate:
                 details={"error": str(e)},
             )
 
-        except subprocess.CalledProcessError as e:
+        except subprocess.TimeoutExpired as e:
             return GateResult(
                 passed=False,
-                message="Build gate failed: Error running mypy",
-                details={"error": str(e), "return_code": e.returncode},
+                message=f"Build gate failed: mypy timed out after {e.timeout} seconds",
+                details={"error": str(e), "timeout": e.timeout},
             )
 
         except Exception as e:
diff --git a/apps/coordinator/src/gates/coverage_gate.py b/apps/coordinator/src/gates/coverage_gate.py
index d658ad2..256fba5 100644
--- a/apps/coordinator/src/gates/coverage_gate.py
+++ b/apps/coordinator/src/gates/coverage_gate.py
@@ -1,6 +1,7 @@
 """CoverageGate - Enforces 85% minimum test coverage via pytest-cov."""
 
 import json
+import os
 import subprocess
 from pathlib import Path
 
@@ -35,6 +36,7 @@ class CoverageGate:
                 capture_output=True,
                 text=True,
                 check=False,  # Don't raise on non-zero exit
+                timeout=300,  # 5 minute timeout
             )
 
             # Try to read coverage data from coverage.json
@@ -94,11 +96,11 @@ class CoverageGate:
                 details={"error": str(e)},
             )
 
-        except subprocess.CalledProcessError as e:
+        except subprocess.TimeoutExpired as e:
             return GateResult(
                 passed=False,
-                message="Coverage gate failed: Error running pytest",
-                details={"error": str(e), "return_code": e.returncode},
+                message=f"Coverage gate failed: pytest timed out after {e.timeout} seconds",
+                details={"error": str(e), "timeout": e.timeout},
             )
 
         except Exception as e:
@@ -111,18 +113,28 @@ class CoverageGate:
     def _extract_coverage_from_json(self) -> float | None:
         """Extract coverage percentage from coverage.json file.
 
+        Uses absolute path resolved from current working directory and validates
+        that the path is within project boundaries to prevent path traversal attacks.
+
         Returns:
             float | None: Coverage percentage or None if file not found
         """
         try:
-            coverage_file = Path("coverage.json")
+            # Get absolute path from current working directory
+            cwd = Path.cwd().resolve()
+            coverage_file = (cwd / "coverage.json").resolve()
+
+            # Validate that coverage file is within project directory (prevent path traversal)
+            if not str(coverage_file).startswith(str(cwd)):
+                return None
+
             if coverage_file.exists():
                 with open(coverage_file) as f:
                     data = json.load(f)
                     percent = data.get("totals", {}).get("percent_covered")
                     if percent is not None and isinstance(percent, (int, float)):
                         return float(percent)
-        except (FileNotFoundError, json.JSONDecodeError, KeyError):
+        except (FileNotFoundError, json.JSONDecodeError, KeyError, OSError):
             pass
         return None
 
diff --git a/apps/coordinator/src/gates/lint_gate.py b/apps/coordinator/src/gates/lint_gate.py
index 7d3524d..97ee44d 100644
--- a/apps/coordinator/src/gates/lint_gate.py
+++ b/apps/coordinator/src/gates/lint_gate.py
@@ -24,6 +24,7 @@ class LintGate:
                 capture_output=True,
                 text=True,
                 check=False,  # Don't raise on non-zero exit
+                timeout=300,  # 5 minute timeout
             )
 
             if result.returncode == 0:
@@ -54,11 +55,11 @@ class LintGate:
                 details={"error": str(e)},
             )
 
-        except subprocess.CalledProcessError as e:
+        except subprocess.TimeoutExpired as e:
             return GateResult(
                 passed=False,
-                message="Lint gate failed: Error running ruff",
-                details={"error": str(e), "return_code": e.returncode},
+                message=f"Lint gate failed: ruff timed out after {e.timeout} seconds",
+                details={"error": str(e), "timeout": e.timeout},
             )
 
         except Exception as e:
diff --git a/apps/coordinator/src/gates/test_gate.py b/apps/coordinator/src/gates/test_gate.py
index bc29cd5..754feda 100644
--- a/apps/coordinator/src/gates/test_gate.py
+++ b/apps/coordinator/src/gates/test_gate.py
@@ -24,6 +24,7 @@ class TestGate:
                 capture_output=True,
                 text=True,
                 check=False,  # Don't raise on non-zero exit
+                timeout=300,  # 5 minute timeout
             )
 
             if result.returncode == 0:
@@ -54,11 +55,11 @@ class TestGate:
                 details={"error": str(e)},
             )
 
-        except subprocess.CalledProcessError as e:
+        except subprocess.TimeoutExpired as e:
             return GateResult(
                 passed=False,
-                message="Test gate failed: Error running pytest",
-                details={"error": str(e), "return_code": e.returncode},
+                message=f"Test gate failed: pytest timed out after {e.timeout} seconds",
+                details={"error": str(e), "timeout": e.timeout},
             )
 
         except Exception as e:
diff --git a/apps/coordinator/src/main.py b/apps/coordinator/src/main.py
index 75da040..d0b1153 100644
--- a/apps/coordinator/src/main.py
+++ b/apps/coordinator/src/main.py
@@ -7,8 +7,11 @@ from contextlib import asynccontextmanager
 from pathlib import Path
 from typing import Any
 
-from fastapi import FastAPI
+from fastapi import FastAPI, Request
 from pydantic import BaseModel
+from slowapi import Limiter, _rate_limit_exceeded_handler
+from slowapi.errors import RateLimitExceeded
+from slowapi.util import get_remote_address
 
 from .config import settings
 from .coordinator import Coordinator
@@ -104,6 +107,9 @@ async def lifespan(app: FastAPI) -> AsyncIterator[dict[str, Any]]:
     logger.info("Mosaic-coordinator shutdown complete")
 
 
+# Initialize rate limiter
+limiter = Limiter(key_func=get_remote_address)
+
 # Create FastAPI application
 app = FastAPI(
     title="Mosaic Coordinator",
@@ -112,6 +118,10 @@ app = FastAPI(
     lifespan=lifespan,
 )
 
+# Register rate limiter
+app.state.limiter = limiter
+app.add_exception_handler(RateLimitExceeded, _rate_limit_exceeded_handler)
+
 
 class HealthResponse(BaseModel):
     """Health check response model."""
diff --git a/apps/coordinator/src/quality_orchestrator.py b/apps/coordinator/src/quality_orchestrator.py
index 551929a..a3e343d 100644
--- a/apps/coordinator/src/quality_orchestrator.py
+++ b/apps/coordinator/src/quality_orchestrator.py
@@ -1,7 +1,9 @@
 """Quality Orchestrator service for coordinating quality gate execution."""
 
 import asyncio
-from typing import Any
+import inspect
+from typing import Any, cast
+from unittest.mock import Mock
 
 from pydantic import BaseModel, Field
 
@@ -127,37 +129,51 @@ class QualityOrchestrator:
             Production gates are run in a thread pool to avoid blocking the event loop.
             Test mocks can be async functions or lambdas returning coroutines.
         """
-        import inspect
-        from typing import cast
-        from unittest.mock import Mock
-
         # Check if gate.check is an async function
         if inspect.iscoroutinefunction(gate.check):
             return cast(GateResult, await gate.check())
 
-        # Check if gate.check is a Mock/MagicMock (testing scenario)
+        # Check if it's a real production gate instance
+        if self._is_real_gate(gate):
+            # Real gate - run in thread pool to avoid blocking event loop
+            return cast(GateResult, await asyncio.to_thread(gate.check))
+
+        # Handle test mocks and callables
+        return await self._handle_test_mock(gate)
+
+    def _is_real_gate(self, gate: Any) -> bool:
+        """Check if gate is a real production gate instance.
+
+        Args:
+            gate: Gate instance to check
+
+        Returns:
+            bool: True if gate is a real production gate
+        """
+        if not inspect.ismethod(gate.check):
+            return False
+
+        gate_class_name = gate.__class__.__name__
+        return gate_class_name in ("BuildGate", "LintGate", "TestGate", "CoverageGate")
+
+    async def _handle_test_mock(self, gate: Any) -> GateResult:
+        """Handle test mocks and callables.
+
+        Args:
+            gate: Gate mock or callable to handle
+
+        Returns:
+            GateResult: Result from the mock
+        """
+        # Check if it's a Mock/MagicMock (testing scenario)
         mock_types = ("Mock", "MagicMock", "AsyncMock")
         if isinstance(gate.check, Mock) or type(gate.check).__name__ in mock_types:
-            # It's a mock - call it and handle the result
             result_or_coro = gate.check()
             if asyncio.iscoroutine(result_or_coro):
                 return cast(GateResult, await result_or_coro)
             return cast(GateResult, result_or_coro)
 
-        # Check if gate.check is a lambda or other callable (could be test or production)
-        # For lambdas in tests that return coroutines, we need to call and await
-        # But we need to avoid calling real production gates outside of to_thread
-        # The distinguishing factor: real gates are methods on BuildGate/LintGate/etc classes
-
-        # Check if it's a bound method on a real gate class
-        if inspect.ismethod(gate.check):
-            # Check if the class is one of our real gate classes
-            gate_class_name = gate.__class__.__name__
-            if gate_class_name in ("BuildGate", "LintGate", "TestGate", "CoverageGate"):
-                # It's a real gate - run in thread pool
-                return cast(GateResult, await asyncio.to_thread(gate.check))
-
-        # For any other callable (lambdas, functions), try calling and see what it returns
+        # For any other callable (lambdas, functions), call and check result
         result_or_coro = gate.check()
         if asyncio.iscoroutine(result_or_coro):
             return cast(GateResult, await result_or_coro)
diff --git a/apps/coordinator/src/webhook.py b/apps/coordinator/src/webhook.py
index 18ea2eb..c68410a 100644
--- a/apps/coordinator/src/webhook.py
+++ b/apps/coordinator/src/webhook.py
@@ -5,6 +5,8 @@ from typing import Any
 
 from fastapi import APIRouter, Header, HTTPException, Request
 from pydantic import BaseModel, Field
+from slowapi import Limiter
+from slowapi.util import get_remote_address
 
 from .config import settings
 from .security import verify_signature
@@ -13,6 +15,9 @@ logger = logging.getLogger(__name__)
 
 router = APIRouter()
 
+# Initialize limiter for this module
+limiter = Limiter(key_func=get_remote_address)
+
 
 class WebhookResponse(BaseModel):
     """Response model for webhook endpoint."""
@@ -34,6 +39,7 @@ class GiteaWebhookPayload(BaseModel):
 
 
 @router.post("/webhook/gitea", response_model=WebhookResponse)
+@limiter.limit("100/minute")  # Per-IP rate limit: 100 requests per minute
 async def handle_gitea_webhook(
     request: Request,
     payload: GiteaWebhookPayload,
diff --git a/apps/coordinator/tests/gates/test_build_gate.py b/apps/coordinator/tests/gates/test_build_gate.py
index 3f1d04d..7dd4c41 100644
--- a/apps/coordinator/tests/gates/test_build_gate.py
+++ b/apps/coordinator/tests/gates/test_build_gate.py
@@ -131,3 +131,37 @@ class TestBuildGate:
             assert result.passed is False
             assert "unexpected error" in result.message.lower()
             assert "error" in result.details
+
+    def test_check_uses_timeout(self) -> None:
+        """Test that check() sets a timeout on subprocess.run."""
+        mock_result = MagicMock()
+        mock_result.returncode = 0
+        mock_result.stdout = "Success: no issues found"
+        mock_result.stderr = ""
+
+        with patch("subprocess.run", return_value=mock_result) as mock_run:
+            gate = BuildGate()
+            gate.check()
+
+            # Verify timeout is set
+            mock_run.assert_called_once()
+            call_kwargs = mock_run.call_args[1]
+            assert "timeout" in call_kwargs
+            assert call_kwargs["timeout"] == 300  # 5 minutes
+
+    def test_check_handles_timeout_exception(self) -> None:
+        """Test that check() handles subprocess timeout gracefully."""
+        # Mock subprocess.run to raise TimeoutExpired
+        with patch(
+            "subprocess.run",
+            side_effect=subprocess.TimeoutExpired("mypy", timeout=300),
+        ):
+            gate = BuildGate()
+            result = gate.check()
+
+            # Verify result
+            assert isinstance(result, GateResult)
+            assert result.passed is False
+            # TimeoutExpired message contains "timed out after"
+            assert "timed out" in result.message.lower() or "timeout" in result.message.lower()
+            assert "error" in result.details
diff --git a/apps/coordinator/tests/gates/test_coverage_gate.py b/apps/coordinator/tests/gates/test_coverage_gate.py
index 4868cce..02b451b 100644
--- a/apps/coordinator/tests/gates/test_coverage_gate.py
+++ b/apps/coordinator/tests/gates/test_coverage_gate.py
@@ -254,3 +254,64 @@ class TestCoverageGate:
                 assert isinstance(result, GateResult)
                 assert result.passed is True
                 assert result.details["coverage_percent"] == 90.0
+
+    def test_check_uses_timeout(self) -> None:
+        """Test that check() sets a timeout on subprocess.run."""
+        mock_result = MagicMock()
+        mock_result.returncode = 0
+        mock_result.stdout = "TOTAL     100     10    90%"
+        mock_result.stderr = ""
+
+        coverage_data = {"totals": {"percent_covered": 90.0}}
+
+        with patch("subprocess.run", return_value=mock_result) as mock_run:
+            with patch("builtins.open", mock_open(read_data=json.dumps(coverage_data))):
+                with patch("json.load", return_value=coverage_data):
+                    gate = CoverageGate()
+                    gate.check()
+
+                    # Verify timeout is set
+                    mock_run.assert_called_once()
+                    call_kwargs = mock_run.call_args[1]
+                    assert "timeout" in call_kwargs
+                    assert call_kwargs["timeout"] == 300  # 5 minutes
+
+    def test_check_handles_timeout_exception(self) -> None:
+        """Test that check() handles subprocess timeout gracefully."""
+        # Mock subprocess.run to raise TimeoutExpired
+        with patch(
+            "subprocess.run",
+            side_effect=subprocess.TimeoutExpired("pytest", timeout=300),
+        ):
+            gate = CoverageGate()
+            result = gate.check()
+
+            # Verify result
+            assert isinstance(result, GateResult)
+            assert result.passed is False
+            # TimeoutExpired message contains "timed out after"
+            assert "timed out" in result.message.lower() or "timeout" in result.message.lower()
+            assert "error" in result.details
+
+    def test_coverage_file_path_is_absolute(self) -> None:
+        """Test that coverage.json path is resolved as absolute and validated."""
+        from pathlib import Path
+
+        mock_result = MagicMock()
+        mock_result.returncode = 0
+        mock_result.stdout = "TOTAL     100     10    90%"
+        mock_result.stderr = ""
+
+        coverage_data = {"totals": {"percent_covered": 90.0}}
+
+        with patch("subprocess.run", return_value=mock_result):
+            # Mock Path.exists to return True for absolute path check
+            with patch.object(Path, "exists", return_value=True):
+                with patch("builtins.open", mock_open(read_data=json.dumps(coverage_data))):
+                    with patch("json.load", return_value=coverage_data):
+                        gate = CoverageGate()
+                        # Access the internal method to verify it uses absolute paths
+                        coverage_percent = gate._extract_coverage_from_json()
+
+                        # Should successfully extract coverage
+                        assert coverage_percent == 90.0
diff --git a/apps/coordinator/tests/gates/test_lint_gate.py b/apps/coordinator/tests/gates/test_lint_gate.py
index c9189e1..b4b2f58 100644
--- a/apps/coordinator/tests/gates/test_lint_gate.py
+++ b/apps/coordinator/tests/gates/test_lint_gate.py
@@ -150,3 +150,37 @@ class TestLintGate:
             assert result.passed is False
             assert "unexpected error" in result.message.lower()
             assert "error" in result.details
+
+    def test_check_uses_timeout(self) -> None:
+        """Test that check() sets a timeout on subprocess.run."""
+        mock_result = MagicMock()
+        mock_result.returncode = 0
+        mock_result.stdout = "All checks passed!"
+        mock_result.stderr = ""
+
+        with patch("subprocess.run", return_value=mock_result) as mock_run:
+            gate = LintGate()
+            gate.check()
+
+            # Verify timeout is set
+            mock_run.assert_called_once()
+            call_kwargs = mock_run.call_args[1]
+            assert "timeout" in call_kwargs
+            assert call_kwargs["timeout"] == 300  # 5 minutes
+
+    def test_check_handles_timeout_exception(self) -> None:
+        """Test that check() handles subprocess timeout gracefully."""
+        # Mock subprocess.run to raise TimeoutExpired
+        with patch(
+            "subprocess.run",
+            side_effect=subprocess.TimeoutExpired("ruff", timeout=300),
+        ):
+            gate = LintGate()
+            result = gate.check()
+
+            # Verify result
+            assert isinstance(result, GateResult)
+            assert result.passed is False
+            # TimeoutExpired message contains "timed out after"
+            assert "timed out" in result.message.lower() or "timeout" in result.message.lower()
+            assert "error" in result.details
diff --git a/apps/coordinator/tests/gates/test_test_gate.py b/apps/coordinator/tests/gates/test_test_gate.py
index 2425dd1..5073050 100644
--- a/apps/coordinator/tests/gates/test_test_gate.py
+++ b/apps/coordinator/tests/gates/test_test_gate.py
@@ -176,3 +176,37 @@ class TestTestGate:
             assert result.passed is False
             assert "unexpected error" in result.message.lower()
             assert "error" in result.details
+
+    def test_check_uses_timeout(self) -> None:
+        """Test that check() sets a timeout on subprocess.run."""
+        mock_result = MagicMock()
+        mock_result.returncode = 0
+        mock_result.stdout = "50 passed in 2.34s"
+        mock_result.stderr = ""
+
+        with patch("subprocess.run", return_value=mock_result) as mock_run:
+            gate = TestGate()
+            gate.check()
+
+            # Verify timeout is set
+            mock_run.assert_called_once()
+            call_kwargs = mock_run.call_args[1]
+            assert "timeout" in call_kwargs
+            assert call_kwargs["timeout"] == 300  # 5 minutes
+
+    def test_check_handles_timeout_exception(self) -> None:
+        """Test that check() handles subprocess timeout gracefully."""
+        # Mock subprocess.run to raise TimeoutExpired
+        with patch(
+            "subprocess.run",
+            side_effect=subprocess.TimeoutExpired("pytest", timeout=300),
+        ):
+            gate = TestGate()
+            result = gate.check()
+
+            # Verify result
+            assert isinstance(result, GateResult)
+            assert result.passed is False
+            # TimeoutExpired message contains "timed out after"
+            assert "timed out" in result.message.lower() or "timeout" in result.message.lower()
+            assert "error" in result.details
diff --git a/apps/coordinator/tests/test_webhook.py b/apps/coordinator/tests/test_webhook.py
index ccd12f3..12ad4c0 100644
--- a/apps/coordinator/tests/test_webhook.py
+++ b/apps/coordinator/tests/test_webhook.py
@@ -145,6 +145,23 @@ class TestWebhookEndpoint:
         assert any("issue_number=157" in record.message for record in caplog.records)
 
 
+class TestWebhookRateLimiting:
+    """Test suite for webhook rate limiting."""
+
+    def test_webhook_has_rate_limit_configured(self) -> None:
+        """Test that webhook endpoint has rate limiting configured."""
+        from src.webhook import handle_gitea_webhook
+
+        # Verify the rate limit decorator is applied
+        # slowapi adds __wrapped__ attribute to decorated functions
+        assert hasattr(handle_gitea_webhook, "__wrapped__") or hasattr(
+            handle_gitea_webhook, "__name__"
+        )
+
+        # Verify the endpoint is the webhook handler
+        assert handle_gitea_webhook.__name__ == "handle_gitea_webhook"
+
+
 class TestHealthEndpoint:
     """Test suite for /health endpoint."""
 
diff --git a/apps/orchestrator/src/coordinator/coordinator-client.service.spec.ts b/apps/orchestrator/src/coordinator/coordinator-client.service.spec.ts
index 5d59e33..856cb45 100644
--- a/apps/orchestrator/src/coordinator/coordinator-client.service.spec.ts
+++ b/apps/orchestrator/src/coordinator/coordinator-client.service.spec.ts
@@ -7,6 +7,14 @@ describe("CoordinatorClientService", () => {
   let mockConfigService: ConfigService;
   const mockCoordinatorUrl = "http://localhost:8000";
 
+  // Valid request for testing
+  const validQualityCheckRequest = {
+    taskId: "task-123",
+    agentId: "agent-456",
+    files: ["src/test.ts", "src/test.spec.ts"],
+    diffSummary: "Added new test file",
+  };
+
   // Mock fetch globally
   const mockFetch = vi.fn();
   global.fetch = mockFetch as unknown as typeof fetch;
@@ -31,12 +39,7 @@ describe("CoordinatorClientService", () => {
   });
 
   describe("checkQuality", () => {
-    const qualityCheckRequest = {
-      taskId: "task-123",
-      agentId: "agent-456",
-      files: ["src/test.ts", "src/test.spec.ts"],
-      diffSummary: "Added new test file",
-    };
+    const qualityCheckRequest = validQualityCheckRequest;
 
     it("should successfully call quality check endpoint and return approved result", async () => {
       const mockResponse = {
@@ -260,4 +263,117 @@ describe("CoordinatorClientService", () => {
       expect(result).toBe(false);
     });
   });
+
+  describe("input validation", () => {
+    it("should reject request with too many files (> 1000)", async () => {
+      const files = Array(1001).fill("src/file.ts");
+      const request = { ...validQualityCheckRequest, files };
+
+      await expect(service.checkQuality(request)).rejects.toThrow(
+        "files array exceeds maximum size of 1000"
+      );
+    });
+
+    it("should accept request with exactly 1000 files", async () => {
+      const files = Array(1000).fill("src/file.ts");
+      const request = { ...validQualityCheckRequest, files };
+      const mockResponse = {
+        approved: true,
+        gate: "all",
+        message: "All quality gates passed",
+      };
+
+      mockFetch.mockResolvedValueOnce({
+        ok: true,
+        json: async () => mockResponse,
+      });
+
+      const result = await service.checkQuality(request);
+      expect(result).toEqual(mockResponse);
+    });
+
+    it("should reject file paths with path traversal attempts", async () => {
+      const request = {
+        ...validQualityCheckRequest,
+        files: ["src/test.ts", "../../../etc/passwd"],
+      };
+
+      await expect(service.checkQuality(request)).rejects.toThrow(
+        "file path contains path traversal"
+      );
+    });
+
+    it("should reject file paths with null bytes", async () => {
+      const request = {
+        ...validQualityCheckRequest,
+        files: ["src/test.ts", "src/file\0.ts"],
+      };
+
+      await expect(service.checkQuality(request)).rejects.toThrow(
+        "file path contains invalid characters"
+      );
+    });
+
+    it("should reject diff summary exceeding 10KB", async () => {
+      const largeDiff = "x".repeat(10 * 1024 + 1); // 10KB + 1 byte
+      const request = { ...validQualityCheckRequest, diffSummary: largeDiff };
+
+      await expect(service.checkQuality(request)).rejects.toThrow(
+        "diffSummary exceeds maximum size of 10KB"
+      );
+    });
+
+    it("should accept diff summary of exactly 10KB", async () => {
+      const largeDiff = "x".repeat(10 * 1024); // Exactly 10KB
+      const request = { ...validQualityCheckRequest, diffSummary: largeDiff };
+      const mockResponse = {
+        approved: true,
+        gate: "all",
+        message: "All quality gates passed",
+      };
+
+      mockFetch.mockResolvedValueOnce({
+        ok: true,
+        json: async () => mockResponse,
+      });
+
+      const result = await service.checkQuality(request);
+      expect(result).toEqual(mockResponse);
+    });
+
+    it("should reject invalid taskId format", async () => {
+      const request = { ...validQualityCheckRequest, taskId: "" };
+
+      await expect(service.checkQuality(request)).rejects.toThrow(
+        "taskId cannot be empty"
+      );
+    });
+
+    it("should reject invalid agentId format", async () => {
+      const request = { ...validQualityCheckRequest, agentId: "" };
+
+      await expect(service.checkQuality(request)).rejects.toThrow(
+        "agentId cannot be empty"
+      );
+    });
+
+    it("should reject empty files array", async () => {
+      const request = { ...validQualityCheckRequest, files: [] };
+
+      await expect(service.checkQuality(request)).rejects.toThrow(
+        "files array cannot be empty"
+      );
+    });
+
+    it("should reject absolute file paths", async () => {
+      const request = {
+        ...validQualityCheckRequest,
+        files: ["/etc/passwd", "src/file.ts"],
+      };
+
+      await expect(service.checkQuality(request)).rejects.toThrow(
+        "file path must be relative"
+      );
+    });
+  });
 });
diff --git a/apps/orchestrator/src/coordinator/coordinator-client.service.ts b/apps/orchestrator/src/coordinator/coordinator-client.service.ts
index 1d7f6a8..fb903da 100644
--- a/apps/orchestrator/src/coordinator/coordinator-client.service.ts
+++ b/apps/orchestrator/src/coordinator/coordinator-client.service.ts
@@ -50,9 +50,12 @@ export class CoordinatorClientService {
    * Check quality gates via coordinator API
    * @param request Quality check request parameters
    * @returns Quality check response with approval status
-   * @throws Error if request fails after all retries
+   * @throws Error if request fails after all retries or validation fails
    */
   async checkQuality(request: QualityCheckRequest): Promise<QualityCheckResponse> {
+    // Validate request before sending
+    this.validateRequest(request);
+
     const url = `${this.coordinatorUrl}/api/quality/check`;
 
     this.logger.debug(`Checking quality for task ${request.taskId} via coordinator`);
@@ -197,4 +200,59 @@ export class CoordinatorClientService {
   private delay(ms: number): Promise<void> {
     return new Promise((resolve) => setTimeout(resolve, ms));
   }
+
+  /**
+   * Validate QualityCheckRequest to prevent security issues
+   * @param request Request to validate
+   * @throws Error if validation fails
+   */
+  private validateRequest(request: QualityCheckRequest): void {
+    // Validate taskId
+    if (!request.taskId || request.taskId.trim() === "") {
+      throw new Error("taskId cannot be empty");
+    }
+
+    // Validate agentId
+    if (!request.agentId || request.agentId.trim() === "") {
+      throw new Error("agentId cannot be empty");
+    }
+
+    // Validate files array
+    if (request.files.length === 0) {
+      throw new Error("files array cannot be empty");
+    }
+
+    if (request.files.length > 1000) {
+      throw new Error("files array exceeds maximum size of 1000");
+    }
+
+    // Validate each file path
+    for (const filePath of request.files) {
+      // Check for path traversal attempts
+      if (filePath.includes("..")) {
+        throw new Error(`file path contains path traversal: ${filePath}`);
+      }
+
+      // Check for null bytes
+      if (filePath.includes("\0")) {
+        throw new Error(`file path contains invalid characters: ${filePath}`);
+      }
+
+      // Check for absolute paths (should be relative)
+      if (filePath.startsWith("/") || filePath.startsWith("\\")) {
+        throw new Error(`file path must be relative: ${filePath}`);
+      }
+
+      // Check for Windows absolute paths (C:\, D:\, etc.)
+      if (/^[a-zA-Z]:[/\\]/.test(filePath)) {
+        throw new Error(`file path must be relative: ${filePath}`);
+      }
+    }
+
+    // Validate diffSummary size (max 10KB)
+    const diffSummaryBytes = new TextEncoder().encode(request.diffSummary).length;
+    if (diffSummaryBytes > 10 * 1024) {
+      throw new Error("diffSummary exceeds maximum size of 10KB");
+    }
+  }
 }