apps/coordinator/src/circuit_breaker.py

@@ -0,0 +1,299 @@
+"""Circuit breaker pattern for preventing infinite retry loops.
+
+This module provides a CircuitBreaker class that implements the circuit breaker
+pattern to protect against cascading failures in coordinator loops.
+
+Circuit breaker states:
+- CLOSED: Normal operation, requests pass through
+- OPEN: After N consecutive failures, all requests are blocked
+- HALF_OPEN: After cooldown, allow one request to test recovery
+
+Reference: SEC-ORCH-7 from security review
+"""
+
+import logging
+import time
+from enum import Enum
+from typing import Any, Callable
+
+logger = logging.getLogger(__name__)
+
+
+class CircuitState(str, Enum):
+    """States for the circuit breaker."""
+
+    CLOSED = "closed"  # Normal operation
+    OPEN = "open"  # Blocking requests after failures
+    HALF_OPEN = "half_open"  # Testing if service recovered
+
+
+class CircuitBreakerError(Exception):
+    """Exception raised when circuit is open and blocking requests."""
+
+    def __init__(self, state: CircuitState, time_until_retry: float) -> None:
+        """Initialize CircuitBreakerError.
+
+        Args:
+            state: Current circuit state
+            time_until_retry: Seconds until circuit may close
+        """
+        self.state = state
+        self.time_until_retry = time_until_retry
+        super().__init__(
+            f"Circuit breaker is {state.value}. "
+            f"Retry in {time_until_retry:.1f} seconds."
+        )
+
+
+class CircuitBreaker:
+    """Circuit breaker for protecting against cascading failures.
+
+    The circuit breaker tracks consecutive failures and opens the circuit
+    after a threshold is reached, preventing further requests until a
+    cooldown period has elapsed.
+
+    Attributes:
+        name: Identifier for this circuit breaker (for logging)
+        failure_threshold: Number of consecutive failures before opening
+        cooldown_seconds: Seconds to wait before allowing retry
+        state: Current circuit state
+        failure_count: Current consecutive failure count
+    """
+
+    def __init__(
+        self,
+        name: str,
+        failure_threshold: int = 5,
+        cooldown_seconds: float = 30.0,
+    ) -> None:
+        """Initialize CircuitBreaker.
+
+        Args:
+            name: Identifier for this circuit breaker
+            failure_threshold: Consecutive failures before opening (default: 5)
+            cooldown_seconds: Seconds to wait before half-open (default: 30)
+        """
+        self.name = name
+        self.failure_threshold = failure_threshold
+        self.cooldown_seconds = cooldown_seconds
+
+        self._state = CircuitState.CLOSED
+        self._failure_count = 0
+        self._last_failure_time: float | None = None
+        self._total_failures = 0
+        self._total_successes = 0
+        self._state_transitions = 0
+
+    @property
+    def state(self) -> CircuitState:
+        """Get the current circuit state.
+
+        This also handles automatic state transitions based on cooldown.
+
+        Returns:
+            Current CircuitState
+        """
+        if self._state == CircuitState.OPEN:
+            # Check if cooldown has elapsed
+            if self._last_failure_time is not None:
+                elapsed = time.time() - self._last_failure_time
+                if elapsed >= self.cooldown_seconds:
+                    self._transition_to(CircuitState.HALF_OPEN)
+        return self._state
+
+    @property
+    def failure_count(self) -> int:
+        """Get current consecutive failure count.
+
+        Returns:
+            Number of consecutive failures
+        """
+        return self._failure_count
+
+    @property
+    def total_failures(self) -> int:
+        """Get total failure count (all-time).
+
+        Returns:
+            Total number of failures
+        """
+        return self._total_failures
+
+    @property
+    def total_successes(self) -> int:
+        """Get total success count (all-time).
+
+        Returns:
+            Total number of successes
+        """
+        return self._total_successes
+
+    @property
+    def state_transitions(self) -> int:
+        """Get total state transition count.
+
+        Returns:
+            Number of state transitions
+        """
+        return self._state_transitions
+
+    @property
+    def time_until_retry(self) -> float:
+        """Get time remaining until retry is allowed.
+
+        Returns:
+            Seconds until circuit may transition to half-open, or 0 if not open
+        """
+        if self._state != CircuitState.OPEN or self._last_failure_time is None:
+            return 0.0
+
+        elapsed = time.time() - self._last_failure_time
+        remaining = self.cooldown_seconds - elapsed
+        return max(0.0, remaining)
+
+    def can_execute(self) -> bool:
+        """Check if a request can be executed.
+
+        This method checks the current state and determines if a request
+        should be allowed through.
+
+        Returns:
+            True if request can proceed, False otherwise
+        """
+        current_state = self.state  # This handles cooldown transitions
+
+        if current_state == CircuitState.CLOSED:
+            return True
+        elif current_state == CircuitState.HALF_OPEN:
+            # Allow one test request
+            return True
+        else:  # OPEN
+            return False
+
+    def record_success(self) -> None:
+        """Record a successful operation.
+
+        This resets the failure count and closes the circuit if it was
+        in half-open state.
+        """
+        self._total_successes += 1
+
+        if self._state == CircuitState.HALF_OPEN:
+            logger.info(
+                f"Circuit breaker '{self.name}': Recovery confirmed, closing circuit"
+            )
+            self._transition_to(CircuitState.CLOSED)
+
+        # Reset failure count on any success
+        self._failure_count = 0
+        logger.debug(f"Circuit breaker '{self.name}': Success recorded, failure count reset")
+
+    def record_failure(self) -> None:
+        """Record a failed operation.
+
+        This increments the failure count and may open the circuit if
+        the threshold is reached.
+        """
+        self._failure_count += 1
+        self._total_failures += 1
+        self._last_failure_time = time.time()
+
+        logger.warning(
+            f"Circuit breaker '{self.name}': Failure recorded "
+            f"({self._failure_count}/{self.failure_threshold})"
+        )
+
+        if self._state == CircuitState.HALF_OPEN:
+            # Failed during test request, go back to open
+            logger.warning(
+                f"Circuit breaker '{self.name}': Test request failed, reopening circuit"
+            )
+            self._transition_to(CircuitState.OPEN)
+        elif self._failure_count >= self.failure_threshold:
+            logger.error(
+                f"Circuit breaker '{self.name}': Failure threshold reached, opening circuit"
+            )
+            self._transition_to(CircuitState.OPEN)
+
+    def reset(self) -> None:
+        """Reset the circuit breaker to initial state.
+
+        This should be used carefully, typically only for testing or
+        manual intervention.
+        """
+        old_state = self._state
+        self._state = CircuitState.CLOSED
+        self._failure_count = 0
+        self._last_failure_time = None
+
+        logger.info(
+            f"Circuit breaker '{self.name}': Manual reset "
+            f"(was {old_state.value}, now closed)"
+        )
+
+    def _transition_to(self, new_state: CircuitState) -> None:
+        """Transition to a new state.
+
+        Args:
+            new_state: The state to transition to
+        """
+        old_state = self._state
+        self._state = new_state
+        self._state_transitions += 1
+
+        logger.info(
+            f"Circuit breaker '{self.name}': State transition "
+            f"{old_state.value} -> {new_state.value}"
+        )
+
+    def get_stats(self) -> dict[str, Any]:
+        """Get circuit breaker statistics.
+
+        Returns:
+            Dictionary with current stats
+        """
+        return {
+            "name": self.name,
+            "state": self.state.value,
+            "failure_count": self._failure_count,
+            "failure_threshold": self.failure_threshold,
+            "cooldown_seconds": self.cooldown_seconds,
+            "time_until_retry": self.time_until_retry,
+            "total_failures": self._total_failures,
+            "total_successes": self._total_successes,
+            "state_transitions": self._state_transitions,
+        }
+
+    async def execute(
+        self,
+        func: Callable[..., Any],
+        *args: Any,
+        **kwargs: Any,
+    ) -> Any:
+        """Execute a function with circuit breaker protection.
+
+        This is a convenience method that wraps async function execution
+        with automatic success/failure recording.
+
+        Args:
+            func: Async function to execute
+            *args: Positional arguments for the function
+            **kwargs: Keyword arguments for the function
+
+        Returns:
+            Result of the function execution
+
+        Raises:
+            CircuitBreakerError: If circuit is open
+            Exception: If function raises and circuit is closed/half-open
+        """
+        if not self.can_execute():
+            raise CircuitBreakerError(self.state, self.time_until_retry)
+
+        try:
+            result = await func(*args, **kwargs)
+            self.record_success()
+            return result
+        except Exception:
+            self.record_failure()
+            raise

apps/coordinator/src/context_monitor.py

@@ -6,6 +6,7 @@ from collections import defaultdict
 from collections.abc import Callable
 from typing import Any
 
+from src.circuit_breaker import CircuitBreaker
 from src.context_compaction import CompactionResult, ContextCompactor, SessionRotation
 from src.models import ContextAction, ContextUsage
 
@@ -19,17 +20,29 @@ class ContextMonitor:
     Triggers appropriate actions based on defined thresholds:
     - 80% (COMPACT_THRESHOLD): Trigger context compaction
     - 95% (ROTATE_THRESHOLD): Trigger session rotation
+
+    Circuit Breaker (SEC-ORCH-7):
+    - Per-agent circuit breakers prevent infinite retry loops on API failures
+    - After failure_threshold consecutive failures, backs off for cooldown_seconds
     """
 
     COMPACT_THRESHOLD = 0.80  # 80% triggers compaction
     ROTATE_THRESHOLD = 0.95  # 95% triggers rotation
 
-    def __init__(self, api_client: Any, poll_interval: float = 10.0) -> None:
+    def __init__(
+        self,
+        api_client: Any,
+        poll_interval: float = 10.0,
+        circuit_breaker_threshold: int = 3,
+        circuit_breaker_cooldown: float = 60.0,
+    ) -> None:
         """Initialize context monitor.
 
         Args:
             api_client: Claude API client for fetching context usage
             poll_interval: Seconds between polls (default: 10s)
+            circuit_breaker_threshold: Consecutive failures before opening circuit (default: 3)
+            circuit_breaker_cooldown: Seconds to wait before retry after circuit opens (default: 60)
         """
         self.api_client = api_client
         self.poll_interval = poll_interval
@@ -37,6 +50,11 @@ class ContextMonitor:
         self._monitoring_tasks: dict[str, bool] = {}
         self._compactor = ContextCompactor(api_client=api_client)
 
+        # Circuit breaker settings for per-agent monitoring loops (SEC-ORCH-7)
+        self._circuit_breaker_threshold = circuit_breaker_threshold
+        self._circuit_breaker_cooldown = circuit_breaker_cooldown
+        self._circuit_breakers: dict[str, CircuitBreaker] = {}
+
     async def get_context_usage(self, agent_id: str) -> ContextUsage:
         """Get current context usage for an agent.
 
@@ -98,6 +116,36 @@ class ContextMonitor:
         """
         return self._usage_history[agent_id]
 
+    def _get_circuit_breaker(self, agent_id: str) -> CircuitBreaker:
+        """Get or create circuit breaker for an agent.
+
+        Args:
+            agent_id: Unique identifier for the agent
+
+        Returns:
+            CircuitBreaker instance for this agent
+        """
+        if agent_id not in self._circuit_breakers:
+            self._circuit_breakers[agent_id] = CircuitBreaker(
+                name=f"context_monitor_{agent_id}",
+                failure_threshold=self._circuit_breaker_threshold,
+                cooldown_seconds=self._circuit_breaker_cooldown,
+            )
+        return self._circuit_breakers[agent_id]
+
+    def get_circuit_breaker_stats(self, agent_id: str) -> dict[str, Any]:
+        """Get circuit breaker statistics for an agent.
+
+        Args:
+            agent_id: Unique identifier for the agent
+
+        Returns:
+            Dictionary with circuit breaker stats, or empty dict if no breaker exists
+        """
+        if agent_id in self._circuit_breakers:
+            return self._circuit_breakers[agent_id].get_stats()
+        return {}
+
     async def start_monitoring(
         self, agent_id: str, callback: Callable[[str, ContextAction], None]
     ) -> None:
@@ -106,22 +154,46 @@ class ContextMonitor:
         Polls context usage at regular intervals and calls callback with
         appropriate actions when thresholds are crossed.
 
+        Uses circuit breaker to prevent infinite retry loops on repeated failures.
+
         Args:
             agent_id: Unique identifier for the agent
             callback: Function to call with (agent_id, action) on each poll
         """
         self._monitoring_tasks[agent_id] = True
+        circuit_breaker = self._get_circuit_breaker(agent_id)
+
         logger.info(
             f"Started monitoring agent {agent_id} (poll interval: {self.poll_interval}s)"
         )
 
         while self._monitoring_tasks.get(agent_id, False):
+            # Check circuit breaker state before polling
+            if not circuit_breaker.can_execute():
+                wait_time = circuit_breaker.time_until_retry
+                logger.warning(
+                    f"Circuit breaker OPEN for agent {agent_id} - "
+                    f"backing off for {wait_time:.1f}s"
+                )
+                try:
+                    await asyncio.sleep(wait_time)
+                except asyncio.CancelledError:
+                    break
+                continue
+
             try:
                 action = await self.determine_action(agent_id)
                 callback(agent_id, action)
+                # Successful poll - record success
+                circuit_breaker.record_success()
             except Exception as e:
-                logger.error(f"Error monitoring agent {agent_id}: {e}")
-                # Continue monitoring despite errors
+                # Record failure in circuit breaker
+                circuit_breaker.record_failure()
+                logger.error(
+                    f"Error monitoring agent {agent_id}: {e} "
+                    f"(circuit breaker: {circuit_breaker.state.value}, "
+                    f"failures: {circuit_breaker.failure_count}/{circuit_breaker.failure_threshold})"
+                )
 
             # Wait for next poll (or until stopped)
             try:
@@ -129,7 +201,15 @@ class ContextMonitor:
             except asyncio.CancelledError:
                 break
 
-        logger.info(f"Stopped monitoring agent {agent_id}")
+        # Clean up circuit breaker when monitoring stops
+        if agent_id in self._circuit_breakers:
+            stats = self._circuit_breakers[agent_id].get_stats()
+            del self._circuit_breakers[agent_id]
+            logger.info(
+                f"Stopped monitoring agent {agent_id} (circuit breaker stats: {stats})"
+            )
+        else:
+            logger.info(f"Stopped monitoring agent {agent_id}")
 
     def stop_monitoring(self, agent_id: str) -> None:
         """Stop background monitoring for an agent.

apps/coordinator/src/coordinator.py

@@ -4,6 +4,7 @@ import asyncio
 import logging
 from typing import TYPE_CHECKING, Any
 
+from src.circuit_breaker import CircuitBreaker, CircuitBreakerError, CircuitState
 from src.context_monitor import ContextMonitor
 from src.forced_continuation import ForcedContinuationService
 from src.models import ContextAction
@@ -24,20 +25,30 @@ class Coordinator:
     - Monitoring the queue for ready items
     - Spawning agents to process issues (stub implementation for Phase 0)
     - Marking items as complete when processing finishes
-    - Handling errors gracefully
+    - Handling errors gracefully with circuit breaker protection
     - Supporting graceful shutdown
+
+    Circuit Breaker (SEC-ORCH-7):
+    - Tracks consecutive failures in the main loop
+    - After failure_threshold consecutive failures, enters OPEN state
+    - In OPEN state, backs off for cooldown_seconds before retrying
+    - Prevents infinite retry loops on repeated failures
     """
 
     def __init__(
         self,
         queue_manager: QueueManager,
         poll_interval: float = 5.0,
+        circuit_breaker_threshold: int = 5,
+        circuit_breaker_cooldown: float = 30.0,
     ) -> None:
         """Initialize the Coordinator.
 
         Args:
             queue_manager: QueueManager instance for queue operations
             poll_interval: Seconds between queue polls (default: 5.0)
+            circuit_breaker_threshold: Consecutive failures before opening circuit (default: 5)
+            circuit_breaker_cooldown: Seconds to wait before retry after circuit opens (default: 30)
         """
         self.queue_manager = queue_manager
         self.poll_interval = poll_interval
@@ -45,6 +56,13 @@ class Coordinator:
         self._stop_event: asyncio.Event | None = None
         self._active_agents: dict[int, dict[str, Any]] = {}
 
+        # Circuit breaker for preventing infinite retry loops (SEC-ORCH-7)
+        self._circuit_breaker = CircuitBreaker(
+            name="coordinator_loop",
+            failure_threshold=circuit_breaker_threshold,
+            cooldown_seconds=circuit_breaker_cooldown,
+        )
+
     @property
     def is_running(self) -> bool:
         """Check if the coordinator is currently running.
@@ -71,10 +89,28 @@ class Coordinator:
         """
         return len(self._active_agents)
 
+    @property
+    def circuit_breaker(self) -> CircuitBreaker:
+        """Get the circuit breaker instance.
+
+        Returns:
+            CircuitBreaker instance for this coordinator
+        """
+        return self._circuit_breaker
+
+    def get_circuit_breaker_stats(self) -> dict[str, Any]:
+        """Get circuit breaker statistics.
+
+        Returns:
+            Dictionary with circuit breaker stats
+        """
+        return self._circuit_breaker.get_stats()
+
     async def start(self) -> None:
         """Start the orchestration loop.
 
         Continuously processes the queue until stop() is called.
+        Uses circuit breaker to prevent infinite retry loops on repeated failures.
         """
         self._running = True
         self._stop_event = asyncio.Event()
@@ -82,11 +118,32 @@ class Coordinator:
 
         try:
             while self._running:
+                # Check circuit breaker state before processing
+                if not self._circuit_breaker.can_execute():
+                    # Circuit is open - wait for cooldown
+                    wait_time = self._circuit_breaker.time_until_retry
+                    logger.warning(
+                        f"Circuit breaker OPEN - backing off for {wait_time:.1f}s "
+                        f"(failures: {self._circuit_breaker.failure_count})"
+                    )
+                    await self._wait_for_cooldown_or_stop(wait_time)
+                    continue
+
                 try:
                     await self.process_queue()
+                    # Successful processing - record success
+                    self._circuit_breaker.record_success()
+                except CircuitBreakerError as e:
+                    # Circuit breaker blocked the request
+                    logger.warning(f"Circuit breaker blocked request: {e}")
                 except Exception as e:
-                    logger.error(f"Error in process_queue: {e}")
-                    # Continue running despite errors
+                    # Record failure in circuit breaker
+                    self._circuit_breaker.record_failure()
+                    logger.error(
+                        f"Error in process_queue: {e} "
+                        f"(circuit breaker: {self._circuit_breaker.state.value}, "
+                        f"failures: {self._circuit_breaker.failure_count}/{self._circuit_breaker.failure_threshold})"
+                    )
 
                 # Wait for poll interval or stop signal
                 try:
@@ -102,7 +159,26 @@ class Coordinator:
 
         finally:
             self._running = False
-            logger.info("Coordinator stopped")
+            logger.info(
+                f"Coordinator stopped "
+                f"(circuit breaker stats: {self._circuit_breaker.get_stats()})"
+            )
+
+    async def _wait_for_cooldown_or_stop(self, cooldown: float) -> None:
+        """Wait for cooldown period or stop signal, whichever comes first.
+
+        Args:
+            cooldown: Seconds to wait for cooldown
+        """
+        if self._stop_event is None:
+            return
+
+        try:
+            await asyncio.wait_for(self._stop_event.wait(), timeout=cooldown)
+            # Stop was requested during cooldown
+        except TimeoutError:
+            # Cooldown completed, continue
+            pass
 
     async def stop(self) -> None:
         """Stop the orchestration loop gracefully.
@@ -200,6 +276,12 @@ class OrchestrationLoop:
     - Quality gate verification on completion claims
     - Rejection handling with forced continuation prompts
     - Context monitoring during agent execution
+
+    Circuit Breaker (SEC-ORCH-7):
+    - Tracks consecutive failures in the main loop
+    - After failure_threshold consecutive failures, enters OPEN state
+    - In OPEN state, backs off for cooldown_seconds before retrying
+    - Prevents infinite retry loops on repeated failures
     """
 
     def __init__(
@@ -209,6 +291,8 @@ class OrchestrationLoop:
         continuation_service: ForcedContinuationService,
         context_monitor: ContextMonitor,
         poll_interval: float = 5.0,
+        circuit_breaker_threshold: int = 5,
+        circuit_breaker_cooldown: float = 30.0,
     ) -> None:
         """Initialize the OrchestrationLoop.
 
@@ -218,6 +302,8 @@ class OrchestrationLoop:
             continuation_service: ForcedContinuationService for rejection prompts
             context_monitor: ContextMonitor for tracking agent context usage
             poll_interval: Seconds between queue polls (default: 5.0)
+            circuit_breaker_threshold: Consecutive failures before opening circuit (default: 5)
+            circuit_breaker_cooldown: Seconds to wait before retry after circuit opens (default: 30)
         """
         self.queue_manager = queue_manager
         self.quality_orchestrator = quality_orchestrator
@@ -233,6 +319,13 @@ class OrchestrationLoop:
         self._success_count = 0
         self._rejection_count = 0
 
+        # Circuit breaker for preventing infinite retry loops (SEC-ORCH-7)
+        self._circuit_breaker = CircuitBreaker(
+            name="orchestration_loop",
+            failure_threshold=circuit_breaker_threshold,
+            cooldown_seconds=circuit_breaker_cooldown,
+        )
+
     @property
     def is_running(self) -> bool:
         """Check if the orchestration loop is currently running.
@@ -286,10 +379,28 @@ class OrchestrationLoop:
         """
         return len(self._active_agents)
 
+    @property
+    def circuit_breaker(self) -> CircuitBreaker:
+        """Get the circuit breaker instance.
+
+        Returns:
+            CircuitBreaker instance for this orchestration loop
+        """
+        return self._circuit_breaker
+
+    def get_circuit_breaker_stats(self) -> dict[str, Any]:
+        """Get circuit breaker statistics.
+
+        Returns:
+            Dictionary with circuit breaker stats
+        """
+        return self._circuit_breaker.get_stats()
+
     async def start(self) -> None:
         """Start the orchestration loop.
 
         Continuously processes the queue until stop() is called.
+        Uses circuit breaker to prevent infinite retry loops on repeated failures.
         """
         self._running = True
         self._stop_event = asyncio.Event()
@@ -297,11 +408,32 @@ class OrchestrationLoop:
 
         try:
             while self._running:
+                # Check circuit breaker state before processing
+                if not self._circuit_breaker.can_execute():
+                    # Circuit is open - wait for cooldown
+                    wait_time = self._circuit_breaker.time_until_retry
+                    logger.warning(
+                        f"Circuit breaker OPEN - backing off for {wait_time:.1f}s "
+                        f"(failures: {self._circuit_breaker.failure_count})"
+                    )
+                    await self._wait_for_cooldown_or_stop(wait_time)
+                    continue
+
                 try:
                     await self.process_next_issue()
+                    # Successful processing - record success
+                    self._circuit_breaker.record_success()
+                except CircuitBreakerError as e:
+                    # Circuit breaker blocked the request
+                    logger.warning(f"Circuit breaker blocked request: {e}")
                 except Exception as e:
-                    logger.error(f"Error in process_next_issue: {e}")
-                    # Continue running despite errors
+                    # Record failure in circuit breaker
+                    self._circuit_breaker.record_failure()
+                    logger.error(
+                        f"Error in process_next_issue: {e} "
+                        f"(circuit breaker: {self._circuit_breaker.state.value}, "
+                        f"failures: {self._circuit_breaker.failure_count}/{self._circuit_breaker.failure_threshold})"
+                    )
 
                 # Wait for poll interval or stop signal
                 try:
@@ -317,7 +449,26 @@ class OrchestrationLoop:
 
         finally:
             self._running = False
-            logger.info("OrchestrationLoop stopped")
+            logger.info(
+                f"OrchestrationLoop stopped "
+                f"(circuit breaker stats: {self._circuit_breaker.get_stats()})"
+            )
+
+    async def _wait_for_cooldown_or_stop(self, cooldown: float) -> None:
+        """Wait for cooldown period or stop signal, whichever comes first.
+
+        Args:
+            cooldown: Seconds to wait for cooldown
+        """
+        if self._stop_event is None:
+            return
+
+        try:
+            await asyncio.wait_for(self._stop_event.wait(), timeout=cooldown)
+            # Stop was requested during cooldown
+        except TimeoutError:
+            # Cooldown completed, continue
+            pass
 
     async def stop(self) -> None:
         """Stop the orchestration loop gracefully.

apps/coordinator/tests/test_circuit_breaker.py

@@ -0,0 +1,495 @@
+"""Tests for circuit breaker pattern implementation.
+
+These tests verify the circuit breaker behavior:
+- State transitions (closed -> open -> half_open -> closed)
+- Failure counting and threshold detection
+- Cooldown timing
+- Success/failure recording
+- Execute wrapper method
+"""
+
+import asyncio
+import time
+from unittest.mock import AsyncMock, patch
+
+import pytest
+
+from src.circuit_breaker import CircuitBreaker, CircuitBreakerError, CircuitState
+
+
+class TestCircuitBreakerInitialization:
+    """Tests for CircuitBreaker initialization."""
+
+    def test_default_initialization(self) -> None:
+        """Test circuit breaker initializes with default values."""
+        cb = CircuitBreaker("test")
+
+        assert cb.name == "test"
+        assert cb.failure_threshold == 5
+        assert cb.cooldown_seconds == 30.0
+        assert cb.state == CircuitState.CLOSED
+        assert cb.failure_count == 0
+
+    def test_custom_initialization(self) -> None:
+        """Test circuit breaker with custom values."""
+        cb = CircuitBreaker(
+            name="custom",
+            failure_threshold=3,
+            cooldown_seconds=10.0,
+        )
+
+        assert cb.name == "custom"
+        assert cb.failure_threshold == 3
+        assert cb.cooldown_seconds == 10.0
+
+    def test_initial_state_is_closed(self) -> None:
+        """Test circuit starts in closed state."""
+        cb = CircuitBreaker("test")
+        assert cb.state == CircuitState.CLOSED
+
+    def test_initial_can_execute_is_true(self) -> None:
+        """Test can_execute returns True initially."""
+        cb = CircuitBreaker("test")
+        assert cb.can_execute() is True
+
+
+class TestCircuitBreakerFailureTracking:
+    """Tests for failure tracking behavior."""
+
+    def test_failure_increments_count(self) -> None:
+        """Test that recording failure increments failure count."""
+        cb = CircuitBreaker("test", failure_threshold=5)
+
+        cb.record_failure()
+        assert cb.failure_count == 1
+
+        cb.record_failure()
+        assert cb.failure_count == 2
+
+    def test_success_resets_failure_count(self) -> None:
+        """Test that recording success resets failure count."""
+        cb = CircuitBreaker("test", failure_threshold=5)
+
+        cb.record_failure()
+        cb.record_failure()
+        assert cb.failure_count == 2
+
+        cb.record_success()
+        assert cb.failure_count == 0
+
+    def test_total_failures_tracked(self) -> None:
+        """Test that total failures are tracked separately."""
+        cb = CircuitBreaker("test", failure_threshold=5)
+
+        cb.record_failure()
+        cb.record_failure()
+        cb.record_success()  # Resets consecutive count
+        cb.record_failure()
+
+        assert cb.failure_count == 1  # Consecutive
+        assert cb.total_failures == 3  # Total
+
+    def test_total_successes_tracked(self) -> None:
+        """Test that total successes are tracked."""
+        cb = CircuitBreaker("test")
+
+        cb.record_success()
+        cb.record_success()
+        cb.record_failure()
+        cb.record_success()
+
+        assert cb.total_successes == 3
+
+
+class TestCircuitBreakerStateTransitions:
+    """Tests for state transition behavior."""
+
+    def test_reaches_threshold_opens_circuit(self) -> None:
+        """Test circuit opens when failure threshold is reached."""
+        cb = CircuitBreaker("test", failure_threshold=3)
+
+        cb.record_failure()
+        assert cb.state == CircuitState.CLOSED
+
+        cb.record_failure()
+        assert cb.state == CircuitState.CLOSED
+
+        cb.record_failure()
+        assert cb.state == CircuitState.OPEN
+
+    def test_open_circuit_blocks_execution(self) -> None:
+        """Test that open circuit blocks can_execute."""
+        cb = CircuitBreaker("test", failure_threshold=2)
+
+        cb.record_failure()
+        cb.record_failure()
+
+        assert cb.state == CircuitState.OPEN
+        assert cb.can_execute() is False
+
+    def test_cooldown_transitions_to_half_open(self) -> None:
+        """Test that cooldown period transitions circuit to half-open."""
+        cb = CircuitBreaker("test", failure_threshold=2, cooldown_seconds=0.1)
+
+        cb.record_failure()
+        cb.record_failure()
+        assert cb.state == CircuitState.OPEN
+
+        # Wait for cooldown
+        time.sleep(0.15)
+
+        # Accessing state triggers transition
+        assert cb.state == CircuitState.HALF_OPEN
+
+    def test_half_open_allows_one_request(self) -> None:
+        """Test that half-open state allows test request."""
+        cb = CircuitBreaker("test", failure_threshold=2, cooldown_seconds=0.1)
+
+        cb.record_failure()
+        cb.record_failure()
+
+        time.sleep(0.15)
+
+        assert cb.state == CircuitState.HALF_OPEN
+        assert cb.can_execute() is True
+
+    def test_half_open_success_closes_circuit(self) -> None:
+        """Test that success in half-open state closes circuit."""
+        cb = CircuitBreaker("test", failure_threshold=2, cooldown_seconds=0.1)
+
+        cb.record_failure()
+        cb.record_failure()
+
+        time.sleep(0.15)
+        assert cb.state == CircuitState.HALF_OPEN
+
+        cb.record_success()
+        assert cb.state == CircuitState.CLOSED
+
+    def test_half_open_failure_reopens_circuit(self) -> None:
+        """Test that failure in half-open state reopens circuit."""
+        cb = CircuitBreaker("test", failure_threshold=2, cooldown_seconds=0.1)
+
+        cb.record_failure()
+        cb.record_failure()
+
+        time.sleep(0.15)
+        assert cb.state == CircuitState.HALF_OPEN
+
+        cb.record_failure()
+        assert cb.state == CircuitState.OPEN
+
+    def test_state_transitions_counted(self) -> None:
+        """Test that state transitions are counted."""
+        cb = CircuitBreaker("test", failure_threshold=2, cooldown_seconds=0.1)
+
+        assert cb.state_transitions == 0
+
+        cb.record_failure()
+        cb.record_failure()  # -> OPEN
+        assert cb.state_transitions == 1
+
+        time.sleep(0.15)
+        _ = cb.state  # -> HALF_OPEN
+        assert cb.state_transitions == 2
+
+        cb.record_success()  # -> CLOSED
+        assert cb.state_transitions == 3
+
+
+class TestCircuitBreakerCooldown:
+    """Tests for cooldown timing behavior."""
+
+    def test_time_until_retry_when_open(self) -> None:
+        """Test time_until_retry reports correct value when open."""
+        cb = CircuitBreaker("test", failure_threshold=2, cooldown_seconds=1.0)
+
+        cb.record_failure()
+        cb.record_failure()
+
+        # Should be approximately 1 second
+        assert 0.9 <= cb.time_until_retry <= 1.0
+
+    def test_time_until_retry_decreases(self) -> None:
+        """Test time_until_retry decreases over time."""
+        cb = CircuitBreaker("test", failure_threshold=2, cooldown_seconds=1.0)
+
+        cb.record_failure()
+        cb.record_failure()
+
+        initial = cb.time_until_retry
+        time.sleep(0.2)
+        after = cb.time_until_retry
+
+        assert after < initial
+
+    def test_time_until_retry_zero_when_closed(self) -> None:
+        """Test time_until_retry is 0 when circuit is closed."""
+        cb = CircuitBreaker("test")
+        assert cb.time_until_retry == 0.0
+
+    def test_time_until_retry_zero_when_half_open(self) -> None:
+        """Test time_until_retry is 0 when circuit is half-open."""
+        cb = CircuitBreaker("test", failure_threshold=2, cooldown_seconds=0.1)
+
+        cb.record_failure()
+        cb.record_failure()
+        time.sleep(0.15)
+
+        assert cb.state == CircuitState.HALF_OPEN
+        assert cb.time_until_retry == 0.0
+
+
+class TestCircuitBreakerReset:
+    """Tests for manual reset behavior."""
+
+    def test_reset_closes_circuit(self) -> None:
+        """Test that reset closes an open circuit."""
+        cb = CircuitBreaker("test", failure_threshold=2)
+
+        cb.record_failure()
+        cb.record_failure()
+        assert cb.state == CircuitState.OPEN
+
+        cb.reset()
+        assert cb.state == CircuitState.CLOSED
+
+    def test_reset_clears_failure_count(self) -> None:
+        """Test that reset clears failure count."""
+        cb = CircuitBreaker("test", failure_threshold=5)
+
+        cb.record_failure()
+        cb.record_failure()
+        assert cb.failure_count == 2
+
+        cb.reset()
+        assert cb.failure_count == 0
+
+    def test_reset_from_half_open(self) -> None:
+        """Test reset from half-open state."""
+        cb = CircuitBreaker("test", failure_threshold=2, cooldown_seconds=0.1)
+
+        cb.record_failure()
+        cb.record_failure()
+        time.sleep(0.15)
+        assert cb.state == CircuitState.HALF_OPEN
+
+        cb.reset()
+        assert cb.state == CircuitState.CLOSED
+
+
+class TestCircuitBreakerStats:
+    """Tests for statistics reporting."""
+
+    def test_get_stats_returns_all_fields(self) -> None:
+        """Test get_stats returns complete statistics."""
+        cb = CircuitBreaker("test", failure_threshold=3, cooldown_seconds=15.0)
+
+        stats = cb.get_stats()
+
+        assert stats["name"] == "test"
+        assert stats["state"] == "closed"
+        assert stats["failure_count"] == 0
+        assert stats["failure_threshold"] == 3
+        assert stats["cooldown_seconds"] == 15.0
+        assert stats["time_until_retry"] == 0.0
+        assert stats["total_failures"] == 0
+        assert stats["total_successes"] == 0
+        assert stats["state_transitions"] == 0
+
+    def test_stats_update_after_operations(self) -> None:
+        """Test stats update correctly after operations."""
+        cb = CircuitBreaker("test", failure_threshold=3)
+
+        cb.record_failure()
+        cb.record_success()
+        cb.record_failure()
+        cb.record_failure()
+        cb.record_failure()  # Opens circuit
+
+        stats = cb.get_stats()
+
+        assert stats["state"] == "open"
+        assert stats["failure_count"] == 3
+        assert stats["total_failures"] == 4
+        assert stats["total_successes"] == 1
+        assert stats["state_transitions"] == 1
+
+
+class TestCircuitBreakerError:
+    """Tests for CircuitBreakerError exception."""
+
+    def test_error_contains_state(self) -> None:
+        """Test error contains circuit state."""
+        error = CircuitBreakerError(CircuitState.OPEN, 10.0)
+        assert error.state == CircuitState.OPEN
+
+    def test_error_contains_retry_time(self) -> None:
+        """Test error contains time until retry."""
+        error = CircuitBreakerError(CircuitState.OPEN, 10.5)
+        assert error.time_until_retry == 10.5
+
+    def test_error_message_formatting(self) -> None:
+        """Test error message is properly formatted."""
+        error = CircuitBreakerError(CircuitState.OPEN, 15.3)
+        assert "open" in str(error)
+        assert "15.3" in str(error)
+
+
+class TestCircuitBreakerExecute:
+    """Tests for the execute wrapper method."""
+
+    @pytest.mark.asyncio
+    async def test_execute_calls_function(self) -> None:
+        """Test execute calls the provided function."""
+        cb = CircuitBreaker("test")
+        mock_func = AsyncMock(return_value="success")
+
+        result = await cb.execute(mock_func, "arg1", kwarg="value")
+
+        mock_func.assert_called_once_with("arg1", kwarg="value")
+        assert result == "success"
+
+    @pytest.mark.asyncio
+    async def test_execute_records_success(self) -> None:
+        """Test execute records success on successful call."""
+        cb = CircuitBreaker("test")
+        mock_func = AsyncMock(return_value="ok")
+
+        await cb.execute(mock_func)
+
+        assert cb.total_successes == 1
+
+    @pytest.mark.asyncio
+    async def test_execute_records_failure(self) -> None:
+        """Test execute records failure when function raises."""
+        cb = CircuitBreaker("test")
+        mock_func = AsyncMock(side_effect=RuntimeError("test error"))
+
+        with pytest.raises(RuntimeError):
+            await cb.execute(mock_func)
+
+        assert cb.failure_count == 1
+
+    @pytest.mark.asyncio
+    async def test_execute_raises_when_open(self) -> None:
+        """Test execute raises CircuitBreakerError when circuit is open."""
+        cb = CircuitBreaker("test", failure_threshold=2)
+
+        mock_func = AsyncMock(side_effect=RuntimeError("fail"))
+
+        with pytest.raises(RuntimeError):
+            await cb.execute(mock_func)
+        with pytest.raises(RuntimeError):
+            await cb.execute(mock_func)
+
+        # Circuit should now be open
+        assert cb.state == CircuitState.OPEN
+
+        # Next call should raise CircuitBreakerError
+        with pytest.raises(CircuitBreakerError) as exc_info:
+            await cb.execute(mock_func)
+
+        assert exc_info.value.state == CircuitState.OPEN
+
+    @pytest.mark.asyncio
+    async def test_execute_allows_half_open_test(self) -> None:
+        """Test execute allows test request in half-open state."""
+        cb = CircuitBreaker("test", failure_threshold=2, cooldown_seconds=0.1)
+
+        mock_func = AsyncMock(side_effect=RuntimeError("fail"))
+
+        with pytest.raises(RuntimeError):
+            await cb.execute(mock_func)
+        with pytest.raises(RuntimeError):
+            await cb.execute(mock_func)
+
+        # Wait for cooldown
+        await asyncio.sleep(0.15)
+        assert cb.state == CircuitState.HALF_OPEN
+
+        # Should allow test request
+        mock_func.side_effect = None
+        mock_func.return_value = "recovered"
+
+        result = await cb.execute(mock_func)
+        assert result == "recovered"
+        assert cb.state == CircuitState.CLOSED
+
+
+class TestCircuitBreakerConcurrency:
+    """Tests for thread safety and concurrent access."""
+
+    @pytest.mark.asyncio
+    async def test_concurrent_failures(self) -> None:
+        """Test concurrent failures are handled correctly."""
+        cb = CircuitBreaker("test", failure_threshold=10)
+
+        async def record_failure() -> None:
+            cb.record_failure()
+
+        # Record 10 concurrent failures
+        await asyncio.gather(*[record_failure() for _ in range(10)])
+
+        assert cb.failure_count >= 10
+        assert cb.state == CircuitState.OPEN
+
+    @pytest.mark.asyncio
+    async def test_concurrent_mixed_operations(self) -> None:
+        """Test concurrent mixed success/failure operations."""
+        cb = CircuitBreaker("test", failure_threshold=100)
+
+        async def record_success() -> None:
+            cb.record_success()
+
+        async def record_failure() -> None:
+            cb.record_failure()
+
+        # Mix of operations
+        tasks = [record_failure() for _ in range(5)]
+        tasks.extend([record_success() for _ in range(3)])
+        tasks.extend([record_failure() for _ in range(5)])
+
+        await asyncio.gather(*tasks)
+
+        # At least some of each should have been recorded
+        assert cb.total_failures >= 5
+        assert cb.total_successes >= 1
+
+
+class TestCircuitBreakerLogging:
+    """Tests for logging behavior."""
+
+    def test_logs_state_transitions(self) -> None:
+        """Test that state transitions are logged."""
+        cb = CircuitBreaker("test", failure_threshold=2)
+
+        with patch("src.circuit_breaker.logger") as mock_logger:
+            cb.record_failure()
+            cb.record_failure()
+
+            # Should have logged the transition to OPEN
+            mock_logger.info.assert_called()
+            calls = [str(c) for c in mock_logger.info.call_args_list]
+            assert any("closed -> open" in c for c in calls)
+
+    def test_logs_failure_warnings(self) -> None:
+        """Test that failures are logged as warnings."""
+        cb = CircuitBreaker("test", failure_threshold=5)
+
+        with patch("src.circuit_breaker.logger") as mock_logger:
+            cb.record_failure()
+
+            mock_logger.warning.assert_called()
+
+    def test_logs_threshold_reached_as_error(self) -> None:
+        """Test that reaching threshold is logged as error."""
+        cb = CircuitBreaker("test", failure_threshold=2)
+
+        with patch("src.circuit_breaker.logger") as mock_logger:
+            cb.record_failure()
+            cb.record_failure()
+
+            mock_logger.error.assert_called()
+            calls = [str(c) for c in mock_logger.error.call_args_list]
+            assert any("threshold reached" in c for c in calls)

apps/coordinator/tests/test_coordinator.py

@@ -744,3 +744,186 @@ class TestCoordinatorActiveAgents:
         await coordinator.process_queue()
 
         assert coordinator.get_active_agent_count() == 3
+
+
+class TestCoordinatorCircuitBreaker:
+    """Tests for Coordinator circuit breaker integration (SEC-ORCH-7)."""
+
+    @pytest.fixture
+    def temp_queue_file(self) -> Generator[Path, None, None]:
+        """Create a temporary file for queue persistence."""
+        with tempfile.NamedTemporaryFile(mode="w", delete=False, suffix=".json") as f:
+            temp_path = Path(f.name)
+        yield temp_path
+        if temp_path.exists():
+            temp_path.unlink()
+
+    @pytest.fixture
+    def queue_manager(self, temp_queue_file: Path) -> QueueManager:
+        """Create a queue manager with temporary storage."""
+        return QueueManager(queue_file=temp_queue_file)
+
+    def test_circuit_breaker_initialized(self, queue_manager: QueueManager) -> None:
+        """Test that circuit breaker is initialized with Coordinator."""
+        from src.coordinator import Coordinator
+
+        coordinator = Coordinator(queue_manager=queue_manager)
+
+        assert coordinator.circuit_breaker is not None
+        assert coordinator.circuit_breaker.name == "coordinator_loop"
+
+    def test_circuit_breaker_custom_settings(self, queue_manager: QueueManager) -> None:
+        """Test circuit breaker with custom threshold and cooldown."""
+        from src.coordinator import Coordinator
+
+        coordinator = Coordinator(
+            queue_manager=queue_manager,
+            circuit_breaker_threshold=3,
+            circuit_breaker_cooldown=15.0,
+        )
+
+        assert coordinator.circuit_breaker.failure_threshold == 3
+        assert coordinator.circuit_breaker.cooldown_seconds == 15.0
+
+    def test_get_circuit_breaker_stats(self, queue_manager: QueueManager) -> None:
+        """Test getting circuit breaker statistics."""
+        from src.coordinator import Coordinator
+
+        coordinator = Coordinator(queue_manager=queue_manager)
+
+        stats = coordinator.get_circuit_breaker_stats()
+
+        assert "name" in stats
+        assert "state" in stats
+        assert "failure_count" in stats
+        assert "total_failures" in stats
+        assert stats["name"] == "coordinator_loop"
+        assert stats["state"] == "closed"
+
+    @pytest.mark.asyncio
+    async def test_circuit_breaker_opens_on_repeated_failures(
+        self, queue_manager: QueueManager
+    ) -> None:
+        """Test that circuit breaker opens after repeated failures."""
+        from src.circuit_breaker import CircuitState
+        from src.coordinator import Coordinator
+
+        coordinator = Coordinator(
+            queue_manager=queue_manager,
+            poll_interval=0.02,
+            circuit_breaker_threshold=3,
+            circuit_breaker_cooldown=0.2,
+        )
+
+        failure_count = 0
+
+        async def failing_process_queue() -> None:
+            nonlocal failure_count
+            failure_count += 1
+            raise RuntimeError("Simulated failure")
+
+        coordinator.process_queue = failing_process_queue  # type: ignore[method-assign]
+
+        task = asyncio.create_task(coordinator.start())
+        await asyncio.sleep(0.15)  # Allow time for failures
+
+        # Circuit should be open after 3 failures
+        assert coordinator.circuit_breaker.state == CircuitState.OPEN
+        assert coordinator.circuit_breaker.failure_count >= 3
+
+        await coordinator.stop()
+        task.cancel()
+        try:
+            await task
+        except asyncio.CancelledError:
+            pass
+
+    @pytest.mark.asyncio
+    async def test_circuit_breaker_backs_off_when_open(
+        self, queue_manager: QueueManager
+    ) -> None:
+        """Test that coordinator backs off when circuit breaker is open."""
+        from src.coordinator import Coordinator
+
+        coordinator = Coordinator(
+            queue_manager=queue_manager,
+            poll_interval=0.02,
+            circuit_breaker_threshold=2,
+            circuit_breaker_cooldown=0.3,
+        )
+
+        call_timestamps: list[float] = []
+
+        async def failing_process_queue() -> None:
+            call_timestamps.append(asyncio.get_event_loop().time())
+            raise RuntimeError("Simulated failure")
+
+        coordinator.process_queue = failing_process_queue  # type: ignore[method-assign]
+
+        task = asyncio.create_task(coordinator.start())
+        await asyncio.sleep(0.5)  # Allow time for failures and backoff
+        await coordinator.stop()
+
+        task.cancel()
+        try:
+            await task
+        except asyncio.CancelledError:
+            pass
+
+        # Should have at least 2 calls (to trigger open), then back off
+        assert len(call_timestamps) >= 2
+
+        # After circuit opens, there should be a gap (cooldown)
+        if len(call_timestamps) >= 3:
+            # Check there's a larger gap after the first 2 calls
+            first_gap = call_timestamps[1] - call_timestamps[0]
+            later_gap = call_timestamps[2] - call_timestamps[1]
+            # Later gap should be larger due to cooldown
+            assert later_gap > first_gap * 2
+
+    @pytest.mark.asyncio
+    async def test_circuit_breaker_resets_on_success(
+        self, queue_manager: QueueManager
+    ) -> None:
+        """Test that circuit breaker resets after successful operation."""
+        from src.circuit_breaker import CircuitState
+        from src.coordinator import Coordinator
+
+        coordinator = Coordinator(
+            queue_manager=queue_manager,
+            poll_interval=0.02,
+            circuit_breaker_threshold=3,
+        )
+
+        # Record failures then success
+        coordinator.circuit_breaker.record_failure()
+        coordinator.circuit_breaker.record_failure()
+        assert coordinator.circuit_breaker.failure_count == 2
+
+        coordinator.circuit_breaker.record_success()
+        assert coordinator.circuit_breaker.failure_count == 0
+        assert coordinator.circuit_breaker.state == CircuitState.CLOSED
+
+    @pytest.mark.asyncio
+    async def test_circuit_breaker_stats_logged_on_stop(
+        self, queue_manager: QueueManager
+    ) -> None:
+        """Test that circuit breaker stats are logged when coordinator stops."""
+        from src.coordinator import Coordinator
+
+        coordinator = Coordinator(queue_manager=queue_manager, poll_interval=0.05)
+
+        with patch("src.coordinator.logger") as mock_logger:
+            task = asyncio.create_task(coordinator.start())
+            await asyncio.sleep(0.1)
+            await coordinator.stop()
+
+            task.cancel()
+            try:
+                await task
+            except asyncio.CancelledError:
+                pass
+
+            # Should log circuit breaker stats on stop
+            info_calls = [str(call) for call in mock_logger.info.call_args_list]
+            assert any("circuit breaker" in call.lower() for call in info_calls)