diff --git a/src/application/handlers/CommitMsgHandler.ts b/src/application/handlers/CommitMsgHandler.ts
index f30e5b1c..dfee6d6b 100644
--- a/src/application/handlers/CommitMsgHandler.ts
+++ b/src/application/handlers/CommitMsgHandler.ts
@@ -122,11 +122,15 @@ export class CommitMsgHandler implements IEventHandler<ICommitMsgEvent> {
         success: true,
       };
     } catch (error) {
-      this.logger.error('Failed to process commit-msg hook', { error });
+      const err = error instanceof Error ? error : new Error(String(error));
+      this.logger.error('Failed to process commit-msg hook', {
+        error: err.message,
+        stack: err.stack,
+      });
       return {
         handler: 'CommitMsgHandler',
         success: false,
-        error: error instanceof Error ? error : new Error(String(error)),
+        error: err,
       };
     }
   }
diff --git a/src/application/handlers/PostCommitHandler.ts b/src/application/handlers/PostCommitHandler.ts
index 29ba17c0..dd7810a9 100644
--- a/src/application/handlers/PostCommitHandler.ts
+++ b/src/application/handlers/PostCommitHandler.ts
@@ -81,11 +81,15 @@ export class PostCommitHandler implements IPostCommitHandler {
         success: true,
       };
     } catch (error) {
-      this.logger?.error('Post-commit handler failed', { error });
+      const err = error instanceof Error ? error : new Error(String(error));
+      this.logger?.error('Post-commit handler failed', {
+        error: err.message,
+        stack: err.stack,
+      });
       return {
         handler: 'PostCommitHandler',
         success: false,
-        error: error instanceof Error ? error : new Error(String(error)),
+        error: err,
       };
     }
   }
diff --git a/src/application/handlers/PromptSubmitHandler.ts b/src/application/handlers/PromptSubmitHandler.ts
index c645da67..30e3a640 100644
--- a/src/application/handlers/PromptSubmitHandler.ts
+++ b/src/application/handlers/PromptSubmitHandler.ts
@@ -121,11 +121,15 @@ export class PromptSubmitHandler implements IPromptSubmitHandler {
         output,
       };
     } catch (error) {
-      this.logger?.error('Prompt submit handler failed', { error });
+      const err = error instanceof Error ? error : new Error(String(error));
+      this.logger?.error('Prompt submit handler failed', {
+        error: err.message,
+        stack: err.stack,
+      });
       return {
         handler: 'PromptSubmitHandler',
         success: false,
-        error: error instanceof Error ? error : new Error(String(error)),
+        error: err,
       };
     }
   }
diff --git a/src/application/handlers/SessionStartHandler.ts b/src/application/handlers/SessionStartHandler.ts
index 5be99a9b..fa5f4b46 100644
--- a/src/application/handlers/SessionStartHandler.ts
+++ b/src/application/handlers/SessionStartHandler.ts
@@ -53,11 +53,15 @@ export class SessionStartHandler implements ISessionStartHandler {
         output,
       };
     } catch (error) {
-      this.logger?.error('Session start handler failed', { error });
+      const err = error instanceof Error ? error : new Error(String(error));
+      this.logger?.error('Session start handler failed', {
+        error: err.message,
+        stack: err.stack,
+      });
       return {
         handler: 'SessionStartHandler',
         success: false,
-        error: error instanceof Error ? error : new Error(String(error)),
+        error: err,
       };
     }
   }
diff --git a/src/application/handlers/SessionStopHandler.ts b/src/application/handlers/SessionStopHandler.ts
index b93b9126..49b65b2b 100644
--- a/src/application/handlers/SessionStopHandler.ts
+++ b/src/application/handlers/SessionStopHandler.ts
@@ -40,11 +40,15 @@ export class SessionStopHandler implements ISessionStopHandler {
         output: result.summary,
       };
     } catch (error) {
-      this.logger?.error('Session stop handler failed', { error });
+      const err = error instanceof Error ? error : new Error(String(error));
+      this.logger?.error('Session stop handler failed', {
+        error: err.message,
+        stack: err.stack,
+      });
       return {
         handler: 'SessionStopHandler',
         success: false,
-        error: error instanceof Error ? error : new Error(String(error)),
+        error: err,
       };
     }
   }
diff --git a/src/infrastructure/logging/Logger.ts b/src/infrastructure/logging/Logger.ts
index 12e2f5f3..5938b574 100644
--- a/src/infrastructure/logging/Logger.ts
+++ b/src/infrastructure/logging/Logger.ts
@@ -22,6 +22,21 @@ const LEVEL_COLORS: Record<LogLevel, string> = {
 
 const RESET = '\x1b[0m';
 
+/** JSON.stringify that handles circular references and Error objects. */
+function safeStringify(obj: unknown): string {
+  const seen = new WeakSet();
+  return JSON.stringify(obj, (_key, value) => {
+    if (value instanceof Error) {
+      return { message: value.message, stack: value.stack };
+    }
+    if (typeof value === 'object' && value !== null) {
+      if (seen.has(value)) return '[Circular]';
+      seen.add(value);
+    }
+    return value;
+  });
+}
+
 function formatTimestamp(): string {
   const now = new Date();
   const pad = (n: number, len = 2) => String(n).padStart(len, '0');
@@ -85,7 +100,7 @@ export class Logger implements ILogger {
     if (!this.isLevelEnabled(level)) return;
 
     const merged = { ...this.bindings, ...context };
-    const contextStr = Object.keys(merged).length > 0 ? ` ${JSON.stringify(merged)}` : '';
+    const contextStr = Object.keys(merged).length > 0 ? ` ${safeStringify(merged)}` : '';
     const timestamp = formatTimestamp();
     const levelUpper = level.toUpperCase().padEnd(5);