fix: improve container error logging to include full stdout/stderr

Always log detailed input/output/stderr on error (not just in verbose
mode), and stop truncating stderr/stdout in structured log fields.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/container-runner.ts

@@ -339,7 +339,9 @@ export async function runContainerAgent(
         ``,
       ];
 
-      if (isVerbose) {
+      const isError = code !== 0;
+
+      if (isVerbose || isError) {
         logLines.push(
           `=== Input ===`,
           JSON.stringify(input, null, 2),
@@ -373,14 +375,6 @@ export async function runContainerAgent(
             .join('\n'),
           ``,
         );
-
-        if (code !== 0) {
-          logLines.push(
-            `=== Stderr (last 500 chars) ===`,
-            stderr.slice(-500),
-            ``,
-          );
-        }
       }
 
       fs.writeFileSync(logFile, logLines.join('\n'));
@@ -392,7 +386,8 @@ export async function runContainerAgent(
             group: group.name,
             code,
             duration,
-            stderr: stderr.slice(-500),
+            stderr,
+            stdout,
             logFile,
           },
           'Container exited with error',
@@ -439,7 +434,8 @@ export async function runContainerAgent(
         logger.error(
           {
             group: group.name,
-            stdout: stdout.slice(-500),
+            stdout,
+            stderr,
             error: err,
           },
           'Failed to parse container output',