Fix/agent stream debug (#37)

* debug: log line length and preview without scrubbing

* fix: use Modal text=True bufsize=1 for line-buffered streaming

Modal buffers all stdout by default until process exits, causing
Claude Code's streaming output to arrive as a single blob.
Using text=True, bufsize=1 enables line-buffered streaming.

Author: nikhilwoodruff

src/policyengine_api/agent_sandbox.py

@@ -97,16 +97,17 @@ def run_claude_code_in_sandbox(
     # Escape the question and config for shell
     escaped_question = question.replace("'", "'\"'\"'")
     escaped_mcp_config = mcp_config_json.replace("'", "'\"'\"'")
-    # Use stdbuf -oL to force line-buffered stdout (prevents buffering issues)
+    # Modal handles line buffering with text=True, bufsize=1
     cmd = (
-        f"stdbuf -oL claude -p '{escaped_question}' "
+        f"claude -p '{escaped_question}' "
         f"--mcp-config '{escaped_mcp_config}' "
         "--output-format stream-json --verbose --max-turns 10 "
         "--allowedTools 'mcp__policyengine__*,Bash,Read,Grep,Glob,Write,Edit' "
         "< /dev/null 2>&1"
     )
     logfire.info("run_claude_code_in_sandbox: executing", cmd=cmd[:200])
-    process = sb.exec("sh", "-c", cmd)
+    # text=True, bufsize=1 enables line-buffered streaming (otherwise Modal buffers all output)
+    process = sb.exec("sh", "-c", cmd, text=True, bufsize=1)
     print("[SANDBOX] claude CLI process started", flush=True)
     logfire.info("run_claude_code_in_sandbox: claude CLI process started, returning")