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Agent Blocks Waiting for User Input in Automated Pipeline

Symptom

• CI/CD job hangs indefinitely — no output, no timeout, no completion
• Agent process shows 0% CPU but never exits — waiting on stdin
• Pipeline times out after 1 hour: “Job exceeded maximum execution time”
• input("Continue? [y/n]: ") hangs in automated environment with no TTY
• Agent asks for clarification mid-task — automated caller cannot respond
• getpass.getpass() blocks without a terminal

Root Cause

Interactive input() calls block until data arrives on stdin. In automated environments (CI runners, Docker without -it, cron jobs, systemd services), stdin is either closed, /dev/null, or a pipe with no writer. The process waits forever. Even well-intentioned confirmation prompts (“Are you sure you want to delete?”) become deadlocks in automation.

Fix

Option 1: Detect non-interactive mode and skip prompts

import sys
import os

def is_interactive() -> bool:
    """
    Check if the process is running interactively (has a real terminal).
    Returns False in CI, Docker without -it, cron, pipes, etc.
    """
    return sys.stdin.isatty() and sys.stdout.isatty()

def safe_confirm(prompt: str, default: bool = True, auto_confirm: bool = False) -> bool:
    """
    Ask for confirmation in interactive mode.
    In non-interactive mode, return the default without blocking.
    """
    if auto_confirm or not is_interactive():
        default_str = "yes" if default else "no"
        print(f"{prompt} [auto-{default_str}]")
        return default

    response = input(f"{prompt} [{'Y/n' if default else 'y/N'}]: ").strip().lower()
    if not response:
        return default
    return response in ("y", "yes")

def safe_input(prompt: str, default: str = "", auto_value: str = None) -> str:
    """
    Read user input in interactive mode.
    Returns default/auto_value in non-interactive mode.
    """
    if auto_value is not None or not is_interactive():
        value = auto_value or default
        print(f"{prompt}{value} [automated]")
        return value

    return input(prompt) or default

# Usage:
if safe_confirm("Delete 500 records?", default=False):
    delete_records()

# In CI: prints "Delete 500 records? [auto-no]" and skips deletion
# Interactively: asks user and waits for y/n

Option 2: Timeout-based input with automatic fallback

import signal
import sys

class InputTimeout(Exception):
    pass

def timed_input(prompt: str, timeout: float = 30.0, default: str = "") -> str:
    """
    Read input with a timeout. Returns default if no response within timeout.
    """
    if not sys.stdin.isatty():
        # Non-interactive: return default immediately
        print(f"{prompt}[no-tty, using default: '{default}']")
        return default

    def _timeout_handler(signum, frame):
        raise InputTimeout()

    old_handler = signal.signal(signal.SIGALRM, _timeout_handler)
    signal.alarm(int(timeout))

    try:
        print(f"{prompt}(auto-select '{default}' in {timeout:.0f}s) ", end="", flush=True)
        response = input()
        return response or default
    except InputTimeout:
        print(f"\nTimeout — using default: '{default}'")
        return default
    except EOFError:
        # stdin was closed (piped input exhausted)
        print(f"\nEOF — using default: '{default}'")
        return default
    finally:
        signal.alarm(0)
        signal.signal(signal.SIGALRM, old_handler)

# Works in all environments:
answer = timed_input("Choose action [skip/retry/abort]: ", timeout=30, default="skip")

Option 3: Use environment variables for automation decisions

import os

class AutomationConfig:
    """
    Read decisions from environment variables for automated runs.
    Fall back to interactive prompts when running manually.
    """

    # Set these env vars in CI to control agent behavior:
    # AGENT_AUTO_CONFIRM=true — confirm all destructive actions
    # AGENT_AUTO_SKIP=true — skip all optional steps
    # AGENT_DRY_RUN=true — simulate without making changes
    # AGENT_MAX_RETRIES=3 — retry count without asking

    def __init__(self):
        self.auto_confirm = os.environ.get("AGENT_AUTO_CONFIRM", "").lower() == "true"
        self.auto_skip = os.environ.get("AGENT_AUTO_SKIP", "").lower() == "true"
        self.dry_run = os.environ.get("AGENT_DRY_RUN", "").lower() == "true"
        self.max_retries = int(os.environ.get("AGENT_MAX_RETRIES", "3"))
        self.non_interactive = not sys.stdin.isatty()

    def confirm_action(self, action: str, is_destructive: bool = False) -> bool:
        if self.dry_run:
            print(f"[DRY RUN] Would execute: {action}")
            return False

        if self.auto_confirm:
            print(f"[AUTO] Confirmed: {action}")
            return True

        if self.auto_skip and not is_destructive:
            print(f"[AUTO SKIP] Skipping: {action}")
            return False

        if self.non_interactive:
            # Default: skip non-destructive, refuse destructive
            decision = not is_destructive
            print(f"[NON-INTERACTIVE] {'Proceeding' if decision else 'Skipping'}: {action}")
            return decision

        return input(f"Execute '{action}'? [y/N]: ").strip().lower() == "y"

cfg = AutomationConfig()

# In CI with AGENT_AUTO_CONFIRM=true: all actions proceed automatically
# Locally without env vars: interactive prompts
if cfg.confirm_action("migrate database schema", is_destructive=True):
    run_migration()

Option 4: Fail-fast instead of blocking on missing input

import sys

class MissingRequiredInput(Exception):
    """Raised when required input is unavailable in non-interactive mode"""
    pass

def require_input(
    prompt: str,
    env_var: str = None,
    required: bool = True,
    default: str = None
) -> str:
    """
    Get required input from env var, stdin, or fail fast.
    In automated mode: env var → default → fail.
    """
    # Check env var first
    if env_var:
        value = os.environ.get(env_var, "")
        if value:
            return value

    # Non-interactive: can't prompt
    if not sys.stdin.isatty():
        if default is not None:
            print(f"Non-interactive mode: using default for '{prompt}': '{default}'")
            return default
        if required:
            raise MissingRequiredInput(
                f"Required input '{prompt}' not provided in non-interactive mode.\n"
                f"Set environment variable '{env_var}' before running." if env_var
                else f"Required input '{prompt}' not provided and no env var configured."
            )
        return ""

    return input(prompt)

# Fail fast with a clear message instead of hanging:
try:
    api_key = require_input(
        "Enter API key: ",
        env_var="MY_SERVICE_API_KEY",
        required=True
    )
except MissingRequiredInput as e:
    print(f"ERROR: {e}")
    sys.exit(1)

Option 5: Pre-flight check for automation requirements

def check_automation_prerequisites() -> None:
    """
    Before running in automated mode, verify all required inputs are available.
    Fail at startup with clear message rather than blocking mid-execution.
    """
    if sys.stdin.isatty():
        return  # Interactive mode — prompts will work

    required_env_vars = [
        ("AGENT_TASK", "The task to execute"),
        ("AGENT_OUTPUT_DIR", "Where to write output"),
        ("MY_API_KEY", "API key for the service"),
    ]

    optional_env_vars = [
        ("AGENT_DRY_RUN", "Set to 'true' to simulate"),
        ("AGENT_AUTO_CONFIRM", "Set to 'true' to skip confirmations"),
    ]

    missing = []
    for var, description in required_env_vars:
        if not os.environ.get(var):
            missing.append(f"  {var}: {description}")

    if missing:
        print("ERROR: Running in non-interactive mode but required env vars are missing:")
        print("\n".join(missing))
        print("\nSet these before running in automation:")
        for var, desc in required_env_vars:
            print(f"  export {var}='...'  # {desc}")
        sys.exit(1)

    print("Automation prerequisites satisfied. Running non-interactively.")
    for var, _ in optional_env_vars:
        val = os.environ.get(var, "not set")
        print(f"  {var}={val}")

# Call at startup:
check_automation_prerequisites()

Option 6: System prompt for non-interactive behavior

System prompt:
"Non-interactive operation rules:

This agent runs in automated mode. There is no human available to answer questions.

Rules:
1. NEVER ask the user a question that requires a response before proceeding.
   If you need information, check the provided context or use your best judgment.

2. If you reach a decision point requiring a choice:
   a. Pick the safer/more conservative option automatically
   b. Explain your choice in the output
   c. Continue without waiting

3. If you need confirmation before a destructive action:
   a. Log the action as 'PENDING — requires human review'
   b. Continue with non-destructive steps
   c. Summarize pending actions at the end

4. If information is genuinely missing and you cannot proceed:
   a. State clearly what is missing
   b. State what you completed so far
   c. Exit gracefully — do NOT block or wait"

Interactive vs Automated Mode Decision Matrix

Situation	Interactive	Automated
Confirmation needed	Prompt user	Check env var or use safe default
Missing optional input	Prompt with default	Use default silently
Missing required input	Prompt (required)	Fail fast with clear message
Destructive action	Confirm first	Require explicit env var flag
Ambiguous input	Ask for clarification	Log ambiguity, use conservative interpretation

Expected Token Savings

CI job hanging for 1 hour until timeout: ~0 tokens but hours of blocked pipeline Non-interactive detection + auto-defaults: job completes in seconds

Environment

• Any agent intended for both interactive use and automation; critical for CI/CD pipeline integration
• Source: direct experience; stdin blocking is the most common failure mode when moving agents from local dev to CI

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