AGENTS.md — Guidelines for AI Coding Agents (term-cli)

AGENTS.md — Guidelines for AI Coding Agents (term-cli)

This repo is term-cli: a single-file Python CLI that wraps tmux to let agents run interactive / long-lived / blocking terminal programs without attaching. It is TTY-first by design.

Read This First

Before issuing term-cli commands, read skills/term-cli/SKILL.md end-to-end. It’s the canonical agent playbook for correct wait strategies and common pitfalls.

• Prefer wait (prompt detection with a strong heuristic) for shells/REPLs; use wait-idle for TUIs (vim/htop/less) or screens without a detectable prompt; use wait-for only when you truly need specific text.

Wait Semantics (Important)

• wait detects a prompt using cursor position + screen content (designed to handle SSH where old prompts remain visible).
• run --wait is equivalent to send command + Enter + wait for prompt.
• wait-idle is “screen stopped changing for N seconds” (best for TUIs / streaming UIs).
• wait-for searches the visible screen for substring matches (optionally case-insensitive). It can match echoed commands too—prefer wait/run -w when possible.

CLI Cheat Sheet (Dense)

Global

• -L/--socket-name NAME — use an isolated tmux server (separate socket). Useful for tests/CI.

Sessions

# Create a sized session in a cwd, preload env, choose shell, start locked
term-cli -L t1 start -s dev -c ./proj -x 120 -y 34 -e FOO=bar -e PYTHONUNBUFFERED=1 --shell /bin/bash -l

# List (shows [LOCKED] marker)
term-cli -L t1 list

# Status (idle/running + process tree + attached + created)
term-cli -L t1 status -s dev

# Resize later (cols only here)
term-cli -L t1 resize -s dev -x 160

# Kill (refuses if humans attached unless -f; refuses if locked)
term-cli -L t1 kill -s dev -f

# Kill all (same protections; checks all unlocked first)
term-cli -L t1 kill -a -f

Running + Waiting

# Run and wait for prompt to return (default wait timeout is ~10s unless -t)
term-cli run -s dev -w -t 120 "pytest -q"

# When you sent input manually (send-text -e / send-key Enter), use wait
term-cli send-text -s dev -e "python3"
term-cli wait -s dev -t 15

# TUIs / no prompt: wait until output settles
term-cli run -s dev "htop"          # no -w here
term-cli wait-idle -s dev -i 2 -t 30 # idle threshold + max timeout

# Wait for one of multiple substrings (screen match, not regex)
term-cli wait-for -s dev -t 30 -i -p "Listening on" "Ready" "Error"
term-cli wait-for -s dev -t 30 -C 3 "Error"  # print match + 3 lines of context

Input

# Literal text (no Enter unless -e)
term-cli send-text -s dev ":wq" -e

# Special keys
term-cli send-key -s dev C-c
term-cli send-key -s dev Escape
term-cli send-key -s dev Up

# Multiline (stdin -> tmux buffer -> paste)
cat <<'EOF' | term-cli send-stdin -s dev
export PATH="$HOME/bin:$PATH"
echo done
EOF

Capture / Logs / Scroll

# Visible screen (trimmed by default)
term-cli capture -s dev

# Last N physical rows from visible screen
term-cli capture -s dev --tail 5

# Include scrollback (-n) and ANSI escapes (-r)
term-cli capture -s dev -n 20 -r

# Pipe output to a file; strips ANSI by default (use -r for raw)
term-cli pipe-log -s dev /tmp/dev.log
term-cli unpipe  -s dev

# Scroll viewport (negative = up). Note: uses copy-mode scroll.
term-cli scroll -s dev -50

Abbreviations (Prefix Matching)

Any unambiguous prefix works.

Known ambiguous prefixes (avoid):

• st, sta → start vs status
• re → resize vs request*
• req → request, request-wait, request-cancel, request-status

Recommended short forms:

• star = start, stat = status, res = resize
• send-t = send-text, send-k = send-key, send-s = send-stdin
• wait-i = wait-idle, wait-f = wait-for
• request (full), request-w / request-c / request-s

Examples:

term-cli star -s a -c . -x 100 -y 30
term-cli ru   -s a -w -t 60 "make test"
term-cli c    -s a -n 10
term-cli wait-i -s a -i 2 -t 20
term-cli request-w -s a -t 300

Behavior Notes (What to Expect)

Defaults & Environment

• Default terminal size: 80x24.
• TERM_CLI_COLS / TERM_CLI_ROWS env vars override defaults.
• start --no-size lets tmux decide size.
• capture trims trailing whitespace and blank lines unless --no-trim.

status

• Prints: session name, idle/running, foreground command (best-effort), screen mode (normal/alternate), size, locked state, attached state, created timestamp, and a process tree.
• “running” is inferred from foreground process markers (best-effort; treat as advisory).
• “Screen: alternate” means a full-screen TUI (vim, htop, less) is active — use wait-idle instead of wait.

pipe-log

• Uses tmux pipe-pane -o so it won’t duplicate an existing pipe.
• Validates the parent directory exists.
• Default mode strips ANSI escapes; --raw keeps them.

kill

• Refuses to kill if locked.
• Refuses to kill if humans are attached, unless --force.
• kill --all first validates all sessions can be killed (unlocked, and unattached unless forced).

Human Collaboration (term-assist)

Agent Side

term-cli start --session remote && term-cli run --session remote "ssh user@host"
term-cli wait --session remote && term-cli capture --session remote  # password prompt or shell (key auth)?
term-cli request --session remote --message "Please complete SSH login (password/MFA)"
term-cli request-wait --session remote && term-cli capture --session remote

Human Side

term-assist list
term-assist attach --session remote
# complete the interaction
# Ctrl+B Enter => done (optional message)
# Ctrl+B d     => detach (if request still pending, agent sees exit code 4)

Locked Sessions

• Create locked: term-cli start --session NAME --locked
• When locked, the agent can only: capture, status, wait*, request*, list, scroll, pipe-log, unpipe.
• Interactive commands (run, send-*, resize, kill) return exit code 5.

Exit Codes (Contract)

Exception mapping used by the CLI:

• FileNotFoundError → 127
• ValueError → 2
• OperationTimeout → 3
• HumanDetached → 4
• AgentLocked → 5
• QueryResult → exit code carried by exception (default 1; non-error query result, printed to stdout)
• RuntimeError → 1

Repo / Codebase Guidelines

Non-Negotiables

• Single-file tool (term-cli): stdlib-only; no Python deps.
• The tool must remain non-interactive: never attach; never depend on an interactive UI.
• Input validation must be explicit and early (--cwd exists, --shell executable, pipe-log parent dir exists, etc.).
• Output is for humans + agents: concise, stable, trimmed.

Design Principles

1. Single file — one executable Python script
2. No deps — stdlib + tmux only
3. Explicit — invalid state fails fast (start if exists; kill if missing; timeouts are errors)
4. Human output — plain text, stable, trimmed
5. Self-documenting — term-cli --help and term-cli <cmd> --help

Code Quality & Testing

1. Determine intended behavior first — don't assume the app or tests are correct.
2. Fix the source — fix app bugs in the app; fix wrong expectations in tests.
3. No hacks — don't add special-cases just to satisfy assertions.
4. No weak tests — don't loosen checks to hide broken behavior.
5. Fix tests when you notice issues — even if it makes failures visible temporarily.
6. Legitimate improvements are not hacks — validation, clearer errors, and consistent behavior are good engineering.
7. Use unique session names in tests — avoid collisions; always cleanup (e.g., finally).
8. Flaky tests are bugs. Never dismiss a test as "flaky" or "pre-existing." Investigate the root cause and fix it — in the test, the app, or both.
9. Never push to the remote repository. The human owner pushes. Agents commit locally only.
10. Never commit with broken tests. Run the full test suite (./run-tests.sh) and pyright before committing. If tests fail, fix them first.

Bug Reporting

Raise potential bugs immediately. If something looks off during development, review, manual testing, or while writing tests, don’t work around it silently—call it out.

Keep documentation updated If --help/docs and the skill disagree, review the source code (source of truth) and improve the documentation.

Style

• Keep the structure: shebang → license → docstring → imports → constants → utilities → commands → CLI.
• Keep tmux usage readable: prefer small helpers over clever inline tmux format strings / quoting tricks.

Typing & type checks (run these):

• Keep from __future__ import annotations as the first import.
• Annotate all params/returns (including pytest fixtures).
• Prefer modern syntax: list[str], dict[str, int], str | None.
• Avoid Any and # type: ignore unless you can justify it.

pyright
# or, if you want to scope it:
pyright term-cli tests/

Naming Conventions

• Constants: SCREAMING_SNAKE_CASE (DEFAULT_COLS, EXIT_TIMEOUT)
• Private functions: _underscore_prefix (_eprint, _run_tmux)
• Command handlers: cmd_ prefix (cmd_list, cmd_start)
• Variables/params: snake_case

Command Handler Pattern

def cmd_example(args: argparse.Namespace) -> None:
    session = args.session
    _require_session(session)     # Validate existence
    _require_unlocked(session)    # Check permissions
    # ... do work ...
    print("Success message")      # Human-readable output

Behavior Consistency

• Timeouts are hard failures (exit 3), not warnings.
• Locked sessions must be enforced uniformly (_require_unlocked).
• wait-for remains substring-based unless intentionally redesigned (and docs/tests updated).

Tests & Local Smoke

If the repo provides a test runner script, use it (it’s typically faster than raw pytest):

./run-tests.sh                 # parallel + serial where needed
./run-tests.sh -s              # sequential (debugging)

Manual smoke (unique session name recommended in tests/CI):

S=smoke-$RANDOM
term-cli start --session "$S" && term-cli run --session "$S" --wait --timeout 10 "echo hello" && term-cli capture --session "$S" && term-cli kill --session "$S" --force

Parallel tests: never use hardcoded session names; always clean up in finally.

Nested tmux testing pattern

To test behavior that requires an attached client (e.g. term-assist attach, verifying kill refuses when humans are attached), use the nested tmux pattern: run tmux attach or term-assist attach inside a helper term-cli session.

tmux normally refuses to nest (it checks $TMUX). Override this by prefixing the command with TMUX='':

helper = unique_session_name()
term_cli("start", "-s", helper, "-x", "60", "-y", "15", check=True)
term_cli("wait", "-s", helper, "-t", "10", check=True)

# Attach to target FROM INSIDE the helper session
term_cli(
    "run", "-s", helper,
    f"TMUX='' {sys.executable} {term_assist_path}"
    f" -L {tmux_socket} attach -s {target}",
)

Setup rules:

1. The helper session needs its own dimensions (e.g. 60x15) — make them different from the target so any resize is detectable.
2. Wait for the helper's shell prompt before running the attach command.
3. After run, poll until the target session shows an attached client:

   from conftest import retry_until
   assert retry_until(
       lambda: self._session_has_client(tmux_socket, target),
       timeout=5.0,
   )
   

Cleanup rules (always in finally):

1. Send the tmux detach sequence to the helper: C-b then d.
2. Wait for the helper's shell prompt to return (the inner tmux has exited).
3. Force-kill the helper session.

finally:
    term_cli("send-key", "-s", helper, "C-b")
    term_cli("send-key", "-s", helper, "d")
    term_cli("wait", "-s", helper, "-t", "5")
    term_cli("kill", "-s", helper, "-f")

This ensures the target has zero attached clients before session_factory teardown tries to kill it. Skipping this can cause "session has attached clients" errors during cleanup.

Examples: test_session.py::TestKill::test_kill_all_atomicity, test_assist.py::TestAttachPreservesSize.