pi-sub-agent

name

pi-sub-agent

description

Launch a pi coding agent as a sub-process in a tmux pane, monitor its progress via JSONL streaming, and report results. Use when delegating a well-defined task (bug fix, feature, refactor) specifically to pi, with live observability. For another CLI use the matching skill (claude-sub-agent, gemini-sub-agent, copilot-sub-agent, kiro-sub-agent); for a whole TODO.md backlog across worktrees use agent-mux. Triggers include "run pi agent", "delegate to pi", "pi sub-agent", "Ralph loop in pi", or any request to run pi in a tmux pane and monitor it.

Pi Sub-Agent Skill

Launch pi coding agents in tmux panes with live monitoring. Depends on the tmux skill for pane interaction.

When to use

• Delegating a well-scoped task (bug fix, feature build, refactor) to a fresh agent
• Running a TALAR or Ralph Wiggum loop where each iteration is a separate agent
• Parallel execution of independent tasks in different panes
• Any situation where you want to observe an agent working without blocking your session

Workflow

1. Write the task prompt to a file

Always use a file — never inline long prompts in shell commands (quoting breaks).

cat > /tmp/task-prompt.md << 'EOF'
Your task description here.
Read TODO.md items X, Y for context.
...
EOF

2. Identify a free tmux pane

Use the tmux skill to find a pane:

bash {SKILLS_DIR}/tmux-remote-control/scripts/tmux-list.sh

Pick a pane in your current session with cmd=bash that isn't running anything.

3. Launch pi in the pane

tmux send-keys -t "{session}:{window}.{pane}" \
  'cd /path/to/repo && pi --models "github-copilot/claude-sonnet-4.6" --no-session --mode json --no-extensions --no-skills --no-prompt-templates --no-themes -p @/tmp/task-prompt.md > /tmp/task-output.jsonl 2>&1 &' Enter

Lean / headless flags:

Flag	Why
--no-session	Ephemeral — no session written to disk, no prior context loaded
--mode json	JSONL stream output for monitoring
-p @file	Non-interactive, process prompt and exit
--no-extensions	Skip extension discovery and loading — avoids scanning for installed extensions
--no-skills	Skip skill loading from disk — reduces startup scan
--no-prompt-templates	Skip prompt template loading
--no-themes	Skip theme loading

All four --no-* flags combined eliminate disk-scanning startup overhead. Use --offline to additionally suppress network calls (e.g. extension update checks):

pi --no-session --mode json \
   --no-extensions --no-skills --no-prompt-templates --no-themes \
   --offline \
   -p @/tmp/task-prompt.md \
   > /tmp/task-output.jsonl 2>&1 &

Other useful flags:

• --models "provider/model" — select specific model
• --tools read,bash,edit,write — already the default; reduce further with e.g. read,bash for read-only tasks
• --append-system-prompt @file — inject persona (see Agent/persona section)

4. Launch the monitor in the same pane

The pi process runs backgrounded (&), so the pane is free for the monitor:

tmux send-keys -t "{session}:{window}.{pane}" \
  "python3 {skill_dir}/scripts/pi-monitor.py /tmp/task-output.jsonl" Enter

The monitor shows a live dashboard: tool calls, files edited, commits, test results, errors, and completion status. Refreshes every 2 seconds. Stops automatically when the agent finishes.

5. Poll for completion from your own session

Don't sleep with increasing intervals — use pi-poll.py which reads the monitor's tmux pane at a fixed interval and reports progress:

python3 {skill_dir}/scripts/pi-poll.py "{session}:{window}.{pane}" --interval 30

This prints one status line every 30 seconds and exits 0 when the agent finishes:

[22:13:00] tools=13  files=...
[22:13:30] tools=15  files=test_adversarial_inputs.py
[22:14:00] tools=20  files=bb-feasibility-check.py, generate-handoff-pa
[22:14:30] tools=25  files=bb-feasibility-check.py, check-repo-permissi
✅ Agent finished after 180s (6 polls)

Options:

• --interval 30 — poll every 30 seconds (default)
• --timeout 1200 — give up after 20 minutes (default)

6. Full launch-monitor-poll pattern (copy-paste ready)

# 1. Write prompt to file
cat > /tmp/task-prompt.md << 'EOF'
Your task description here.
EOF

# 2. Identify target pane (must be in YOUR session)
TARGET="{session}:{window}.{pane}"

# 3. Launch pi + monitor in the target pane
tmux send-keys -t "$TARGET" \
  "cd /path/to/repo && pi --models 'github-copilot/claude-sonnet-4.6' --no-session --mode json --no-extensions --no-skills --no-prompt-templates --no-themes -p @/tmp/task-prompt.md > /tmp/task-output.jsonl 2>&1 &" Enter
sleep 5
tmux send-keys -t "$TARGET" \
  "python3 {SKILLS_DIR}/pi-sub-agent/scripts/pi-monitor.py /tmp/task-output.jsonl" Enter

# 4. Poll from your session (blocks until done or timeout)
python3 {SKILLS_DIR}/pi-sub-agent/scripts/pi-poll.py "$TARGET" --interval 30

# 5. Kill monitor and verify
tmux send-keys -t "$TARGET" C-c
git log --oneline -5

7. Verify results

After the agent finishes:

# Kill monitor
tmux send-keys -t "{session}:{window}.{pane}" C-c

# Check commits
git log --oneline -5

# Run tests
just test  # or pytest, etc.

Common patterns

TALAR iteration (Test → Analyze → Learn → Adjust → Retest)

Each iteration is a separate pi launch:

Iteration 1: Write prompt → Launch pi → Monitor → Verify → Analyze gaps
Iteration 2: Write refined prompt → Launch pi → Monitor → Verify → Analyze
...

The prompt file changes each iteration based on what the previous one revealed.

Ralph Wiggum (stateless TDD)

Use --no-session so each invocation starts fresh. The prompt specifies red-green-refactor for each bug/feature. The agent commits atomically.

Parallel workers

Launch in different panes with different prompt files:

# Pane 0.0: bug fixes
tmux send-keys -t "session:0.0" 'pi ... -p @/tmp/bugfix-prompt.md > /tmp/bugfix.jsonl 2>&1 &' Enter

# Pane 2.1: feature work
tmux send-keys -t "session:2.1" 'pi ... -p @/tmp/feature-prompt.md > /tmp/feature.jsonl 2>&1 &' Enter

Monitor each with a separate pi-monitor.py instance.

Agent / persona injection

Pi resolves @file syntax in --append-system-prompt, so you can load persona files directly:

# Append a persona on top of pi's default coding assistant prompt
pi --no-session --mode json \
   --append-system-prompt @{SKILLS_DIR}/bart-adversarial-reviewer/references/bart.md \
   -p @/tmp/task-prompt.md \
   > /tmp/pi-output.jsonl 2>&1

# Or replace the system prompt entirely
pi --no-session --mode json \
   --system-prompt @{SKILLS_DIR}/bart-adversarial-reviewer/references/bart.md \
   -p @/tmp/task-prompt.md \
   > /tmp/pi-output.jsonl 2>&1

The @path is resolved relative to cwd. Both absolute and relative paths work.

In tmux:

tmux send-keys -t "$TARGET" \
  "cd /path/to/repo && pi --no-session --mode json --append-system-prompt @{SKILLS_DIR}/bart-adversarial-reviewer/references/bart.md -p @/tmp/task.md > /tmp/pi-output.jsonl 2>&1 &" Enter

Troubleshooting

Prompt gets mangled by shell quoting: Always use @/tmp/file.md — never inline.

Agent runs forever: Check if it's stuck in a retry loop. Read the JSONL:

tail -5 /tmp/task-output.jsonl | python3 -c "import json,sys; [print(json.loads(l).get('type','?')) for l in sys.stdin]"

Monitor shows "RUNNING" but file stopped growing: The agent may have errored silently. Check:

stat -c%s /tmp/task-output.jsonl  # note size
sleep 10
stat -c%s /tmp/task-output.jsonl  # compare

Wrong pane: Always use tmux-list.sh first. Use your own session, not a random one.