plan-task

Take one task from the current slice's task list and turn it into a concrete plan: which files to touch, what code to write, how to verify. Output lives at M###-S##-T##-PLAN.md.

Anti-Pattern: "The task summary is enough, I'll figure out files during execution"

No. Tasks without pre-committed file paths drift. An agent (human or AI) asked to "add signup form" will discover mid-stream that the form lives in three different places and pick the wrong one. File paths in the task plan are a concurrency primitive -- they prevent two tasks from editing the same file by accident, and they make scope-drift detection possible.

Iron rule

A task must fit in one context window. If the plan feels too big, split into two tasks. Signals the task is too big:

• More than ~5 files touched
• Multiple unrelated concerns (e.g. schema change + UI change + new test infra)
• The verification step needs more than 2 commands

When in doubt, split. Smaller tasks ship faster than oversized ones.

Checklist

You MUST create a TodoWrite task for each of these items:

1. Run preamble -- detect current slice + next unplanned task
2. HARD-GATE: slice must exist -- abort if no active slice
3. Confirm task selection -- show the task line from slice-plan, confirm it's next
4. Ask file list -- exact paths to create / modify / delete
5. Ask task body -- what the code does, in prose + pseudocode
6. Ask verification -- 1-2 commands that prove done
7. Ask fits-one-context-window check -- sanity-check or split
8. Write M###-S##-T##-PLAN.md
9. Update STATE.md -- active_task: T##
10. Report + return -- task ready to execute or dispatch to subagent

Preamble

_PROJECT_DIR="${CLAUDE_PROJECT_DIR:-$PWD}"
cd "$_PROJECT_DIR" 2>/dev/null || true
_PROJECT_SLUG=$(basename "$(git rev-parse --show-toplevel 2>/dev/null)" 2>/dev/null || basename "$(pwd)")

if [ -d "$_PROJECT_DIR/.ytstack" ]; then
  _YT_DIR="$_PROJECT_DIR/.ytstack"
elif [ -d "$HOME/.ytstack/projects/$_PROJECT_SLUG" ]; then
  _YT_DIR="$HOME/.ytstack/projects/$_PROJECT_SLUG"
else
  _YT_DIR=""
fi

_HAS_YTSTACK=$([ -n "$_YT_DIR" ] && echo yes || echo no)

_NON_INTERACTIVE=false
if [ -n "$YTSTACK_NON_INTERACTIVE" ] || [ -n "$OPENCLAW_SESSION" ] || [ -n "$CLAUDE_AGENT_TEAM_MEMBER" ]; then
  _NON_INTERACTIVE=true
fi

_CURRENT_MILESTONE=none
_ACTIVE_SLICE=none
if [ -f "$_YT_DIR/STATE.md" ]; then
  _CURRENT_MILESTONE=$(sed -n 's/^current_milestone: *//p' "$_YT_DIR/STATE.md" | head -1)
  _ACTIVE_SLICE=$(sed -n 's/^active_slice: *//p' "$_YT_DIR/STATE.md" | head -1)
fi

# If no active slice in STATE.md, infer the first unfinished slice from ROADMAP
if [ "$_ACTIVE_SLICE" = "none" ] || [ -z "$_ACTIVE_SLICE" ]; then
  ROADMAP="$_YT_DIR/$_CURRENT_MILESTONE-ROADMAP.md"
  if [ -f "$ROADMAP" ]; then
    _ACTIVE_SLICE=$(grep -oE '^- \[ \] S[0-9][0-9] --' "$ROADMAP" | head -1 | grep -oE 'S[0-9][0-9]')
  fi
fi

_SLICE_PLAN="$_YT_DIR/$_CURRENT_MILESTONE-$_ACTIVE_SLICE-PLAN.md"

# Next unplanned task = first un-elaborated task in slice-plan
# (Un-elaborated = listed in slice-plan but no corresponding T##-PLAN.md file exists)
_NEXT_TASK=""
if [ -f "$_SLICE_PLAN" ]; then
  for t in $(grep -oE '^- \[ \] T[0-9][0-9] --' "$_SLICE_PLAN" | grep -oE 'T[0-9][0-9]'); do
    _TASK_FILE="$_YT_DIR/$_CURRENT_MILESTONE-$_ACTIVE_SLICE-$t-PLAN.md"
    if [ ! -f "$_TASK_FILE" ]; then
      _NEXT_TASK="$t"
      break
    fi
  done
fi

echo "HAS_YTSTACK: $_HAS_YTSTACK"
echo "YTSTACK_NON_INTERACTIVE: $_NON_INTERACTIVE"
echo "CURRENT_MILESTONE: $_CURRENT_MILESTONE"
echo "ACTIVE_SLICE: $_ACTIVE_SLICE"
echo "SLICE_PLAN: $_SLICE_PLAN"
echo "NEXT_TASK: ${_NEXT_TASK:-none}"

Procedure

Step 2: HARD-GATE

If HAS_YTSTACK=no: abort with "run init-project first". If CURRENT_MILESTONE=none: abort with "run plan-milestone first". If ACTIVE_SLICE=none or slice-plan missing: abort with "run slice-milestone first". If NEXT_TASK=none: report "all tasks in {ACTIVE_SLICE} are planned. Next: execute them or run /ytstack:plan-task again if you add a task to the slice-plan." STOP.

Step 3: Confirm task selection

Read the task line from {SLICE_PLAN}. Grep pattern: ^- \[ \] {NEXT_TASK} -- (.*)$. Extract the description.

Report (no AskUserQuestion -- just show):

Next unplanned task in {CURRENT_MILESTONE}-{ACTIVE_SLICE}:

{NEXT_TASK} -- {TASK_DESCRIPTION}

Planning this now. If this isn't the task you want, /exit and edit the slice-plan to reorder.

Step 4: Ask file list

Use AskUserQuestion (open-ended):

Which files does {NEXT_TASK} touch? List exact paths with action:

• Create: path/to/new-file.ext
• Modify: path/to/existing.ext (line range if specific, e.g. :123-145)
• Delete: path/to/obsolete.ext

Rule: >5 files touched is a code smell. Consider splitting the task.

Remember as _FILE_LIST.

Step 5: Ask task body

Use AskUserQuestion (open-ended):

Describe what the code in this task does. Prose is fine -- pseudocode is better. For UI: what interaction and what outcome. For backend: what request/response. For infra: what resource + what state.

Not "implement signup" -- but "signup form POSTs to /api/signup with JSON body {email, password}. Server validates email regex, hashes password with argon2, inserts row into users table, returns 201 + session cookie. Failure cases: duplicate email → 409, invalid regex → 400."

Remember as _TASK_BODY.

Step 6: Ask verification

Use AskUserQuestion (open-ended):

How do we verify this task is done? 1-2 commands max. Real commands you could run now.

Good: bun test test/auth/signup.test.ts or curl -X POST localhost:3000/api/signup -d '{"email":"a@b.c","password":"test1234"}'

Bad: "manual test" or "check it works" -- those aren't falsifiable.

Remember as _VERIFICATION.

Step 7: Fits-one-context-window check

Use AskUserQuestion (multi-choice):

Sanity check: does this task fit one context window? Look at your answers to Steps 4-6.

RECOMMENDATION: A. If you needed to talk yourself into "yes, it fits", it probably doesn't -- split.

A) Yes, fits comfortably. (Completeness: 10/10) B) Maybe -- borderline, might overflow. (Completeness: 6/10, risk: high) C) No -- I should split this task first.

If C: emit "Splitting needed. Run /exit, edit the slice-plan to replace this task with two tasks, then re-run /ytstack:plan-task." STOP.

If B: ask user to confirm before proceeding (don't silently overlook the risk).

If A: proceed.

Step 8: Write M###-S##-T##-PLAN.md

---
milestone: {CURRENT_MILESTONE}
slice: {ACTIVE_SLICE}
task: {NEXT_TASK}
project: {PROJECT_NAME}
created: {ISO_TIMESTAMP}
status: planned
---

# {CURRENT_MILESTONE}-{ACTIVE_SLICE}-{NEXT_TASK} -- Task Plan

**Summary:** {TASK_DESCRIPTION}

## Files

{FILE_LIST}

## What this does

{TASK_BODY}

## Verification

```bash
{VERIFICATION}

Success: command exits 0 and shows expected output. Failure: re-read plan, check if spec drifted.

Done signal

Run /ytstack:summarize-task after execution to mark complete and advance STATE.md.

### Step 9: Update STATE.md

Use Edit tool. If `YTSTACK_NON_INTERACTIVE` is `false` (i.e. `CLAUDE_AGENT_TEAM_MEMBER` is unset):
- Change `active_slice: <old>` → `active_slice: {ACTIVE_SLICE}`
- Change `active_task: <old>` → `active_task: {NEXT_TASK}`

If `YTSTACK_NON_INTERACTIVE` is `true` (running as swarm teammate): skip both frontmatter writes. Log:
> `[ytstack:plan-task] skipping STATE.md active_slice/active_task write -- running as swarm teammate (CLAUDE_AGENT_TEAM_MEMBER set)`

Bump `last_updated` regardless.

Update Status line: `**Status:** {CURRENT_MILESTONE} / {ACTIVE_SLICE} / {NEXT_TASK} planned -- ready to execute.`

### Step 10: Report + return

Report:

> Task **{CURRENT_MILESTONE}-{ACTIVE_SLICE}-{NEXT_TASK}** planned.
>
> File: `{SLICE_PLAN_DIR}/{CURRENT_MILESTONE}-{ACTIVE_SLICE}-{NEXT_TASK}-PLAN.md`
>
> STATE.md: `active_slice = {ACTIVE_SLICE}`, `active_task = {NEXT_TASK}`.
> (Skipped if running as swarm teammate.)
>
> Next: execute the task (manually, or dispatch to a subagent, or wait for `ytstack:spawn-milestone-team` M006). When the code is done and verification passes, run `/ytstack:summarize-task`.

## Terminal State

Valid terminal states:
- Return after writing task-plan file + updating STATE.md
- Abort if gates fail (HAS_YTSTACK / CURRENT_MILESTONE / ACTIVE_SLICE / NEXT_TASK unresolved)
- Abort if user picks C in Step 7 (task too big, split needed)

Do NOT invoke `ytstack:summarize-task` automatically -- the user / subagent must execute the task first. Do NOT start writing code from within this skill -- that's the execution phase, a separate concern.