---
name: plan
description: Use when a milestone spec exists in docs/specs/ and a new iteration is starting. Produces a placeholder-free, bite-sized implementation plan in docs/plans/ that the implement skill can execute task-by-task. Hard-gate before any implementation work.
---

# plan — spec → executable plan

> **Violating the letter of these rules is violating the spirit.**

## Overview

A plan is the contract between design (spec) and execution
(`implement`). It commits the file structure, names every file
that will be created or modified, and decomposes work into bites
small enough that a subagent can execute one in 2-5 minutes
without making judgement calls outside its remit.

Plans live at `docs/plans/<iteration>.md`, the header
references the parent spec, and the commit-per-task pattern
matches the existing JOURNAL style.

## When to Use / Skipping

Triggers:
- A spec at `docs/specs/<milestone>.md` is approved.
- A new iteration within an active milestone is starting.

May be skipped when:
- The work is a bug fix where the RED test from `debug` IS the
  plan (handoff goes straight to `implement` mini-mode).
- The work is a trivial mechanical edit (one file, ≤30 LOC, no
  design judgement).

**Never skipped** for a standard iteration within an active
milestone. "I know the milestone, plan from memory" is exactly the
failure mode this skill prevents.

## The Iron Law

```
NO PLACEHOLDERS — TBD, TODO, "implement later", "similar to Task N",
or "add appropriate error handling" are PLAN FAILURES.
EVERY STEP THAT CHANGES CODE INCLUDES THE CODE.
EVERY STEP THAT RUNS A COMMAND INCLUDES THE COMMAND AND EXPECTED OUTPUT.
```

Non-negotiable.

## The Process

### Step 1 — Read the parent spec

Read `docs/specs/<milestone>.md` in full. NOT from memory. Even if
the spec is recent and you wrote it yourself, re-read it before
planning.

The spec is the source of truth; the plan is the projection of one
iteration's worth of work onto a task list.

### Step 2 — Map file structure

Before defining tasks, list every file the iteration will create or
modify, and what each one is responsible for. This is where
decomposition decisions are locked in.

```markdown
**Files this plan creates or modifies:**

- Create: `crates/ailang-codegen/src/<new>.rs` — <one-line
  responsibility>
- Modify: `crates/ailang-check/src/typeclass.rs` — adds
  <responsibility>
- Test: `crates/ail/tests/e2e.rs` — adds <case>
```

Files that change together stay in the same task. Files that change
independently get separate tasks.

### Step 3 — Write tasks, bite-sized

Each task is a logical unit of change (one feature, one fix, one
extension). Each task contains steps; each step is ONE action that
takes 2-5 minutes:

```markdown
### Task N: <Component Name>

**Files:**
- Create: `<exact path>`
- Modify: `<exact path>:<line range if known>`
- Test: `<exact path>`

- [ ] **Step 1: Write the failing test**

```rust
#[test]
fn test_<specific_behaviour>() {
    let result = function(input);
    assert_eq!(result, expected);
}
```

- [ ] **Step 2: Run test to verify it fails**

Run: `cargo test --workspace -p <crate> test_<specific_behaviour>`
Expected: FAIL with "<exact expected message>"

- [ ] **Step 3: Write minimal implementation**

```rust
fn function(input: T) -> U {
    // exact code
}
```

- [ ] **Step 4: Run test to verify it passes**

Run: `cargo test --workspace -p <crate> test_<specific_behaviour>`
Expected: PASS

- [ ] **Step 5: Commit**

```bash
git add <paths>
git commit -m "iter <X>.<n>: <subject>"
```
```

### Step 4 — Plan header

Every plan starts with this header:

```markdown
# <Iteration Title> — Implementation Plan

> **Parent spec:** `docs/specs/<milestone>.md`
>
> **For agentic workers:** REQUIRED SUB-SKILL: use `skills/implement`
> to run this plan. Steps use `- [ ]` checkboxes for tracking.

**Goal:** <one sentence>

**Architecture:** <2-3 sentences>

**Tech Stack:** <key crates/libs touched>

---
```

### Step 5 — Self-review

Before committing the plan, run this checklist inline:

1. **Spec coverage:** every spec section has a task that implements
   it. If a section has no task, add one.
2. **Placeholder scan:** grep for "TBD", "TODO", "implement later",
   "similar to Task", "add appropriate error handling". Any hit is
   a plan failure to fix.
3. **Type consistency:** function names, type names, file paths
   referenced across tasks must match. `clearLayers()` in Task 3
   and `clearFullLayers()` in Task 7 is a bug.
4. **Step granularity:** every step is 2-5 minutes. If a step is
   "implement the parser", split it.

Fix issues inline. No need to re-review — fix and commit.

### Step 6 — Commit and hand off

```bash
git add docs/plans/<iteration>.md
git commit -m "plan: <iteration> <subject>"
```

Hand off to `implement` with: path to the plan file + optional
task focus ("only Tasks 1-3 this run").

## Handoff Contract

| Direction | Carrier |
|-----------|---------|
| `brainstorm` → `plan` | path to `docs/specs/<milestone>.md` + iteration scope ("this iteration covers spec section X+Y") |
| `plan` → `implement` | path to `docs/plans/<iteration>.md` + optional task-range focus |
| `plan` → `brainstorm` (bounce) | spec contains placeholders or contradictions: name the offending section, request revision |

## Common Rationalisations

| Excuse | Reality |
|--------|---------|
| "TBD in step 4 lets me ship the plan tonight, fill in tomorrow" | Half-decided plans get re-litigated mid-iteration, costing more than the night's sleep saved. Make the decision tonight or close the laptop. |
| "Bundle Tasks 3 and 4, both small, single commit" | The red-green-refactor cycle is the unit of verification. Bundled commits make bisection lie. If 3 and 4 are inseparable, they're one task — rewrite the decomposition. |
| "Spec is recent, I wrote it, plan from memory" | Memory diverges from disk. 15 minutes of re-reading is the cheapest insurance in the cycle. |
| "Step 5 'implement the parser' is fine, I'll detail it at execution time" | Then it's not a step, it's a wish. Steps are bite-sized OR the plan isn't done. |
| "Task 7 is similar to Task 4, just say so" | The executor may read tasks out of order. Repeat the code. |
| "The spec has a TBD too, I can pass it through" | Bounce back to `brainstorm`. Plans inherit spec gaps; spec gaps are not plan placeholders. |

## Red Flags — STOP

- Any of: "TBD", "TODO", "fill in later", "similar to", "add
  appropriate <X>" — fix or bounce.
- Steps that describe what to do without showing how
- Function/type/path names that don't match across tasks
- Step descriptions longer than the code they describe
- Header missing parent spec reference
- Self-review skipped because "the plan looks fine"

## Cross-references

- **Input source:** `skills/brainstorm/SKILL.md` — produces the
  spec this skill consumes.
- **Output target:** `skills/implement/SKILL.md` — runs the plan
  task-by-task.
- **No private agents.** This skill is dialogue-driven (orchestrator
  + spec).
