---
name: planner
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` and the header references
the parent spec. The plan decomposes work into tasks; each task is
the unit of review (spec-compliance and quality gates inside
`implement`), not the unit of commit. Commits are a Boss-only
decision taken at the end of the iter against the full working-tree
diff.

## 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

Dispatch `ailang-plan-recon` with the spec path and iteration scope.
Read the returned file-map. Lift the relevant entries into the plan's
"Files this plan creates or modifies" section; the Boss may add or
amend entries that recon missed.

Dispatch carrier:

| Field | Content |
|-------|---------|
| `spec_path` | path to the parent spec |
| `iteration_scope` | which sections of the spec this iteration covers |
| `focus_hint` | optional — subsystem or symbol to prioritise |

Recon does NOT decide decomposition. Two recon dispatches per planner
run is unusual but legitimate (e.g. one for the main spec sections,
one with a sharper `focus_hint` for a tricky subsystem). Three or
more is a smell — re-read the spec; the iteration scope is probably
too broad.

The plan's "Files this plan creates or modifies" section keeps the
same shape:

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

- Create: `<exact path>` — <one-line responsibility>
- Modify: `<exact path>:<line range if known>`
- Test: `<exact path>` — <one-line case description>
```

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
```

No `git commit` step. Implement tasks leave their work in the
working tree; the Boss commits at the end of the iter.

### 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 handing the plan off, 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.
5. **No commit steps:** task templates must not contain
   `git commit` instructions. Implement tasks leave work in the
   working tree.
6. **Pin/replacement substring contiguity:** when a task ships a
   test asserting `contains("<substring>")` (or a grep) AND another
   task's verbatim replacement body is what must contain that
   substring, the substring must appear *contiguously* in that
   replacement body — no soft-wrap splitting it across two lines.
   Two authoritative artefacts (exact pin vs. exact replacement)
   that cannot both be applied literally is a plan defect, not an
   implementer judgement call. This is the recurring grep/contains
   line-wrap family (iter-revert Concern 2; iter effect-doc-honesty
   Task 2) — scrub it here, every plan that pairs a presence-pin
   with a verbatim text edit.
7. **Compile-gate vs. deferred-caller ordering:** when a task
   changes a function signature (or any change that makes the
   *whole crate* fail to compile until N call sites are updated)
   AND that task ends with a `cargo build`/`cargo test` "0 errors"
   gate, every caller the signature change touches MUST be threaded
   *inside that same task* — not deferred to a later task. A
   "0-errors" gate is unsatisfiable while any caller is still
   unthreaded (hard `error[E0061]`), so a plan that defers a caller
   (e.g. "the `check_fn` call site is handled in Task 4") past an
   earlier task's compile gate is internally contradictory: the
   executor is forced to pull the deferred code forward to satisfy
   the gate, silently resequencing the plan. Either fold all
   caller-threading into the signature-change task, or make the
   gate a *partial* build of just the changed module with the
   crate-wide build deferred to the task that finishes threading.
   This is the recurring "compile-gate depends on a caller the plan
   defers past the gate" family (iter loop-recur.2 Concern 1) —
   scrub it here, every plan with a signature-change task.
8. **Verification-command filter strings must resolve.** Every
   literal `cargo test … <filter>` / `grep <pat>` / `cargo test
   --test <name>` in a Run step is itself a load-bearing artefact:
   if its filter substring matches **no** test (or its `--test`
   target file does not exist), the step silently asserts nothing —
   a green "0 passed; 0 filtered" reads as success while proving
   the opposite of the gate's intent. For every such command,
   either (a) the filter substring must be one verified to match
   ≥1 real named test/line in the current tree (name it, do not
   guess from the feature word — e.g. tail-app guards are
   `*_tail_position_*` / `*musttail*`, NOT `tail`), or (b) use the
   unfiltered suite plus an explicit result-count assertion
   (`… | awk '{p+=$4} END{print p}'`, expected ≥ a stated baseline)
   so "nothing ran" cannot masquerade as "nothing regressed". This
   is the recurring "literal verification filter doesn't resolve to
   its evident target" family (iter loop-recur.3 Concern) — scrub
   every Run step whose assertion lives in a filter string.

Fix issues inline.

### Step 6 — Hand off

The plan sits in the working tree as an unstaged file at
`docs/plans/<iteration>.md`. Hand off to `implement` with: path to
the plan file + optional task focus ("only Tasks 1-3 this run").

The Boss commits the plan when handing it forward (suggested
commit subject: `plan: <iteration> <subject>`). The planner skill
does not perform the commit itself.

## Handoff Contract

| Direction | Carrier |
|-----------|---------|
| `brainstorm` → `planner` | path to `docs/specs/<milestone>.md` + iteration scope ("this iteration covers spec section X+Y") |
| `planner` → `implement` | path to `docs/plans/<iteration>.md` + optional task-range focus |
| `planner` → `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" | Tasks are the unit of review (spec-check + quality-check fire once per task). Bundling collapses two reviews into one and hides the smaller change inside the bigger one. 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.
- **Agents dispatched:**
  - `skills/planner/agents/ailang-plan-recon.md` — Step 2,
    file-structure mapping (read-only). Mandatory; the Boss does
    NOT do recon in-context.
