---
name: subagent-implement
description: "Full implementation pipeline: scout → plan → review → code → build verify → review → fix. Use when the user invokes /implement."
---

# /implement — Standard Implementation Pipeline

## Agent Roster

| Agent | Role |
|-------|------|
| scout | Fast codebase recon |
| planner | Detailed implementation plans |
| plan-reviewer | Reviews plans for correctness and risk |
| coder | Primary implementation |
| coder-parallel | Parallel implementation tasks (fan-out) |
| reviewer | Cross-family code review |
| fixer | Applies review feedback precisely |

## Phase 1: Scout → Plan → Review (chain)

```js
await subagent({ chain: [
  { agent: "scout",         task: "Explore the codebase for: {task}" },
  { agent: "planner",       task: "Create a detailed implementation plan for: {task}" },
  { agent: "plan-reviewer", task: "Review the plan for correctness, completeness, and risk." }
]})
```

The chain creates `scout.md`, `plan.md`, `plan-review.md` in the chain artifact dir.

Read `plan-review.md` from the artifact dir. If **NEEDS_REVISION** or **REJECTED**, loop: tell the planner what to fix, re-run the reviewer. If **APPROVED**, proceed to Phase 2.

## Phase 2: Implement

```js
// Single coder:
await subagent({ agent: "coder", task: `Read and implement the plan at <chain_dir>/plan.md` })

// Or parallel coders (if plan has independent sections):
await subagent({ tasks: [
  { agent: "coder-parallel", task: `Implement Part A from <chain_dir>/plan.md` },
  { agent: "coder-parallel", task: `Implement Part B from <chain_dir>/plan.md` }
]})
```

Use the chain dir path from Phase 1's result.

## Phase 3: Build Verification

After the coder finishes, independently verify the build — don't trust the coder's report:

```bash
# Run a full build, not just type-check. Shaders, linkers, and bundlers may fail.
# Adapt to project: cargo build, npm run build, etc.
```

## Phase 4: Review → Fix

```js
await subagent({ agent: "reviewer", output: `${chainDir}/review.md`, task: "Review all changes made" })
```

Read `review.md`. If issues found:

```js
await subagent({ agent: "fixer", task: `Read and apply the review feedback in ${chainDir}/review.md` })
```

## Phase 5: Next Steps & Workflow Summary

After all phases complete, give the user a brief summary of what is next to take use of the implementation and an honoest evaluation of the workflow:

- **What needs wiring and where**: Point to where the user can take the implementation into use
- **What happened**: which phases ran, any plan review loops, whether fixes were needed
- **Issues**: any agent silent failures, fallbacks used, build errors, or unexpected behavior
- **Agent quality**: did any agent misinterpret the task, produce poor output, or need hand-holding? Name the agent and the problem.
- **Skill improvements**: did this workflow reveal gaps in the skill instructions or agent prompts? Note what should change

Be concise — a few lines is enough when things went well. Only expand on problems.

## Parallel Coders Within a Chain

Fan-out/fan-in inside a chain (useful when plan sections are independent):

```js
await subagent({ chain: [
  { agent: "scout", task: "Explore the codebase for: {task}" },
  { agent: "planner", task: "..." },
  { parallel: [
    { agent: "coder-parallel", task: "Read the plan at {chain_dir}/plan.md. Implement Part A" },
    { agent: "coder-parallel", task: "Read the plan at {chain_dir}/plan.md. Implement Part B" }
  ]},
  { agent: "reviewer", task: "Review all changes from {previous}" }
]})
```

## Step Overrides

Override agent defaults per step:

```js
await subagent({ chain: [
  { agent: "scout", output: "context.md" },
  { agent: "planner", reads: ["context.md"], output: "plan.md" },
  { agent: "plan-reviewer", reads: ["plan.md"] }
]})
```

## Chain Mechanics

Chain mode (`subagent({ chain: [...] })`) runs agents sequentially in a shared temp directory (`{chain_dir}`). Each step:
1. The framework injects `[Read from:]` and `[Write to:]` directives from the agent's `defaultReads` and `output` frontmatter
2. The agent reads upstream files, does its work, and writes its deliverable to the `[Write to:]` path using the `write` tool
3. The agent returns a brief text summary; `{previous}` carries this summary to the next step
4. Variable substitution: `{task}` = original task, `{previous}` = prior step's brief ack, `{chain_dir}` = artifact dir path

Key behaviors:
- Data flows through FILES (`scout.md` → `plan.md` → `plan-review.md`), not through `{previous}`
- `{previous}` contains only a brief summary from the prior step — do NOT rely on it for full context
- The framework validates that the expected output file was created
- The chain result includes `📁 Artifacts: /tmp/pi-chain-runs/<id>/` — use this path to read files for branching decisions

Reviewer and fixer run as single agents (not in chains). Pass file paths in the task string and use the `output` parameter to capture their output.

## Fallback Strategy

When a subagent call returns no output (silent failure), apply cross-family model fallback. **Do not fall back to doing the work yourself** — always retry with the fallback model first.

1. **First attempt**: Use the agent's default model
2. **If silent failure or error**: Retry with the fallback model using `model` override
3. **If the fallback also fails**: Report the double-failure to the user. Still do not do the work yourself.

```js
// Example: scout fails silently, retry with fallback
subagent({ agent: "scout", task: "...", model: "anthropic/claude-haiku-4-5" })
```

| Agent | Primary | Fallback |
|-------|---------|----------|
| scout | zai/glm-4.7-flash | anthropic/claude-haiku-4-5 |
| planner, coder | zai/glm-5.1 | anthropic/claude-opus-4-6 |
| coder-parallel | zai/glm-4.7 | anthropic/claude-sonnet-4-6 |
| plan-reviewer, reviewer | anthropic/claude-opus-4-6 | zai/glm-5.1 |
| fixer | anthropic/claude-sonnet-4-6 | zai/glm-5.1 |

## Adaptive Routing

Do not run the full pipeline for a one-line fix. Use your judgment — a single coder call may suffice.