Subagent Driven Development

Subagent-Driven Development

Execute plan by dispatching fresh subagent per task, with two-stage review after each: spec compliance review first, then code quality review.

Core principle: Fresh subagent per task + two-stage review (spec then quality) = high quality, fast iteration

When to Use

Use this skill when all three conditions are met:

• You have an implementation plan with defined tasks
• The tasks are mostly independent (not tightly coupled)
• You want to stay in the current session (not open parallel worktrees)

Use planning:executing-plans instead when you need an isolated, separately-gated session. Use manual execution when you don't yet have a plan or tasks are tightly coupled.

The Process

digraph process {
    rankdir=TB;

    subgraph cluster_per_task {
        label="Per Task";
        "Dispatch implementer subagent (./implementer-prompt.md)" [shape=box];
        "Implementer subagent asks questions?" [shape=diamond];
        "Answer questions, provide context" [shape=box];
        "Implementer subagent implements, tests, commits, self-reviews" [shape=box];
        "Dispatch spec + quality reviewers IN PARALLEL (./spec-reviewer-prompt.md + ./code-quality-reviewer-prompt.md)" [shape=box];
        "Spec reviewer subagent confirms code matches spec?" [shape=diamond];
        "Implementer subagent fixes spec gaps" [shape=box];
        "Code quality reviewer subagent approves (wait for both)?" [shape=diamond];
        "Code quality reviewer subagent approves?" [shape=diamond];
        "Implementer subagent fixes quality issues" [shape=box];
        "Mark task complete in TodoWrite" [shape=box];
    }

    "Read plan, extract all tasks with full text, note context, create TodoWrite" [shape=box];
    "More tasks remain?" [shape=diamond];
    "Dispatch final code reviewer subagent for entire implementation" [shape=box];
    "Finalize branch: full tests + commit + PR/merge" [shape=box style=filled fillcolor=lightgreen];

    "Read plan, extract all tasks with full text, note context, create TodoWrite" -> "Dispatch implementer subagent (./implementer-prompt.md)";
    "Dispatch implementer subagent (./implementer-prompt.md)" -> "Implementer subagent asks questions?";
    "Implementer subagent asks questions?" -> "Answer questions, provide context" [label="yes"];
    "Answer questions, provide context" -> "Dispatch implementer subagent (./implementer-prompt.md)";
    "Implementer subagent asks questions?" -> "Implementer subagent implements, tests, commits, self-reviews" [label="no"];
    "Implementer subagent implements, tests, commits, self-reviews" -> "Dispatch spec + quality reviewers IN PARALLEL (./spec-reviewer-prompt.md + ./code-quality-reviewer-prompt.md)";
    "Dispatch spec + quality reviewers IN PARALLEL (./spec-reviewer-prompt.md + ./code-quality-reviewer-prompt.md)" -> "Spec reviewer subagent confirms code matches spec?";
    "Spec reviewer subagent confirms code matches spec?" -> "Implementer subagent fixes spec gaps" [label="no"];
    "Implementer subagent fixes spec gaps" -> "Dispatch spec + quality reviewers IN PARALLEL (./spec-reviewer-prompt.md + ./code-quality-reviewer-prompt.md)" [label="re-review"];
    "Spec reviewer subagent confirms code matches spec?" -> "Code quality reviewer subagent approves (wait for both)?" [label="yes"];
    "Code quality reviewer subagent approves (wait for both)?" -> "Implementer subagent fixes quality issues" [label="no"];
    "Implementer subagent fixes quality issues" -> "Dispatch spec + quality reviewers IN PARALLEL (./spec-reviewer-prompt.md + ./code-quality-reviewer-prompt.md)" [label="re-review"];
    "Code quality reviewer subagent approves (wait for both)?" -> "Mark task complete in TodoWrite" [label="yes"];
    "Mark task complete in TodoWrite" -> "More tasks remain?";
    "More tasks remain?" -> "Dispatch implementer subagent (./implementer-prompt.md)" [label="yes"];
    "More tasks remain?" -> "Dispatch final code reviewer subagent for entire implementation" [label="no"];
    "Dispatch final code reviewer subagent for entire implementation" -> "Finalize branch: full tests + commit + PR/merge";
}

Parallel review note: After each implementation task, dispatch the spec-reviewer and code-quality-reviewer in the same turn — both are read-only and have no dependency on each other's output. Wait for both to complete, then act on their combined findings.

Re-review routing after fixes:

• If spec reviewer found issues: implementer fixes them, then re-run both reviewers in the same turn (spec compliance may have affected quality too).
• If spec reviewer already passed and only quality issues remain: re-dispatch only the code quality reviewer — spec compliance was already verified and does not need to re-run.

Only mark the task complete when both spec and quality reviewers have passed in the same review round.

Model Selection

If think-tool is available, invoke it before dispatching the implementer for each task: reason about task complexity, hidden dependencies between files, and which model tier is appropriate. This turns the narrative guidance below into an auditable per-task decision.

Use the least powerful model that can handle each role to conserve cost and increase speed.

Mechanical implementation tasks (isolated functions, clear specs, 1-2 files): use a fast, cheap model. Most implementation tasks are mechanical when the plan is well-specified.

Integration and judgment tasks (multi-file coordination, pattern matching, debugging): use a standard model.

Architecture, design, and review tasks: use the most capable available model.

Task complexity signals:

• Touches 1-2 files with a complete spec → cheap model
• Touches multiple files with integration concerns → standard model
• Requires design judgment or broad codebase understanding → most capable model

Handling Implementer Status

Implementer subagents report one of four statuses. Handle each appropriately:

DONE: Proceed to spec compliance review.

DONE_WITH_CONCERNS: Read the concerns first — if they touch correctness or scope, address before review; if they're observations only (e.g., "file is getting large"), note and proceed to review. If think-tool is available and the concerns are ambiguous, invoke it to reason: does this touch correctness or scope, and what is the right action?

NEEDS_CONTEXT: Provide the missing information and re-dispatch with the same prompt + new context.

BLOCKED: Something must change before retrying. If think-tool is available, invoke it before deciding how to proceed — reason over: what specifically blocked the subagent, whether the plan has a gap, whether model escalation vs. task decomposition is the right remedy, and what context to add on re-dispatch. Then: provide more context and re-dispatch, escalate to a more capable model, break the task into smaller pieces, or surface to the human if the plan itself is wrong. Never retry the same model with the same inputs.

Never ignore an escalation or force the same model to retry without changes. If the implementer said it's stuck, something needs to change.

Prompt Templates

• ./implementer-prompt.md - Dispatch implementer subagent
• ./spec-reviewer-prompt.md - Dispatch spec compliance reviewer subagent
• ./code-quality-reviewer-prompt.md - Dispatch code quality reviewer subagent

Example Workflow

See references/example-workflow.md for a full concrete trace. For context on why this approach works better than alternatives, see references/rationale.md.

Red Flags

Never:

• Start implementation on main/master branch without explicit user consent
• Skip reviews (spec compliance OR code quality)
• Proceed with unfixed issues
• Dispatch multiple implementation subagents in parallel (conflicts)
• Make subagent read plan file (provide full text instead)
• Skip scene-setting context (subagent needs to understand where task fits)
• Ignore subagent questions (answer before letting them proceed)
• Accept "close enough" on spec compliance (spec reviewer found issues = not done)
• Skip review loops (reviewer found issues = implementer fixes = review again)
• Re-run spec reviewer when spec already passed and only quality issues remain — if spec reviewer already passed, re-dispatch only the code quality reviewer after quality fixes
• Let implementer self-review replace actual review (both are needed)
• Act on only one review result while the other is still running — wait for both, then decide
• Move to next task while either review has open issues

If subagent asks questions:

• Answer clearly and completely
• Provide additional context if needed
• Don't rush them into implementation

If reviewer finds issues:

• Implementer (same subagent) fixes them
• Reviewer reviews again
• Repeat until approved
• Don't skip the re-review

If subagent fails task:

• Dispatch fix subagent with specific instructions
• Don't try to fix manually (context pollution)

Integration

Before dispatching (do these yourself):

• Isolated workspace — start on a dedicated branch or worktree, never main/master, so parallel task commits don't land on a shared branch. Set this up manually; there is no separate skill for it here.
• write:writing-plans — produces the plan this skill executes.

During execution:

• develop:test-driven-development — each dispatched subagent drives its task test-first.
• Code review — reviewer subagents use the bundled ./spec-reviewer-prompt.md and ./code-quality-reviewer-prompt.md templates; no external review skill is required.

Finishing: after the final reviewer passes, close the branch yourself — run the full test suite, commit, then open a PR or merge per the repo's flow — and settle the done-verdict with completion:verification-before-completion.

Alternative: planning:executing-plans — a separately-gated session instead of same-session subagent execution.

Harness mode: harness:harness may map this skill as an Implement-subgoal executor. Nothing changes in the loop above; the plan arrives as a SetGoal goal-spec and the final reviewer verdict feeds the harness QualityGate instead of your own done-check. Opt-in per run, never pre-wired.