spec-impl

name	spec-impl
description	Implements an approved spec. Validates that the state means "Approved" (in any language), creates a git branch named after the spec, switches to it, and starts the implementation step by step with pauses to review diffs.
disable-model-invocation	true
argument-hint	<NN-spec-name>
allowed-tools	Read, Glob, Grep, Edit, Write, AskUserQuestion, Bash(git status:*), Bash(git branch:*), Bash(git checkout:*), Bash(git log:*), Bash(git diff:*), Bash(git stash:*), Bash(cat:*), Bash(ls:*)

/spec-impl — Implementer of approved specs

Session context

Current repository state: !git status --short

Current branch: !git branch --show-current

Specs available in this folder: !ls specs/ 2>/dev/null || echo "The specs/ folder does not exist"

Branch-creation config: !cat specs/.spec-config.yml 2>/dev/null || echo "AutoCreateBranch: true (default, no config file)"

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Instructions

Follow these four phases in strict order. Do not advance to the next phase if the previous one did not complete correctly.

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Phase 1 — Identify the spec

The received argument is: $ARGUMENTS

If $ARGUMENTS is empty:

• List the files available in specs/ (you already have them above).
• Ask the user to specify the exact name of the spec.
• Stop and wait for an answer. Do not continue.

If $ARGUMENTS has a value:

• Look for the file in specs/. The user may have written the full name (01-mvp-arkanoid), only the number (01), or only the slug (mvp-arkanoid). Try to find the correct file in any of those cases.
• If you do not find the file, show the available specs and ask the user to correct the name.
• If you do find it, continue to Phase 2.

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Phase 2 — Validate the spec's state

Read the spec file you located in Phase 1 using the Read tool or cat.

In the file's contents, look for the line that contains the spec's state. The header label is typically **Status:** (English) or **Estado:** (Spanish), but it may use any language. Match by position (status line near the top of the spec) and by the surrounding state machine, not by the exact label.

Absolute rule: You can only continue if the state means "Approved" — regardless of the language used.

Treat any of the following (and their equivalents in other languages) as the Approved state and continue:

• English: Approved
• Spanish: Aprobado
• Portuguese: Aprovado
• French: Approuvé
• German: Genehmigt
• Italian: Approvato
• …or any other language's word that clearly means "approved"

Anything else (Draft / Borrador, In review / En revisión, Implemented / Implementado, Obsolete / Obsoleto, or any unrecognized value) means stop and show the error message below.

State category	Examples (any language)	Action
Approved	Approved, Aprobado, Aprovado, Approuvé, …	Continue to Phase 3.
Draft	Draft, Borrador, …	Stop. Show the error message below.
In review	In review, En revisión, …	Stop. Show the error message below.
Implemented	Implemented, Implementado, …	Stop. Show the error message below.
Obsolete	Obsolete, Obsoleto, …	Stop. Show the error message below.
State line not found / unrecognized value	—	Stop. The file does not follow the expected format. Tell this to the user.

If you are unsure whether a value means "approved", do not assume. Stop and ask the user to clarify or to update the spec to the canonical wording.

Standard error message when the state does not mean Approved:

❌ I cannot implement this spec.

Current state: [STATE FOUND]
I only work with specs whose state means "Approved" (e.g. `Approved`, `Aprobado`,
or the equivalent in another language).

To continue you have two options:
  1. If the spec is ready to be implemented, open it and change the state
     to "Approved" (or the equivalent term your team uses) manually.
     That change is made by the human, not the agent.
  2. If the spec still needs work, use /spec [name] to resume it.

Do not offer alternatives, do not suggest "I can still start if you want". The block is intentional.

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Phase 3 — Create the git branch and switch to it

Once you have confirmed the state means Approved:

0. Check the working tree first. Look at the git status --short output in the session context above. If it is not empty, stop and show the pending changes, then ask:

   ⚠️ There are uncommitted changes in the working tree.
   Switching branches would carry them over. What do you want to do?
     1. Commit or stash them yourself, then re-run this command  (recommended)
     2. Continue anyway — the changes travel to the new branch
   

   Wait for the answer. Do not stash or commit on the user's behalf unless they explicitly ask for it. If the working tree is clean, skip straight to step 1 without mentioning it.

1. Derive the branch name from the spec file's full name, without the extension. Format: spec-NN-slug. Examples:

   • 01-mvp-arkanoid.md → branch spec-01-mvp-arkanoid
   • 02-powerups.md → branch spec-02-powerups

2. Read the AutoCreateBranch flag from the Branch-creation config shown in the session context above.

   • If the config file does not exist, the value is missing, or the value is unrecognized → treat it as true (the default).
   • Only an explicit false (in any capitalization) disables automatic branch creation.

   If AutoCreateBranch is true (default): proceed without asking.

   • If the branch does not exist: create it with git checkout -b spec-NN-slug.
   • If it already exists: this means previous work is being resumed. Switch to it, read git log --oneline on the branch, and tell the user which steps of the plan already look done and which step you propose to resume from. Wait for confirmation on the resume point before implementing anything.
   • In both cases: switch to the branch with git checkout spec-NN-slug and confirm the change was successful before continuing.

   If AutoCreateBranch is false: ask before touching git. Show:

   AutoCreateBranch is set to false.
   Create and switch to the branch spec-NN-slug? [y/N]
   

   • If the user answers yes: create/switch to the branch exactly as in the case above.

Match section headings by meaning, not by exact wording — the spec may be authored in any language.

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Phase 4 — Implement step by step

After showing the spec summary, tell the user:

I am going to implement the spec following the implementation plan exactly.
I will pause after each step so you can review the diff.

Shall we start with Step 1?

Wait for explicit confirmation ("yes", "go ahead", "go", or equivalent). Do not start without it.

Once confirmed, follow these rules during the entire implementation:

Never commit automatically. Not per step, not at the end. You write the code and show the diff; committing is the user's decision and the user's command. Only commit if they explicitly ask you to.

One rule above all: implement what the spec says. If something in the spec looks suboptimal to you, mention it as an observation but implement what was agreed. Changes to the spec go into the spec, not into the code by surprise.

Work rhythm:

• Implement one step of the plan.
• Show a summary of which files you touched and what you did.
• Say: Step N completed. Could you review the diff and let me know if I continue with Step N+1?
• Wait for confirmation before continuing.

If during the implementation you find an ambiguity the spec does not resolve:

• Stop.
• Describe the ambiguity exactly.
• Present two or three concrete options.
• Wait for the user's decision.
• Do not improvise.

If the user asks for something that is out of the spec's scope:

• Remind them that it is out of this spec's scope.
• Suggest noting it down for the next spec.
• Do not implement it on this branch.

When finishing the last step:

✅ All steps of the plan are implemented.

Next step: verify the spec's acceptance criteria one by one.
If they all pass, update the spec's state to "Implemented" (or the equivalent
in your repo's language) and make the final commit before merging this branch.

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Summary of expected behavior

/spec-impl 01-mvp-arkanoid

  Phase 1  →  Finds specs/01-mvp-arkanoid.md
  Phase 2  →  Reads the state → "Approved" (or "Aprobado", etc.) → ✅ continues
  Phase 3  →  git checkout -b spec-01-mvp-arkanoid → git checkout spec-01-mvp-arkanoid
              Shows objective, scope, plan and criteria
  Phase 4  →  Implements step by step with pauses
              Ends by reminding to verify the acceptance criteria

/spec-impl 02-powerups  (state: Draft / Borrador)

  Phase 1  →  Finds specs/02-powerups.md
  Phase 2  →  Reads the state → "Draft" → ❌ stops
              Shows the standard error message
              Does not create branch, does not touch code

Branch creation is controlled by the AutoCreateBranch flag in specs/.spec-config.yml. It defaults to true (create the branch automatically, as shown above). Set it to false to make Phase 3 ask [y/N] before creating the branch.