Eng

eng

Platform-agnostic engineering agent with two modes — --plan, --build — each a distinct protocol in its own ref file, selected by the invocation flag. This file is the shared spine: it routes to the active mode but never runs a mode's work itself.

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Step 0 — Route to the active mode

Read the invocation flag and load exactly one mode protocol:

| Flag | Read | |------|------| | --plan | refs/plan/protocol.md | | --plan report= | refs/plan/report-fix.md (instead of protocol.md) | | --build | refs/build/protocol.md | | --build report= | refs/build/report-fix.md (instead of protocol.md) | | --build roadmap= | refs/build/protocol-roadmap.md (instead of protocol.md) |

Exactly one mode flag must be present (--plan | --build). If zero or more than one is given, emit:

Hard failure: exactly one mode flag required (--plan | --build). Got: .

Stop.

--todo is no longer a mode. Todos are now written by eng --plan in the same pass as the engineering section — there is no separate todo wave. An invocation carrying --todo hard-fails:

Hard failure: --todo is no longer a mode — todos are written by `eng --plan` in the same pass. Re-run with --plan.

Stop. roadmap= (a --build-only field) loads refs/build/protocol-roadmap.md instead of refs/build/protocol.md: it turns this session into an autonomous product-operations orchestrator executing a whole roadmap/roadmap.md phase-by-phase, spawning eng/pre-merge subagents (pre-merge is the single CI gate — it absorbed /review + /test).

Otherwise read the active mode file fully first — it defines the mode-specific input rules, summary content, work steps, and output contract. The numbered steps below are the shared spine; they run for every mode and point to the active mode file where the path diverges.

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Step 1 — Input validation

Three input sources. The PRD/exec-table source is the default for every mode; report is an alternate available on both modes, and roadmap is a --build-only alternate.

PRD/exec-table source (all modes)

Requires four fields. Hard-refuse if any is missing:

| Field | Value | |-------|-------| | mode flag | --plan or --build | | prd-path | Path to the PRD .md file containing the execution table | | rows | Semicolon-separated exec-table Feature identifiers for this invocation — each the exact : — text of a Feature cell (e.g. F2: Track streak — Schema migration) | | agent | This invocation's agent identity (e.g. eng-backend) — the exec-table Agent column value for the assigned rows; names the ## Engineering — heading and confirms row ownership. |

If any field is missing, emit:

Hard failure: missing required field(s): . Provide the mode flag, prd-path, rows, and agent to continue.

Stop. The active mode file may add mode-specific input rules — apply those too.

Alternate sources

• report= — build or plan from a failed run's issues file (report-prd--.json) instead of an exec-table. On --build, required fields, rejections, path-validity failures, and the finding→issue-ticket projection live in refs/build/report-fix.md. On --plan, the same source plans the fix tickets for the issues file's findings — required fields, rejections, and the fix-plan output contract live in refs/plan/report-fix.md.
• roadmap= — --build only: hand the whole roadmap to the orchestrator (refs/build/protocol-roadmap.md), which derives per-PRD fields for each leaf subagent. Required fields and rejections live in that file.

--plan accepts report but rejects roadmap; passing more than one input source is a hard failure (ambiguous source) — exact messages in the mode refs.

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Step 2 — Pre-flight: read everything in one pass

Before any output, read the spec, devkit, and relevant codebase files in one consolidated scan.

Orchestrated fast path (scoped context injected). When an orchestrator (plan-em or the roadmap orchestrator) has injected scoped excerpts — the assigned rows, the relevant PRD feature sections, and a devkit digest — work from those directly; do not re-read the full PRD or every devkit file. The PRD path is always supplied as an escape hatch: read the full PRD (or a specific devkit file) on demand only when an excerpt is insufficient to resolve a row.

Standalone path (default when nothing is injected). Read the full PRD at prd-path, locate the Execution Table, and select rows whose Feature column text exactly matches one of the assigned rows. A rows identifier matching no Feature cell, or a matched row whose Agent column differs from the agent field, is a hard failure — emit it and stop. On the report source there is no exec-table, no rows, and no ownership to confirm — read the file and project its issues[] per refs/build/report-fix.md.

Devkit files (read in parallel with the PRD, unless a digest was injected): devkit/AHA.md (past learnings relevant to the rows), devkit/GLOSSARY.md (canonical terms; flag PRD deviations), CLAUDE.md at project root (tech-stack constraints on every file-path/approach decision), devkit/ARCHITECTURE.md (validate scope against system layers; flag conflicts as gaps), devkit/DESIGN-SYSTEM.md (reusable components). If devkit/ does not exist, emit a single warning and continue; a missing individual file is a per-file warning, then continue.

Codebase scan (in parallel): read files relevant to the assigned rows, matched by concern type (schema migration → migrations/schema; API contract → handlers, routes, OpenAPI; client mobile/web → screens/pages, components, services/clients; tests → existing test files; webhook → event emitters, queue handlers). For each, determine Modify (exists) or Create (does not), and note naming conventions, patterns, and constraints — they constrain the output. Eng derives all implementation paths from this scan and the spec; report's issues[].file marks where a symptom was observed, not a path to blindly edit.

Complete pre-flight before Step 3; emit no output during it.

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Step 3 — Pre-run (1 of 2): Summary + approval gate

Emit a short summary (3–4 lines max) — content per the active mode file's "Summary content" section — then ask:

AskUserQuestion:
  "Does this summary look right?"
  Options:
    - Yes, proceed
    - No, needs correction
    - I have a follow-up question

• Yes, proceed: continue to Step 4.
• No, needs correction: rewrite the summary once with the correction and re-ask; if still rejected, stop and ask the user to clarify scope.
• I have a follow-up question: enter the interview (Step 3a), then re-present the summary.

Never proceed to Step 4 without an explicit "Yes, proceed." (Under an autonomy contract — e.g. an orchestrator running hands-off — treat this gate as pre-approved and proceed.)

Step 3a — User interview (on demand)

Ask up to 3 focused questions, one at a time — each naming the specific row or PRD section it concerns, with 3–4 concrete AskUserQuestion options (never open-ended). If more than 3 ambiguities exist, list them and ask which to prioritise. Then resume where the protocol paused — do not restart.

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Step 4 — Pre-run (2 of 2): Coding standards

Coding standards come from /cook, pulled via explicit flags (never a prose summary) so the call is cacheable and the P0 floor always loads. Runs on --build only: --plan does not call /cook — its design doc + todo tickets are grounded in the CLAUDE.md + devkit/ARCHITECTURE.md stack constraints read in Step 2; standards are pulled later, at build time. On --build, resolve standards one of two ways:

• Orchestrated (payload injected): when the prompt carries a standards payload section (an orchestrator compiled it once for this stack and injected it), use it and do not call /cook. Default on orchestrated runs.
• Standalone (call cook yourself): when no payload is injected, call /cook once with explicit flags — stack→flag table in refs/build/protocol.md. Always include --global (guarantees the P0 floor + 8 concern refs); an identical flag set repeats as a cook cache hit. Read fully; surface any uncovered stack as a named gap in the build summary.

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Step 5 — Run the active mode's work and emit output

Follow the work steps and output contract in the active mode file, where the modes diverge:

• --plan → in one pass, append the ## Engineering — section, fill the Execution steps + Files columns, and write the ## Todos — tickets that decompose each owned F-ID (no implementation code written; inline snippets/pseudocode encouraged).
• --build → write code to derived paths; emit a build summary.

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Step 6 — Scope enforcement (continuous)

Throughout Steps 2–5, enforce strict scope: act only on what the assigned exec-table rows specify; make no additional refactors, unrelated file touches, or out-of-scope changes. A row that cannot be resolved from the PRD, exec-table, or codebase scan → surface it as a named gap (plan / review) or block and ask (build). Never resolve ambiguity by assumption.

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References

• refs/plan/protocol.md — --plan: summary content, output contract, exact-identifier rule, and the ## Todos — ticket-writing spec run in the same pass. refs/plan/template-todo.md — the ticket schema (F-T ids, the seven fields, rendering, rules, empty-block sentinel, the ticket-sizing rule) that --build reads mechanically. refs/plan/template-eng-plan.md — §1–13 output format.
• refs/plan/report-fix.md — --plan's report source: required fields, rejections, and the fix-plan output contract for planning the fixes to a failed run's issues file.
• refs/build/protocol.md — --build: branch contract, report source, coding-standards flag table, work steps, per-ticket pair review, commit/PR contract. refs/build/protocol-exec.md — Execution-steps column format. refs/build/report-fix.md — report source + the finding→issue-ticket projection and kind discriminator.
• refs/build/pair-review.md — per-ticket pair-review subagent: platform-parameterised principal-engineer persona, unnecessary-code-only mandate, one-revision-round blocking contract (loaded on the build hot path).
• refs/build/protocol-roadmap.md — --build roadmap= orchestrator: executes roadmap/roadmap.md phase-by-phase, spawning subagents and injecting per-stack standards.
• .claude/scripts/eng-db-touch.sh — production/data guardrail; the orchestrator pauses for sign-off when it trips.
• .claude/scripts/eng-comment-scan.sh — deterministic A4 comment scan; flags added symbol declarations with no plain-English comment above them (--staged or a diff range).
• .claude/scripts/eng-commit-cap.sh — A5 commit-size measurement on the staged diff (>500 changed LOC, >300 with --breaking) — advisory: always exits 0, prints CAP_OK/CAP_EXCEEDED for the agent to judge split-or-commit; --oversize-reason records the justification when committing over-cap anyway.
• Contract: the ## Engineering — and ## Todos — headings written by --plan (same pass) are how plan-em detects the section is ready and how --build locates its spec. Do not rename them.

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: ndisisnd
• Source: ndisisnd/msg
• License: MIT

Install and usage instructions live in the source repository linked above.