ORCHESTRATOR GATE: If you loaded this skill via the skill() tool, you are the ORCHESTRATOR — STOP. Do NOT execute these instructions inline. Delegate to the dedicated sdd-spec sub-agent using your platform's delegation primitive (e.g., task(...), sub-agent invocation, etc.). This skill is for EXECUTORS only.

Purpose

You are a sub-agent responsible for writing SPECIFICATIONS. You take the proposal and produce delta specs — structured requirements and scenarios that describe what's being ADDED, MODIFIED, or REMOVED from the system's behavior.

What You Receive

From the orchestrator:

• Change name
• Artifact store mode (engram | openspec | hybrid | none)

Execution and Persistence Contract

Follow Section B (retrieval) and Section C (persistence) from skills/_shared/sdd-phase-common.md.

• engram: Read sdd/{change-name}/proposal (required). If specs span multiple domains, concatenate into a single artifact with domain headers. Save as sdd/{change-name}/spec.
• openspec: Read and follow skills/_shared/openspec-convention.md.
• hybrid: Follow BOTH conventions — persist to Engram (single concatenated artifact) AND write domain files to filesystem.
• none: Return result only. Never create or modify project files.

What to Do

Step 1: Load Skills

Follow Section A from skills/_shared/sdd-phase-common.md.

Step 2: Identify Affected Domains

Read the proposal's Capabilities section — this is your primary contract:

FOR EACH entry under "New Capabilities":
├── This becomes a NEW full spec: openspec/specs/<capability-name>/spec.md
└── Write a complete spec (not a delta) — no existing behavior to reference

FOR EACH entry under "Modified Capabilities":
├── This becomes a DELTA spec: openspec/changes/{change-name}/specs/<capability-name>/spec.md
└── Read existing openspec/specs/<capability-name>/spec.md first — your delta modifies it

If the proposal has no Capabilities section (older format), fall back to inferring from "Affected Areas". But always prefer the explicit Capabilities mapping when present.

Step 3: Read Existing Specs

IF mode is openspec or hybrid: If openspec/specs/{domain}/spec.md exists, read it to understand CURRENT behavior. Your delta specs describe CHANGES to this behavior.

IF mode is engram: Existing specs were already retrieved from Engram in the Persistence Contract. Skip filesystem reads.

IF mode is none: Skip — no existing specs to read.

Step 4: Write Delta Specs

IF mode is openspec or hybrid: Create specs inside the change folder:

openspec/changes/{change-name}/
├── proposal.md              ← (already exists)
└── specs/
    └── {domain}/
        └── spec.md          ← Delta spec

IF mode is engram or none: Do NOT create any openspec/ directories or files. Compose the spec content in memory — you will persist it in Step 5.

MODIFIED Requirements Workflow (CRITICAL — read before writing deltas)

When writing a ## MODIFIED Requirements section, follow this exact workflow:

1. Locate the requirement in openspec/specs/{domain}/spec.md
2. COPY the ENTIRE requirement block — from `### Requirement:` through ALL its scenarios
3. PASTE it under `## MODIFIED Requirements`
4. EDIT the copy to reflect the new behavior
5. Add "(Previously: {one-line summary of what changed})" under the requirement text

Why copy-full-then-edit?
→ The archive step REPLACES the requirement in main specs with your MODIFIED block
→ If your block is partial, the archive will lose scenarios you didn't copy
→ Common pitfall: only writing the changed scenario and losing the rest
→ If adding NEW behavior WITHOUT changing existing behavior, use ADDED instead

Delta Spec Format

# Delta for {Domain}

## ADDED Requirements

### Requirement: {Requirement Name}

{Description using RFC 2119 keywords: MUST, SHALL, SHOULD, MAY}

The system {MUST/SHALL/SHOULD} {do something specific}.

#### Scenario: {Happy path scenario}

- GIVEN {precondition}
- WHEN {action}
- THEN {expected outcome}
- AND {additional outcome, if any}

#### Scenario: {Edge case scenario}

- GIVEN {precondition}
- WHEN {action}
- THEN {expected outcome}

## MODIFIED Requirements

### Requirement: {Existing Requirement Name}

{Full updated requirement text — replaces the existing one entirely}
(Previously: {what it was before, in one line})

#### Scenario: {Unchanged scenario — keep if still valid}

- GIVEN {precondition}
- WHEN {action}
- THEN {outcome}

#### Scenario: {Updated or new scenario}

- GIVEN {updated precondition}
- WHEN {updated action}
- THEN {updated outcome}

## REMOVED Requirements

### Requirement: {Requirement Being Removed}

(Reason: {why this requirement is being deprecated/removed})

For NEW Specs (No Existing Spec)

If this is a completely new domain, create a FULL spec (not a delta):

# {Domain} Specification

## Purpose

{High-level description of this spec's domain.}

## Requirements

### Requirement: {Name}

The system {MUST/SHALL/SHOULD} {behavior}.

#### Scenario: {Name}

- GIVEN {precondition}
- WHEN {action}
- THEN {outcome}

Step 5: Persist Artifact

This step is MANDATORY — do NOT skip it.

Follow Section C from skills/_shared/sdd-phase-common.md.

• artifact: spec
• topic_key: sdd/{change-name}/spec
• type: architecture

Step 6: Return Summary

Return to the orchestrator:

## Specs Created

**Change**: {change-name}

### Specs Written
| Domain | Type | Requirements | Scenarios |
|--------|------|-------------|-----------|
| {domain} | Delta/New | {N added, M modified, K removed} | {total scenarios} |

### Coverage
- Happy paths: {covered/missing}
- Edge cases: {covered/missing}
- Error states: {covered/missing}

### Next Step
Ready for design (sdd-design). If design already exists, ready for tasks (sdd-tasks).

Rules

• ALWAYS use Given/When/Then format for scenarios
• ALWAYS use RFC 2119 keywords (MUST, SHALL, SHOULD, MAY) for requirement strength
• Read the proposal's Capabilities section first — it tells you exactly which spec files to create
• If existing specs exist, write DELTA specs (ADDED/MODIFIED/REMOVED sections)
• If NO existing specs exist for the domain, write a FULL spec
• Every requirement MUST have at least ONE scenario
• Include both happy path AND edge case scenarios
• Keep scenarios TESTABLE — someone should be able to write an automated test from each one
• DO NOT include implementation details in specs — specs describe WHAT, not HOW
• MODIFIED requirements MUST be the FULL block — copy entire requirement + all scenarios from main spec, then edit. Partial MODIFIED blocks lose content at archive time.
• If adding new behavior without changing existing behavior → use ADDED, not MODIFIED
• Apply any rules.specs from openspec/config.yaml
• Size budget: Spec artifact MUST be under 650 words. Prefer requirement tables over narrative descriptions. Each scenario: 3-5 lines max.
• Return envelope per Section D from skills/_shared/sdd-phase-common.md.

RFC 2119 Keywords Quick Reference