openspec-aware

# OpenSpec-aware Authoring (Claude Code plugin)

This skill is a **shared sub-procedure** invoked by the Chorus stage skills (proposal, develop, yolo) whenever the user wants spec-driven authoring through the [OpenSpec CLI](https://github.com/Fission-AI/OpenSpec). It is opt-in:

- Activates when **all three** signals hold (see §1): `CHORUS_OPENSPEC_MODE` is not `off`, an `openspec/` directory exists at the project root, and the `openspec` CLI is on `PATH`.
- Otherwise the calling skill falls back to its existing free-form behavior.

When you reach a point in proposal / develop / yolo where this skill is referenced, **read the value of `CHORUS_OPENSPEC_ACTIVE` from the SessionStart context** (see §1) and branch on it. Do not re-run the detection block — the SessionStart hook has already done it once for this session.

---

## §1. Detection — already done at SessionStart

The Chorus plugin's SessionStart hook (`bin/on-session-start.sh`) computes `CHORUS_OPENSPEC_ACTIVE` once when the session opens and writes a `## OpenSpec Mode` section into the plugin's injected context. The value of `CHORUS_OPENSPEC_ACTIVE` is `1` only when **all three** of these hold:

1. `CHORUS_OPENSPEC_MODE` is **not** set to `off` (explicit opt-out wins).
2. The project root contains an `openspec/` directory (i.e. someone ran `openspec init` here).
3. The `openspec` CLI is on `PATH`.

Both signals (2) and (3) are required because the OpenSpec authoring path needs the working directory **and** the CLI — having one without the other leaves the workflow unrunnable. If signal (2) holds but (3) does not, the SessionStart hook surfaces a "OpenSpec repo detected — install with: `npm i -g @fission-ai/openspec`" hint to the user; the agent should pass this through if asked rather than silently choosing free-form.

### How to read the value

You should already see something like this in your context (look for the `## OpenSpec Mode` section near the top of the conversation):

```
## OpenSpec Mode

CHORUS_OPENSPEC_ACTIVE=1 (openspec/ directory + openspec CLI both present)
```

or:

```
## OpenSpec Mode

CHORUS_OPENSPEC_ACTIVE=0 (no openspec/ directory at /path/to/repo/openspec)
```

Branch:

- `CHORUS_OPENSPEC_ACTIVE=1` → follow §3 (OpenSpec authoring).
- `CHORUS_OPENSPEC_ACTIVE=0` → return to the calling skill's free-form path. **Do not** scaffold `openspec/changes/`. **Do not** add the slug line to the proposal description.

### Manual fallback

If you're in a sub-shell, sub-agent, or session that did not see SessionStart context (e.g. you were spawned mid-session and the parent's context was not forwarded), reconstruct the value yourself with the same three checks:

```bash
if [ "${CHORUS_OPENSPEC_MODE:-}" = "off" ]; then
  CHORUS_OPENSPEC_ACTIVE=0
elif [ ! -d "${CLAUDE_PROJECT_DIR:-$PWD}/openspec" ]; then
  CHORUS_OPENSPEC_ACTIVE=0
elif ! openspec --version >/dev/null 2>&1; then
  CHORUS_OPENSPEC_ACTIVE=0
else
  CHORUS_OPENSPEC_ACTIVE=1
fi
```

Use this only when SessionStart context is genuinely unavailable — duplicating the detection is wasteful when the hook already computed it.

---

## §2. ⛔ Two non-negotiable rules

Both are enforced at review time. Both have caused incidents in past releases.

### Rule 1 — Mirror via the wrapper, never re-type document content from agent output

Document/draft mirror calls (`chorus_pm_add_document_draft`, `chorus_pm_update_document_draft`, `chorus_pm_update_document`) **MUST** go through:

```
chorus-api.sh mcp-tool <tool_name> "$PAYLOAD"
```

`chorus-api.sh` is on `PATH` — call it by name.

with `$PAYLOAD` built using `json_encode_file` (defined in §3.4). Calling these tools directly from the agent's MCP harness with a hand-typed `content` field is a **protocol violation** for OpenSpec mode and will fail review. Reasons:

1. **Token cost.** Re-typing a multi-thousand-line markdown body through the LLM burns input + output tokens for every draft. The wrapper streams bytes through `jq -Rs '.'` — content never enters LLM context. A typical 3-doc proposal mirror via the script costs roughly zero content-tokens; via direct MCP it routinely costs 20k+.
2. **Byte-equality.** `jq -Rs '.'` is a byte-faithful encoder: backslashes, quotes, newlines, code-fence content, zero-width chars all survive. LLM re-emission has a non-zero failure rate on long markdown — table alignment drifts, fence escapes get "fixed", long URLs wrap. The byte-equality guarantee (modulo trailing `\n`) holds **only** on the wrapper path.
3. **Single source of truth.** With the wrapper, the local `openspec/changes/<slug>/*.md` is authoritative and Chorus is a mirror. With agent re-typing, authority splits between local file and whatever the LLM happened to output — a future diff cannot tell which one is correct.

### Rule 2 — Halt on error via `chorus_check_response`

Every wrapper call must check three signals: wrapper exit code, `"error":` in body, empty body. Bare `RC=$?` is **insufficient** — the wrapper exits 0 on HTTP 401 (auth failure) with empty body, so a single-signal check silently misses the most common runtime failure. See §6 for the helper definition.

---

## §3. OpenSpec mode authoring

### 3.1 Pick a slug

`openspec/changes/<slug>/` is the local change folder. The slug must be:

- kebab-case (`add-export-csv`, not `addExportCsv` or `add_export_csv`),
- derived from the source Idea title,
- unique within `openspec/changes/`.

Record it for later steps:

```bash
SLUG="add-export-csv"
```

### 3.2 Scaffold the change folder

```bash
openspec new change "$SLUG" --description "<one-line idea summary>"
```

This creates `openspec/changes/$SLUG/` with `README.md` and `.openspec.yaml`. Then author by hand:

| Local file | Purpose | Mirror as `Document.type` |
|---|---|---|
| `proposal.md` | Why + What Changes + Capabilities + Impact | `prd` |
| `design.md` | Architecture, contracts, risks | `tech_design` |
| `specs/<capability>/spec.md` | Delta spec (`## ADDED Requirements` + Scenarios) | `spec` (one draft per