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. 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 follows the resolved SPEC_MODE — spec-lite (the default when OpenSpec isn't usable) or free-form (=off).

See also — spec-lite (the lightweight fallback): OpenSpec (this skill) stays the default whenever it is usable (openspec/ dir + CLI, not disabled). When OpenSpec is absent or disabled — or when CHORUS_SPEC_MODE=lite is set explicitly — the mode resolves to spec-lite: a Chorus-native, git-tracked model with a durable local spec .chorus/specs/<slug>/spec.md per capability (edited in place, never synced), plus one dated folder per change effort .chorus/specs/<slug>/<YYYY-MM-DD>-<change-slug>/ of plain-markdown docs named by Document type (prd.md, tech_design.md, …), those dated-folder docs each mirrored 1:1 into a persistent Chorus Document via the same --arg-file transport, with no CLI and no strict validation. A session that resolves to OpenSpec follows everything below unchanged. See the spec-lite skill (skills/spec-lite/SKILL.md).

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) resolves the active spec mode once when the session opens and writes a ## Spec Mode section into the plugin's injected context. When the resolved mode is a usable OpenSpec, that section also carries a CHORUS_OPENSPEC_ACTIVE=1 line. 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 ## Spec Mode section near the top of the conversation). This skill is only loaded when the mode resolved to a usable OpenSpec, so you should see:

## Spec Mode

CHORUS_SPEC_MODE=openspec (explicit; openspec/ directory + openspec CLI both present)

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

Branch:

• CHORUS_OPENSPEC_ACTIVE=1 → follow §3 (OpenSpec authoring).
• No CHORUS_OPENSPEC_ACTIVE=1 line (the section shows CHORUS_SPEC_MODE=lite / off, or you were spawned without SessionStart context) → this skill is a no-op; return to the calling skill's path. Do not scaffold openspec/changes/. Do not add the slug line to the proposal description. (Reconstruct the value with the manual fallback below if you genuinely have no context.)

Manual fallback (no SessionStart context)

If you're in a sub-shell, sub-agent, or session that did not see the ## Spec Mode section (e.g. spawned mid-session without the parent's context), do not hand-roll the detection — source the same resolver the hook uses, so there is one computation of the mode:

# The resolver sits beside the plugin hooks; ${CLAUDE_PLUGIN_ROOT} is the plugin
# root Claude Code exports (the same var hooks.json uses).
RESOLVER="${CLAUDE_PLUGIN_ROOT}/bin/resolve-spec-mode.sh"
if [ -f "$RESOLVER" ]; then
  . "$RESOLVER"   # sets SPEC_MODE (lite|openspec|off), SPEC_FAIL (non-empty ⇒ halt),
                  # and CHORUS_OPENSPEC_ACTIVE (1 only for a usable openspec)
else
  echo "resolve-spec-mode.sh not found; set CHORUS_SPEC_MODE explicitly and re-launch" >&2
fi

Then: if SPEC_FAIL is non-empty, halt and surface it; if CHORUS_OPENSPEC_ACTIVE=1 follow §3; otherwise this skill is a no-op — return to the caller, which follows the resolved SPEC_MODE (spec-lite or free-form). If you genuinely cannot locate the helper, set CHORUS_SPEC_MODE explicitly and re-launch rather than guessing — never re-derive the rule inline (the hook/helper is the single source of truth).

§2. ⛔ Two non-negotiable rules

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

Rule 1 — Fill content from the file (CLI preferred, bash-wrapper fallback); 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 fill the content field from the local file's bytes, never from a hand-typed body. 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. Use whichever transport is available, preferred first:

• Primary — the chorus CLI: chorus mcp call <tool_name> '<json-without-content>' --arg-file content=<file>. --arg-file content=<path> reads the file's raw bytes and injects them as the JSON content string, byte-exact — the CLI's built-in replacement for json_encode_file, so no helper is needed. See §3.6. Requires chorus >= 0.17.0 (the chorus mcp subcommand was added then; an older CLI errors with "unknown command"); on any version or unknown-command failure, upgrade with npm install -g @chorus-aidlc/chorus.
• Fallback — the chorus-api.sh wrapper, when chorus is not on PATH: build $PAYLOAD with the json_encode_file helper and call chorus-api.sh mcp-tool <tool_name> "$PAYLOAD" (chorus-api.sh is on PATH — call it by name). Defined in the §3.6 fallback block.

New to the chorus CLI? See the chorus-cli skill for install, configuring agents (chorus agents add|remove|list), the connection env vars, and chorus mcp basics.

Acting identity — which agent the call acts as. chorus mcp call resolves the agent from, in order: CHORUS_AGENT_PROFILE (a name or UUID) → CHORUS_URL + CHORUS_API_KEY in the environment → the single agent configured in ~/.chorus/daemon.json. A daemon-woken session already has CHORUS_AGENT_PROFILE set. If a mirror call fails with Multiple agents … specify --agent (several agents configured and no profile/creds in the env), pass your own identity explicitly: chorus mcp call <tool> … --agent <your-agentUuid> — your UUID is in your chorus_checkin result, and chorus agents lists every configured name/UUID.

Reasons (they apply to both paths):

1. Token cost. Re-typing a multi-thousand-line markdown body through the LLM burns input + output tokens for every draft. Both the CLI's --arg-file and the fallback's json_encode_file stream the file's bytes into the JSON string — content never enters LLM context. A typical 3-doc proposal mirror costs roughly zero content-tokens this way; via direct MCP with a re-typed body it routinely costs 20k+.
2. Byte-equality. A file-fill path (CLI --arg-file, or the fallback's 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 exact byte-equality guarantee holds only on a file-fill path, never on LLM re-emission.
3. Single source of truth. With a file-fill mirror, 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:

SLUG="add-export-csv"

3.2 Scaffold the change folder

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

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

Use openspec instructions <artifact> --change "$SLUG" (artifacts: proposal, specs, design, tasks) for templates.

3.3 Spec file shape (verified against openspec instructions specs)

A delta spec lists one or more block headers — ## ADDED Requirements, ## MODIFIED Requirements, ## REMOVED Requirements, ## RENAMED Requirements — and within each, ### Requirement: entries. Mix freely in the same file; only include the blocks you actually need.

## ADDED Requirements

Append a brand-new Requirement to the long-term spec.

## ADDED Requirements

### Requirement: <name>
<requirement text — use SHALL / MUST for normative behavior>

#### Scenario: <name>
- **WHEN** <condition>
- **THEN** <expected outcome>

## MODIFIED Requirements

Whole-block replacement, not merge. Whatever you write here completely replaces the existing same-named Requirement in the long-term spec — title, description, and all scenarios. Half-writing it deletes the rest.

## MODIFIED Requirements

### Requirement: <existing name>
<full updated requirement text>

#### Scenario: <name>
- **WHEN** <condition>
- **THEN** <expected outcome>

#### Scenario: <other name>
- **WHEN** <condition>
- **THEN** <expected outcome>

Always include every scenario you want the post-archive spec to have, even ones that were already present and unchanged.

## REMOVED Requirements

Delete a Requirement from the long-term spec. The block under the heading is just the requirement name(s) you're removing — no scenarios needed.

## REMOVED Requirements

### Requirement: <existing name>

## RENAMED Requirements

Rename a Requirement's title. Body and scenarios are preserved as-is in the long-term spec; use MODIFIED instead if you need to change anything besides the title.

## RENAMED Requirements

### Requirement: <old name> -> <new name>

Critical formatting rules (verified):

• Scenarios MUST use exactly 4 hashtags (#### Scenario:). 3 hashtags or a bullet list silently fail validation.
• Every ### Requirement: under ADDED or MODIFIED MUST have at least one #### Scenario:.
• MODIFIED blocks MUST include the full updated content — they overwrite, not patch.
• Use SHALL / MUST for normative requirements; avoid should / may.
• The merge into openspec/specs/<capability>/spec.md happens at openspec archive time (§3.9), not at proposal time. While the proposal is in flight, Chorus only sees the delta file as one spec Document — there is no half-merged state for the skill to reason about.

Optional:

openspec validate "$SLUG"

3.4 Filling the content field byte-exact

The document content must be inserted byte-for-byte from the local file — never re-typed by the LLM. Two mechanisms, preferred first:

• Primary — chorus mcp call … --arg-file content=<path> (§3.6). The CLI reads the file's raw bytes and injects them as the JSON content string. This is the byte-faithful replacement for json_encode_file, so on the CLI path no helper is needed — pass the base JSON without a content field and let --arg-file fill it.
• Fallback — json_encode_file (defined in the §3.6 fallback block, used only when chorus is not on PATH). With jq available it streams the file through jq -Rs '.'; the pure-shell branch matches chorus-api.sh's own escaping when jq is missing.

Round-trip verification is exact: a trailing newline difference is real drift and MUST NOT be normalized or ignored.

3.5 Create the proposal container with the slug provenance line

Use the regular chorus_pm_create_proposal MCP tool (no wrapper required for this single call — the description is short, the LLM-emitted version is fine). The description must carry exactly one line:

OpenSpec change slug: <slug>

• on its own line (no other text on that line),
• literal prefix OpenSpec change slug: (capital O, capital S, single space after colon),
• no trailing punctuation,
• value matches the slug passed to openspec new change.

This line is machine-grep-able by future runs of this skill and by the §3.9 archive trigger.