no-mistakes(document): Sync onboard documentation

docs/FEATURES.md

@@ -38,6 +38,7 @@
   - [Model Profiles](#26-model-profiles)
 - [Brownfield Features](#brownfield-features)
   - [Codebase Mapping](#27-codebase-mapping)
+  - [Existing Codebase Onboarding](#27b-existing-codebase-onboarding)
 - [Utility Features](#utility-features)
   - [Debug System](#28-debug-system)
   - [Todo Management](#29-todo-management)
@@ -789,7 +790,7 @@
 
 **Command:** `/gsd-map-codebase [area]`
 
-**Purpose:** Analyze an existing codebase before starting a new project, so GSD understands what exists.
+**Purpose:** Analyze an existing codebase before starting a new project or as the mapping handoff from `/gsd-onboard`, so GSD understands what exists.
 
 **Requirements:**
 - REQ-MAP-01: System MUST spawn parallel mapper agents for each analysis area
@@ -817,6 +818,27 @@ only the subtrees the phase actually changed. Each produced document carries
 `last_mapped_commit` in its YAML frontmatter so drift can be measured
 against the mapping point, not HEAD.
 
+### 27b. Existing Codebase Onboarding
+
+**Command:** `/gsd-onboard [--fast] [--text]`
+
+**Purpose:** Guide first-time setup for an existing repository by checking brownfield state, routing through codebase mapping and docs ingest, then handing off to project initialization without silently overwriting planning artifacts.
+
+**Requirements:**
+- REQ-ONBOARD-01: System MUST detect existing code, package manifests, planning documents, partial `.planning/` state, and complete or missing codebase-map files.
+- REQ-ONBOARD-02: System MUST hand off to `/gsd-map-codebase` or `/gsd-map-codebase --fast` when brownfield code lacks a complete `.planning/codebase/` map.
+- REQ-ONBOARD-03: System MUST offer `/gsd-ingest-docs` before `/gsd-new-project` when ADR/PRD/SPEC/RFC candidates exist and no project exists.
+- REQ-ONBOARD-04: System MUST refuse to report onboarding complete until `PROJECT.md`, `REQUIREMENTS.md`, `ROADMAP.md`, and `STATE.md` all exist.
+- REQ-ONBOARD-05: System MUST create or confirm `.planning/onboarding/SUMMARY.md` only after project setup exists.
+- REQ-ONBOARD-06: System MUST support `--text` for numbered plain-text gates on runtimes without interactive menus.
+
+**Produces:**
+| Artifact | Description |
+|----------|-------------|
+| `.planning/codebase/` | Codebase map produced by the `/gsd-map-codebase` handoff |
+| `.planning/PROJECT.md`, `REQUIREMENTS.md`, `ROADMAP.md`, `STATE.md` | Planning setup produced by `/gsd-new-project` or `/gsd-ingest-docs` |
+| `.planning/onboarding/SUMMARY.md` | Onboarding status, artifact index, and next-command summary |
+
 ### 27a. Post-Execute Codebase Drift Detection
 
 **Introduced by:** #2003