Update Feature Documentation

Generate or update documentation for the current feature branch. Analyzes all changes (commits, diffs) between the feature branch and base branch, then creates or updates docs/features/<index>_<feature-name>/README.md with incremental indexing based on existing feature docs. Use when documenting a feature branch, creating feature documentation from branch changes, or updating existing feature docs after additional commits. <example> Context: User wants to document their feature branch user: "/update-feature-docs" </example> <example> Context: User wants to document changes user: "document this feature branch" </example> <example> Context: User wants to update existing feature docs user: "update the feature docs with my latest changes" </example> <example> Context: User specifies a base branch user: "/update-feature-docs develop" </example>

Read ALL changed files to understand the full scope of the feature.

Step 2: Determine Feature Name

Derive the feature name from the branch name:

• feature/user-notifications -> user-notifications
• feat/add-payment-gateway -> add-payment-gateway
• fix/login-redirect -> login-redirect
• my-awesome-feature -> my-awesome-feature

Strip common prefixes: feature/, feat/, fix/, bugfix/, hotfix/, chore/, refactor/.

Step 3: Determine Feature Index

Check existing feature directories in docs/features/ to determine the next incremental index:

# List existing feature directories
ls -d docs/features/*/  2>/dev/null

Feature directories follow the pattern <index>_<name> (e.g., 001_user-auth, 002_payment-gateway).

• If no feature directories exist, start with index 001
• If existing directories exist, find the highest index and increment by 1
• Use zero-padded 3-digit format: 001, 002, ..., 010, ..., 100

If a directory for this feature already exists (matching by feature name, ignoring index), this is an update — use the existing directory and index.

Step 4: Generate or Update Feature Documentation

Create or update docs/features/<index>_<feature-name>/README.md with the following sections:

# Feature: <Feature Name (human-readable)>

> Branch: `<branch-name>` | Base: `<base-branch>` | Commits: <count>

## Overview

<What the feature does and why, derived from commit messages and code changes.
1-2 paragraphs maximum.>

## Architecture

<Mermaid diagram showing new/modified components and their interactions.
Use a C4 Component diagram, sequence diagram, or flowchart — whichever best
illustrates the feature.>

## Changes Summary

### New Files
| File | Purpose |
|------|---------|
| `path/to/file` | Description |

### Modified Files
| File | Changes |
|------|---------|
| `path/to/file` | What changed and why |

### Configuration Changes
| Key | Description | Default |
|-----|-------------|---------|
| `ENV_VAR` | What it controls | `value` |

## API Changes

<New or modified endpoints. Include method, path, request/response if applicable.
If no API changes, omit this section.>

| Method | Path | Description |
|--------|------|-------------|
| POST | /api/v1/resource | Creates a new resource |

## Data Model Changes

<New tables, columns, schema modifications, migrations.
If no data model changes, omit this section.>

## Dependencies

<New packages or services added.
If no new dependencies, omit this section.>

| Package | Version | Purpose |
|---------|---------|---------|
| `package-name` | `^1.0.0` | Why it was added |

## Testing

<How to test the feature — key scenarios and commands.>

For updates to existing feature docs:

• Preserve the existing content structure
• Update sections that have changed based on new commits
• Add new entries to the Changes Summary
• Update the Overview if the feature scope has expanded
• Update diagrams if architecture has changed

Step 5: Update Feature Index

Update docs/features/README.md to include the new or updated feature:

# Features

| Index | Feature | Description | Branch | Status |
|-------|---------|-------------|--------|--------|
| 001 | [User Auth](001_user-auth/README.md) | Authentication and authorization | `feature/user-auth` | Documented |
| 002 | [Payment Gateway](002_payment-gateway/README.md) | Payment processing integration | `feature/payment-gateway` | Documented |

If the feature already exists in the index, update its description if needed.

Step 6: Validate

• Validate all mermaid diagrams using the mermaid MCP server
• Verify all file paths referenced in the Changes Summary still exist
• Verify internal links are correct

Output

Print a summary:

Feature documented: <Feature Name>
  Directory:  docs/features/<index>_<feature-name>/
  Branch:     <branch-name> (<N> commits ahead of <base-branch>)
  Files analyzed: <N> changed files
  Status:     [Created | Updated]

Important

• Always use mermaid diagrams — at minimum one diagram showing the feature's architecture or flow
• Use the mermaid MCP server (mcp__plugin_media-plugin_mermaid__*) to validate diagram syntax
• Base everything on actual code changes — do not speculate about intent
• If the feature modifies existing architecture, note what changed from the previous state
• Omit sections that have no relevant content (e.g., no API changes) rather than leaving them empty
• Keep the documentation concise and scannable — use tables and bullet points
• The index is always zero-padded 3-digit: 001, 002, etc.