docs: add spec for specsync rules command

Adds cmd_rules spec with companion files (tasks.md, context.md)
covering the new declarative rules listing command.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: corvid-agent

specs/cmd_rules/cmd_rules.spec.md

@@ -0,0 +1,82 @@
+---
+module: cmd_rules
+version: 1
+status: stable
+files:
+  - src/commands/rules.rs
+db_tables: []
+tracks: []
+depends_on:
+  - specs/commands/commands.spec.md
+  - specs/config/config.spec.md
+  - specs/types/types.spec.md
+---
+
+# Cmd Rules
+
+## Purpose
+
+Implements the `specsync rules` command. Lists all active validation rules — both built-in (from `specsync.json` `rules` section) and custom declarative rules (from `customRules` array). Shows configuration status, severity, rule type, and filter criteria.
+
+## Public API
+
+### Exported Functions
+
+| Function | Parameters | Returns | Description |
+|----------|-----------|---------|-------------|
+| `cmd_rules` | `root: &Path` | `()` | Load config and display all built-in and custom validation rules |
+
+### Internal Functions
+
+| Function | Parameters | Returns | Description |
+|----------|-----------|---------|-------------|
+| `print_builtin` | `name: &str, description: &str, value: Option<String>` | `()` | Print a built-in rule with its active/off status |
+
+## Invariants
+
+1. Built-in rules always display, showing "active" with value when configured or "off" when unset
+2. Five built-in rules listed: `max_changelog_entries`, `require_behavioral_examples`, `min_invariants`, `max_spec_size_kb`, `require_depends_on`
+3. Custom rules section only displays when `customRules` is non-empty; otherwise shows guidance to add them
+4. Each custom rule displays name, severity (color-coded), type, and optional section/pattern/min_words/applies_to/message fields
+5. Severity colors: error → red, warning → yellow, info → blue
+
+## Behavioral Examples
+
+### Scenario: No custom rules defined
+
+- **Given** `specsync.json` has no `customRules` array
+- **When** `specsync rules` runs
+- **Then** built-in rules are listed, followed by "No custom rules defined." with guidance text
+
+### Scenario: Custom rules with filters
+
+- **Given** a custom rule with `appliesTo: { status: "stable", module: "^auth" }`
+- **When** `specsync rules` runs
+- **Then** the rule shows `applies_to: status=stable, module=/^auth/`
+
+## Error Cases
+
+| Condition | Behavior |
+|-----------|----------|
+| Missing `specsync.json` | Config loader handles this (not this module's concern) |
+
+## Dependencies
+
+### Consumes
+
+| Module | What is used |
+|--------|-------------|
+| config | `load_config` |
+| types | `CustomRuleType`, `RuleSeverity` |
+
+### Consumed By
+
+| Module | What is used |
+|--------|-------------|
+| cli (main.rs) | Entry point for `specsync rules` |
+
+## Change Log
+
+| Date | Change |
+|------|--------|
+| 2026-04-10 | Initial spec |

specs/cmd_rules/context.md

@@ -0,0 +1,12 @@
+# cmd_rules — Context
+
+## Design Decisions
+
+- **Read-only command**: `rules` is purely informational — it reads config and displays, never modifies state.
+- **Built-in rules always shown**: Even when all are "off", they're listed so users know what's available to configure.
+- **Color-coded severity**: Matches the color scheme used in `specsync check` output for consistency.
+
+## Related
+
+- Custom rules are defined in `specsync.json` under the `customRules` key.
+- Custom rule validation logic lives in `src/validator.rs`, not in this command module.

specs/cmd_rules/tasks.md

@@ -0,0 +1,3 @@
+# cmd_rules — Tasks
+
+No open tasks.