add comprehensive documentation (#9537)

docs/misc/install.func/INSTALL_FUNC_FUNCTIONS_REFERENCE.md

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+# install.func Functions Reference
+
+Complete reference of all functions in install.func with detailed usage information.
+
+## Function Index
+
+- `setting_up_container()` - Initialize container setup
+- `network_check()` - Verify network connectivity
+- `update_os()` - Update OS packages
+- `verb_ip6()` - Enable IPv6
+- `motd_ssh()` - Configure SSH and MOTD
+- `customize()` - Apply container customizations
+- `cleanup_lxc()` - Final container cleanup
+
+---
+
+## Core Functions
+
+### setting_up_container()
+
+Display setup message and initialize container environment.
+
+**Signature**:
+```bash
+setting_up_container
+```
+
+**Purpose**: Announce container initialization and set initial environment
+
+**Usage**:
+```bash
+#!/usr/bin/env bash
+source /dev/stdin <<<"$FUNCTIONS_FILE_PATH"
+
+setting_up_container
+# Output: ⏳ Setting up container...
+```
+
+---
+
+### network_check()
+
+Verify network connectivity with automatic retry logic.
+
+**Signature**:
+```bash
+network_check
+```
+
+**Purpose**: Ensure internet connectivity before critical operations
+
+**Behavior**:
+- Pings 8.8.8.8 (Google DNS)
+- 3 attempts with 5-second delays
+- Exits with error if all attempts fail
+
+**Usage**:
+```bash
+network_check
+# If no internet: Exits with error message
+# If internet OK: Continues to next step
+```
+
+**Error Handling**:
+```bash
+if ! network_check; then
+  msg_error "No internet connection"
+  exit 1
+fi
+```
+
+---
+
+### update_os()
+
+Update OS packages with error handling.
+
+**Signature**:
+```bash
+update_os
+```
+
+**Purpose**: Prepare container with latest packages
+
+**On Debian/Ubuntu**:
+- Runs: `apt-get update && apt-get upgrade -y`
+
+**On Alpine**:
+- Runs: `apk update && apk upgrade`
+
+**Usage**:
+```bash
+update_os
+```
+
+---
+
+### verb_ip6()
+
+Enable IPv6 support in container (optional).
+
+**Signature**:
+```bash
+verb_ip6
+```
+
+**Purpose**: Enable IPv6 if needed for application
+
+**Usage**:
+```bash
+verb_ip6              # Enable IPv6
+network_check         # Verify connectivity with IPv6
+```
+
+---
+
+### motd_ssh()
+
+Configure SSH daemon and MOTD for container access.
+
+**Signature**:
+```bash
+motd_ssh
+```
+
+**Purpose**: Setup SSH and create login message
+
+**Configures**:
+- SSH daemon startup and keys
+- Custom MOTD displaying application access info
+- SSH port and security settings
+
+**Usage**:
+```bash
+motd_ssh
+# SSH is now configured and application info is in MOTD
+```
+
+---
+
+### customize()
+
+Apply container customizations and final setup.
+
+**Signature**:
+```bash
+customize
+```
+
+**Purpose**: Apply any remaining customizations
+
+**Usage**:
+```bash
+customize
+```
+
+---
+
+### cleanup_lxc()
+
+Final cleanup and completion of installation.
+
+**Signature**:
+```bash
+cleanup_lxc
+```
+
+**Purpose**: Remove temporary files and finalize installation
+
+**Cleans**:
+- Temporary installation files
+- Package manager cache
+- Log files from installation process
+
+**Usage**:
+```bash
+cleanup_lxc
+# Installation is now complete and ready
+```
+
+---
+
+## Common Patterns
+
+### Basic Installation Pattern
+
+```bash
+#!/usr/bin/env bash
+source /dev/stdin <<<"$FUNCTIONS_FILE_PATH"
+
+setting_up_container
+network_check
+update_os
+
+# ... application installation ...
+
+motd_ssh
+customize
+cleanup_lxc
+```
+
+### With IPv6 Support
+
+```bash
+#!/usr/bin/env bash
+source /dev/stdin <<<"$FUNCTIONS_FILE_PATH"
+
+setting_up_container
+verb_ip6              # Enable IPv6
+network_check
+update_os
+
+# ... application installation ...
+```
+
+### With Error Handling
+
+```bash
+#!/usr/bin/env bash
+source /dev/stdin <<<"$FUNCTIONS_FILE_PATH"
+
+catch_errors          # Setup error trapping
+setting_up_container
+
+if ! network_check; then
+  msg_error "Network connectivity failed"
+  exit 1
+fi
+
+update_os
+```
+
+---
+
+**Last Updated**: December 2025
+**Total Functions**: 7
+**Maintained by**: community-scripts team