Clarify OMOS-only features and host-mount portability in docs

Two related documentation fixes for users mounting ~/.config/opencode
from the host:

1. Gate oh-my-opencode-slim references (file and agents) to the OMOS
   variant in the Custom opencode config sections and data persistence
   tables. Base-variant users no longer see oh-my-opencode-slim.json
   listed as if it were always present.

2. Add a portability note warning that host-absolute paths in
   opencode.json (e.g. file:///usr/local/lib/node_modules/... or
   file:///opt/homebrew/...) will not resolve inside the Linux
   container, and to prefer bare package specifiers that work on
   both macOS and Linux hosts.

DOCKER_HUB.md

@@ -231,7 +231,7 @@ Understanding what survives container restarts and what doesn't:
 | `/home/developer/.rustup` | Named volume (if configured) | ✅ Yes — Docker volume | Rust toolchains |
 | `/home/developer/.cargo` | Named volume (if configured) | ✅ Yes — Docker volume | Cargo binaries, registry cache |
 | `/home/developer/.vscode-server` | Named volume (if configured) | ✅ Yes — Docker volume | VS Code server and extensions |
-| `/home/developer/.config/opencode` | Host bind mount (if configured) | ✅ Yes — lives on host | opencode.json, oh-my-opencode-slim.json, skills |
+| `/home/developer/.config/opencode` | Host bind mount (if configured) | ✅ Yes — lives on host | opencode.json, skills, plus `oh-my-opencode-slim.json` on the OMOS variant |
 
 ### Key points
 
@@ -245,7 +245,7 @@ Understanding what survives container restarts and what doesn't:
 
 ## Custom opencode Config
 
-For full control over opencode settings (MCP servers, custom models, oh-my-opencode-slim agents, etc.), mount the entire config directory from the host:
+For full control over opencode settings (MCP servers, custom models, and — on the OMOS variant — oh-my-opencode-slim agents), mount the entire config directory from the host:
 
 ```bash
 docker run -it --rm \
@@ -256,6 +256,8 @@ docker run -it --rm \
 
 This persists all configuration changes across container restarts. When an existing `opencode.json` is found, the `OPENCODE_PROVIDER` auto-config is skipped.
 
+> **Portability note:** The mounted config runs inside a Linux container. Any absolute paths inside `opencode.json` (for example, host-specific `plugin` entries like `file:///usr/local/lib/node_modules/...` or `file:///opt/homebrew/...`) will not resolve inside the container. Prefer bare package specifiers (e.g. `"oh-my-opencode-slim"`) that resolve via `node_modules` lookup, which works on both macOS and Linux hosts.
+
 ## Neovim Configuration
 
 The image includes neovim 0.12 with `EDITOR=nvim` set by default. To use your own neovim config (and have plugins auto-install via lazy.nvim on first start), mount it from the host:

README.md

@@ -128,14 +128,16 @@ docker compose exec -u developer devbox aws --version
 
 ### Custom opencode config
 
-For full control over opencode settings (MCP servers, custom models, oh-my-opencode-slim agents, etc.), mount the entire config directory from the host:
+For full control over opencode settings (MCP servers, custom models, and — on the OMOS variant — oh-my-opencode-slim agents), mount the entire config directory from the host:
 
 ```yaml
 volumes:
   - ~/.config/opencode:/home/developer/.config/opencode
 ```
 
-This persists all configuration changes across container restarts, including `opencode.json`, `oh-my-opencode-slim.json`, and skills. When an existing `opencode.json` is found, the `OPENCODE_PROVIDER` auto-config is skipped.
+This persists all configuration changes across container restarts, including `opencode.json`, skills, and (on the OMOS variant) `oh-my-opencode-slim.json`. When an existing `opencode.json` is found, the `OPENCODE_PROVIDER` auto-config is skipped.
+
+> **Portability note:** The mounted config runs inside a Linux container. Any absolute paths inside `opencode.json` (for example, host-specific `plugin` entries like `file:///usr/local/lib/node_modules/...` or `file:///opt/homebrew/...`) will not resolve inside the container. Prefer bare package specifiers (e.g. `"oh-my-opencode-slim"`) that resolve via `node_modules` lookup, which works on both macOS and Linux hosts.
 
 ### Custom skills
 
@@ -498,7 +500,7 @@ Container (Debian trixie)
 | `/home/developer/.rustup` | Named volume `devbox-rustup` (if configured) | ✅ Yes | Rust toolchains |
 | `/home/developer/.cargo` | Named volume `devbox-cargo` (if configured) | ✅ Yes | Cargo binaries, registry cache |
 | `/home/developer/.vscode-server` | Named volume `devbox-vscode` (if configured) | ✅ Yes | VS Code server and extensions |
-| `/home/developer/.config/opencode` | Host bind mount (if configured) | ✅ Yes | opencode.json, oh-my-opencode-slim.json, skills |
+| `/home/developer/.config/opencode` | Host bind mount (if configured) | ✅ Yes | opencode.json, skills, plus `oh-my-opencode-slim.json` on the OMOS variant |
 
 **opencode config** (`opencode.json`) is auto-generated from `OPENCODE_PROVIDER` on each start. It sets provider and model only — no MCP servers. To persist config changes and use custom settings, mount the config directory from the host (see Custom opencode config above).