docs: add server mode and shell function examples for tmux integration

- Add --port flag requirement for tmux subagent pane spawning
- Add Fish shell function example with automatic port allocation
- Add Bash/Zsh equivalent function example
- Document how subagent panes work (opencode attach flow)
- Add OPENCODE_PORT environment variable documentation
- Add server mode reference section with opencode serve command

docs/configurations.md

@@ -259,6 +259,7 @@ Run background subagents in separate tmux panes for **visual multi-agent executi
 
 1. **Must run inside tmux**: The feature only activates when OpenCode is already running inside a tmux session
 2. **Tmux installed**: Requires tmux to be available in PATH
+3. **Server mode**: OpenCode must run with `--port` flag to enable subagent pane spawning
 
 ### How It Works
 
@@ -268,17 +269,133 @@ When `tmux.enabled` is `true` and you're inside a tmux session:
 - Panes are automatically closed when the subagent completes
 - Layout is automatically adjusted based on your configuration
 
-**Example workflow**:
+### Running OpenCode with Tmux Subagent Support
+
+To enable tmux subagent panes, OpenCode must run in **server mode** with the `--port` flag. This starts an HTTP server that subagent panes connect to via `opencode attach`.
+
+**Basic setup**:
 ```bash
 # Start tmux session
 tmux new -s dev
 
-# Run OpenCode inside tmux
-opencode
+# Run OpenCode with server mode (port 4096)
+opencode --port 4096
 
 # Now background agents will appear in separate panes
 ```
 
+**Recommended: Shell Function**
+
+For convenience, create a shell function that automatically handles tmux sessions and port allocation. Here's an example for Fish shell:
+
+```fish
+# ~/.config/fish/config.fish
+function oc
+    set base_name (basename (pwd))
+    set path_hash (echo (pwd) | md5 | cut -c1-4)
+    set session_name "$base_name-$path_hash"
+    
+    # Find available port starting from 4096
+    function __oc_find_port
+        set port 4096
+        while test $port -lt 5096
+            if not lsof -i :$port >/dev/null 2>&1
+                echo $port
+                return 0
+            end
+            set port (math $port + 1)
+        end
+        echo 4096
+    end
+    
+    set oc_port (__oc_find_port)
+    set -x OPENCODE_PORT $oc_port
+    
+    if set -q TMUX
+        # Already inside tmux - just run with port
+        opencode --port $oc_port $argv
+    else
+        # Create tmux session and run opencode
+        set oc_cmd "OPENCODE_PORT=$oc_port opencode --port $oc_port $argv; exec fish"
+        if tmux has-session -t "$session_name" 2>/dev/null
+            tmux new-window -t "$session_name" -c (pwd) "$oc_cmd"
+            tmux attach-session -t "$session_name"
+        else
+            tmux new-session -s "$session_name" -c (pwd) "$oc_cmd"
+        end
+    end
+    
+    functions -e __oc_find_port
+end
+```
+
+**Bash/Zsh equivalent**:
+
+```bash
+# ~/.bashrc or ~/.zshrc
+oc() {
+    local base_name=$(basename "$PWD")
+    local path_hash=$(echo "$PWD" | md5sum | cut -c1-4)
+    local session_name="${base_name}-${path_hash}"
+    
+    # Find available port
+    local port=4096
+    while [ $port -lt 5096 ]; do
+        if ! lsof -i :$port >/dev/null 2>&1; then
+            break
+        fi
+        port=$((port + 1))
+    done
+    
+    export OPENCODE_PORT=$port
+    
+    if [ -n "$TMUX" ]; then
+        opencode --port $port "$@"
+    else
+        local oc_cmd="OPENCODE_PORT=$port opencode --port $port $*; exec $SHELL"
+        if tmux has-session -t "$session_name" 2>/dev/null; then
+            tmux new-window -t "$session_name" -c "$PWD" "$oc_cmd"
+            tmux attach-session -t "$session_name"
+        else
+            tmux new-session -s "$session_name" -c "$PWD" "$oc_cmd"
+        fi
+    fi
+}
+```
+
+**How subagent panes work**:
+
+1. Main OpenCode starts HTTP server on specified port (e.g., `http://localhost:4096`)
+2. When a background agent spawns, Oh My OpenCode creates a new tmux pane
+3. The pane runs: `opencode attach http://localhost:4096 --session <session-id>`
+4. Each subagent pane shows real-time streaming output
+5. Panes are automatically closed when the subagent completes
+
+**Environment variables**:
+
+| Variable | Description |
+|----------|-------------|
+| `OPENCODE_PORT` | Default port for the HTTP server (used if `--port` not specified) |
+
+### Server Mode Reference
+
+OpenCode's server mode exposes an HTTP API for programmatic interaction:
+
+```bash
+# Standalone server (no TUI)
+opencode serve --port 4096
+
+# TUI with server (recommended for tmux integration)
+opencode --port 4096
+```
+
+| Flag | Default | Description |
+|------|---------|-------------|
+| `--port` | `4096` | Port for HTTP server |
+| `--hostname` | `127.0.0.1` | Hostname to listen on |
+
+For more details, see the [OpenCode Server documentation](https://opencode.ai/docs/server/).
+
 ## Git Master
 
 Configure git-master skill behavior: