refactor(tmux-launch-agent): extract tmux-open helper, add modelflag

common/misc/tmux-launch-agent/agents-seed.md

@@ -7,28 +7,33 @@ agents:
   - name: pi
     binary: pi
     args: "@{prompt}"
+    modelflag: "--model"
     description: "My primary agent harness. Accepts prompt file via {prompt}."
 
   - name: opencode
     binary: opencode
     args: ""
+    modelflag: "-m"
     description: "OpenCode agent. Pipes stdin via cat."
     note: "Uses stdin piping: args must be empty, prompt via pipe."
 
   - name: goose
     binary: goose
     args: ""
+    modelflag: "--model"
     description: "Goose agent. Accepts prompt file via -i flag."
     note: "Uses stdin piping: args must be empty, prompt via pipe."
 
   - name: codex
     binary: codex
     args: "@{prompt}"
+    modelflag: "-m"
     description: "OpenAI Codex. Accepts prompt file via {prompt}."
 
   - name: claude
     binary: claude
     args: ""
+    modelflag: "--model"
     description: "Anthropic Claude CLI. Pipes stdin via cat."
     note: "Uses stdin piping: args must be empty, prompt via pipe."
 ```
@@ -36,9 +41,10 @@ agents:
 ## Field meanings
 
 | Field | Description |
-|-------|-------------|
+| ------- | ------------- |
 | `name` | Display name used in menus and `--agent` flag |
 | `binary` | Command name expected on PATH |
 | `args` | Static arguments appended after the binary. May include `{prompt}` which is substituted at invocation time with the absolute path to the prompt file. Empty string means stdin piping (prompt is piped via `cat`). |
 | `description` | Short human-readable description for the setup menu |
+| `modelflag` | CLI flag used to select a model (e.g. `--model`, `-m`). Injected into the inner command when `--model <name>` is passed by the user. |
 | `note` | Optional additional context |