feat: add CLI flags support to attach command

[simondmorias]

Summary

Add support for --model, --session, --continue, --prompt, --agent, --title, and --command flags to the opencode attach command, bringing feature parity with the main TUI and run commands.

Changes

• Added CLI flags to AttachCommand builder:

  • --model / -m - Model to use (format: provider/model)
  • --session / -s - Session ID to continue
  • --continue / -c - Continue the last session
  • --prompt / -p - Prompt to use
  • --agent - Agent to use
  • --title - Title for the session
  • --command - Command to run (uses prompt for args)

• Updated Args interface to include title and command properties

• Implemented stdin piping support for prompts in attach command

• Added command pre-fill support in home route - prepends / to command name and combines with prompt

• Updated documentation with complete flag reference and usage examples

Usage Examples

# Attach with specific model and agent
opencode attach http://localhost:4096 --model anthropic/claude-3-5-sonnet --agent build

# Attach and continue last session
opencode attach http://localhost:4096 --continue

# Attach with pre-filled command
opencode attach http://localhost:4096 --command commit --prompt "with conventional format"

# Attach and provide initial prompt
echo "Review this code" | opencode attach http://localhost:4096 --prompt "and suggest improvements"

# Attach to specific session with title
opencode attach http://localhost:4096 --session abc123 --title "Bug fix session"

Files Changed

• packages/opencode/src/cli/cmd/tui/attach.ts - Added flag definitions and argument passing
• packages/opencode/src/cli/cmd/tui/context/args.tsx - Extended Args interface
• packages/opencode/src/cli/cmd/tui/routes/home.tsx - Added command pre-fill logic
• packages/web/src/content/docs/cli.mdx - Added attach command documentation

Testing

• No new TypeScript errors introduced (verified with bun typecheck)
• All flags follow the same patterns as the thread command for consistency
• Documentation includes examples and complete flag reference
• Manual test: bun run --cwd packages/opencode --conditions=browser src/index.ts \ attach http://localhost:4096 --agent plan

Notes

• The --format flag was intentionally not added as it's only relevant for non-interactive output (like the run command), not for the TUI
• Pre-existing TypeScript errors in script/build.ts and src/mcp/index.ts are unrelated to these changes