[WIP] Add Mistral Vibe as coding agent

[Copilot]

Thanks for assigning this issue to me. I'm starting to work on it and will keep this PR's description up to date as I form a plan and make progress.

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<issue_title>Add Mistral Vibe as coding agent</issue_title>
<issue_description>After talking with Pini Wietchner at Mistral we will take a look at adding support for Mistral Vibe

@pelikhan is tidying up the internal engineering to make sure adding new coding agents is reasonably straight-forward.

I asked Opus to take a look at the coding agent features needed, download Mistral Vibe CLI and analyze what's what according what's needed. Here's what it came up with

Technical Requirements for Coding Agent CLI Integration with gh-aw

Support Comparison Table

Requirement	Copilot CLI	Claude Code	Codex	Mistral Vibe
P0 - Core CLI
Non-interactive mode	✅ --prompt	✅ --print	✅ exec subcommand	✅ -p (programmatic mode)
Prompt input	✅ --prompt "..."	✅ positional arg	✅ exec "..."	✅ positional or -p "..."
Prompt from file	✅ stdin/shell	✅ stdin/shell	✅ stdin/shell	✅ stdin/shell
Exit codes	✅	✅	✅	✅
Installation method	npm @github/copilot	npm @anthropic-ai/claude-code	npm @openai/codex	curl install script (uv/pip)
P0 - Authentication
API key via env var	✅ COPILOT_GITHUB_TOKEN	✅ ANTHROPIC_API_KEY	✅ OPENAI_API_KEY	✅ MISTRAL_API_KEY
P1 - MCP Integration
MCP config file	✅ --mcp-config	✅ --mcp-config	⚠️ In development	⚠️ config.toml only¹
Tool allow-listing	✅ --allow-tool	✅ --allowed-tools	⚠️ Limited	✅ --enabled-tools²
Granular tool perms	✅ server(tool)	✅ mcp__server__tool	❌	⚠️ glob/regex patterns
P1 - Logging
Structured logs	✅ JSONL session files	✅ --debug-file	⚠️ Text logs	✅ --output json|streaming
Log file output	✅ --log-dir	✅ --debug-file	⚠️ stderr redirect	⚠️ session logs only³
Verbose mode	✅ --log-level all	✅ --verbose	⚠️ Limited	⚠️ config-based
Token usage in logs	✅	✅	⚠️	⚠️ Session summary
Tool calls in logs	✅	✅	⚠️	✅
P2 - Configuration
Custom model	✅ --model	✅ --model	✅ -c model=	⚠️ config.toml only
Max turns/iterations	❌	✅ --max-turns	❌	✅ --max-turns
Max cost limit	❌	❌	❌	✅ --max-price
Custom CLI args	✅	✅	✅	✅
P2 - Security
Directory access control	✅ --add-dir	❌	❌	⚠️ Trust folder system
Network restrictions	⚠️ Via AWF sandbox	⚠️ Via AWF sandbox	⚠️ Via AWF sandbox	❌
Auto-approve mode	❌ (uses sandbox)	✅ --dangerously-skip-permissions	✅ --dangerously-bypass...	✅ -p auto-approves
Disable confirmations	✅ --accept	✅ --disable-slash-commands	✅ (part of bypass)	✅ -p mode
P2 - Advanced
Agent/system prompt files	✅ --agent	❌	❌	✅ --agent NAME⁴
Built-in web-fetch	✅	✅	❌	❌
Built-in web-search	❌	✅	✅ --search	❌
Plugin system	✅ copilot plugin install	❌	❌	✅ Skills system
Session resume	❌	❌	❌	✅ --continue, --resume
Working directory	✅ --workdir (planned)	❌	❌	✅ --workdir

Legend: ✅ Full support | ⚠️ Partial/limited | ❌ Not supported

Footnotes

¹ Mistral Vibe MCP: MCP servers configured via ~/.vibe/config.toml [[mcp_servers]] section, not CLI flag. Supports stdio, http, streamable-http transports.

² Vibe tool patterns: --enabled-tools supports exact names, glob patterns (bash*), and regex (re:^pattern$).

³ Vibe logging: Session logs stored in ~/.vibe/logs/. JSON output via --output json only in programmatic mode.

⁴ Vibe agents: References TOML files in ~/.vibe/agents/NAME.toml, not markdown files.

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Requirements for gh-aw Integration

1. Core CLI Interface

Essential:

• Non-interactive execution mode: CLI must support fully automated, non-interactive operation (no user prompts/confirmations)
• Prompt/instruction input: Accept multi-line natural language instructions via:
  • Command-line argument (e.g., --prompt "instruction" or positional argument)
  • File input (e.g., --prompt-file /path/to/prompt.txt)
  • Stdin (pipe input)
• Exit codes: Return 0 on success, non-zero on failure
• Installation: Installable via npm (npm install -g @mistral/vibe-cli) or provide equivalent installation method

2. Authentication

Essential:

• Support API key authentication via environment variable (e.g., MISTRAL_API_KEY)
• Document required API key permissions/scopes

3. MCP (Model Context Protocol) Integration

Highly Recommended:

• Support MCP server configuration via JSON config file (e.g., --mcp-config /path/to/config.json)
• Support tool allow-listing to restrict which MCP tools the agent can invoke
  • Granular permissions: `--allow-tool server_name(tool_n...

• Fixes Add Mistral Vibe as coding agent #16145

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