feat(export): install server requirements

[peter-gy]

Summary

Add a server-owned installation contract for export requirements.

The client sends an export format. The server resolves its missing packages and setup requirements, installs them into the server Python environment, and returns refreshed availability for every server-backed export format.

• Uses uv when available and pip otherwise.
• Runs package installation outside the event loop.
• Installs Playwright Chromium through a typed setup requirement with a 10-minute timeout.
• Requires edit capability and verifies the requested format after installation.

The export dialog consumes this contract in #10471.

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Project	Deployment	Actions	Updated (UTC)
marimo-docs	Ready	Preview	Aug 6, 2026 12:04pm

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Coverage Report for ./frontend

Status	Category	Percentage	Covered / Total
🔵	Lines	78.81%	81571 / 103492
🔵	Statements	78.81%	81571 / 103492
🔵	Functions	71.22%	693 / 973
🔵	Branches	79.37%	4858 / 6120

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[cubic-dev-ai]

All reported issues were addressed across 14 files

Architecture diagram

sequenceDiagram
    participant Client as Export Dialog (Client)
    participant API as Export API Endpoint
    participant Util as Server Utils
    participant UV as UvPackageManager
    participant Pip as PipPackageManager
    participant Deps as Export Dependencies
    participant Sub as subprocess

    Note over Client,Sub: NEW: Install Export Requirements Flow

    Client->>API: POST /api/export/requirements/install {format: "pdf"}
    API->>API: enforce_consumer_capability("edit")
    
    API->>Deps: _get_export_format_availability("pdf")
    Deps->>Deps: get_missing_export_packages()
    Deps->>Deps: get_missing_export_setup()
    Deps-->>API: {missing_packages: ["nbconvert[webpdf]"], missing_setup: [...]}

    alt Missing packages exist
        API->>Util: install_packages_on_server({"nbconvert[webpdf]": ""})
        
        Note over Util: Try uv first, then pip
        
        Util->>UV: is_manager_installed()
        alt uv available
            UV-->>Util: True
            Util->>UV: install("nbconvert[webpdf]", version=None)
            UV->>UV: _install_with_cache_fallback()
            Note over UV: Runs via asyncio.to_thread to avoid blocking event loop
            UV-->>Util: True
        else uv not available
            UV-->>Util: False
            Util->>Pip: is_manager_installed()
            Pip-->>Util: True
            Util->>Pip: install("nbconvert[webpdf]", version=None)
            Pip-->>Util: True
        end
        Util-->>API: Success
        
        API->>Deps: _get_export_format_availability("pdf")
        Deps-->>API: {missing_packages: [], missing_setup: [{"name": "playwright-chromium"}]}
    end

    alt Missing setup exists
        API->>Deps: install_export_setup("playwright-chromium")
        Deps->>Sub: subprocess.run([python, -m, playwright, install, chromium])
        Note over Deps,Sub: Runs via asyncio.to_thread with 600s timeout
        Sub-->>Deps: CompletedProcess(returncode=0)
        Deps-->>API: Success
    end

    API->>Deps: _get_export_availability()
    Deps-->>API: {"formats": [{"format":"html",...}, {"format":"pdf","dependenciesAvailable":true},...]}

    alt Target format still unresolved
        API-->>Client: 500 SERVER_ERROR
    else All requirements resolved
        API-->>Client: 200 ExportAvailabilityResponse
    end

    Note over Client,Sub: Failure paths
    alt Playwright install fails
        Deps->>Sub: subprocess.run()
        Sub-->>Deps: TimeoutExpired or returncode != 0
        Deps->>Deps: raise RuntimeError
        Deps-->>API: Error
        API-->>Client: 500 SERVER_ERROR
    else Package install fails
        Util->>Pip: install()
        Pip-->>Util: False
        Util->>Util: raise RuntimeError
        Util-->>API: Error
        API-->>Client: 500 SERVER_ERROR
    end

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