📦 Validate required system dependencies at CLI startup

[szmyty]

Title: 📦 Validate required system dependencies at CLI startup

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Description

Ensure required tools are available before running pipeline.

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Goals

• fail fast with clear errors
• improve user experience

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Requirements

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1. Check for Required Tools

• pandoc
• tectonic (if PDF requested)

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2. Validation Logic

At startup:

check tool availability before pipeline runs

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3. Error Messages

Example:

Pandoc not found. Please install pandoc to continue.

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4. Optional

• skip tectonic check if PDF not requested

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Tests

• simulate missing tool (optional)

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Acceptance Criteria

• dependencies validated at startup
• clear error messages
• no confusing runtime failures