👀 Implement watch mode for automatic rebuild on file changes

[szmyty]

Title: 👀 Implement watch mode for automatic rebuild on file changes

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Description

Add a watch mode to automatically rebuild when files change.

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Goals

• improve developer workflow
• enable live iteration

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Requirements

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1. CLI Command

renderflow watch input.md

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2. File Watching

Watch:

- input file
- config file
- templates directory

Use:

notify crate

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3. Debounce

• prevent rapid repeated triggers
• delay execution slightly

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4. Rebuild Behavior

on change → re-run pipeline

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5. Logging

File changed → rebuilding...

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Tests

• manual testing acceptable (watch behavior)

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Acceptance Criteria

• watch command implemented
• file changes trigger rebuild
• debounce works
• CLI stable