Add ADR for interface modules

[pditommaso]

Summary

This ADR proposes interface modules - abstract module definitions that declare input/output contracts without implementation. Concrete modules can implement these interfaces, and users select the target implementation at runtime via configuration.

This enables:

• Tool benchmarking (run same data through multiple tools)
• User customization (swap implementations without modifying workflow code)
• LLM-assisted pipeline construction (semantic discovery of interchangeable tools)

Key Design Decisions

• Minimal syntax impact: No new DSL keywords; uses meta.yaml fields
• type: interface in meta.yaml marks a module as an abstract contract
• implements: <interface> declares that a module complies with an interface
• Resolution via config: modules.interfaces {} block in nextflow.config
• Three resolution strategies: static, parameter-based, and per-sample closure

Example

# Interface module meta.yaml
name: nf-core/msa-alignment
type: interface
input: [...]
output: [...]

# Implementation module meta.yaml
name: nf-core/clustalo-align
implements: nf-core/msa-alignment@>=1.0.0

// nextflow.config
modules {
    interfaces {
        'nf-core/msa-alignment' = params.aligner
    }
}

Related

• Discussion: Modules: ideas about tagging and grouping modules schemas#11
• Reference implementation: https://github.com/mirpedrol/class-modules

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