Preset inheritance and composition — DRY config for related presets

[santoyaworobey2]

We have 15 MDA presets that share a lot of common config. For example, all our "summarize" variants share the same max_output_tokens, temperature, and retry policy — they only differ in provider and model.

Currently we duplicate everything:

# summarize-openai
provider: openai
model: gpt-4.1
temperature: 0.2
max_output_tokens: 1024
retry: {max_attempts: 3, backoff: exponential}
cache: {ttl: 3600}

# summarize-anthropic (90% identical)
provider: anthropic
model: claude-sonnet-4-5-20250514
temperature: 0.2
max_output_tokens: 1024
retry: {max_attempts: 3, backoff: exponential}
cache: {ttl: 3600}

Proposal: Preset inheritance with override:

# Base preset
summarize-base:
  abstract: true
  temperature: 0.2
  max_output_tokens: 1024
  retry: {max_attempts: 3, backoff: exponential}
  cache: {ttl: 3600}

# Concrete presets inherit
summarize-openai:
  extends: summarize-base
  provider: openai
  model: gpt-4.1

summarize-anthropic:
  extends: summarize-base
  provider: anthropic
  model: claude-sonnet-4-5-20250514

This would also support composition (mixing in shared retry/cache configs). Makes maintaining 15+ presets much less error-prone.