ADR 0005 — Model routing & the architect–editor split

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• Status: Proposed
• Date: 2026-06-05
• Relates to: ADR 0001 · improvement-proposal.md §6.4

Context

Alfred has a clean provider abstraction (src/providers/) but uses one config.model for everything (src/repl.ts resolveConfig, default glm-5.1) — expensive reasoning and cheap mechanical edits pay the same model. There is no architect/editor split, no per-role routing, and no fallback. This contradicts the repo's own CLAUDE.md Rule 6 (token budget is a hard constraint).

The proven coding-agent pattern is architect/editor separation: a strong reasoning model plans the change in prose; a fast, cheap model applies it as precise edits. Aider reports this decomposition yields SOTA edit-benchmark results. Generalize to tiered routing (plan / code / sub-agent tiers) and fallback chains.

Decision

1. Role-based model map — extend QueryConfig (src/query/types.ts) + src/config/manager.ts with {architect, editor, subagent} slots, each resolvable to a provider+model.
2. Architect/editor in the harness — in the ADR 0001/§5.3 verify-fix loop, run the architect model to produce a plan and the editor model to turn it into fileEdit calls.
3. Provider fallback — in the retry layer (review R1.1): on overloaded, fail over to the other provider.

Consequences

• Positive: better edit accuracy (the proven win) and lower cost (cheap model does the mechanical work); honors the repo's token-budget rule; resilience via fallback.
• Negative/cost: more config surface; two models per task means two prompt formats to maintain; routing logic must stay deterministic (ADR 0001 P3), not model-decided.
• Phasing: role map + fallback P1 (M); architect/editor in harness P2 (builds on §5).

Alternatives considered

• A learned router (RouteLLM-style). Deferred: adds a model/dependency for marginal gain over a static role map at single-user scale.
• One strong model for everything. Rejected: violates the token-budget rule and leaves the measured architect/editor accuracy gain on the table.

References

See improvement-proposal.md §11 — [R1] Aider architect/editor mode.