Architecture

Surface architectural friction and propose deepening opportunities: refactors that turn shallow modules into deep ones. The aim is testability and AI-navigability.

This skill also runs at the start, before there is friction to find: setting up a new codebase or area means choosing its structure and conventions. Greenfield skips the exploration and candidate list; go straight to the interview against the conventions below, and write what settles into ARCHITECTURE.md.

The conventions this skill owns are indexed in conventions/, loaded when the work touches them; implement follows them while building.

Fast by default: scope the exploration to the area the user names or the friction they describe, present the top candidates, and hold the rival-interface sub-agent fan-out until asked. Deep mode (the deep skill is active): whole-codebase sweep, full candidate list, sub-agent interface exploration on the picked candidate.

Glossary

Use these terms exactly in every suggestion. Consistent language is the point. Don't drift into "component," "service," "API," or "boundary." Full definitions in LANGUAGE.md.

• Module: anything with an interface and an implementation (function, class, package, slice).
• Interface: everything a caller must know to use the module: types, invariants, error modes, ordering, config. Not just the type signature.
• Implementation: the code inside.
• Depth: leverage at the interface, a lot of behavior behind a small interface. Deep = high leverage. Shallow = interface nearly as complex as the implementation.
• Seam: where an interface lives; a place behavior can be altered without editing in place. (Use this, not "boundary.")
• Adapter: a concrete thing satisfying an interface at a seam.
• Leverage: what callers get from depth.
• Locality: what maintainers get from depth (change, bugs, knowledge concentrated in one place).

Key principles (see LANGUAGE.md for the full list):

• Deletion test: imagine deleting the module. If complexity vanishes, it was a pass-through. If complexity reappears across N callers, it was earning its keep.
• The interface is the test surface.
• One adapter = hypothetical seam. Two adapters = real seam.
• A shared interface is a published promise. More than one consumer means deepening behind it additively, never reshaping what callers already depend on; a breaking change to a shared seam is a migration to plan, not a refactor to slip in.

This skill is informed by the project's domain model: CONTEXT.md and any docs/adr/. The domain language gives names to good seams; ADRs record decisions the skill should not re-litigate. See CONTEXT-FORMAT.md and ADR-FORMAT.md.

Process

Greenfield (no code to find friction in): skip to step 3 and interview against the conventions above.

1. Explore

Read existing documentation first:

• ARCHITECTURE.md at the root: the prior map of modules, seams, and invariants. Re-derive only what changed since it was written.
• CONTEXT.md (or CONTEXT-MAP.md + each CONTEXT.md in a multi-context repo)
• Relevant ADRs in docs/adr/ (and any context-scoped docs/adr/ directories)

If any of these files don't exist, proceed silently. Don't flag their absence or suggest creating them upfront. Exception: when ARCHITECTURE.md is missing on a nontrivial codebase, offer once to seed it from this run's exploration, using FORMAT.md; write only what the user confirms.

Then walk the codebase, in a subagent when the harness dispatches one (subagent_type=Explore), otherwise here, scoped to the area the user named. Don't follow rigid heuristics. Explore organically and note where you experience friction:

• Where does understanding one concept require bouncing between many small modules?
• Where are modules shallow (interface nearly as complex as the implementation)?
• Where have pure functions been extracted just for testability, but the real bugs hide in how they're called (no locality)?
• Where do tightly-coupled modules leak across their seams?
• Which parts of the codebase are untested, or hard to test through their current interface?

Apply the deletion test to anything you suspect is shallow: would deleting it concentrate complexity, or just move it? A "yes, concentrates" is the signal you want.

2. Present candidates

Present a numbered list of deepening opportunities. For each candidate:

• Files: which files/modules are involved
• Problem: why the current architecture is causing friction
• Solution: plain English description of what would change
• Benefits: explained in terms of locality and leverage, and also in how tests would improve

Use CONTEXT.md vocabulary for the domain, and LANGUAGE.md vocabulary for the architecture. If CONTEXT.md defines "Order," talk about "the Order intake module", not "the FooBarHandler," and not "the Order service."

ADR conflicts: if a candidate contradicts an existing ADR, only surface it when the friction is real enough to warrant revisiting the ADR. Mark it clearly (e.g. "contradicts ADR-0007, but worth reopening because…"). Don't list every theoretical refactor an ADR forbids.

Do NOT propose interfaces yet. Ask the user: "Which of these would you like to explore?"

3. Interview loop

Once the user picks a candidate, run the core-interview skill against it. The decision tree to walk: constraints, dependencies, the shape of the deepened module, what sits behind the seam, what tests survive.

Side effects happen inline as decisions crystallize:

• Naming a deepened module after a concept not in CONTEXT.md? Add the term to CONTEXT.md, same discipline as /drill (see CONTEXT-FORMAT.md). If it doesn't exist, create it lazily when the first term is resolved.
• Sharpening a fuzzy term during the conversation? Update CONTEXT.md right there.
• Did the settled design change the system's shape (new module, moved seam, new invariant)? Update ARCHITECTURE.md right there, per FORMAT.md.
• User rejects the candidate with a load-bearing reason? Offer an ADR, framed as: "Want me to record this as an ADR so future architecture reviews don't re-suggest it?" Only offer when the reason would actually be needed by a future explorer to avoid re-suggesting the same thing. Skip ephemeral reasons ("not worth it right now") and self-evident ones. See ADR-FORMAT.md.
• Want to explore alternative interfaces for the deepened module? See INTERFACE.md.

When the settled design is implementation work, write the spec to docs/specs/<slug>.md per SPEC-FORMAT.md, with the deepened interface and the tests that survive as its acceptance criteria, and hand it to implement.