ad-deepen

name	ad-deepen
description	Surface deepening opportunities in the codebase using the Ousterhout/Feathers vocabulary from WORKFLOW §8 (Module / Interface / Depth / Seam / Adapter / Leverage / Locality). Three-phase process — explore organically, present numbered candidates with deletion-test framing, grilling loop on the chosen candidate. Pairs with `ad-drift` (audit detects drift; deepen proposes refactors). Triggers on "deepen", "refactor for depth", "shallow module", "deletion test", "two-adapters rule", "interface is the test surface", "leverage", "locality", "/ad-deepen".
summary	Surface deepening opportunities using WORKFLOW §8 vocabulary (Module / Interface / Depth / Seam / Adapter / Leverage / Locality). Three phases — explore, present numbered candidates with deletion-test framing, grill the chosen one. Pairs with `ad-drift`.

<background_information> Implements ADR-0020 (doc/adr/0020-deep-modules-vocabulary.md) — operational counterpart to the WORKFLOW §8 architectural vocabulary. Surfaces deepening opportunities and walks the user through them. Process scaffold; no primary file output.

Use this only when design friction is real: repeated behavior, callers that need a stable seam, or a module whose interface exposes too much. Architectural deepening is premature for a one-shot ≤200-line experiment. Per ADR-0020 §4.

Codex auto-trigger on description keywords is less mature than Claude Code's. If auto-invocation does not fire when the user mentions deepening, shallow modules, the deletion test, or the two-adapters rule, invoke this skill manually. </background_information>

Step 0 — confirm regime. Deepen is for the *stable-codebase, friction-visible* regime. Run when at least one holds: - A module's interface is roughly as complex as its implementation (shallow module candidate). - A concept is bouncing between modules across recent changes (locality candidate). - A test cannot exercise the real bug pattern at the call site (interface-is-test-surface candidate). - An adapter has been introduced for a hypothetical second implementation (two-adapters-rule violation). - The user explicitly asks "where should this be refactored?" against a stable surface.

Route elsewhere when:

• The change is a one-line fix or mechanical refactor → no scaffold needed.
• The codebase is a one-shot script (≤200 lines, no callers): deepening is premature; ship the experiment first.
• The friction is a bug, not a shape — ad-diagnose (WORKFLOW §15).
• The friction is a naming/vocabulary drift — ad-domain.
• The friction is missing context, not module shape — ad-grill-me.

Step 1 — explore organically. Before naming candidates, read.

1. Read CONTEXT.md if it exists. Anchor domain vocabulary; deepening proposals must use Customer, Order, Triage role — not Service, Handler, Manager.
2. Read ARCHITECTURE.md if it exists. Read accepted ADRs in doc/adr/ covering the surface you are about to walk.
3. Walk the codebase noting friction:
   • Concepts bouncing between modules (locality fault).
   • Interfaces as wide as their implementations (shallow modules — apply the deletion test).
   • Tests that mock four things to exercise one path (test-surface fault).
   • Adapters with one concrete implementation (two-adapters-rule violation, if no second is planned).

Read with eyes for shape, not bugs. The friction is in module geometry; the bug-finding skill is ad-diagnose.

Step 2 — present candidates numbered. For each deepening opportunity, produce a short numbered entry:

### Candidate N: <one-line title using domain + architectural vocabulary>

**Files involved:** `src/foo.ts:42`, `src/bar.ts`.

**Friction:** <one-paragraph plain English — what hurts today, who feels it, when>.

**Proposal:** <one-paragraph plain English — what changes about the module shape>.

**Vocabulary check:** <Module / Interface / Seam / Adapter / Depth / Leverage / Locality applied here, per WORKFLOW §8>.

**Deletion test:** <if you imagine deleting the module today, what ?   →          →    ,  >.

 .

 .

 .

Number candidates 1, 2, 3, ... Order by leverage × locality (largest impact first, lowest blast radius among ties). Cap at five.

Step 3 — grilling loop on the chosen candidate. The user picks one candidate by number. Drop into a grilling loop on that one:

1. Walk the decision tree of the proposal branch by branch (one question per turn, recommendation included). Reuse the ad-grill-me discipline.
2. Add new domain terms to CONTEXT.md lazily via ad-domain as the proposal surfaces them.
3. Offer an ADR only when the three criteria pass (hard to reverse, surprising without context, real trade-off). Most refactors do not need an ADR.
4. When the proposal stabilizes: route to ad-tdg (WORKFLOW §9) for the implementation pass with ground-truth pair + TDM + criterion-based selection.

Reject candidates the grilling loop reveals as wrong-shaped. Better to discard at this stage than to ship a deepening that doesn't deepen.

Vocabulary discipline (always on). Per ADR-0020, use the canonical vocabulary verbatim — the full glossary (terms to use, terms to avoid, domain-noun application) is in references/vocabulary.md.

<output_contract> Structured conversation. No primary file written. Side-effects:

• CONTEXT.md updates land via ad-domain when the proposal surfaces new domain terms.
• ADR drafts land via ad-adr when the three-criteria test passes.
• Implementation lands via ad-tdg after the proposal stabilizes — that skill produces the verified code change.

Each session produces:

1. A numbered list of candidates (Step 2), capped at five.
2. A picked candidate with the grilling loop transcript (Step 3).
3. Routing to ad-tdg with the ground-truth pair seeded from the proposal. </output_contract>

Next

• After candidates surface but before picking: /ad-drift for a broader drift check; the audit may reorder priorities.
• After picking and grilling stabilizes: /ad-tdg to implement under WORKFLOW §9 discipline.
• If the proposal touches load-bearing architecture: /ad-adr to record the decision (only when the three-criteria test passes).
• If the deepening exposed a domain-vocabulary drift: /ad-domain to update CONTEXT.md.
• If the candidates all turned out to be bug-symptoms rather than shape-symptoms: /ad-diagnose (WORKFLOW §15).