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npx skills@latest add mattpocock/skills/triage-issue
```
- **improve-codebase-architecture** — Explore a codebase for architectural improvement opportunities, focusing on deepening shallow modules and improving testability.
- **improve-codebase-architecture** — Find deepening opportunities in a codebase, informed by the domain language in `CONTEXT.md` and the decisions in `docs/adr/`.
```
npx skills@latest add mattpocock/skills/improve-codebase-architecture
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When a term is resolved, update `CONTEXT.md` right there. Don't batch these up — capture them as they happen. Use the format in [CONTEXT-FORMAT.md](./CONTEXT-FORMAT.md).
Don't couple `CONTEXT.md` to implementation details. Only include terms that are meaningful to domain experts.
### Offer ADRs sparingly
Only offer to create an ADR when all three are true:
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---
name: github-triage
description: Triage GitHub issues through a label-based state machine with interactive grilling sessions. Use when user wants to triage issues, review incoming bugs or feature requests, prepare issues for an AFK agent, or manage issue workflow.
description: Triage GitHub issues through a label-based state machine. Use when user wants to create an issue, triage issues, review incoming bugs or feature requests, prepare issues for an AFK agent, or manage issue workflow.
---
# GitHub Issue Triage
@@ -97,13 +97,13 @@ Tell the maintainer:
Then wait for the maintainer's direction. They may:
- Agree and ask you to apply labels → do it
- Want to flesh it out → start a grilling session
- Want to flesh it out → start a /domain-model session
- Override with a different state → apply their choice
- Want to discuss → have a conversation
### Step 3: Bug reproduction (bugs only)
If the issue is categorized as a bug, attempt to reproduce it before starting a grilling session. This will vary by codebase, but do your best:
If the issue is categorized as a bug, attempt to reproduce it before starting a /domain-model session. This will vary by codebase, but do your best:
- Read the reporter's reproduction steps (if provided)
- Explore the codebase to understand the relevant code paths
@@ -112,11 +112,11 @@ If the issue is categorized as a bug, attempt to reproduce it before starting a
- If reproduction fails, report that too — the bug may be environment-specific, already fixed, or the report may be inaccurate
- If the report lacks enough detail to attempt reproduction, note that — this is a strong signal the issue should move to `needs-info`
The reproduction attempt informs the grilling session and the agent brief. A confirmed reproduction with a known code path makes for a much stronger brief.
The reproduction attempt informs the /domain-model session and the agent brief. A confirmed reproduction with a known code path makes for a much stronger brief.
### Step 4: Grilling session (if needed)
### Step 4: /domain-model session (if needed)
If the issue needs to be fleshed out before it's ready for an agent, interview the maintainer to build a complete specification.
If the issue needs to be fleshed out before it's ready for an agent, interview the maintainer to build a complete specification. Use the /domain-model skill.
### Step 5: Apply the outcome
@@ -133,13 +133,13 @@ Depending on the outcome:
When the maintainer explicitly tells you to move an issue to a specific state (e.g. "move #42 to ready-for-agent"), trust their judgment and apply the label directly.
Still show a confirmation of what you're about to do: which labels will be added/removed, and whether you'll post a comment or close the issue. But skip the grilling session entirely.
Still show a confirmation of what you're about to do: which labels will be added/removed, and whether you'll post a comment or close the issue. But skip the /domain-model session entirely.
If moving to `ready-for-agent` without a grilling session, ask the maintainer if they want to write a brief agent brief comment or skip it.
If moving to `ready-for-agent` without a /domain-model session, ask the maintainer if they want to write a brief agent brief comment or skip it.
## Needs Info Output
When moving an issue to `needs-info`, post a comment that captures the grilling progress and tells the reporter what's needed:
When moving an issue to `needs-info`, post a comment that captures the interview progress and tells the reporter what's needed:
```markdown
## Triage Notes
@@ -155,7 +155,7 @@ When moving an issue to `needs-info`, post a comment that captures the grilling
- question 2
```
Include everything resolved during the grilling session in "established so far" — this work should not be lost. The questions for the reporter should be specific and actionable, not vague ("please provide more info").
Include everything resolved during the /domain-model session in "established so far" — this work should not be lost. The questions for the reporter should be specific and actionable, not vague ("please provide more info").
## Resuming Previous Sessions
@@ -165,4 +165,4 @@ When triaging an issue that already has triage notes from a previous session:
2. Parse what was already established
3. Check if the reporter has answered any outstanding questions
4. Present the maintainer with an updated picture: "Here's where we left off, and here's what the reporter has said since"
5. Continue the grilling from where it stopped — do not re-ask resolved questions
5. Continue the /domain-model session from where it stopped — do not re-ask resolved questions
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# Deepening
How to deepen a cluster of shallow modules safely, given its dependencies. Assumes the vocabulary in [LANGUAGE.md](LANGUAGE.md) — **module**, **interface**, **seam**, **adapter**.
## Dependency categories
When assessing a candidate for deepening, classify its dependencies. The category determines how the deepened module is tested across its seam.
### 1. In-process
Pure computation, in-memory state, no I/O. Always deepenable — merge the modules and test through the new interface directly. No adapter needed.
### 2. Local-substitutable
Dependencies that have local test stand-ins (PGLite for Postgres, in-memory filesystem). Deepenable if the stand-in exists. The deepened module is tested with the stand-in running in the test suite. The seam is internal; no port at the module's external interface.
### 3. Remote but owned (Ports & Adapters)
Your own services across a network boundary (microservices, internal APIs). Define a **port** (interface) at the seam. The deep module owns the logic; the transport is injected as an **adapter**. Tests use an in-memory adapter. Production uses an HTTP/gRPC/queue adapter.
Recommendation shape: *"Define a port at the seam, implement an HTTP adapter for production and an in-memory adapter for testing, so the logic sits in one deep module even though it's deployed across a network."*
### 4. True external (Mock)
Third-party services (Stripe, Twilio, etc.) you don't control. The deepened module takes the external dependency as an injected port; tests provide a mock adapter.
## Seam discipline
- **One adapter means a hypothetical seam. Two adapters means a real one.** Don't introduce a port unless at least two adapters are justified (typically production + test). A single-adapter seam is just indirection.
- **Internal seams vs external seams.** A deep module can have internal seams (private to its implementation, used by its own tests) as well as the external seam at its interface. Don't expose internal seams through the interface just because tests use them.
## Testing strategy: replace, don't layer
- Old unit tests on shallow modules become waste once tests at the deepened module's interface exist — delete them.
- Write new tests at the deepened module's interface. The **interface is the test surface**.
- Tests assert on observable outcomes through the interface, not internal state.
- Tests should survive internal refactors — they describe behaviour, not implementation. If a test has to change when the implementation changes, it's testing past the interface.
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# Interface Design
When the user wants to explore alternative interfaces for a chosen deepening candidate, use this parallel sub-agent pattern. Based on "Design It Twice" (Ousterhout) — your first idea is unlikely to be the best.
Uses the vocabulary in [LANGUAGE.md](LANGUAGE.md) — **module**, **interface**, **seam**, **adapter**, **leverage**.
## Process
### 1. Frame the problem space
Before spawning sub-agents, write a user-facing explanation of the problem space for the chosen candidate:
- The constraints any new interface would need to satisfy
- The dependencies it would rely on, and which category they fall into (see [DEEPENING.md](DEEPENING.md))
- A rough illustrative code sketch to ground the constraints — not a proposal, just a way to make the constraints concrete
Show this to the user, then immediately proceed to Step 2. The user reads and thinks while the sub-agents work in parallel.
### 2. Spawn sub-agents
Spawn 3+ sub-agents in parallel using the Agent tool. Each must produce a **radically different** interface for the deepened module.
Prompt each sub-agent with a separate technical brief (file paths, coupling details, dependency category from [DEEPENING.md](DEEPENING.md), what sits behind the seam). The brief is independent of the user-facing problem-space explanation in Step 1. Give each agent a different design constraint:
- Agent 1: "Minimize the interface — aim for 13 entry points max. Maximise leverage per entry point."
- Agent 2: "Maximise flexibility — support many use cases and extension."
- Agent 3: "Optimise for the most common caller — make the default case trivial."
- Agent 4 (if applicable): "Design around ports & adapters for cross-seam dependencies."
Include both [LANGUAGE.md](LANGUAGE.md) vocabulary and CONTEXT.md vocabulary in the brief so each sub-agent names things consistently with the architecture language and the project's domain language.
Each sub-agent outputs:
1. Interface (types, methods, params — plus invariants, ordering, error modes)
2. Usage example showing how callers use it
3. What the implementation hides behind the seam
4. Dependency strategy and adapters (see [DEEPENING.md](DEEPENING.md))
5. Trade-offs — where leverage is high, where it's thin
### 3. Present and compare
Present designs sequentially so the user can absorb each one, then compare them in prose. Contrast by **depth** (leverage at the interface), **locality** (where change concentrates), and **seam placement**.
After comparing, give your own recommendation: which design you think is strongest and why. If elements from different designs would combine well, propose a hybrid. Be opinionated — the user wants a strong read, not a menu.
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# Language
Shared vocabulary for every suggestion this skill makes. Use these terms exactly — don't substitute "component," "service," "API," or "boundary." Consistent language is the whole point.
## Terms
**Module**
Anything with an interface and an implementation. Deliberately scale-agnostic — applies equally to a function, class, package, or tier-spanning slice.
_Avoid_: unit, component, service.
**Interface**
Everything a caller must know to use the module correctly. Includes the type signature, but also invariants, ordering constraints, error modes, required configuration, and performance characteristics.
_Avoid_: API, signature (too narrow — those refer only to the type-level surface).
**Implementation**
What's inside a module — its body of code. Distinct from **Adapter**: a thing can be a small adapter with a large implementation (a Postgres repo) or a large adapter with a small implementation (an in-memory fake). Reach for "adapter" when the seam is the topic; "implementation" otherwise.
**Depth**
Leverage at the interface — the amount of behaviour a caller (or test) can exercise per unit of interface they have to learn. A module is **deep** when a large amount of behaviour sits behind a small interface. A module is **shallow** when the interface is nearly as complex as the implementation.
**Seam** _(from Michael Feathers)_
A place where you can alter behaviour without editing in that place. The *location* at which a module's interface lives. Choosing where to put the seam is its own design decision, distinct from what goes behind it.
_Avoid_: boundary (overloaded with DDD's bounded context).
**Adapter**
A concrete thing that satisfies an interface at a seam. Describes *role* (what slot it fills), not substance (what's inside).
**Leverage**
What callers get from depth. More capability per unit of interface they have to learn. One implementation pays back across N call sites and M tests.
**Locality**
What maintainers get from depth. Change, bugs, knowledge, and verification concentrate at one place rather than spreading across callers. Fix once, fixed everywhere.
## Principles
- **Depth is a property of the interface, not the implementation.** A deep module can be internally composed of small, mockable, swappable parts — they just aren't part of the interface. A module can have **internal seams** (private to its implementation, used by its own tests) as well as the **external seam** at its interface.
- **The deletion test.** Imagine deleting the module. If complexity vanishes, the module wasn't hiding anything (it was a pass-through). If complexity reappears across N callers, the module was earning its keep.
- **The interface is the test surface.** Callers and tests cross the same seam. If you want to test *past* the interface, the module is probably the wrong shape.
- **One adapter means a hypothetical seam. Two adapters means a real one.** Don't introduce a seam unless something actually varies across it.
## Relationships
- A **Module** has exactly one **Interface** (the surface it presents to callers and tests).
- **Depth** is a property of a **Module**, measured against its **Interface**.
- A **Seam** is where a **Module**'s **Interface** lives.
- An **Adapter** sits at a **Seam** and satisfies the **Interface**.
- **Depth** produces **Leverage** for callers and **Locality** for maintainers.
## Rejected framings
- **Depth as ratio of implementation-lines to interface-lines** (Ousterhout): rewards padding the implementation. We use depth-as-leverage instead.
- **"Interface" as the TypeScript `interface` keyword or a class's public methods**: too narrow — interface here includes every fact a caller must know.
- **"Boundary"**: overloaded with DDD's bounded context. Say **seam** or **interface**.
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# Reference
## Dependency Categories
When assessing a candidate for deepening, classify its dependencies:
### 1. In-process
Pure computation, in-memory state, no I/O. Always deepenable — just merge the modules and test directly.
### 2. Local-substitutable
Dependencies that have local test stand-ins (e.g., PGLite for Postgres, in-memory filesystem). Deepenable if the test substitute exists. The deepened module is tested with the local stand-in running in the test suite.
### 3. Remote but owned (Ports & Adapters)
Your own services across a network boundary (microservices, internal APIs). Define a port (interface) at the module boundary. The deep module owns the logic; the transport is injected. Tests use an in-memory adapter. Production uses the real HTTP/gRPC/queue adapter.
Recommendation shape: "Define a shared interface (port), implement an HTTP adapter for production and an in-memory adapter for testing, so the logic can be tested as one deep module even though it's deployed across a network boundary."
### 4. True external (Mock)
Third-party services (Stripe, Twilio, etc.) you don't control. Mock at the boundary. The deepened module takes the external dependency as an injected port, and tests provide a mock implementation.
## Testing Strategy
The core principle: **replace, don't layer.**
- Old unit tests on shallow modules are waste once boundary tests exist — delete them
- Write new tests at the deepened module's interface boundary
- Tests assert on observable outcomes through the public interface, not internal state
- Tests should survive internal refactors — they describe behavior, not implementation
## Issue Template
<issue-template>
## Problem
Describe the architectural friction:
- Which modules are shallow and tightly coupled
- What integration risk exists in the seams between them
- Why this makes the codebase harder to navigate and maintain
## Proposed Interface
The chosen interface design:
- Interface signature (types, methods, params)
- Usage example showing how callers use it
- What complexity it hides internally
## Dependency Strategy
Which category applies and how dependencies are handled:
- **In-process**: merged directly
- **Local-substitutable**: tested with [specific stand-in]
- **Ports & adapters**: port definition, production adapter, test adapter
- **Mock**: mock boundary for external services
## Testing Strategy
- **New boundary tests to write**: describe the behaviors to verify at the interface
- **Old tests to delete**: list the shallow module tests that become redundant
- **Test environment needs**: any local stand-ins or adapters required
## Implementation Recommendations
Durable architectural guidance that is NOT coupled to current file paths:
- What the module should own (responsibilities)
- What it should hide (implementation details)
- What it should expose (the interface contract)
- How callers should migrate to the new interface
</issue-template>
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---
name: improve-codebase-architecture
description: Explore a codebase to find opportunities for architectural improvement, focusing on making the codebase more testable by deepening shallow modules. Use when user wants to improve architecture, find refactoring opportunities, consolidate tightly-coupled modules, or make a codebase more AI-navigable.
description: Find deepening opportunities in a codebase, informed by the domain language in CONTEXT.md and the decisions in docs/adr/. Use when the user wants to improve architecture, find refactoring opportunities, consolidate tightly-coupled modules, or make a codebase more testable and AI-navigable.
---
# Improve Codebase Architecture
Explore a codebase like an AI would, surface architectural friction, discover opportunities for improving testability, and propose module-deepening refactors as GitHub issue RFCs.
Surface architectural friction and propose **deepening opportunities** — refactors that turn shallow modules into deep ones. The aim is testability and AI-navigability.
A **deep module** (John Ousterhout, "A Philosophy of Software Design") has a small interface hiding a large implementation. Deep modules are more testable, more AI-navigable, and let you test at the boundary instead of inside.
## 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](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 behaviour behind a small interface. **Deep** = high leverage. **Shallow** = interface nearly as complex as the implementation.
- **Seam** — where an interface lives; a place behaviour 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](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.**
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](../domain-model/CONTEXT-FORMAT.md) and [ADR-FORMAT.md](../domain-model/ADR-FORMAT.md).
## Process
### 1. Explore the codebase
### 1. Explore
Use the Agent tool with subagent_type=Explore to navigate the codebase naturally. Do NOT follow rigid heuristics — explore organically and note where you experience friction:
Read existing documentation first:
- Where does understanding one concept require bouncing between many small files?
- Where are modules so shallow that the interface is 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?
- Where do tightly-coupled modules create integration risk in the seams between them?
- Which parts of the codebase are untested, or hard to test?
- `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)
The friction you encounter IS the signal.
If any of these files don't exist, proceed silently — don't flag their absence or suggest creating them upfront.
Then use the Agent tool with `subagent_type=Explore` to walk the codebase. 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, show:
Present a numbered list of deepening opportunities. For each candidate:
- **Cluster**: Which modules/concepts are involved
- **Why they're coupled**: Shared types, call patterns, co-ownership of a concept
- **Dependency category**: See [REFERENCE.md](REFERENCE.md) for the four categories
- **Test impact**: What existing tests would be replaced by boundary tests
- **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](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. User picks a candidate
### 3. Grilling loop
### 4. Frame the problem space
Once the user picks a candidate, drop into a grilling conversation. Walk the design tree with them — constraints, dependencies, the shape of the deepened module, what sits behind the seam, what tests survive.
Before spawning sub-agents, write a user-facing explanation of the problem space for the chosen candidate:
Side effects happen inline as decisions crystallize:
- The constraints any new interface would need to satisfy
- The dependencies it would need to rely on
- A rough illustrative code sketch to make the constraints concrete — this is not a proposal, just a way to ground the constraints
Show this to the user, then immediately proceed to Step 5. The user reads and thinks about the problem while the sub-agents work in parallel.
### 5. Design multiple interfaces
Spawn 3+ sub-agents in parallel using the Agent tool. Each must produce a **radically different** interface for the deepened module.
Prompt each sub-agent with a separate technical brief (file paths, coupling details, dependency category, what's being hidden). This brief is independent of the user-facing explanation in Step 4. Give each agent a different design constraint:
- Agent 1: "Minimize the interface — aim for 1-3 entry points max"
- Agent 2: "Maximize flexibility — support many use cases and extension"
- Agent 3: "Optimize for the most common caller — make the default case trivial"
- Agent 4 (if applicable): "Design around the ports & adapters pattern for cross-boundary dependencies"
Each sub-agent outputs:
1. Interface signature (types, methods, params)
2. Usage example showing how callers use it
3. What complexity it hides internally
4. Dependency strategy (how deps are handled — see [REFERENCE.md](REFERENCE.md))
5. Trade-offs
Present designs sequentially, then compare them in prose.
After comparing, give your own recommendation: which design you think is strongest and why. If elements from different designs would combine well, propose a hybrid. Be opinionated — the user wants a strong read, not just a menu.
### 6. User picks an interface (or accepts recommendation)
### 7. Create GitHub issue
Create a refactor RFC as a GitHub issue using `gh issue create`. Use the template in [REFERENCE.md](REFERENCE.md). Do NOT ask the user to review before creating — just create it and share the URL.
- **Naming a deepened module after a concept not in `CONTEXT.md`?** Add the term to `CONTEXT.md` — same discipline as `/domain-model` (see [CONTEXT-FORMAT.md](../domain-model/CONTEXT-FORMAT.md)). Create the file lazily if it doesn't exist.
- **Sharpening a fuzzy term during the conversation?** Update `CONTEXT.md` right there.
- **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](../domain-model/ADR-FORMAT.md).
- **Want to explore alternative interfaces for the deepened module?** See [INTERFACE-DESIGN.md](INTERFACE-DESIGN.md).
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---
name: ubiquitous-language
description: Extract a DDD-style ubiquitous language glossary from the current conversation, flagging ambiguities and proposing canonical terms. Saves to UBIQUITOUS_LANGUAGE.md. Use when user wants to define domain terms, build a glossary, harden terminology, create a ubiquitous language, or mentions "domain model" or "DDD".
disable-model-invocation: true
---
# Ubiquitous Language