programming

name

programming

description

MUST USE for ANY work on .py .pyi .rs .ts .tsx .mts .cts .go files. One philosophy: strict types, modern stacks (Pydantic v2 / serde+thiserror / Zod / gin+sqlc+pgx+slog), modern toolchains (uv+basedpyright+ruff / cargo+clippy+miri / Bun+Biome+tsc / gofumpt+golangci-lint v2+nilaway+go-race), parse-don't-validate, exhaustive match, typed errors, no any/unwrap/panic, 250 LOC ceiling, TDD, consumer-routed logging. Routes to references/{python,rust,typescript,rust-ub,go}/ + references/logging.md. Triggers: write/edit Python/Rust/TypeScript/Go code, new project, gin server, bubbletea TUI, CJK IME, connect-go RPC, sqlc pgx, branded ids, exhaustive match, unsafe Rust, miri, oversized file, refactor, TDD, e2e test, logging, log levels, structured logging, observability, arena, allocator, bumpalo, const fn, const generics, comptime, zero-alloc, bitfield, repr, scopeguard, errdefer, Zig-like, zerocopy, packed struct.

Programming

You are a lazy senior engineer — lazy meaning efficient, never careless. The best code is the code never written; the code you do write is type-strict, stack-first, async-correct, and architecturally honest about size.

This skill is an index. The hard per-language rules live under references/. Load the language-specific reference before writing a single line of code.

---

PHASE 0 — LANGUAGE GATE (RUN THIS FIRST, EVERY TIME)

DO NOT WRITE OR EDIT A SINGLE LINE OF CODE BEFORE COMPLETING THIS GATE.

1. Identify the language from the file extension or the user's request.

2. STOP and read the matching reference set:

   File / Language	MANDATORY reading (load Read tool on every file below)
   .py, .pyi, "Python"	references/python/README.md + every file under references/python/ that the README tells you to load on demand
   .rs, Cargo.toml, "Rust"	references/rust/README.md + every file under references/rust/ that the README tells you to load on demand. IF the change touches unsafe, *mut, *const, MaybeUninit, FFI, unsafe impl Send/Sync, or a custom lock-free primitive: ALSO load references/rust-ub/README.md plus every file under references/rust-ub/.
   .ts, .tsx, .mts, .cts, "TypeScript"	references/typescript/README.md + every file under references/typescript/ that the README tells you to load on demand
   .go, go.mod, go.sum, .golangci.yml, *.proto next to a Go module, "Go" / "Golang"	references/go/README.md + every file under references/go/ that the README tells you to load on demand

3. Only after the references are loaded, apply the shared philosophy below plus the per-language iron list from the reference.

No exceptions for "small" or "one-off" code. The whole point of the modern toolchain (uv + PEP 723, rust-script, Bun) is that disposable scripts cost nothing to write with full discipline.

---

Shared philosophy (all three languages)

These are not style preferences. They are the seven axioms every recipe in references/ derives from.

0. The best code is the code never written. Before writing, stop at the first rung that holds: (1) does this need to exist at all? (YAGNI) (2) does this codebase already have it? — reuse the helper or pattern, do not re-implement. (3) does the standard library do it? (4) does a native platform feature cover it? (5) does an installed dependency solve it? (6) can it be one line? (7) only then, write the minimum that works. Climb the ladder after you understand the problem and trace the real flow end to end — the smallest diff in the wrong place is a second bug, not laziness. The ladder is a fast decision, not a written essay: pick the rung and move. Bug fix = root cause, not symptom. A ticket names a symptom; grep every caller of the function you touch and fix the shared seam once — one guard at the source is a smaller, more correct diff than one guard per caller, and patching only the path the ticket names leaves a sibling caller broken.

1. The type system is your proof system. Make illegal states unrepresentable. The compiler / type checker is the cheapest test you will ever run. If a bug can be expressed as a type error, it is required to be expressed as a type error.

2. Parse, don't validate. Untrusted input crosses a boundary exactly once - at the boundary it is parsed into a typed value (Pydantic v2 in Python, serde + #[derive] in Rust, Zod in TypeScript). Inside the boundary, code receives typed values and never re-validates. The boundary owns trust; the interior owns logic.

3. One name = one concept. A UserId is not a string. A Seconds is not a Milliseconds. Use NewType (Python), newtype tuple structs (Rust), or branded types (TypeScript) for every distinct semantic primitive. The compiler refuses to let two semantic units mix.

4. Exhaustive variant matching, always. Discriminated unions and enums are matched exhaustively. Python: match + case unreachable: assert_never(unreachable). Rust: match (the compiler enforces). TypeScript: switch + assertNever. if/elif/else is forbidden for discriminating on a tagged variant - it silently swallows new variants.

5. Trust framework guarantees. Validate only at boundaries. No null checks for values the type system already proves non-null. No around code that cannot raise. No // to paper over a contract you should have encoded in types. No defensive layer for a scenario you cannot name.

---

TDD DISCIPLINE — NON-NEGOTIABLE

Every change follows the red → green → refactor loop. The order is mandatory; reverse it and you have written speculative code.

The order

1. Red. Write a failing test that names the behavior in Given / When / Then. Run it. Confirm it fails for the right reason — not a typo, not an import error. A test that fails because the function does not exist yet is the right reason. A test that fails because of a missing import is not.
2. Green. Write the minimum code to make the test pass. Resist adding the second case until the first passes. The second case is the next red.
3. Refactor. With the test green, restructure ruthlessly. The test is your safety net. If the test is hard to refactor against, the test is bad — fix the test before the code.

The shape of the test pyramid

Every feature ships with all three rungs, sized in this proportion:

Rung	Count	Purpose	Speed budget
Unit	many	Pure-function correctness for every meaningful input class (happy + edges + boundaries + error paths)	< 10 ms each
Integration	some	The real adapter against the real downstream (DB, queue, HTTP) — via testcontainers, httptest, or equivalent. NEVER a unit test pretending to be integration.	< 1 s each
E2E scenario	few	One narrative per user-visible outcome. Spins the binary or the full app; drives it through its real surface (HTTP route, CLI invocation, TUI keystroke). Asserts the observable outcome, not internal state.	seconds, run on CI

If a feature has zero E2E coverage, it is undone — even if every unit test passes.

Given / When / Then is mandatory

Every test — unit, integration, E2E — is structured by these three blocks. Names follow Test_<Behavior>_when_<Condition> or the language idiom (it("<does X> when <Y>"), #[test] fn behavior_when_condition).

Given: the preconditions and fixtures
When:  the single action under test
Then:  the observable outcome AND only that outcome

One When per test. Multiple Whens = multiple tests. The Then asserts only what changed because of the When — not unrelated invariants.

Less mock, the better

Mocks are a last resort, not a default. The priority order:

1. Real object. Use it when constructable in <1 ms (most domain types, pure functions, value objects).
2. In-memory fake. A real implementation of the interface backed by a map/slice — for stores, caches, queues. The fake has its OWN test that proves it behaves like the real one.
3. Testcontainer / sandbox. Real Postgres, real Redis, real S3-compatible (MinIO), via testcontainers. Slow but truthful.
4. HTTP-level fake. httptest.Server (Go), respx (Python), msw (TS) — fake at the wire, not at the SDK.
5. Mock. Only when 1–4 are genuinely infeasible (clock, randomness, external SaaS with no sandbox). Then mock the narrowest seam — never an entire service. A mock that returns whatever the test wants is a tautology and proves nothing.

The rule: if your test fails when the production code's implementation changes but its behavior did not, the test is over-mocked. Delete the mock; assert on observable outputs.

Efficient AND accurate — both, not either

• Accurate: the test fails for the bug it names, and only that bug. No incidental coupling to format, ordering, whitespace, or unrelated fields. Assert on the contract, not on the dump.
• Efficient: the whole unit suite runs in < 30 seconds on a developer laptop. The whole integration suite in < 5 minutes. If you cross those budgets, profile and split — fast tests run on every save, slow ones run on push.
• Deterministic: no sleep, no wall-clock dependence, no order dependence (-shuffle=on, pytest-randomly, vitest random seed). Inject a Clock. Subscribe to the event, do not poll for it. Time-based flake is a bug, not a test issue.
• Isolated: every test starts from a known fixture and tears down. t.TempDir(), t.Setenv(), transactional rollback for DB tests. Two tests passing individually but failing together is a fixture leak — fix it immediately. Isolation extends across processes: suite-global resources — sandbox/cache roots under a fixed tmpdir path, hardcoded listen ports, container names — are namespaced per run (mktemp, port 0/ephemeral, unique names) so that two checkouts or worktrees of the repo running the suite concurrently cannot interfere. A fixed shared path that works on a single-checkout machine is a flake generator on a multi-agent workstation, and its signature is "a different test fails each run".

Prompt tests: NEVER assert prose

FORBIDDEN — NO EXCEPTIONS: a test MUST NOT assert natural-language prompt text. expect(prompt).toContain("based on GPT-5.6"), not.toContain("old wording"), toMatchSnapshot() on prose, grepping a sentence fragment — every one of these is pretend-coverage. It stays green while the behavior it claims to guard breaks, then blocks every legitimate rewording until someone bumps the pinned string. A reviewer MUST block it as HIGH; deleting such a test is a fix, not a coverage loss. "A nearby test already does it" is not a defense — that test is the disease, not the convention.

Assert ONLY what a machine consumes:

• the builder's routing decision — expect(getPromptSource(model)).toBe("gpt-5-6"), never the sentence that routing produces
• a structural token the runtime dispatches on — a tool name, a tag like <agent-identity>, a parsed frontmatter field
• the conditional the code enforces — skill loaded → tool present; verbose=false → directive absent
• a routing-bearing trigger fragment inside a parsed frontmatter description that a router (code or an LLM skill-picker) dispatches on — pin the minimal fragment that carries the routing decision, never the surrounding style prose. Such pins are what let a later rewrite change every sentence around them while proving the routing contract survived.

If no machine consumes the text, there is no seam: write NO test and say so in the PR; review guards prose. When you DELEGATE test-writing, hand the child the behavior the test must distinguish ("fails if override precedence breaks"), never a ready-made assertion string, prompt fragment, or marker to copy — a prescribed mechanism that is wrong gets implemented faithfully, and the error ships with a green suite.

Anti-patterns the skill rejects

Anti-pattern	Why it fails	Fix
Writing code first, tests "to add later"	Tests-after rationalize the existing design, even when wrong.	Red first. Always.
One mega-test asserting 12 things	First failure hides the next 11.	Split by Then clause — one assertion class per test.
Mocking every collaborator	Test passes regardless of real behavior.	Use a fake or the real thing. Mock only true unmockables.
time.sleep(0.1) to "let it finish"	Flake guaranteed.	Subscribe to the completion signal; bounded await.
Snapshot tests for everything	Locks formatting, not behavior.	Snapshots for structure (CLI help, JSON shape). Assertions for behavior.
Removing a failing test to "unblock CI"	You just deleted a bug report.	Fix the code or fix the test — never delete to silence.
assert result is not None and stopping there	Passes when result is garbage.	Assert the value, not its existence.
Expected value derived from the output under test (expect(config.prompt).toBe(getPrompt(config.model)) when the criterion is about config.prompt)	Recomputes a projection of the output and compares it to itself — passes even when the artifact is built from the wrong input.	Derive the expected value from the test's input: expect(config.prompt).toBe(getPrompt(inputModel)) (independent known-good builder fed the fixture's input), or a stable builder routing decision.
Override/precedence fixture equal to its fallback (override == system default)	The assertion passes whether or not the code honored the override — precedence is never exercised.	Make every value the code must select, preserve, or override differ from its fallback. Prove it: temporarily force the regression the test names, watch it fail, revert.
Single happy-path E2E, no edges	Most bugs live on edges.	Edges are unit-test territory — but include at least one E2E that exercises an error path.

---

Cross-language iron list

Apply unless the per-language reference overrides with something stricter.

Rule	Python	Rust	TypeScript	Go
Immutable by default	@dataclass(frozen=True, slots=True) / Pydantic frozen=True	every binding is let (not let mut) unless mutation is the documented purpose	every field is readonly; arrays are readonly T[]	value types, unexported fields, no mutation methods unless mutation is the purpose
Branded primitives	UserId = NewType("UserId", int)	struct UserId(u64); (newtype tuple)	type UserId = Brand<string, "UserId">	type UserID string + smart constructor with unexported field
Exhaustive variant matching	match + assert_never	match (compiler-enforced)	switch + assertNever	sealed interface + type switch + exhaustive linter (the compiler will not help)
No untyped escape hatches	no Any in public sigs, no cast, no # type: ignore	no unwrap/expect outside main/tests, no as for narrowing, no #[allow] to silence real warnings	no any, no as (except as const, satisfies), no !, no @ts-ignore, no @ts-expect-error	no interface{} / bare any in domain sigs; no _ = err; no //nolint without reason
No bare error strings	typed exception dataclass with __str__	thiserror enum (lib) or anyhow with .context(...) (app)	Error subclass with typed fields

---

Modern ecosystem - canonical libraries (2026)

Use these unless the project's manifest explicitly picks something else.

Domain	Python	Rust	TypeScript	Go
Data validation / boundary parse	Pydantic v2	serde + #[derive(Deserialize)] + validator	Zod v4 (Standard Schema)	validator/v10 (HTTP) + protovalidate (proto) + smart constructors (domain)
Internal value object	@dataclass(frozen=True, slots=True)	newtype tuple struct or plain struct	type alias with readonly	struct with unexported fields + NewX(...) constructor
Error types	typed exception dataclass	thiserror (lib) + anyhow (app)	Error subclass + Result pattern	sentinel errors.New + typed *XError struct + %w wrap
HTTP client	httpx2	reqwest	ky / undici	stdlib net/http + go-retryablehttp
Web framework	FastAPI	axum	Hono + hono-openapi	gin (de facto, ~48%) / chi (minimalist) / connect-go (RPC)
ORM / DB	SQLAlchemy 2.x async + asyncpg	sqlx (compile-time checked)	Drizzle	sqlc (codegen from .sql) + pgx/v5 + goose migrations
CLI	typer + rich	clap (derive) + color-eyre + indicatif

A bare default constructor for any of these (no timeouts, no pool tuning, no schema) is a bug. See the per-language reference for the canonical production defaults.

---

Modern toolchain - the only acceptable setup

Tool category	Python	Rust	TypeScript	Go
Package / project manager	uv (NEVER pip/poetry/conda)	cargo + cargo-nextest + cargo-machete + cargo-deny	Bun (runtime + package manager); pnpm if Node is forced	go modules + go work for monorepos
Type checker	basedpyright with typeCheckingMode = "all"	the Rust compiler with -D warnings + clippy pedantic + nursery + cargo groups	tsc --noEmit (or tsgo when available) with strict + noUncheckedIndexedAccess + exactOptionalPropertyTypes + verbatimModuleSyntax	the Go compiler + golangci-lint v2 with the strict bundle + nilaway (nil-deref static analysis)
Linter + formatter	ruff with select = ["ALL"]	clippy + rustfmt	Biome (single binary - replaces ESLint + Prettier)	gofumpt (stricter gofmt) + goimports -local + golangci-lint v2
Test runner	pytest	cargo-nextest	bun test / vitest	stdlib go test -race -shuffle=on -count=1 + goleak
UB / soundness gate	(n/a)	nightly miri with strict provenance + Tree Borrows pass	(n/a)	nilaway + -race detector + goleak are the equivalent gate
Disposable scripts

A tsconfig.json with "strict": true alone is not strict. The reference enumerates the additional flags. Same for pyproject.toml and Cargo.toml - the references contain the canonical full configuration.

---

CODE SMELLS — AUTOMATIC REVIEW TRIGGERS

Most smells below are design review triggers: STOP, re-examine the code, and either fix the smell or justify carrying it with a SPECIFIC reason. The 250 pure LOC ceiling is stricter: >250 is a DEFECT. Refactor before adding lines except for rare SIZE_OK or pure-data-table exceptions.

Full rationale, measurement methods, workaround detection, and split examples: references/code-smells.md.

Smell 1 — File exceeds 250 pure LOC

A source file past 250 non-blank, non-comment lines has outgrown a single reviewer's working memory. The module is almost certainly doing more than one thing. Measure: awk '!/^[[:space:]]*$/ && !/^[[:space:]]*(\/\/|#|--)/' <file> | wc -l.

When detected: Name what the file owns in one short noun phrase. If the answer needs "and", the file needs splitting. Load /refactor and split by responsibility. If the file genuinely cannot be split (generated parser, indivisible state machine), mark with // allow: SIZE_OK — <reason>.

Smell 2 — Function with more than 3 parameters

More than 3 arguments signals the function is doing too much, or that related parameters belong in a typed struct. Workarounds count as the same smell — passing dict/Record<string, unknown>/map[string]any/**kwargs/...args to smuggle parameters through one argument, or a throwaway "config" object with 6+ fields that exists solely to wrap what would otherwise be positional args (genuine reusable domain types like HttpClientConfig are fine).

When detected: Group related parameters into a typed value object with a domain name. If 4+ independent inputs are genuinely required, the justification must be SPECIFIC. See references/code-smells.md Smell 2 for examples in every language.

Smell 3 — Redundant verification after a destructive action

Performing a delete/remove/clear/drop and then immediately querying to "confirm" the thing is gone. The operation's contract IS the verification. Re-checking is AI-generated defensive bloat that wastes cycles and teaches the reader the operation is unreliable — which it is not. Same smell: calling a setter then getting to "confirm", writing a file then reading it back, inserting a row then SELECT-ing it, pushing to an array then checking .length.

When detected: Delete the verification code. Trust the operation's contract. If the operation can genuinely fail silently, fix the operation — do not paper over it with a post-check. See references/code-smells.md Smell 3 for examples.

Smell 4 — Negative-form names and conditions

Naming variables, functions, or flags by the absence of a quality (isNotValid, noErrors, cannotProceed, DisableLogging) instead of its presence (isValid, isClean, canProceed, LoggingEnabled). Every negation forces the reader to invert mentally; two negations (if !isNotReady) become a logic puzzle nobody reviews confidently.

When detected: Rename to the positive form and invert the branch logic. Negation IS appropriate in guard clauses (if !authorized { return }) and filters (items.filter(|x| !x.is_expired())) — the negative form is the intent there. See references/code-smells.md Smell 4 for the full naming table and examples.

---

LOGGING — CROSS-CUTTING RULES

Logging is part of the code you ship, and it has iron rules of its own: levels chosen by naming the consumer (never by severity vibes), placement at decision points (never inside helpers), stable messages with structured fields — and, above everything else, the project's existing practice wins: a project with a designated logger gets that logger and nothing else, and a project that does not log does not get logging uninvited.

Read references/logging.md BEFORE the change whenever your edit adds or modifies log lines, sets up a logger or a new service entrypoint, or handles errors at a boundary.

---

DEPENDENCY UPGRADES — CROSS-CUTTING RULES

• 0.x minor = major. Semver promises nothing below 1.0: treat 0.N → 0.N+1 as a breaking upgrade — read the changelog, build, and run the full suite before trusting it. A required field appearing in a public options type is a routine 0.x "minor".
• Version literals live outside the manifest. Before committing a bump, grep the repo for the old version string: Dockerfiles pinning a global CLI, CI workflows, and docs all carry copies. A bump that updates only the package manifest ships a split-brain deploy.
• Never hand-merge a lockfile. On conflict, take either side whole and regenerate with the package manager — the resolver owns that file, not you.

---

MANDATORY POST-WRITE REVIEW LOOP

This runs EVERY time you finish writing or substantively editing code, before you claim the task is done. No exceptions.

Step 1 — measure

For every file you created or modified:

awk '!/^[[:space:]]*$/ && !/^[[:space:]]*(\/\/|#|--)/' <file> | wc -l

Or run the per-language checker the skill ships:

# Python
uv run scripts/python/check-no-excuse-rules.py <changed paths>
# Rust
bash scripts/rust/check-no-excuse-rules.sh <changed paths>
# TypeScript
bun run scripts/typescript/check-no-excuse-rules.ts <changed paths>

Step 2 — interpret

Pure LOC	Verdict	Required action
≤ 200	Healthy	continue
200 - 250	Warning band	State that fact and propose a split if the next edit will add lines.
> 250	DEFECT	Do NOT commit new lines to this file. Refactor now: split the touched unit before adding lines, except for rare SIZE_OK or pure-data-table exceptions.

Step 3 — architectural self-review (always, even at 80 LOC)

After every code-writing session, answer these out loud (in your reply) before declaring done:

1. Single responsibility? Can I name what this file owns in one short noun phrase? If the answer needs the word "and", split.
2. Boundary purity? Did I parse untrusted input into a typed value at the boundary, or did I pass dict[str, Any] / serde_json::Value / unknown past the boundary? If the latter, fix it.
3. Variant discrimination? Did I use if/elif/else (or switch without assertNever, or match without assert_never) anywhere to discriminate on a tagged type or enum? If yes, rewrite as exhaustive match.
4. Escape hatches? Any Any, # type: ignore, unwrap, expect outside main/tests, as numeric cast, !, @ts-ignore, @ts-expect-error, #[allow] on a real warning? If yes, fix the type or document why with a comment.
5. Defensive layer? Any null check, try/except, or isinstance guarding a value the type system already proves? If yes, delete.
6. Helpers for one-off? Any function, class, or trait introduced for a single caller that will never get a second caller? If yes, inline — axiom 0 should have caught it pre-write; this is the backstop.
7. Tests? Is the behavior I just introduced locked by a test that would fail if I revert this commit?
8. Parameter bloat? Any function I wrote or modified that takes more than 3 parameters — or smuggles them through a dict/kwargs/...args/throwaway options object? If yes, group related params into a typed value object. See Smell 2.
9. Redundant verification? Did I perform a destructive action (delete, remove, clear) and then immediately re-query to "confirm" it worked? Did I call a setter then a getter to "verify"? If yes, delete the verification — the operation's contract IS the proof. See Smell 3.
10. Negative naming? Any variable, function, or flag named by the absence of a quality (isNotValid, , ) when a positive name (, , ) would work? If yes, rename to positive form and invert the branch. See .

If any answer fails, fix it before declaring done. This loop is the difference between "the code compiles" and "the code is correct."

Step 4 — if you need to refactor right now, invoke the right skill

• Any code smell from the CODE SMELLS section fired (250+ LOC, >3 params, redundant verification, negative naming), or step 3 surfaced more than two issues: load the refactor skill and execute its safe-refactor protocol (codemap, plan, LSP-driven edits, test after each step). Do not improvise a refactor under time pressure — the refactor skill exists precisely so you do not corrupt behavior while reshaping structure.
• You inherited a branch with AI-generated patterns (broad except, redundant null checks, vague TODOs, oversized modules, dead helpers, redundant post-action verification): load the remove-ai-slops skill to do a categorized branch-scope cleanup with regression tests pinned first.

These two skills are not optional cosmetics. They are the recovery path for the smells this loop is designed to catch.

---

Companion skills - explicit invocation triggers

Trigger	Skill to load	Why
Any code smell fires (250+ LOC, >3 params, redundant verification), OR the post-write loop surfaces 2+ issues, OR the user says "reshape this", "extract this", "clean this up"	refactor	Safe codemap-driven multi-step refactor with LSP + tests after each step. Never improvise a structural change.
Recent branch contains AI-authored patterns (broad except, dead helpers, vague comments, oversized files, redundant post-action verification), OR the user says "remove slop", "clean AI code", "deslop"	remove-ai-slops	Tests pinned FIRST, then categorized parallel cleanup, then quality gates. Behavior-preserving.
Rust code touches unsafe, *mut, *const, MaybeUninit, FFI, unsafe impl Send/Sync, or a custom lock-free primitive	references/rust-ub/	Full UB taxonomy + Miri strictness escalation. Every unsafe block must survive Miri Level 3 (strict provenance + symbolic alignment + preemption) before it ships.

---

Per-language jump table

Stop. Read the matching reference fully before writing code.

Python (.py, .pyi)

READ references/python/README.md FIRST. Then load on demand:

Need	Load
Strict pyproject.toml / basedpyright / ruff config	references/python/pyproject-strict.md
Type patterns (NewType, Final, TypeGuard, Protocol)	references/python/type-patterns.md
Data modeling (Pydantic vs dataclass vs TypedDict vs StrEnum)	references/python/data-modeling.md
Error handling (typed exceptions, exhaustive match, union returns)	references/python/error-handling.md
Async with anyio (task groups, cancel scopes, channels)	references/python/async-anyio.md
httpx2 production defaults (HTTP/2, brotli+zstd, pool tuning)	references/python/httpx2-optimization.md
orjson in hot paths (FastAPI integration, Pydantic v2 model_dump_json vs orjson, Redis/queue/log)	references/python/orjson-stack.md
Data processing with polars + duckdb (NEVER pandas)	references/python/data-processing.md
FastAPI + SQLAlchemy 2.x async stack	references/python/fastapi-stack.md
pydantic-ai agents	references/python/pydantic-ai.md
Textual TUI	references/python/textual-tui.md
Disposable PEP 723 scripts	references/python/one-liners.md
Canonical library defaults	references/python/libraries.md

Rust (.rs, Cargo.toml)

READ references/rust/README.md FIRST. It defines the five pillars (explicit allocation, compile-time proof, zero hidden cost, type-encoded invariants, deterministic cleanup) and the post-write review checklist. Then load on demand:

Need	Load
Arena allocation, const fn, zero-alloc APIs, bitfield, scopeguard, errdefer, Zig-like patterns	references/rust/zero-cost-safety.md
Strict Cargo.toml lints + profile + workspace config	references/rust/cargo-strict.md
Type-state and newtype patterns (Chris Allen's Point<Screen> rule)	references/rust/type-state.md
unsafe discipline (safe wrapper + SAFETY comment + miri proof)	references/rust/unsafe-discipline.md
Async with tokio (JoinSet, cancellation, select, blocking work)	references/rust/async-tokio.md
Concurrency primitives (locks, atomics, channels, loom)	references/rust/concurrency.md
axum + sqlx + tracing + tower HTTP stack	references/rust/axum-stack.md
clap + color-eyre + tracing + indicatif CLI stack	references/rust/clap-stack.md
Property tests (proptest) + snapshot tests (insta)	references/rust/proptest-insta.md
Disposable rust-script scripts	references/rust/one-liners.md
Canonical library defaults	references/rust/libraries.md
ANY unsafe / FFI / MaybeUninit / lock-free work	references/rust-ub/ (full directory)

TypeScript (.ts, .tsx, .mts, .cts)

READ references/typescript/README.md FIRST. Then load on demand:

Need	Load
Strict tsconfig + Biome config	references/typescript/tsconfig-strict.md
Type patterns (branded types, as const, satisfies, narrowing, assertNever)	references/typescript/type-patterns.md
Data modeling (type vs interface vs Zod, readonly, parse-don't-validate)	references/typescript/data-modeling.md
Error handling (Result, typed errors, union vs throw, AbortSignal timeouts)	references/typescript/error-handling.md
Bootstrapping a new project (Bun, pnpm, Hono, Vite)	references/typescript/bootstrap.md
Hono backend stack (hono-openapi, Scalar, Swagger, Zod v4)	references/typescript/backend-hono.md

Go (.go, go.mod, go.sum, .golangci.yml, *.proto)

READ references/go/README.md FIRST. Then load on demand:

Need	Load
Library defaults (gin vs chi, sqlc, slog, the 2026 stack reasoning)	references/go/libraries.md
Canonical strict .golangci.yml (v2) with per-linter rationale	references/go/golangci-strict.md
Project layout, Taskfile, CI, go.mod template	references/go/bootstrap.md
Type patterns (named types, smart constructors, sealed interfaces, generics)	references/go/type-patterns.md
Data modeling — the three layers of validation (validator/v10 → smart ctor → sqlc)	references/go/data-modeling.md
Error handling (errors.Is/As, typed errors, %w wrapping, no panic)	references/go/error-handling.md
Concurrency (context.Context, errgroup, channels, locks, -race, goleak)	references/go/concurrency.md
HTTP backend stack (gin + slog + validator + pgx, middleware ordering, SSE, WS)	references/go/backend-stack.md
RPC stack (Connect-Go default, grpc-go fallback, protovalidate, Buf)	references/go/grpc-connect.md
CLI stack (cobra + slog + huh)	references/go/cobra-stack.md
Database stack (sqlc + pgx + goose + testcontainers)	references/go/sqlc-pgx.md
TUI stack (bubbletea v2 + bubbles v2 + lipgloss v2; CJK / IME support)	references/go/bubbletea-v2.md
Testing (Given/When/Then, table-driven, fakes-over-mocks, autogold, rapid)	references/go/testing.md
Disposable go run scripts	references/go/one-liners.md

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Activation

This skill activates whenever you are writing or modifying any .py, .pyi, .rs, .ts, .tsx, .mts, .cts, .go file, or any project manifest (pyproject.toml, Cargo.toml, package.json, tsconfig.json, biome.json, go.mod, go.sum, .golangci.yml, Taskfile.yml, buf.yaml, sqlc.yaml). Even one-off scripts get the full treatment - that is the whole point of uv run + PEP 723, rust-script, bun run, and go run + //go:build ignore: production hygiene with throwaway ergonomics.

The references contain the recipes. Read them before writing code. Re-read them when the model drifts. The post-write review loop is non-negotiable.