active-svelte/docs/conventions.md

# Active conventions

This document captures the **mandatory naming and structure
conventions** for the Active framework codebase. Every new module,
type, constant, and file must comply. Existing code that drifts from
these rules is treated as audit debt and migrated module by module.

The goal is single-rule homogeneity: a developer learns the convention
once and applies it everywhere. No exceptions without an explicit
decision recorded here.

---

## 1. Module identifier — full English word

Every artifact and lib that pairs with one is identified by a stable
**full English word** that doubles as filesystem name, alias and
canonical wire identifier:

| Folder | Alias | Wire / value |
|---|---|---|
| `arts/active-app/`, `libs/active-app/` | `$active-app` | `'app'` |
| `arts/auth/`, `libs/auth/`, `svrs/auth/` | `$auth` | `'auth'` |
| `arts/bus/`, `libs/bus/` | `$bus` | `'bus'` |
| `arts/cache/`, `libs/cache/`, `svrs/cache/` | `$cache` | `'cache'` |
| `arts/connection/` | `$connection` | `'connection'` |
| `libs/dom/` | `$libs/dom` | `'dom'` |
| `libs/errs/` | `$libs/errs` | `'errs'` |
| `arts/frontend/` | `$frontend` | `'frontend'` |
| `arts/formats/` (+ `currency/`, `numbers/`, `units/`, `dates/`) | `$formats` | `'formats'` |
| `arts/http/`, `libs/http/` | `$http` | `'http'` |
| `arts/lang/`, `libs/lang/` | `$lang` | `'lang'` |
| `arts/logger/`, `libs/logger/` | `$logger` | `'logger'` |
| `arts/permissions/`, `libs/permissions/`, `svrs/permissions/` | `$permissions` | `'permissions'` |
| `arts/session/` | `$session` | `'session'` |
| `arts/sium/` | `$sium` | `'sium'` (proper name of the validator) |
| `arts/storage/` | `$storage` | `'storage'` |
| `arts/timer/`, `libs/timer/` | `$timer` | `'timer'` |

### Special cases

- **`active-app`** uses a hyphen in the alias because `$app` is a
  reserved namespace in SvelteKit (`$app/stores`, `$app/navigation`).
  The constants and class names still use `App` / `APP_*`; the
  `active-` prefix only appears in filesystem and alias.

- **`lang`** and **`sium`** are kept as-is. `lang` is the standard
  HTML/i18n term (`<html lang="…">`); `sium` is the proper name of
  the validator (like `zod`, `valibot`). They are not abbreviations.

- **`errs`** is the framework's own error system. Kept short
  intentionally because it sits at the foundation; lowering it to
  `'errs'` keeps the wire format compact for codes like
  `'errs::format_invalid'`.

### What this replaces

Earlier the codebase used 4-letter abbreviations (`buss`, `cach`,
`conn`, `sess`, `stor`, `timr`, `logr`, `aapp`, `fmts`, `fend`,
`perm`, `curr`, `unts`, `nums`). That convention has been removed:
abbreviations created cognitive load with no real benefit.

---

## 2. Constant naming — `<MOD>_<CATEGORY>_<NAME>`

Every categorical module-level constant follows the pattern:

```
<MOD>_<CATEGORY>_<NAME>
```

- **`<MOD>`** — the module's identifier in caps. For most modules this
  matches the filesystem (`STORAGE_*`, `BUS_*`, `CACHE_*`, `LOGGER_*`,
  `TIMER_*`, `CONNECTION_*`, `SESSION_*`, `FORMATS_*`, `FRONTEND_*`,
  `HTTP_*`, `LANG_*`, `AUTH_*`, `SIUM_*`, `DOM_*`, `ERRS_*`).

  **Exception**: the `permissions` module uses `PERMISSION_*` (singular)
  because the constants describe the concept ("a permission effect",
  "a permission decision"), not the module collection. The `S` is
  reserved for the folder/alias/wire which group the system as a
  whole.

  **Exception**: the `active-app` module uses `APP_*` (without the
  `active-` prefix) because the `active-` prefix is purely a
  disambiguator forced by SvelteKit's reserved `$app` namespace.

- **`<CATEGORY>`** — what kind of constant it is. Picked from the
  fixed vocabulary in section 3.
- **`<NAME>`** — the specific value's identifier in
  `UPPER_SNAKE_CASE`.

### Examples

```ts
// good
BUS_DIAGNOSTIC_EVENTS
BUS_DEFAULT_MAX_LISTENERS_PER_EVENT
BUS_ERR_DISPOSED
SESSION_EVENT_LIFECYCLE_ADOPTED
PERMISSION_METHOD_CHECK
TIMER_STATE_PENDING
CONNECTION_REASON_AUTH_FAILED
CACHE_LIMIT_DEFAULT_MAX_ENTRIES
STORAGE_MODULE                       // value: 'storage'
APP_MODULE                           // value: 'app'
PERMISSION_MODULE                    // value: 'permissions'

// bad
BUSS_DIAGNOSTIC_EVENTS               // 4-letter alias is dead (rule 1)
DEFAULT_TIMER_SCOPE_SEPARATOR        // category before module (rule 2)
PERMISSIONS_EFFECT_ALLOW             // wrong shape: concept is singular
AUTO_REAUTH_USER_IDENTITY_CHANGE     // missing module prefix (rule 1)
```

### Sub-categories

When a category needs internal hierarchy, append additional segments
in the `<NAME>` part, not in `<CATEGORY>`:

```ts
// good
BUS_LISTENER_ERROR_MODE_THROW
SESSION_EVENT_LIFECYCLE_ADOPTED
SESSION_EVENT_LIFECYCLE_REVOKED
PERMISSION_DEFAULT_REMOTE_FAILURE_BACKOFF_MS

// bad
BUS_LISTENER_ERR_MODE_THROW       // category split across underscores
```

---

## 3. Category vocabulary — fixed list

Only these category tokens are allowed. Adding a new category is a
deliberate decision recorded in this document, not an ad-hoc choice
inside a module.

| Category | Use |
|---|---|
| `MODULE` | The module's identifier as a string constant. **Single source of truth** for the module's identity. Used wherever the module's identifier is needed: logger category, error message prefix, event scope, etc. Every module declares exactly one `<MOD>_MODULE = '<value>'`. |
| `ERR` | Error codes (`ErrCode` values from `$libs/errs`) |
| `EVENT` | Bus or lifecycle event names (string discriminators) |
| `DIAGNOSTIC_EVENTS` | Event values published through `Logger` (catalog object) |
| `METHOD` | Method labels for error messages (`ensureLive(METHOD)`) |
| `STATE` | Tagged-union state discriminators |
| `STATUS` | Tagged-union status discriminators |
| `KIND` | Tagged-union kind discriminators |
| `REASON` | Tagged-union reason discriminators |
| `TYPE` | Tagged-union type discriminators (when none of the above fits) |
| `MODE` | Mode discriminators (e.g. listener error mode) |
| `DEFAULT` | Default values for options |
| `LIMIT` | Maximum / minimum values |
| `ID_PREFIX` | Prefix used by ID factories |
| `LOG_MSG` | Log message strings |
| `ERROR_MSG` | Error message strings (technical, dev-facing). Must use a template referencing `<MOD>_MODULE` for the prefix, never a hardcoded literal: `` `[${MOD_MODULE}] ...` ``. |
| `ERROR_MESSAGES` | Catalogue object (`<MOD>_ERROR_MESSAGES: ErrorMessages`) indexed by `ErrCode`. Static strings or `(...args) => string` factories. |
| `CONTEXT_KEY` | Svelte context keys |

Categories that are **not** in this list (e.g. `AUTO_REAUTH`,
`AUTO_INVALIDATE`, `BACKOFF`, `BUFFER_POLICY`, `CHANNEL_STATE`) must
fold into one of the above. Examples:

- `CONNECTION_AUTO_REAUTH_*` → `CONNECTION_REASON_AUTO_REAUTH_*` if
  the value drives a "why this happened" branch, or
  `CONNECTION_MODE_AUTO_REAUTH_*` if it configures behavior.
- `CACHE_AUTO_INVALIDATE_*` → `CACHE_MODE_AUTO_INVALIDATE_*`.
- `CONNECTION_BUFFER_POLICY_*` → `CONNECTION_MODE_BUFFER_*`.

When in doubt, propose the addition here before introducing it.

---

## 4. Error codes (`ErrCode`) — special case under rule 2

Error codes from `$libs/errs` follow rule 2 with category `ERR`. Each
module declares one `<MOD>_ERR` seed and builds the individual codes
from it via `errCode(parent, segment)` so the module string never
appears as a literal in error declarations:

```ts
import { errCode, moduleSeed, type ErrCode, type ModuleSeed } from '$libs/errs';

export const BUS_ERR: ModuleSeed = moduleSeed('bus');                          // 'bus::'
export const BUS_ERR_DISPOSED: ErrCode = errCode(BUS_ERR, 'disposed');         // 'bus::disposed'
export const BUS_ERR_INVALID_PAYLOAD: ErrCode = errCode(BUS_ERR, 'invalid_payload');
export const BUS_ERR_LISTENER: ErrCode = errCode(BUS_ERR, 'listener');         // 'bus::listener'
export const BUS_ERR_LISTENER_FAILED: ErrCode = errCode(BUS_ERR_LISTENER, 'failed'); // 'bus::listener.failed'
```

The constant's `<NAME>` part mirrors the path segments inside the
runtime value: `BUS_ERR_LISTENER_FAILED` ↔ `'bus::listener.failed'`.
The module name lives in exactly one place: `moduleSeed('bus')`.

The `::` separator distinguishes module from hierarchy. `errCode`
picks the right separator automatically — `::` after a seed, `.`
between segments. A helper `codeToLangPath(c)` converts
`'bus::listener.failed'` → `'bus.listener.failed'` for the i18n
path.

### Family matching

A single predicate `matches(err, family)` from `$libs/errs` covers
both common cases. `family` can be:

- A **module seed** (`BUS_ERR`) — matches any error from that
  module regardless of hierarchy.
- An **`ErrCode`** — matches the code itself or any hierarchical
  descendant within the same module.

```ts
matches(err, BUS_ERR_DISPOSED)   // exact code
matches(err, BUS_ERR_LISTENER)   // any descendant of bus::listener
matches(err, BUS_ERR)            // any error declared by bus
```

### Error class names — full English word

Error classes use the full English word **of the concept**, not the
module's `<MOD>_*` prefix. The class name is consumer-facing API; the
constant prefix is internal organization:

```ts
// good
StorageInvalidTypeError      // class
STORAGE_ERR_INVALID_TYPE     // constant

BusDisposedError             // class
BUS_ERR_DISPOSED             // constant

PermissionDeniedError        // class — singular concept
PERMISSION_ERR_DENIED        // constant — singular prefix

AppAlreadyCreatedError       // class — no Active prefix
APP_ERR_ALREADY_CREATED      // constant
```

---

## 5. String values inside diagnostic / event constants

Every string value emitted as an event identifier must start with the
module's identifier (rule 1) followed by `.` and the value-specific
path:

```ts
// good — value carries the module scope
export const CONNECTION_DIAGNOSTIC_EVENTS = {
  AUTH_FAILED: 'connection.auth_failed',
  RECONNECT_EXHAUSTED: 'connection.reconnect_exhausted'
} as const;

// bad — bare value collides across modules
export const CONNECTION_DIAGNOSTIC_EVENTS = {
  AUTH_FAILED: 'auth_failed',          // collides with auth.* events
  LISTENER_THREW: 'listener_threw'     // collides with session and timer
} as const;
```

---

## 6. File and folder structure

| Layer | Rule |
|---|---|
| `libs/<mod>/` | Pure contracts: types, constants, error classes, helpers. No Svelte runes, no engine state. |
| `arts/<mod>/` | Runtime engine + `*.svelte.ts` active wrappers. May import from `$libs/<mod>` and from its own files. |
| `arts/<mod>/index.ts` | Public barrel. Re-exports the artifact's surface. |
| `arts/<mod>/errors.ts` | Single home for the module's error infrastructure: `<MOD>_ERR` seed, `<MOD>_ERR_*` codes, `<MOD>_ERROR_MESSAGES` catalog, error classes and `is*Error` guards. **Do not split** these across `consts.ts` and `errors.ts`; everything error-related lives together. |
| `arts/<mod>/test/` | Tests for engine and active wrappers. |
| `svrs/<mod>/` | Server-side counterparts (cookies, db adapters, route handlers). |
| `arts/active-app/` | Composition root. Allowed to import any `$<mod>`. |

**Cross-artifact imports are forbidden** (`arts/X` cannot import
`$Y`). Sole exception: `arts/active-app/`.

---

## 7. When this document is updated

- A new category in section 3 requires a record-of-decision: who, when,
  why.
- Module names are frozen: a new artifact picks a name not yet taken;
  renaming an existing module is a breaking change.
- Drift found in the codebase that violates these rules is filed as an
  audit finding and resolved in a dedicated commit.

Last updated: `2026-05-02` — full English word convention, dropping
the 4-letter alias rule.