version: "1.0.1" name: polystella-contributor description: Edit the PolyStella package source. Use when adding a file-format adapter, adding a CLI subcommand, adding a translation provider, modifying the cache contract, debugging a translation regression, or otherwise working on the package itself (not consuming it).

polystella-contributor

You are editing the PolyStella package source. This skill is recipes for the common contributor tasks.

If you are integrating PolyStella into a downstream Astro project, STOP and load polystella-consumer instead.

Read first:

• `AGENTS.md` — orientation, invariants, boundaries.
• `ARCHITECTURE.md` — subsystem reference.

Then come back here for step-by-step task recipes.

Recipes

• Add a file-format adapter
• Add a CLI subcommand
• Add a translation provider
• Change the cache contract
• Debug a translation regression
• Modify a runtime API
• Edit UI-string handling
• Strict tsconfig patterns
• Testing conventions

Add a file-format adapter

<a id="add-adapter"></a>

When to use: Supporting a new file extension (.xml, .html, .po, custom format).

Contract: FileTypeAdapter in src/parsing/adapter.ts. See #adapter-contract.

Steps:

1. Implement the adapter at src/parsing/adapters/<name>.ts:

```ts import type { FileTypeAdapter, AdapterExtractOptions, AdapterApplyOptions } from "../adapter.js"; import type { Segment } from "../extract.js";

export const myFormatAdapter: FileTypeAdapter<MyParsedShape> = { extensions: [".myext"],

parse(source, sourcePath) { // Pure. No I/O. Throw on syntactic errors — the per-pair // try/catch in runTranslationPass will surface them without // aborting the build. },

extractSegments(parsed, source, opts): Segment[] { // Emit { id, text } per translatable unit. // IDs must be unique within a single file. // Empty text → no segment (translating "" is meaningless). },

applyTranslations(parsed, source, translations, opts): string { // Splice translations back into source bytes. // INVARIANT 3: produce the EXACT bytes that will be PUT to R2. // Weave any AI-translation marker from opts.topLevelAdditions // into the output here, not after. },

selectedValuesForHash(parsed, source, opts): Record<string, unknown> { // Snapshot of values that feed the cache hash. Only fields // your adapter considers translatable should appear here. },

peekNoTranslate(parsed): boolean { // Return true when the source is opted out via your format's // convention (e.g. top-level noTranslate: true). },

// Optional: rewriteUrls(bytes, opts): string { ... }, // post-cache; idempotent groupSegments(parsed, segments): Segment[][] { ... }, // INVARIANT 2 documentContext(parsed, opts): string | undefined { ... }, }; ```

1. Register in src/parsing/registry.ts:

``ts import { myFormatAdapter } from "./adapters/myformat.js"; // ... registerAdapter(myFormatAdapter); ``

First-registered wins. If your adapter claims an extension another adapter already owns, your registration is silently ignored. The order at the bottom of registry.ts is the de-facto priority.

1. Add tests under tests/parsing/adapters/<name>.test.ts. Mirror the structure of an existing adapter test (tests/parsing/adapters/toml.test.ts is a good template — it's structured-data-flavoured like most new adapters will be).

Required test coverage:

• parse round-trip (parse → reserialize via applyTranslations with no translations → byte-identical)
• extractSegments produces expected IDs
• applyTranslations splices correctly
• selectedValuesForHash snapshots ONLY translatable fields
• peekNoTranslate honours your format's opt-out convention
• If you implement rewriteUrls: idempotent on already-rewritten input
• If you implement groupSegments: flat(result) === segments (reference-equal)

1. No changes to `src/translation/run.ts` or `src/storage/cache.ts`. The orchestrator dispatches by extension via the registry; the cache layer is format-agnostic. If you find yourself editing either, you're doing something wrong.

1. Verify:

``sh pnpm test pnpm exec tsc --noEmit ``

1. Update the contributor README's status table and any per-format docs.

Add a CLI subcommand

<a id="add-cli-subcommand"></a>

When to use: Adding a new top-level verb (polystella <verb>).

Pattern: Each subcommand owns its argv parsing and a run<Name>(args, deps) handler. The dispatcher in src/cli.ts is a thin router.

Steps:

1. Create src/cli/<name>.ts:

```ts export interface MySubcommandArgs { // Parsed flags. help: boolean; someFlag?: string; }

export const MY_SUBCOMMAND_USAGE = `polystella my-subcommand

<description>

Usage: polystella my-subcommand [flags]

Flags: --some-flag <value> ... --help Print this message.

Exit codes: 0 ok 1 config error 2 <subcommand-specific failure> `;

export function parseMySubcommandArgs(argv: ReadonlyArray<string>): MySubcommandArgs { // Throw on unknown flag or missing value — accept-then-reject // would silently swallow typos. }

export interface MySubcommandDeps { cwd: string; log: (msg: string) => void; err: (msg: string) => void; // Add fakeable I/O / clock / etc. for tests. }

export async function runMySubcommand(args: MySubcommandArgs, deps: MySubcommandDeps): Promise<number> { // Return process exit code. } ```

1. Wire dispatch in src/cli.ts:

• Add to the Subcommand union type.
• Add the literal to parseSubcommand's if (first === "translate" || ...) check.
• Add a case to main()'s switch statement.
• Update TOP_LEVEL_USAGE to mention the new verb.

1. Add tests:

• tests/cli/<name>.test.ts for the argv parser + handler (with stubbed deps).
• Extend tests/cli.test.ts if the top-level dispatch needs new coverage (it usually does — add at least one "dispatches my-subcommand to the right handler" case).

1. If consumers typically wrap the subcommand in a pnpm script (e.g. pnpm i18n:sync), document the pattern in the docs site's CLI section. Don't add the wrapper to this package — consumer projects own their own scripts.

1. Verify:

``sh pnpm test pnpm exec tsc --noEmit pnpm build node dist/cli.js my-subcommand --help # sanity-check the emitted CLI ``

Add a translation provider

<a id="add-provider"></a>

When to use: Adding a third translator (e.g. OpenAI, Bedrock).

Contract: Translator in src/translation/provider.ts. See #translator-contract.

Steps:

1. Add a config variant to the provider zod schema in src/config/options.ts:

```ts const newProviderSchema = z.object({ kind: z.literal("new-provider"), apiKey: z.string(), model: modelSpecSchema, // string | per-locale map maxTokens: z.number().int().positive().default(8192), endpoint: z.string().url().optional(), });

// Add to the discriminated union: const providerSchema = z.discriminatedUnion("kind", [workersAISchema, anthropicSchema, newProviderSchema]); ```

1. Implement the translator factory in src/translation/provider.ts:

```ts function createNewProviderTranslator( provider: NewProviderConfig, locale: string, fetchImpl: typeof fetch, ): Translator { const modelId = resolveModelId(provider.model, locale);

return { modelId, async translate(systemPrompt, userPrompt, signal) { const res = await fetchImpl(endpoint, { method: "POST", headers: { ... }, body: JSON.stringify({ ... }), ...(signal !== undefined ? { signal } : {}), });

if (!res.ok) { const text = await res.text().catch(() => ""); const message = [polystella] new-provider request failed: ${res.status} ${res.statusText}${text ? \n${text} : ""}; if (PERMANENT_HTTP_STATUSES.has(res.status)) { throw new PermanentProviderError(message); } throw new Error(message); }

const data = await res.json(); // Extract the model's raw text; caller validates via parseResponse. // Round-trip via JSON.stringify if the provider pre-parses on the server. return text; }, }; } ```

1. Wire into createTranslator:

``ts if (provider.kind === "new-provider") { return createNewProviderTranslator(provider, locale, fetchImpl); } ``

1. Permanent vs retriable — PERMANENT_HTTP_STATUSES is {400, 401, 403, 404, 422}. Don't widen this without thinking about what flaky responses might wrongly skip retry. 5xx, 408, 425, 429 are retriable. Ask first before adding statuses (per AGENTS.md Boundaries).

1. Add tests at tests/translation/provider.test.ts covering:

• Happy path (mock fetch returns expected shape).
• Each permanent status → PermanentProviderError.
• 5xx → plain Error (retriable).
• Network error → plain Error.
• Unexpected response shape → clear error message with raw response preview.
• signal propagation to fetch.

1. Document the new provider in the package README's config section.

Change the cache contract

<a id="change-cache-contract"></a>

When to use: Modifying any input to the cache hash formula.

Severity: Cache-wide invalidation. Every cached translation across every consumer becomes a miss on the next build.

Steps:

1. Read #cache-key. The current formula is:

`` hash = sha256(body + selectedFrontmatterValues + glossaryHash + modelId) ``

1. Stop. Coordinate with the owner before merging. This is Invariant 1 in AGENTS.md. The change needs to be in a major version bump and called out in CHANGELOG.

1. If you're confident this is the right change:

• Edit src/storage/hash.ts (the computeSourceHash function).
• Update the formula description in ARCHITECTURE.md#cache-key.
• Update AGENTS.md Invariant #1.
• Update the hash test pin in tests/storage/hash.test.ts — it pins a literal hash to catch accidental formula drift. Compute the new literal and replace it.
• Add a CHANGELOG entry under a "Breaking changes" heading.
• Bump the major version (or 0.x minor pre-1.0).

1. Verify:

``sh pnpm test pnpm exec tsc --noEmit ``

The pinned-hash test will catch drift if you missed the test update.

Debug a translation regression

<a id="debug-translation"></a>

When to use: A translation that used to work is wrong, missing, or failing.

Diagnostic flow:

1. Reproduce on the fixture. If the regression is reported against a consumer's content, reduce to the smallest source file that reproduces. Add it under tests/fixtures/ if it's worth a regression test.

1. Inspect what the cache layer planned:

``sh polystella translate --dry-run --file 'path/to/source.md' # or in a consumer repo: pnpm translate --dry-run --file 'path/to/source.md' ``

Output includes the planned R2 key. If the key is wrong, the bug is in computeSourceHash or buildR2Key.

1. Inspect the staged output:

``sh cat <root>/.astro/i18n-staging/<locale>/<source-path> ``

Compare to expected. Is the AI-translation marker (aiTranslated: true) present? Are URLs rewritten? Is the body translated at all?

1. Inspect the build report:

``sh cat dist/i18n-r2-report.json | jq '.entries[] | select(.sourcePath == "<path>")' ``

Outcome will be hit, miss, override, error, or localSkipped. Read the corresponding code path in src/storage/cache.ts or src/source/overrides.ts.

1. Crank up verbosity:

``sh LOG_LEVEL=debug polystella translate --file 'path/to/source.md' ``

Emits per-batch detail (segment count, batch count, oversize warnings, retry attempts).

1. Bypass the cache: delete the relevant R2 object, or delete the local index entry:

``sh rm <root>/.astro/i18n-staging/.polystella-cache.json ``

1. Bypass R2 entirely by passing r2Override: null to runTranslationPass (test-only). Useful for isolating the translator from the cache layer.

1. Common regression causes:

• Adapter parse not idempotent — calling it twice produces different output. (Asserted by some tests; if you added a new adapter, add this test.)
• Cache key formula input added/removed without updating consumers.
• Workers AI maxTokens was lowered — multi-segment translation truncated to invalid JSON.
• Glossary YAML syntax error — silently ignored on load, term not applied.
• noTranslate: true accidentally set in source frontmatter.
• Override file path mismatch — locale or mirrored-path slug differs from source.
• URL rewriter doubling prefixes — confirm both rewrite layers are idempotent on already-rewritten input.

Modify a runtime API

<a id="modify-runtime-api"></a>

When to use: Editing Astro.locals.t, lhref, getLocalizedEntry, getLocalizedCollection, the React hooks, or the middleware that binds them.

Files:

• src/runtime/middleware.ts — request middleware; pre-binds locale to all four locals.
• src/runtime/middleware-core.ts — middleware body (test-friendly extract).
• src/runtime/get-localized-entry.ts, get-localized-collection.ts — fetcher implementations.
• src/runtime/localized-href.ts — URL prefixer.
• src/runtime/custom-loader-runtime.ts — the bridge (module-scoped singleton shared with sibling collections).
• src/runtime/locals.ts — TypeScript ambient declarations for Astro.locals. Was locals.d.ts until the dist-emit rework; renamed so tsc emits both an empty .js and the .d.ts declarations, and runtime/index.ts pulls it in via a side-effect import (the previous triple-slash <reference path> directive gets stripped by tsc at emit time).
• src/react/index.ts — useTranslations, useLocalizedHref hooks.

Key contracts:

• Bridge timing (Invariant 5) — the bridge must be set in astro:config:setup before sibling collections register. Edits that defer bridge setup will silently break sibling content loading.
• Per-locale closures — t, lhref, getLocalizedEntry, getLocalizedCollection are pre-bound to the request's locale by the middleware. Don't expose unbound versions in .astro files — they're imported separately from polystella/runtime for non-template contexts.

Steps:

1. Edit the relevant runtime file.
2. Update src/runtime/locals.ts if you're changing the shape of Astro.locals.
3. Update the polystella-consumer skill's "Runtime APIs" section.
4. Add tests under tests/runtime/:

• Behaviour test for the new/changed function.
• Middleware-binding test if the locals shape changes (tests/runtime/middleware.test.ts).

1. Don't forget the React side — useTranslations / useLocalizedHref and their consumer-side wiring (getDictionary).

Edit UI-string handling

<a id="edit-ui-strings"></a>

When to use: Changing drift detection rules, sync writer behaviour, AI-fill orchestration, or the {{token}} validator.

Files:

• src/i18n/drift.ts — checkI18nDrift, loadAndCheckDrift.
• src/i18n/sync.ts — key reconciliation; layout-aware JSON writer (formatLocaleFile).
• src/i18n/ui-translate.ts — AI-fill orchestrator; parallel-locale execution; {{token}} validator + retry wrapper.
• src/i18n/loader.ts, i18n/index.ts — content-layer loader, dictionary fetcher.
• src/cli/check-ui.ts, sync-ui.ts, translate-ui.ts — CLI handlers.

Key contracts:

• Three drift failure modes — missing keys, extra keys, empty-placeholder values (a non-default locale has "" where the source has a non-empty string). The build's astro:config:setup drift check and the check-ui CLI use the SAME predicate. If you add a fourth failure mode, update both.
• Layout-aware sync writer — parses the source file's text (not just its JSON) to recover key order and blank-line section breaks. The output mirrors that layout for every locale. Don't drop this — every sync would churn diffs.
• `{{token}}` validator runs OUTSIDE `translateBatch` — the orchestrator's retry wrapper sets maxRetries: 0 on translateBatch. Don't add a second retry layer.
• Parallel locales catch errors internally — translate-ui runs locales in parallel via runWithConcurrency. Workers MUST catch every error and record it on the per-locale outcome — never re-throw. Re-throwing kills the whole run.

See #ui-strings.

Strict tsconfig patterns

<a id="strict-tsconfig"></a>

All four stricter TypeScript flags are on (noUncheckedIndexedAccess, exactOptionalPropertyTypes, noImplicitReturns, noFallthroughCasesInSwitch). Patterns that come up repeatedly:

noUncheckedIndexedAccess

Indexed access returns T | undefined. Patterns:

// ❌ Old:
const first = arr[0];
first.foo; // type error: first might be undefined
// ✅ Guard:
const first = arr[0];
if (first === undefined) continue;
first.foo;
// ✅ Destructure with default (when default is safe):
const [first = defaultValue] = arr;

exactOptionalPropertyTypes

foo?: string is NOT the same as foo: string | undefined. Callers passing undefined explicitly need the latter:

// ❌ Old:
interface Opts {
  signal?: AbortSignal;
}
function foo(opts: { signal?: AbortSignal }) {
  inner({ signal: opts.signal }); // type error: opts.signal might be `undefined` literal
}
// ✅ When the callee accepts explicit `undefined`:
interface Opts {
  signal?: AbortSignal | undefined;
}

noImplicitReturns

Every code path returns. Add explicit return to early-exit branches:

function foo(): number {
  if (cond) {
    sideEffect();
    return 0;
  } // explicit return
  return 1;
}

Replacing ! and any

! and any are banned outside test code. Replace with:

// ❌
const value = map.get(key)!;
const data = JSON.parse(x) as any;
// ✅
const value = map.get(key);
if (value === undefined) throw new Error(`unexpected: ${key} not in map`);
const data = JSON.parse(x) as unknown;
if (typeof data !== "object" || data === null) throw new Error(`unexpected: ${x}`);
// narrow via structural type guards from here.

Testing conventions

<a id="testing"></a>

• Tests live under tests/<src-dir>/<basename>.test.ts. Top-level exceptions: tests/cli.test.ts (top-level dispatch + translate-subcommand parsing), tests/cli/ (per-subcommand handlers), tests/smoke.test.ts (end-to-end integration smoke).
• Vitest config in vitest.config.ts. singleThread: true — faster than multi-worker at this scale.
• Fakeable boundaries: each subsystem accepts a deps-shaped object so tests can inject stubs. The CLI's runCheckUi(args, deps) shape is the canonical example.
• For tests that need a clean adapter registry: call resetRegistry() before re-registering.
• For tests that exercise R2: use the in-memory R2 client at tests/helpers/in-memory-r2.ts (or whatever the equivalent helper is).
• For tests that exercise the translator: pass translatorOverrides to runTranslationPass with a fake Translator.
• For smoke tests: drive polystella(options) with stubbed Astro context against a real temp project. tests/smoke.test.ts is the template.
• For the doc-claims test (tests/docs.test.ts): pins file paths and command names referenced in AGENTS.md / ARCHITECTURE.md. If you move a file or rename a subcommand, update both the docs AND this test.

Verify before pushing:

pnpm test
pnpm exec tsc --noEmit