diff --git a/lib/providers/anthropic.mjs b/lib/providers/anthropic.mjs
new file mode 100644
index 0000000..143c464
--- /dev/null
+++ b/lib/providers/anthropic.mjs
@@ -0,0 +1,453 @@
+/**
+ * lib/providers/anthropic.mjs — Anthropic Claude provider plugin
+ *
+ * Authority: OLP ALIGNMENT.md § Authority 1 — anthropic plugin governed by
+ *   `claude -p` from `@anthropic-ai/claude-code`.
+ *   OCP server.mjs inherits cli.js 2.1.89 audit pin at fork (per ALIGNMENT.md
+ *   § Provider authority pins).
+ *
+ * Spawn pattern ported from:
+ *   OCP server.mjs:384-414  (buildCliArgs — -p / --model / --output-format / --no-session-persistence)
+ *   OCP server.mjs:480-607  (spawnClaudeProcess — env cleanup, spawn, stdin write)
+ *   OCP server.mjs:422-468  (messagesToPrompt — text serialization)
+ *
+ * Auth reading ported from:
+ *   OCP server.mjs:864-888  (getOAuthCredentials — env → .credentials.json → keychain)
+ *   OCP server.mjs:531-534  (env cleanup: delete ANTHROPIC_API_KEY, ANTHROPIC_BASE_URL,
+ *                             ANTHROPIC_AUTH_TOKEN before spawn)
+ *
+ * Contract version: 1.0 (ADR 0002 § "Provider contract (v1.0 interface)" + D4 contractVersion fold-in)
+ *
+ * Status at D4: CANDIDATE. Not yet Enabled per ALIGNMENT.md § Provider Inventory.
+ * The plugin is present in STATIC_REGISTRY but enabled: false is the default config.
+ * POST /v1/chat/completions continues to return 503 until D5 flips the enabled flag
+ * in ~/.olp/config.json after E2E audit passes.
+ *
+ * Lossy translations (per ADR 0003 § "Lossy-translation documentation requirement"):
+ *   - `response_format: json_object` — Anthropic `claude -p` does not natively honor this
+ *     field; a system-prompt augmentation is injected ("Reply with valid JSON only.").
+ *   - `top_p` — not mapped to a `claude -p` flag; dropped silently. `claude -p` does not
+ *     expose --top-p.
+ *   - `tool_choice: "required"` — not a `claude -p` flag; dropped.
+ *   - Request-level `tools[]` — `claude -p --output-format text` is a text-in/text-out
+ *     CLI and does not consume structured tool definitions on the wire. The array is
+ *     silently dropped; if a caller wants tool-use they should pre-prompt the model
+ *     about the tools in the system message. ALIGNMENT.md Rule 2 forbids inventing
+ *     a wire format Anthropic's CLI does not accept.
+ *   - Assistant-message `tool_calls` and `tool_call_id` (IR messages representing prior
+ *     turns where the assistant invoked a tool) — same reason as above; dropped.
+ *     If a multi-turn conversation includes tool-call history, the textual content is
+ *     preserved but the structured call metadata is lost.
+ *
+ * Quota status: null at D4. Anthropic does not expose a programmatic quota endpoint.
+ *   TODO(2026-06-16): one-shot audit per ALIGNMENT.md § One-shot Triggered Audits.
+ *   After 2026-06-15 Agent SDK Credit billing split takes effect, re-evaluate whether
+ *   a programmatic credit-pool balance API exists and pin it here if found.
+ */
+
+import { spawn as defaultSpawn } from 'node:child_process';
+import { execFileSync, execSync } from 'node:child_process';
+import { existsSync, readFileSync } from 'node:fs';
+import { join } from 'node:path';
+import { homedir } from 'node:os';
+import { ProviderError } from './base.mjs';
+
+// ── Binary resolution ─────────────────────────────────────────────────────
+// OLP_CLAUDE_BIN env takes priority, then falls back to 'claude' from PATH.
+// Ported from OCP server.mjs:87-123 (resolveClaude) — simplified for plugin
+// scope (OCP's multi-path nvm/fnm/asdf resolution is omitted; OLP plugins
+// use the simpler env-override-first pattern and rely on PATH for the rest).
+//
+// OCP server.mjs:88: if (process.env.CLAUDE_BIN) { ... return process.env.CLAUDE_BIN; }
+// OLP uses OLP_CLAUDE_BIN to avoid colliding with OCP's CLAUDE_BIN if both are
+// installed on the same machine.
+function resolveClaudeBin() {
+  return process.env.OLP_CLAUDE_BIN || 'claude';
+}
+
+// ── Auth artifact reading ─────────────────────────────────────────────────
+// Ported from OCP server.mjs:864-888 (getOAuthCredentials).
+// Priority order (matching OCP exactly):
+//   1. CLAUDE_CODE_OAUTH_TOKEN env var — explicit override, highest precedence
+//   2. ~/.claude/.credentials.json (Linux file-based path)
+//   3. macOS keychain via `security find-generic-password`
+//      Both label formats tried: "claude-code-credentials" and "Claude Code-credentials"
+//
+// Returns { accessToken, refreshToken?, expiresAt? } or null.
+// Throws nothing — null means "not found, try next".
+export function readAuthArtifact() {
+  // 1. Env var — OCP server.mjs:866-868
+  if (process.env.CLAUDE_CODE_OAUTH_TOKEN) {
+    return { accessToken: process.env.CLAUDE_CODE_OAUTH_TOKEN };
+  }
+
+  // 2. Linux/cross-platform file-based credentials — OCP server.mjs:871-875
+  // Note: OCP uses ~/.claude/.credentials.json (dot-prefix), not ~/.claude/credentials.json.
+  // This matches the actual path Claude Code writes to.
+  try {
+    const credPath = join(homedir(), '.claude', '.credentials.json');
+    const raw = readFileSync(credPath, 'utf8');
+    const creds = JSON.parse(raw);
+    if (creds?.claudeAiOauth?.accessToken) return creds.claudeAiOauth;
+  } catch { /* fall through */ }
+
+  // 3. macOS keychain — OCP server.mjs:877-885
+  // Only attempted on darwin to avoid shell-out overhead on other platforms.
+  if (process.platform === 'darwin') {
+    for (const label of ['claude-code-credentials', 'Claude Code-credentials']) {
+      try {
+        const raw = execFileSync('security', [
+          'find-generic-password', '-s', label, '-w',
+        ], { encoding: 'utf8', timeout: 5000 }).trim();
+        const creds = JSON.parse(raw);
+        if (creds?.claudeAiOauth?.accessToken) return creds.claudeAiOauth;
+      } catch { /* try next */ }
+    }
+  }
+
+  return null;
+}
+
+// ── IR → prompt text serialization ───────────────────────────────────────
+// OCP server.mjs:422-468 (messagesToPrompt) — no session management in OLP;
+// we always pass the full serialized messages as stdin to `claude -p`.
+//
+// `claude -p` reads its prompt from stdin when no prompt argument is given.
+// OCP server.mjs:542 confirms: `proc.stdin.write(prompt); proc.stdin.end();`
+// The format OCP uses is: system → "[System] <text>", assistant → "[Assistant] <text>",
+// user → raw text. We port the same format.
+//
+// ADR 0003 § Translation direction model: the plugin owns irToNative.
+export function irToAnthropic(irRequest) {
+  const parts = [];
+
+  for (const msg of irRequest.messages) {
+    const text = typeof msg.content === 'string'
+      ? msg.content
+      : JSON.stringify(msg.content);
+
+    if (msg.role === 'system') {
+      parts.push(`[System] ${text}`);
+    } else if (msg.role === 'assistant') {
+      parts.push(`[Assistant] ${text}`);
+    } else if (msg.role === 'tool') {
+      // Tool result — pass as annotated user turn so the model knows it's a tool response.
+      const nameAnnotation = msg.name ? ` (${msg.name})` : '';
+      parts.push(`[Tool Result${nameAnnotation}] ${text}`);
+    } else {
+      // user
+      parts.push(text);
+    }
+  }
+
+  // Lossy: response_format json_object → system-prompt augmentation.
+  // ADR 0003 § Lossy-translation documentation requirement.
+  if (irRequest.response_format?.type === 'json_object') {
+    parts.unshift('[System] Reply with valid JSON only. Do not include any prose outside the JSON structure.');
+  }
+
+  return parts.join('\n\n');
+}
+
+// ── Anthropic SSE chunk → IR ResponseChunk ────────────────────────────────
+// `claude -p --output-format text` emits raw text to stdout (not NDJSON/SSE).
+// This matches OCP server.mjs:735-748: each `proc.stdout.on('data', d => ...)` chunk
+// is raw text content — no JSON envelope. The plugin converts raw text chunks to
+// IR delta chunks, and produces a synthetic stop chunk at close.
+//
+// For streaming: each text chunk → IRResponseChunk { type: 'delta', content: <text> }
+// For non-streaming: the full accumulated stdout → single text → emit delta + stop.
+//
+// `claude -p --output-format json` would emit a JSON envelope, but OCP uses `text`
+// (OCP server.mjs:385: "--output-format", "text"), so we port the same.
+export function anthropicChunkToIR(rawText, isFirstChunk = false) {
+  return {
+    type: 'delta',
+    ...(isFirstChunk && { role: 'assistant' }),
+    content: rawText,
+  };
+}
+
+// Synthesize the stop chunk (called at proc.on('close', ...) with code 0).
+export function anthropicStopToIR(finishReason = 'stop') {
+  return {
+    type: 'stop',
+    finish_reason: finishReason,
+  };
+}
+
+// ── CLI args builder ──────────────────────────────────────────────────────
+// Ported from OCP server.mjs:384-414 (buildCliArgs), stripped of session
+// management (OLP is stateless per AGENTS.md § "No conversation state").
+//
+// OCP server.mjs:385: const args = ["-p", "--model", cliModel, "--output-format", "text"];
+// OCP server.mjs:392: args.push("--no-session-persistence");  // when no sessionInfo
+// OCP server.mjs:395-400: --dangerously-skip-permissions or --allowedTools
+//
+// OLP variant: always --no-session-persistence (stateless). No permissions flags at D4.
+function buildCliArgs(model) {
+  return [
+    '-p',
+    '--model', model,
+    '--output-format', 'text',
+    '--no-session-persistence',
+  ];
+}
+
+// ── Env cleanup ───────────────────────────────────────────────────────────
+// OCP server.mjs:531-534: deletes ANTHROPIC_API_KEY, ANTHROPIC_BASE_URL,
+// ANTHROPIC_AUTH_TOKEN before spawn to prevent env-level override collisions
+// with the OAuth token the CLI manages internally.
+// OCP server.mjs:530: const env = { ...process.env };
+function buildSpawnEnv() {
+  const env = { ...process.env };
+  // OCP server.mjs:531: delete env.CLAUDECODE;
+  delete env.CLAUDECODE;
+  // OCP server.mjs:532: delete env.ANTHROPIC_API_KEY;
+  delete env.ANTHROPIC_API_KEY;
+  // OCP server.mjs:533: delete env.ANTHROPIC_BASE_URL;
+  delete env.ANTHROPIC_BASE_URL;
+  // OCP server.mjs:534: delete env.ANTHROPIC_AUTH_TOKEN;
+  delete env.ANTHROPIC_AUTH_TOKEN;
+  return env;
+}
+
+// ── Spawn function (core) ─────────────────────────────────────────────────
+// Returns an AsyncIterator<IRResponseChunk> per ADR 0002 § Provider contract.
+// `spawnImpl` is swappable for tests (dependency injection, no real binary needed).
+//
+// OCP server.mjs:542: const proc = spawn(CLAUDE, cliArgs, { env, stdio: ["pipe", "pipe", "pipe"] });
+// OCP server.mjs:586-587: proc.stdin.write(prompt); proc.stdin.end();
+async function* _spawnAndStream(irRequest, authContext, spawnImpl) {
+  const auth = authContext ?? readAuthArtifact();
+  if (!auth?.accessToken) {
+    throw new ProviderError(
+      'No Anthropic OAuth token found. Run `claude auth login` or set CLAUDE_CODE_OAUTH_TOKEN.',
+      'AUTH_MISSING',
+    );
+  }
+
+  const bin = resolveClaudeBin();
+  const args = buildCliArgs(irRequest.model);
+  const env = buildSpawnEnv();
+
+  // Inject OAuth token so the CLI can authenticate.
+  // OCP server.mjs:864-888: the token is read from keychain/.credentials.json/env
+  // and passed as CLAUDE_CODE_OAUTH_TOKEN for the spawn invocation.
+  // We set it explicitly here so the plugin is self-contained.
+  env.CLAUDE_CODE_OAUTH_TOKEN = auth.accessToken;
+
+  const prompt = irToAnthropic(irRequest);
+
+  // OCP server.mjs:542: spawn(CLAUDE, cliArgs, { env, stdio: ["pipe", "pipe", "pipe"] })
+  const proc = spawnImpl(bin, args, { env, stdio: ['pipe', 'pipe', 'pipe'] });
+
+  // OCP server.mjs:586-587: proc.stdin.write(prompt); proc.stdin.end();
+  proc.stdin.write(prompt);
+  proc.stdin.end();
+
+  // Yield IR chunks as they arrive from stdout.
+  let isFirstChunk = true;
+  let accumulatedStderr = '';
+
+  // Convert proc events to an async generator using a push-buffer + signal approach.
+  const chunks = [];
+  let done = false;
+  let exitCode = null;
+  let exitSignal = null;
+  let resolveNext = null;
+
+  function push(item) {
+    chunks.push(item);
+    if (resolveNext) {
+      const r = resolveNext;
+      resolveNext = null;
+      r();
+    }
+  }
+
+  proc.stdout.on('data', (d) => {
+    const text = d.toString();
+    push({ type: 'data', text });
+  });
+
+  proc.stderr.on('data', (d) => {
+    accumulatedStderr += d.toString();
+  });
+
+  proc.on('error', (err) => {
+    push({ type: 'error', err });
+  });
+
+  proc.on('close', (code, signal) => {
+    exitCode = code;
+    exitSignal = signal;
+    done = true;
+    push({ type: 'close' });
+  });
+
+  // Drain the chunk buffer
+  while (true) {
+    if (chunks.length === 0) {
+      if (done) break;
+      // Wait for the next event
+      await new Promise((resolve) => { resolveNext = resolve; });
+      continue;
+    }
+
+    const item = chunks.shift();
+
+    if (item.type === 'error') {
+      throw new ProviderError(`claude spawn error: ${item.err.message}`, 'SPAWN_FAILED');
+    }
+
+    if (item.type === 'close') {
+      break;
+    }
+
+    if (item.type === 'data') {
+      yield anthropicChunkToIR(item.text, isFirstChunk);
+      isFirstChunk = false;
+    }
+  }
+
+  // Process close
+  if (exitCode !== 0) {
+    const errMsg = accumulatedStderr.slice(0, 300) || `claude exit ${exitCode}`;
+    // Map known exit patterns to IR error chunk, then throw
+    throw new ProviderError(errMsg, 'SPAWN_FAILED');
+  }
+
+  // Normal exit: emit stop chunk
+  yield anthropicStopToIR('stop');
+}
+
+// ── spawn (public, contract method) ──────────────────────────────────────
+// The public spawn method conforms to ADR 0002 § Provider contract:
+//   spawn: async (irRequest, authContext) => AsyncIterator<ResponseChunk>
+//
+// The `_spawnImpl` field is the injection point for tests.
+// Tests set `anthropic._spawnImpl = mockSpawn` before calling `anthropic.spawn()`.
+let _spawnImpl = defaultSpawn;
+
+export async function* spawn(irRequest, authContext) {
+  yield* _spawnAndStream(irRequest, authContext, _spawnImpl);
+}
+
+// Test hook: allows tests to inject a mock spawn without importing child_process.
+// Set anthropic._spawnImpl = mockFn before calling spawn(); reset after.
+export { _spawnImpl };
+export function __setSpawnImpl(impl) { _spawnImpl = impl; }
+export function __resetSpawnImpl() { _spawnImpl = defaultSpawn; }
+
+// ── estimateCost ──────────────────────────────────────────────────────────
+// Best-effort token estimation using the chars/4 heuristic.
+// Basis: OpenAI Cookbook "How to count tokens" rule-of-thumb: ~4 characters per token
+// for English prose. This is approximate; actual tokenization differs per model.
+// Reference: https://cookbook.openai.com/examples/how_to_count_tokens_with_tiktoken
+//
+// usd: null at D4 — Anthropic per-million-token rates not yet pinned.
+// TODO: populate usd once rates are confirmed post-2026-06-15 billing-split audit.
+export function estimateCost(request) {
+  if (!request?.messages) return null;
+
+  let inputChars = 0;
+  for (const msg of request.messages) {
+    const text = typeof msg.content === 'string'
+      ? msg.content
+      : JSON.stringify(msg.content);
+    inputChars += text.length;
+  }
+
+  // Rough output estimate: assume response is ~50% of input length.
+  const outputCharsEstimate = Math.ceil(inputChars * 0.5);
+
+  return {
+    inputTokens: Math.ceil(inputChars / 4),
+    outputTokensEstimate: Math.ceil(outputCharsEstimate / 4),
+    currency: 'USD',
+    usd: null, // not pinned at D4
+  };
+}
+
+// ── quotaStatus ───────────────────────────────────────────────────────────
+// Returns null at D4. Anthropic does not expose a programmatic quota endpoint.
+// TODO(2026-06-16 one-shot audit per ALIGNMENT.md § One-shot Triggered Audits):
+// After the 2026-06-15 Agent SDK Credit billing-split takes effect, check whether
+// the Agent SDK Credit pool exposes a balance/usage API endpoint. If it does,
+// implement here and update this comment with the endpoint URL + version pin.
+export async function quotaStatus(_authContext) {
+  return null;
+}
+
+// ── healthCheck ───────────────────────────────────────────────────────────
+// Does NOT spawn a real claude -p request (deferred to D5 E2E audit).
+// Checks: (1) binary exists, (2) auth artifact exists.
+// Ported from OCP server.mjs:363-377 (checkAuth) — simplified to existence
+// checks only; no live execution (per D4 spec constraint).
+export async function healthCheck({ _binaryExistsFn, _authReadFn } = {}) {
+  const t0 = Date.now();
+
+  // 1. Binary check
+  const binaryExists = _binaryExistsFn ?? _defaultBinaryExists;
+  if (!binaryExists()) {
+    return { ok: false, latencyMs: Date.now() - t0, error: 'claude binary not found' };
+  }
+
+  // 2. Auth artifact check
+  const authRead = _authReadFn ?? readAuthArtifact;
+  const auth = authRead();
+  if (!auth?.accessToken) {
+    return { ok: false, latencyMs: Date.now() - t0, error: 'auth artifact missing' };
+  }
+
+  return { ok: true, latencyMs: Date.now() - t0 };
+}
+
+function _defaultBinaryExists() {
+  const bin = resolveClaudeBin();
+  if (bin !== 'claude') {
+    // Explicit path given — check directly
+    return existsSync(bin);
+  }
+  // 'claude' from PATH — use which
+  try {
+    execSync('which claude', { encoding: 'utf8', timeout: 3000, stdio: ['ignore', 'pipe', 'ignore'] });
+    return true;
+  } catch {
+    return false;
+  }
+}
+
+// ── Provider export ───────────────────────────────────────────────────────
+// Conforms to ADR 0002 § "Provider contract (v1.0 interface)" including D4
+// contractVersion fold-in per reviewer F3.
+
+import modelsRegistryRaw from '../../models-registry.json' with { type: 'json' };
+
+const _registryModels = (modelsRegistryRaw?.providers?.anthropic?.models ?? []).map(m => m.id);
+
+const anthropic = {
+  name: 'anthropic',
+  displayName: 'Anthropic Claude',
+  contractVersion: '1.0',
+  models: _registryModels,
+  auth: {
+    type: 'oauth',
+    storage: 'keychain',
+    // Portable path via os.homedir() per hygiene requirement
+    path: join(homedir(), '.claude', '.credentials.json'),
+    refresh: 'auto',
+  },
+  spawn,
+  estimateCost,
+  quotaStatus,
+  healthCheck,
+  hints: {
+    requiresTTY: false,
+    concurrentSpawnSafe: true,
+    maxConcurrent: 4,
+  },
+};
+
+export default anthropic;
diff --git a/lib/providers/base.mjs b/lib/providers/base.mjs
index 8537f7c..c272c00 100644
--- a/lib/providers/base.mjs
+++ b/lib/providers/base.mjs
@@ -30,6 +30,7 @@
  * @typedef {Object} ProviderContractV1
  * @property {string} name               - unique lowercase key
  * @property {string} displayName        - human-readable name
+ * @property {'1.0'} contractVersion     - must be '1.0' for v1.0 plugins (D4 fold-in per reviewer F3)
  * @property {string[]} models           - model strings this provider serves
  * @property {ProviderAuth} auth
  * @property {function} spawn            - async (irRequest, authContext) => AsyncIterator<IRResponseChunk>
@@ -68,6 +69,13 @@ export function validateProvider(p) {
     errors.push('displayName must be a non-empty string');
   }
 
+  // contractVersion: required to be exactly '1.0' for v1.0 plugins (D4 fold-in per reviewer F3)
+  // Per ADR 0002 § Mitigations: "The contract is versioned. v1.0 is the subset in this ADR;
+  // future additions require ADR amendment plus a contract-version bump."
+  if (p.contractVersion !== '1.0') {
+    errors.push(`contractVersion must be '1.0', got ${JSON.stringify(p.contractVersion)}`);
+  }
+
   if (!Array.isArray(p.models)) {
     errors.push('models must be an array of strings');
   } else if (p.models.some(m => typeof m !== 'string')) {
diff --git a/lib/providers/index.mjs b/lib/providers/index.mjs
index fa60ef1..35bbdd9 100644
--- a/lib/providers/index.mjs
+++ b/lib/providers/index.mjs
@@ -9,26 +9,30 @@
  * one entry to STATIC_REGISTRY below, (3) README § "Supported Providers",
  * (4) inclusion ADR per ADR 0006.
  *
- * At D3 (Phase 1 Day 1), the registry is intentionally empty.
- * 0 Enabled Providers per ALIGNMENT.md § Provider Inventory.
- * Phase 1 Day 2+ will add the anthropic plugin.
+ * At D4 (Phase 1 Day 2), the anthropic plugin is added to STATIC_REGISTRY
+ * as a Candidate. It is NOT Enabled by default — a config with
+ * { enabled: { anthropic: true } } is required, which only happens after D5
+ * E2E audit passes per ALIGNMENT.md § Provider Inventory.
  */
 
 import { validateProvider } from './base.mjs';
+import anthropicDefault from './anthropic.mjs';
+
+// Normalize default export pattern
+const anthropic = anthropicDefault;
 
 // ── Static registry ───────────────────────────────────────────────────────
 
-// Phase 1 Day 2+ will add imports here, e.g.:
-//   import * as anthropic from './anthropic.mjs';
-// And push to STATIC_REGISTRY, e.g.:
-//   STATIC_REGISTRY.push(anthropic.default ?? anthropic);
-
-const STATIC_REGISTRY = [];
+const STATIC_REGISTRY = [
+  anthropic,
+];
 
 // ── Registry functions ────────────────────────────────────────────────────
 
 /**
  * Loads and validates providers, filtering by the enabled set in config.
+ * At D4, the anthropic provider is Candidate only — it will not appear in
+ * the loaded Map unless config.enabled.anthropic === true (set by D5 after E2E).
  *
  * @param {{ enabled?: Record<string,boolean> }} [config={}]
  * @returns {Map<string, import('./base.mjs').ProviderContractV1>}
@@ -55,7 +59,7 @@ export function loadProviders(config = {}) {
  * Returns the first provider in `loadedProviders` whose `models[]` includes
  * the exact `modelString`. Returns null if no provider is found.
  *
- * This is the naive lookup strategy for D3. Phase 2+ may add prefix/alias
+ * This is the naive lookup strategy for D4. Phase 2+ may add prefix/alias
  * matching once models-registry.json is consulted per AGENTS.md SPOT policy.
  *
  * @param {Map<string, import('./base.mjs').ProviderContractV1>} loadedProviders
@@ -71,9 +75,22 @@ export function getProviderForModel(loadedProviders, modelString) {
   return null;
 }
 
+/**
+ * Looks up a provider by name in the loaded Map. Returns null if not found.
+ * Useful for tests that need to access a specific provider directly.
+ *
+ * @param {Map<string, import('./base.mjs').ProviderContractV1>} loadedProviders
+ * @param {string} name
+ * @returns {import('./base.mjs').ProviderContractV1|null}
+ */
+export function getProviderByName(loadedProviders, name) {
+  return loadedProviders.get(name) ?? null;
+}
+
 /**
  * Returns all provider names in the static registry (whether enabled or not).
  * Used by /health and diagnostics.
+ * At D4: returns ['anthropic'] (the candidate roster).
  *
  * @returns {string[]}
  */
diff --git a/models-registry.json b/models-registry.json
index 3e306a0..de0e24d 100644
--- a/models-registry.json
+++ b/models-registry.json
@@ -1,5 +1,37 @@
 {
   "version": "0.1.0-bootstrap",
-  "comment": "OLP models registry — SPOT for (provider, model) → metadata per CLAUDE.md release_kit overlay. v0.1 founding ships zero Enabled Providers per ALIGNMENT.md § Provider Inventory, so 'providers' is empty. Each Phase audit that transitions a Candidate to Enabled populates its provider's entry here. Schema validated by .github/workflows/alignment.yml; provider keys must match ALIGNMENT.md inventory.",
-  "providers": {}
+  "comment": "OLP models registry — SPOT for (provider, model) → metadata per CLAUDE.md release_kit overlay. v0.1 founding shipped zero Enabled Providers per ALIGNMENT.md § Provider Inventory. D4 populates providers.anthropic as Candidate; D5 transitions to Enabled pending E2E audit. Schema validated by .github/workflows/alignment.yml; provider keys must match ALIGNMENT.md inventory.",
+  "providers": {
+    "anthropic": {
+      "displayName": "Anthropic Claude",
+      "tier": "D",
+      "candidate": true,
+      "models": [
+        {
+          "id": "claude-opus-4-7",
+          "displayName": "Claude Opus 4.7",
+          "contextWindow": 200000,
+          "deprecated": false
+        },
+        {
+          "id": "claude-sonnet-4-6",
+          "displayName": "Claude Sonnet 4.6",
+          "contextWindow": 200000,
+          "deprecated": false
+        },
+        {
+          "id": "claude-haiku-4-5",
+          "displayName": "Claude Haiku 4.5",
+          "contextWindow": 200000,
+          "deprecated": false
+        }
+      ],
+      "aliases": {
+        "claude": "claude-sonnet-4-6",
+        "sonnet": "claude-sonnet-4-6",
+        "opus": "claude-opus-4-7",
+        "haiku": "claude-haiku-4-5"
+      }
+    }
+  }
 }
diff --git a/test-features.mjs b/test-features.mjs
index 46d2fbe..88eecdc 100644
--- a/test-features.mjs
+++ b/test-features.mjs
@@ -1,15 +1,18 @@
 /**
- * test-features.mjs — OLP D3 test suite
+ * test-features.mjs — OLP D4 test suite (extends D3)
  *
  * Uses Node's built-in node:test runner. No external dependencies.
  * Run: node test-features.mjs  (or: npm test)
  *
  * Authority: ADR 0002 (provider contract), ADR 0003 (IR v1.0)
+ *   D4 adds: Anthropic plugin conformance, IR translation, mock-spawn behaviour.
  */
 
 import { describe, it, before, after } from 'node:test';
 import assert from 'node:assert/strict';
 import { request as httpRequest } from 'node:http';
+import { EventEmitter } from 'node:events';
+import { homedir } from 'node:os';
 
 // ── Modules under test ────────────────────────────────────────────────────
 
@@ -22,7 +25,19 @@ import {
   SSE_DONE,
 } from './lib/ir/ir-to-openai.mjs';
 import { validateProvider, ProviderError, withTimeout } from './lib/providers/base.mjs';
-import { loadProviders, getProviderForModel, listAllProviderNames } from './lib/providers/index.mjs';
+import { loadProviders, getProviderForModel, getProviderByName, listAllProviderNames } from './lib/providers/index.mjs';
+import anthropic, {
+  irToAnthropic,
+  anthropicChunkToIR,
+  anthropicStopToIR,
+  readAuthArtifact,
+  estimateCost as anthropicEstimateCost,
+  quotaStatus as anthropicQuotaStatus,
+  healthCheck as anthropicHealthCheck,
+  __setSpawnImpl,
+  __resetSpawnImpl,
+} from './lib/providers/anthropic.mjs';
+import modelsRegistry from './models-registry.json' with { type: 'json' };
 
 // ── Helpers ───────────────────────────────────────────────────────────────
 
@@ -37,11 +52,12 @@ function makeIR(overrides = {}) {
   };
 }
 
-/** Minimal valid provider stub that satisfies the v1.0 contract */
+/** Minimal valid provider stub that satisfies the v1.0 contract (including D4 contractVersion) */
 function makeProvider(overrides = {}) {
   return {
     name: 'stub',
     displayName: 'Stub Provider',
+    contractVersion: '1.0',
     models: ['stub-model-v1'],
     auth: { type: 'none', storage: 'none', path: '', refresh: null },
     spawn: async function* () { yield { type: 'stop', finish_reason: 'stop' }; },
@@ -459,7 +475,12 @@ describe('Provider contract validation', () => {
 // ── Suite 5: Plugin registry ──────────────────────────────────────────────
 
 describe('Plugin registry', () => {
-  it('empty STATIC_REGISTRY → loadProviders returns empty Map', () => {
+  it('STATIC_REGISTRY has 1 entry (anthropic candidate) at D4', () => {
+    // D4: anthropic is in STATIC_REGISTRY but default config has enabled:false
+    assert.equal(listAllProviderNames().length, 1);
+  });
+
+  it('loadProviders with empty config → empty Map (anthropic not enabled)', () => {
     const m = loadProviders({});
     assert.equal(m.size, 0);
   });
@@ -469,8 +490,8 @@ describe('Plugin registry', () => {
     assert.equal(m.size, 0);
   });
 
-  it('listAllProviderNames returns empty array at D3', () => {
-    assert.deepEqual(listAllProviderNames(), []);
+  it('listAllProviderNames returns [anthropic] at D4', () => {
+    assert.deepEqual(listAllProviderNames(), ['anthropic']);
   });
 
   it('getProviderForModel returns null when no providers loaded', () => {
@@ -493,9 +514,455 @@ describe('Plugin registry', () => {
     const m = new Map([['alpha', p]]);
     assert.equal(getProviderForModel(m, 'beta-v1'), null);
   });
+
+  it('getProviderByName returns null for empty loaded map', () => {
+    const m = new Map();
+    assert.equal(getProviderByName(m, 'anthropic'), null);
+  });
+
+  it('getProviderByName returns provider when found', () => {
+    const p = makeProvider({ name: 'alpha', models: ['alpha-v1'] });
+    const m = new Map([['alpha', p]]);
+    assert.ok(getProviderByName(m, 'alpha') !== null);
+    assert.equal(getProviderByName(m, 'alpha').name, 'alpha');
+  });
+
+  it('anthropic provider passes contract validation (STATIC_REGISTRY entry)', () => {
+    // Even though anthropic is Candidate (not enabled by default), it must
+    // pass contract validation at module load — loadProviders() validates all
+    // registry entries regardless of enabled flag.
+    const { valid, errors } = validateProvider(anthropic);
+    assert.equal(valid, true, `Validation errors: ${errors.join('; ')}`);
+  });
 });
 
-// ── Suite 6: HTTP integration tests ──────────────────────────────────────
+// ── Suite 6: Anthropic plugin (D4) ───────────────────────────────────────
+//
+// All tests in this suite are UNIT tests. No real `claude` binary is invoked.
+// Mock spawn is injected via __setSpawnImpl / __resetSpawnImpl.
+// Tests verify: contract conformance, contractVersion enforcement, registry
+// consistency, IR translation, mock-spawn stream, healthCheck, estimateCost.
+
+/**
+ * Creates a fake spawn that emits canned stdout chunks then exits cleanly.
+ * Returns a fake ChildProcess-like EventEmitter with stdin, stdout, stderr.
+ * @param {string[]} stdoutChunks — text chunks emitted in order
+ * @param {number} [exitCode=0]
+ */
+function makeMockSpawn(stdoutChunks, exitCode = 0) {
+  return function mockSpawnImpl(_bin, _args, _opts) {
+    const proc = new EventEmitter();
+    proc.stdout = new EventEmitter();
+    proc.stderr = new EventEmitter();
+    proc.stdin = {
+      write: () => {},
+      end: () => {
+        // Emit stdout chunks and close asynchronously
+        setImmediate(async () => {
+          for (const chunk of stdoutChunks) {
+            proc.stdout.emit('data', Buffer.from(chunk));
+          }
+          proc.stdout.emit('end');
+          proc.stderr.emit('end');
+          proc.emit('close', exitCode, null);
+        });
+      },
+    };
+    proc.killed = false;
+    proc.kill = () => {};
+    return proc;
+  };
+}
+
+describe('Anthropic plugin (D4)', () => {
+
+  // ── Test 1: Contract conformance ──────────────────────────────────────
+  it('anthropic module satisfies validateProvider() — all 10 fields present', () => {
+    const { valid, errors } = validateProvider(anthropic);
+    assert.equal(valid, true, `Validation errors: ${errors.join('; ')}`);
+    // Verify all 10 contract fields explicitly
+    assert.ok('name' in anthropic, 'missing: name');
+    assert.ok('displayName' in anthropic, 'missing: displayName');
+    assert.ok('contractVersion' in anthropic, 'missing: contractVersion');
+    assert.ok('models' in anthropic, 'missing: models');
+    assert.ok('auth' in anthropic, 'missing: auth');
+    assert.ok(typeof anthropic.spawn === 'function', 'missing: spawn');
+    assert.ok(typeof anthropic.estimateCost === 'function', 'missing: estimateCost');
+    assert.ok(typeof anthropic.quotaStatus === 'function', 'missing: quotaStatus');
+    assert.ok(typeof anthropic.healthCheck === 'function', 'missing: healthCheck');
+    assert.ok('hints' in anthropic, 'missing: hints');
+  });
+
+  // ── Test 2: contractVersion enforced ─────────────────────────────────
+  it('validateProvider rejects provider missing contractVersion', () => {
+    const p = makeProvider();
+    delete p.contractVersion;
+    const r = validateProvider(p);
+    assert.equal(r.valid, false);
+    assert.ok(r.errors.some(e => e.includes('contractVersion')));
+  });
+
+  it('validateProvider rejects contractVersion: "0.9"', () => {
+    const p = makeProvider({ contractVersion: '0.9' });
+    const r = validateProvider(p);
+    assert.equal(r.valid, false);
+    assert.ok(r.errors.some(e => e.includes('contractVersion')));
+  });
+
+  it('validateProvider accepts contractVersion: "1.0"', () => {
+    const p = makeProvider({ contractVersion: '1.0' });
+    const r = validateProvider(p);
+    assert.equal(r.valid, true);
+  });
+
+  it('validateProvider rejects contractVersion: undefined', () => {
+    const p = makeProvider({ contractVersion: undefined });
+    const r = validateProvider(p);
+    assert.equal(r.valid, false);
+    assert.ok(r.errors.some(e => e.includes('contractVersion')));
+  });
+
+  // ── Test 3: models match registry ────────────────────────────────────
+  it('anthropic.models matches models-registry.json providers.anthropic.models', () => {
+    const registryIds = modelsRegistry.providers.anthropic.models.map(m => m.id);
+    assert.deepEqual(anthropic.models, registryIds);
+  });
+
+  it('anthropic.models contains the three expected model IDs', () => {
+    assert.ok(anthropic.models.includes('claude-opus-4-7'));
+    assert.ok(anthropic.models.includes('claude-sonnet-4-6'));
+    assert.ok(anthropic.models.includes('claude-haiku-4-5'));
+    assert.equal(anthropic.models.length, 3);
+  });
+
+  // ── Test 4: getProviderForModel finds anthropic for each model ────────
+  it('getProviderForModel finds anthropic for claude-sonnet-4-6 when enabled', () => {
+    const loaded = new Map([['anthropic', anthropic]]);
+    const result = getProviderForModel(loaded, 'claude-sonnet-4-6');
+    assert.ok(result !== null);
+    assert.equal(result.name, 'anthropic');
+  });
+
+  it('getProviderForModel finds anthropic for claude-opus-4-7 when enabled', () => {
+    const loaded = new Map([['anthropic', anthropic]]);
+    const result = getProviderForModel(loaded, 'claude-opus-4-7');
+    assert.ok(result !== null);
+    assert.equal(result.name, 'anthropic');
+  });
+
+  it('getProviderForModel finds anthropic for claude-haiku-4-5 when enabled', () => {
+    const loaded = new Map([['anthropic', anthropic]]);
+    const result = getProviderForModel(loaded, 'claude-haiku-4-5');
+    assert.ok(result !== null);
+    assert.equal(result.name, 'anthropic');
+  });
+
+  // ── Test 5: irToAnthropic translation ────────────────────────────────
+  it('irToAnthropic: user message → plain text', () => {
+    const ir = makeIR({
+      model: 'claude-sonnet-4-6',
+      messages: [{ role: 'user', content: 'Hello world' }],
+    });
+    const prompt = irToAnthropic(ir);
+    assert.ok(typeof prompt === 'string');
+    assert.ok(prompt.includes('Hello world'));
+    assert.ok(!prompt.includes('[System]'));
+    assert.ok(!prompt.includes('[Assistant]'));
+  });
+
+  it('irToAnthropic: system + user → system annotation + user text', () => {
+    const ir = makeIR({
+      model: 'claude-sonnet-4-6',
+      messages: [
+        { role: 'system', content: 'You are a helper.' },
+        { role: 'user', content: 'What is 2+2?' },
+      ],
+    });
+    const prompt = irToAnthropic(ir);
+    assert.ok(prompt.includes('[System] You are a helper.'));
+    assert.ok(prompt.includes('What is 2+2?'));
+  });
+
+  it('irToAnthropic: assistant turn → [Assistant] annotation', () => {
+    const ir = makeIR({
+      model: 'claude-sonnet-4-6',
+      messages: [
+        { role: 'user', content: 'Hi' },
+        { role: 'assistant', content: 'Hello!' },
+        { role: 'user', content: 'Bye' },
+      ],
+    });
+    const prompt = irToAnthropic(ir);
+    assert.ok(prompt.includes('[Assistant] Hello!'));
+  });
+
+  it('irToAnthropic: response_format json_object injects system prompt', () => {
+    const ir = makeIR({
+      model: 'claude-sonnet-4-6',
+      messages: [{ role: 'user', content: 'Give JSON' }],
+      response_format: { type: 'json_object' },
+    });
+    const prompt = irToAnthropic(ir);
+    assert.ok(prompt.includes('Reply with valid JSON only'));
+  });
+
+  it('irToAnthropic: tool result turn → [Tool Result] annotation', () => {
+    const ir = makeIR({
+      model: 'claude-sonnet-4-6',
+      messages: [
+        { role: 'user', content: 'Search for something' },
+        { role: 'tool', content: '{"results": []}', name: 'search' },
+      ],
+    });
+    const prompt = irToAnthropic(ir);
+    assert.ok(prompt.includes('[Tool Result'));
+    assert.ok(prompt.includes('search'));
+  });
+
+  it('irToAnthropic: array content is JSON-stringified', () => {
+    const ir = makeIR({
+      model: 'claude-sonnet-4-6',
+      messages: [{ role: 'user', content: [{ type: 'text', text: 'hi' }] }],
+    });
+    const prompt = irToAnthropic(ir);
+    assert.ok(typeof prompt === 'string');
+    assert.ok(prompt.includes('text'));
+  });
+
+  // ── Test 6: anthropicChunkToIR and anthropicStopToIR ─────────────────
+  it('anthropicChunkToIR: produces delta chunk with content', () => {
+    const chunk = anthropicChunkToIR('Hello ', false);
+    assert.equal(chunk.type, 'delta');
+    assert.equal(chunk.content, 'Hello ');
+    assert.ok(!('role' in chunk));
+  });
+
+  it('anthropicChunkToIR: first chunk includes role=assistant', () => {
+    const chunk = anthropicChunkToIR('Hello', true);
+    assert.equal(chunk.type, 'delta');
+    assert.equal(chunk.role, 'assistant');
+    assert.equal(chunk.content, 'Hello');
+  });
+
+  it('anthropicStopToIR: produces stop chunk with finish_reason', () => {
+    const chunk = anthropicStopToIR('stop');
+    assert.equal(chunk.type, 'stop');
+    assert.equal(chunk.finish_reason, 'stop');
+  });
+
+  // ── Test 7: mock spawn — AsyncIterator yields correct IR chunks ───────
+  it('spawn with mock: yields delta chunks then stop chunk', async () => {
+    const fakeSpawn = makeMockSpawn(['Hello', ' world']);
+    __setSpawnImpl(fakeSpawn);
+    try {
+      const ir = makeIR({
+        model: 'claude-sonnet-4-6',
+        stream: true,
+        messages: [{ role: 'user', content: 'Hi' }],
+      });
+      const authCtx = { accessToken: '<fake-oauth-token>' };
+      const chunks = [];
+      for await (const chunk of anthropic.spawn(ir, authCtx)) {
+        chunks.push(chunk);
+      }
+      // Should have 2 delta chunks + 1 stop chunk
+      const deltas = chunks.filter(c => c.type === 'delta');
+      const stops = chunks.filter(c => c.type === 'stop');
+      assert.ok(deltas.length >= 1, `Expected at least 1 delta, got ${deltas.length}`);
+      assert.equal(stops.length, 1, `Expected 1 stop, got ${stops.length}`);
+      const allContent = deltas.map(c => c.content).join('');
+      assert.equal(allContent, 'Hello world');
+    } finally {
+      __resetSpawnImpl();
+    }
+  });
+
+  it('spawn with mock: first delta chunk has role=assistant', async () => {
+    const fakeSpawn = makeMockSpawn(['Test output']);
+    __setSpawnImpl(fakeSpawn);
+    try {
+      const ir = makeIR({
+        model: 'claude-sonnet-4-6',
+        stream: true,
+        messages: [{ role: 'user', content: 'Hello' }],
+      });
+      const authCtx = { accessToken: '<fake-oauth-token>' };
+      const chunks = [];
+      for await (const chunk of anthropic.spawn(ir, authCtx)) {
+        chunks.push(chunk);
+      }
+      const firstDelta = chunks.find(c => c.type === 'delta');
+      assert.ok(firstDelta, 'No delta chunk found');
+      assert.equal(firstDelta.role, 'assistant');
+    } finally {
+      __resetSpawnImpl();
+    }
+  });
+
+  it('spawn with mock: non-zero exit code throws ProviderError', async () => {
+    const fakeSpawn = makeMockSpawn([], 1);
+    __setSpawnImpl(fakeSpawn);
+    try {
+      const ir = makeIR({
+        model: 'claude-sonnet-4-6',
+        stream: true,
+        messages: [{ role: 'user', content: 'Hi' }],
+      });
+      const authCtx = { accessToken: '<fake-oauth-token>' };
+      let caught = null;
+      try {
+        // eslint-disable-next-line no-unused-vars
+        for await (const _chunk of anthropic.spawn(ir, authCtx)) {
+          // drain
+        }
+      } catch (e) {
+        caught = e;
+      }
+      assert.ok(caught instanceof ProviderError, `Expected ProviderError, got ${caught?.constructor?.name}`);
+      assert.equal(caught.code, 'SPAWN_FAILED');
+    } finally {
+      __resetSpawnImpl();
+    }
+  });
+
+  it('spawn throws ProviderError(AUTH_MISSING) when no auth context and no env/file', async () => {
+    const fakeSpawn = makeMockSpawn(['output']);
+    __setSpawnImpl(fakeSpawn);
+    // Temporarily clear the env var if set
+    const savedToken = process.env.CLAUDE_CODE_OAUTH_TOKEN;
+    delete process.env.CLAUDE_CODE_OAUTH_TOKEN;
+    try {
+      const ir = makeIR({
+        model: 'claude-sonnet-4-6',
+        stream: false,
+        messages: [{ role: 'user', content: 'Hi' }],
+      });
+      let caught = null;
+      try {
+        // Pass null as authContext to force re-read
+        for await (const _chunk of anthropic.spawn(ir, null)) { // eslint-disable-line no-unused-vars
+          // may or may not throw depending on whether credentials exist on this machine
+        }
+      } catch (e) {
+        caught = e;
+      }
+      // If credentials.json or keychain exists on the test machine, this won't throw.
+      // We only assert that IF it throws, it's AUTH_MISSING.
+      if (caught !== null) {
+        assert.ok(caught instanceof ProviderError, `Expected ProviderError, got ${caught?.constructor?.name}`);
+        assert.equal(caught.code, 'AUTH_MISSING');
+      }
+    } finally {
+      if (savedToken !== undefined) process.env.CLAUDE_CODE_OAUTH_TOKEN = savedToken;
+      __resetSpawnImpl();
+    }
+  });
+
+  // ── Test 8: healthCheck — binary not found ────────────────────────────
+  it('healthCheck returns {ok: false, error: "claude binary not found"} when binary absent', async () => {
+    const result = await anthropicHealthCheck({
+      _binaryExistsFn: () => false,
+      _authReadFn: () => ({ accessToken: '<fake-token>' }),
+    });
+    assert.equal(result.ok, false);
+    assert.equal(result.error, 'claude binary not found');
+    assert.ok(typeof result.latencyMs === 'number');
+  });
+
+  // ── Test 9: healthCheck — auth artifact missing ───────────────────────
+  it('healthCheck returns {ok: false, error: "auth artifact missing"} when auth missing', async () => {
+    const result = await anthropicHealthCheck({
+      _binaryExistsFn: () => true,
+      _authReadFn: () => null,
+    });
+    assert.equal(result.ok, false);
+    assert.equal(result.error, 'auth artifact missing');
+    assert.ok(typeof result.latencyMs === 'number');
+  });
+
+  it('healthCheck returns {ok: true} when binary and auth present', async () => {
+    const result = await anthropicHealthCheck({
+      _binaryExistsFn: () => true,
+      _authReadFn: () => ({ accessToken: '<fake-token>' }),
+    });
+    assert.equal(result.ok, true);
+    assert.ok(typeof result.latencyMs === 'number');
+  });
+
+  // ── Test 10: estimateCost shape ───────────────────────────────────────
+  it('estimateCost returns object with four fields for a valid request', () => {
+    const request = makeIR({
+      model: 'claude-sonnet-4-6',
+      messages: [
+        { role: 'system', content: 'You are a helper.' },
+        { role: 'user', content: 'Count to ten.' },
+      ],
+    });
+    const result = anthropicEstimateCost(request);
+    assert.ok(result !== null, 'estimateCost returned null');
+    assert.ok('inputTokens' in result, 'missing inputTokens');
+    assert.ok('outputTokensEstimate' in result, 'missing outputTokensEstimate');
+    assert.ok('currency' in result, 'missing currency');
+    assert.ok('usd' in result, 'missing usd');
+    assert.equal(result.currency, 'USD');
+    assert.equal(result.usd, null); // not pinned at D4
+    assert.ok(result.inputTokens > 0, 'inputTokens should be > 0');
+    assert.ok(result.outputTokensEstimate >= 0, 'outputTokensEstimate should be >= 0');
+  });
+
+  it('estimateCost returns null for null/missing request', () => {
+    assert.equal(anthropicEstimateCost(null), null);
+    assert.equal(anthropicEstimateCost({}), null);
+  });
+
+  // ── Test 11: quotaStatus ──────────────────────────────────────────────
+  it('quotaStatus returns null at D4', async () => {
+    const result = await anthropicQuotaStatus({});
+    assert.equal(result, null);
+  });
+
+  // ── Test 12: auth object shape ────────────────────────────────────────
+  it('anthropic.auth has correct shape', () => {
+    assert.equal(typeof anthropic.auth.type, 'string');
+    assert.equal(typeof anthropic.auth.storage, 'string');
+    assert.equal(typeof anthropic.auth.path, 'string');
+    assert.ok(anthropic.auth.path.includes('.claude'), 'auth.path should reference .claude directory');
+    // Portability check: path must start with the runtime homedir() value (set at module load)
+    // rather than a hardcoded literal.  Since path.join(homedir(), ...) produces the home dir
+    // as a prefix, we verify it matches what homedir() returns at test time.
+    assert.ok(
+      anthropic.auth.path.startsWith(homedir()),
+      `auth.path "${anthropic.auth.path}" should start with homedir() "${homedir()}"`,
+    );
+    assert.ok(typeof anthropic.auth.refresh === 'string' || anthropic.auth.refresh === null);
+  });
+
+  // ── Test 13: hints shape ──────────────────────────────────────────────
+  it('anthropic.hints has correct shape', () => {
+    assert.equal(typeof anthropic.hints.requiresTTY, 'boolean');
+    assert.equal(typeof anthropic.hints.concurrentSpawnSafe, 'boolean');
+    assert.ok(Number.isInteger(anthropic.hints.maxConcurrent) && anthropic.hints.maxConcurrent > 0);
+    assert.equal(anthropic.hints.requiresTTY, false);
+  });
+
+  // ── Test 14: loadProviders with anthropic enabled ─────────────────────
+  it('loadProviders with {enabled: {anthropic: true}} returns Map of size 1', () => {
+    const loaded = loadProviders({ enabled: { anthropic: true } });
+    assert.equal(loaded.size, 1);
+    assert.ok(loaded.has('anthropic'));
+  });
+
+  it('anthropic loaded via loadProviders passes contract and has correct models', () => {
+    const loaded = loadProviders({ enabled: { anthropic: true } });
+    const p = loaded.get('anthropic');
+    const { valid, errors } = validateProvider(p);
+    assert.equal(valid, true, `Contract errors: ${errors.join('; ')}`);
+    assert.ok(p.models.includes('claude-sonnet-4-6'));
+  });
+
+});
+
+// ── Suite 7: HTTP integration tests ──────────────────────────────────────
 
 describe('HTTP integration', () => {
   let serverInstance;