feat(sandbox): Phase 7 PR-A — @anthropic-ai/sandbox-runtime dep + doctor + ADR 0014

Lays the foundation for multi-tenant provider spawning isolation per
ADR 0014 § Decision. NO production wiring — PR-B (anthropic.mjs spawn
wrap) lands separately and requires bubblewrap + socat + ripgrep
installed on PI231 first.

Files:
- package.json: add @anthropic-ai/sandbox-runtime ^0.0.52
- lib/sandbox/doctor.mjs (new): preflight checkSandboxAvailability +
  describeSandboxStatus; pure module, no state, no initialize() call
- server.mjs: /health response gains 'sandbox' field with availability
  + missing deps + install hint; result memoized via _sandboxStatusCache;
  __resetSandboxStatusCache() test seam exported
- docs/adr/0014-sandbox-runtime-integration.md (new): 4-PR layered
  rollout decision per Iron Rule 11; PR-B/C/D acceptance criteria
  previewed; 6 spike pitfalls recorded; 282 lines
- CHANGELOG.md: Unreleased entry under Phase 7 PR-A
- test-features.mjs Suite 42 (+8 tests, 797 → 805, all pass)

Authority:
- @anthropic-ai/sandbox-runtime v0.0.52 — anthropic-experimental org
  https://github.com/anthropic-experimental/sandbox-runtime
- 2026-05-28 PoC spike (verdict YELLOW; report at /tmp/sandbox-spike/
  on PI231): clean arm64 install, dep check fail-closed behaviour
  confirmed, three PoC scripts parked
- cc-mem incident memory § 4 (prior-art search — ecosystem hasn't
  solved multi-tenant fs/tool isolation)
- ADR 0009 Amendment 1 § Caveats #3 — sandbox is cloud prerequisite
- docs/plans/cloud-deployment-family.md § 5

Spike note (macOS): on dev Mac mini with rg via Homebrew,
SandboxManager.isSupportedPlatform()=true and checkDependencies()
returns no errors — macOS uses built-in sandbox-exec, not bwrap.
/health.sandbox.available=true on macOS dev, false on PI231 until
apt install.

Operational follow-ups (NOT this PR):
1. sudo apt-get install -y bubblewrap socat ripgrep on PI231 (5-min window)
2. PR-B: lib/providers/anthropic.mjs spawn wrap + negative test
   (in-sandbox cat of OAuth token MUST fail)
3. PR-C: lib/providers/codex.mjs wrap with enableWeakerNestedSandbox:true
4. PR-D: cloud deployment plan update + unblock

Tests: 797 → 805 (all pass, 0 fail).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

server.mjs

@@ -70,6 +70,11 @@ import {
   ENV_OWNER_KEY_ID,
 } from './lib/keys.mjs';
 import { appendAuditEvent } from './lib/audit.mjs';
+// Phase 7 / PR-A — sandbox availability preflight module (ADR 0014).
+// checkSandboxAvailability is called lazily at first /health hit and memoized
+// process-wide (bwrap/socat install state does not change at runtime; we don't
+// want a child_process.execFileSync per /health call).
+import { checkSandboxAvailability } from './lib/sandbox/doctor.mjs';
 // Phase 3 / D50 — management endpoints consume the audit aggregate query layer.
 // D81 (Phase 5) — adds aggregateProviderQuota for quota_v2 shape.
 import {
@@ -221,6 +226,20 @@ export function __resetRequestCounters() {
   _activeRequests = 0;
 }
 
+// ── Phase 7 PR-A: sandbox availability cache ──────────────────────────────
+// checkSandboxAvailability() forks `which bwrap` / `which socat` / `which rg`
+// and imports @anthropic-ai/sandbox-runtime. Neither can change at runtime —
+// bwrap is either installed or it isn't. Memoize the first result to avoid
+// repeated child_process.execFileSync calls on every /health hit.
+//
+// _sandboxStatusCache: null  → not yet fetched
+//                      object → memoized result from checkSandboxAvailability()
+let _sandboxStatusCache = null;
+/** @internal — test seam: reset sandbox cache between tests. */
+export function __resetSandboxStatusCache() {
+  _sandboxStatusCache = null;
+}
+
 // ── Startup config ────────────────────────────────────────────────────────
 // Read ~/.olp/config.json once at startup. Provides:
 //   - providers.enabled   → which providers are loaded (ADR 0002 § Disable model)
@@ -859,10 +878,48 @@ async function handleHealth(req, res) {
       providerStatuses[name] = { ok: false, error: e.message, activeSpawns };
     }
   }
+  // Phase 7 PR-A (ADR 0014): sandbox availability field.
+  // Result is memoized process-wide in _sandboxStatusCache — bwrap/socat
+  // install state does not change at runtime. If the library call throws for
+  // any reason, the field is still included with available: false + error
+  // (don't crash /health).
+  if (_sandboxStatusCache === null) {
+    try {
+      _sandboxStatusCache = await checkSandboxAvailability();
+    } catch (e) {
+      _sandboxStatusCache = {
+        available: false,
+        missing: [],
+        details: { platform: process.platform, error: String(e?.message ?? e) },
+      };
+    }
+  }
+  const sandboxField = {
+    available: _sandboxStatusCache.available,
+    missing: _sandboxStatusCache.missing ?? [],
+    platform: _sandboxStatusCache.details?.platform ?? process.platform,
+  };
+  if (!_sandboxStatusCache.available) {
+    // Include human-readable install hint for owner-tier callers.
+    const missingDeps = (_sandboxStatusCache.missing ?? []).filter(
+      m => m === 'bubblewrap' || m === 'socat' || m === 'ripgrep',
+    );
+    if (missingDeps.length > 0) {
+      sandboxField.message =
+        `Sandbox dependencies not available: ${missingDeps.map(m => `${m} not installed`).join(', ')}.` +
+        ` Install: sudo apt-get install -y ${missingDeps.join(' ')}`;
+    } else if (_sandboxStatusCache.details?.error) {
+      sandboxField.message = `Sandbox check error: ${_sandboxStatusCache.details.error}`;
+    } else if (_sandboxStatusCache.details?.libError) {
+      sandboxField.message = `Sandbox library error: ${_sandboxStatusCache.details.libError}`;
+    }
+  }
+
   const fullPayload = {
     ok: true,
     version: VERSION,
     providers: { enabled, available, status: providerStatuses },
+    sandbox: sandboxField,
   };
   if (anonymousKey !== null) fullPayload.anonymousKey = anonymousKey;
   sendJSON(res, 200, fullPayload);