feat(client): inbox mechanism, write-guard, SPARQL injection hardening

Polyfill capabilities landed for Festipod's T02 features (all generic,
zero-domain — the consumer injects the domain).

- inbox: implement the previously-stubbed namespace. post(target,{from?,
  payload,ts?}) deposits {from,payload,ts} as RDF via docs.sparqlUpdate (the
  real injected ng, never makeNg); read/materialize + watch emulate the curator
  in-lib (deposits read via docs.sparqlQuery). `from` optional = anonymity.
- write-guard: caps.hasWritePolicy() + ng-proxy.sparql_update rejects when the
  target doc is under a write policy and the current user lacks its write cap;
  passthrough otherwise (no regression). Read-cap registry unchanged.
- sparql.ts (new): escapeLiteral / escapeIri / assertNuri, exported from index.
  store-registry now escapes every literal and validates/encodes every IRI-
  position value — closes a SPARQL-injection hole where an untrusted username
  could inject triples into the shim (the account→doc-NURI trust root).

Tests: inbox, sparql (incl. injection), ng-proxy write-guard, isolation-active.
68 tests pass; tsc --noEmit rc=0.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/client/test/sparql.test.ts

@@ -0,0 +1,78 @@
+import { test, expect } from "bun:test";
+import { escapeLiteral, escapeIri, assertNuri } from "../src/sparql";
+
+// --- escapeLiteral --------------------------------------------------------
+
+test("escapeLiteral escapes backslash, quote and whitespace controls", () => {
+  expect(escapeLiteral('a"b')).toBe('a\\"b');
+  expect(escapeLiteral("a\\b")).toBe("a\\\\b");
+  expect(escapeLiteral("a\nb")).toBe("a\\nb");
+  expect(escapeLiteral("a\rb")).toBe("a\\rb");
+  expect(escapeLiteral("a\tb")).toBe("a\\tb");
+});
+
+test("escapeLiteral backslash-then-quote order does not double-escape", () => {
+  // `\` first so a raw `"` never becomes `\"` before the quote pass mangles it.
+  expect(escapeLiteral('\\"')).toBe('\\\\\\"');
+});
+
+test("escapeLiteral output can no longer close a SPARQL literal", () => {
+  const injected = '" ; <urn:evil> "pwn';
+  const escaped = escapeLiteral(injected);
+  // No RAW double-quote survives — every `"` is preceded by a backslash.
+  expect(/(^|[^\\])"/.test(escaped)).toBe(false);
+});
+
+// --- escapeIri ------------------------------------------------------------
+
+test("escapeIri passes ordinary printable identifier chars through unchanged", () => {
+  expect(escapeIri("alice")).toBe("alice");
+  expect(escapeIri("a.b-c_d:e/f")).toBe("a.b-c_d:e/f");
+});
+
+test("escapeIri percent-encodes every IRI-breaking character", () => {
+  expect(escapeIri("a>b")).toBe("a%3Eb");
+  expect(escapeIri("a<b")).toBe("a%3Cb");
+  expect(escapeIri('a"b')).toBe("a%22b");
+  expect(escapeIri("a b")).toBe("a%20b");
+  expect(escapeIri("a\nb")).toBe("a%0Ab");
+  expect(escapeIri("a\tb")).toBe("a%09b");
+  expect(escapeIri("a\\b")).toBe("a%5Cb");
+});
+
+test("escapeIri neutralises a full breakout attempt", () => {
+  const attack = 'x> <urn:evil> "pwn';
+  const encoded = escapeIri(attack);
+  // The encoded username cannot contain a raw `>`, `<`, `"` or space, so it
+  // cannot escape the surrounding <PREFIX:...> IRI.
+  expect(encoded).not.toMatch(/[<>" ]/);
+});
+
+test("escapeIri handles unicode without corrupting it (round-trips via decode)", () => {
+  const u = "élan";
+  // "é" is a printable letter → left as-is; a space would be encoded.
+  expect(escapeIri(u)).toBe("élan");
+  expect(escapeIri("é ")).toBe("é%20");
+});
+
+// --- assertNuri -----------------------------------------------------------
+
+test("assertNuri returns valid NURIs unchanged", () => {
+  expect(assertNuri("did:ng:o:doc1")).toBe("did:ng:o:doc1");
+  expect(assertNuri("urn:ng-eventually:shim")).toBe("urn:ng-eventually:shim");
+  expect(assertNuri("did:ng:PRIV")).toBe("did:ng:PRIV");
+});
+
+test("assertNuri throws on empty / non-string", () => {
+  expect(() => assertNuri("")).toThrow(/invalid NURI/);
+  // @ts-expect-error deliberately wrong type
+  expect(() => assertNuri(null)).toThrow(/invalid NURI/);
+});
+
+test("assertNuri throws on IRI-breaking characters", () => {
+  expect(() => assertNuri("did:ng:o> <urn:evil")).toThrow(/IRI-forbidden/);
+  expect(() => assertNuri('did:ng:"x')).toThrow(/IRI-forbidden/);
+  expect(() => assertNuri("did:ng: x")).toThrow(/IRI-forbidden/);
+  expect(() => assertNuri("did:ng:\nx")).toThrow(/IRI-forbidden/);
+  expect(() => assertNuri("did:ng:\tx")).toThrow(/IRI-forbidden/);
+});