diff --git a/core/testing/__tests__/fixtures.contract.test.ts b/core/testing/__tests__/fixtures.contract.test.ts
new file mode 100644
index 0000000..6d454e2
--- /dev/null
+++ b/core/testing/__tests__/fixtures.contract.test.ts
@@ -0,0 +1,35 @@
+import { describe, expect, it } from "vitest";
+import { discoverFixtureFiles } from "@/core/testing/fixtureRegistry";
+
+/**
+ * SDK-upgrade fixture contract (issue #26).
+ *
+ * Fixtures are intentionally decentralized — one `fixtures/` directory per
+ * feature slice, owned by that slice's contributor — so there is no single
+ * fixtures root to hand-audit after a `@stellar/stellar-sdk` bump. Most
+ * fixtures call real SDK constructors (`Keypair`, `TransactionBuilder`,
+ * `xdr.*`) at module-evaluation time rather than hand-typing values, which
+ * means a renamed export, changed constructor signature, or removed enum
+ * member throws the moment the fixture module loads — this test just needs
+ * to load every one of them and surface exactly which file broke.
+ *
+ * Deliberately-invalid fixture *values* (e.g. `notAnEnvelopeXdr`,
+ * `notBase64`) are untouched by this: they're plain strings a slice's own
+ * tests decode and expect to fail, not something this contract should flag.
+ */
+describe("fixture SDK-upgrade contract", () => {
+  const fixtures = discoverFixtureFiles();
+
+  it("discovers at least one fixture per feature slice with a fixtures directory", () => {
+    expect(fixtures.length).toBeGreaterThan(0);
+  });
+
+  it.each(fixtures.map((f) => [f.relativePath, f] as const))(
+    "%s imports cleanly against the installed SDK",
+    async (_label, fixture) => {
+      await expect(
+        import(/* @vite-ignore */ fixture.absolutePath)
+      ).resolves.toBeDefined();
+    }
+  );
+});
diff --git a/core/testing/fixtureRegistry.ts b/core/testing/fixtureRegistry.ts
new file mode 100644
index 0000000..7236340
--- /dev/null
+++ b/core/testing/fixtureRegistry.ts
@@ -0,0 +1,56 @@
+import { readdirSync, statSync } from "node:fs";
+import path from "node:path";
+
+const FEATURES_DIR = path.resolve(process.cwd(), "features");
+const FIXTURE_DIR_NAME = "fixtures";
+const FIXTURE_FILE_RE = /\.fixture\.tsx?$/;
+
+export interface FixtureFileEntry {
+  /** Feature slice this fixture belongs to, e.g. "fee-stats". */
+  slice: string;
+  /** Absolute path to the fixture file. */
+  absolutePath: string;
+  /** Path relative to the repo root, used for reporting. */
+  relativePath: string;
+}
+
+/**
+ * Walks `features/*/fixtures/*.fixture.ts(x)` and returns every fixture
+ * file found, grouped by the slice that owns it.
+ *
+ * Fixtures are intentionally decentralized — one directory per slice, owned
+ * by that slice's contributor — so this discovers them by walking every
+ * feature directory rather than assuming a single shared fixtures root.
+ */
+export function discoverFixtureFiles(): FixtureFileEntry[] {
+  const entries: FixtureFileEntry[] = [];
+  let slices: string[];
+  try {
+    slices = readdirSync(FEATURES_DIR).filter((name) =>
+      statSync(path.join(FEATURES_DIR, name)).isDirectory()
+    );
+  } catch {
+    return entries;
+  }
+
+  for (const slice of slices) {
+    const fixturesDir = path.join(FEATURES_DIR, slice, FIXTURE_DIR_NAME);
+    let files: string[];
+    try {
+      files = readdirSync(fixturesDir);
+    } catch {
+      continue;
+    }
+    for (const file of files) {
+      if (!FIXTURE_FILE_RE.test(file)) continue;
+      const absolutePath = path.join(fixturesDir, file);
+      entries.push({
+        slice,
+        absolutePath,
+        relativePath: path.relative(process.cwd(), absolutePath)
+      });
+    }
+  }
+
+  return entries.sort((a, b) => a.relativePath.localeCompare(b.relativePath));
+}
diff --git a/docs/ARCHITECTURE.md b/docs/ARCHITECTURE.md
index a943d1b..6e5ff21 100644
--- a/docs/ARCHITECTURE.md
+++ b/docs/ARCHITECTURE.md
@@ -99,13 +99,26 @@ module would test the mock instead of the code.
 ## Quality gates
 
 ```bash
-npm run check    # registry → lint → test → verify:features → build
+npm run check    # registry → lint → test → verify:features → verify:issues → verify:fixtures → build
 ```
 
 CI runs the same steps on every pull request, including
 `npm run verify:features`, which fails a slice that does not meet the contract,
-and `npm run verify:issues`, which preserves a backlog of at least 40
-independent specifications with a stable 20-issue advanced wave.
+`npm run verify:issues`, which preserves a backlog of at least 40
+independent specifications with a stable 20-issue advanced wave, and
+`npm run verify:fixtures`, which imports every `features/*/fixtures/*.fixture.ts`
+file and fails with the specific file if a `@stellar/stellar-sdk` upgrade
+broke it.
+
+### SDK upgrades
+
+Fixtures are decentralized — one `fixtures/` directory per slice, owned by
+that slice's contributor — so there is no single place to eyeball after
+bumping `@stellar/stellar-sdk`. Most fixtures build their values with real SDK
+calls (`Keypair`, `TransactionBuilder`, `xdr.*`) rather than hand-typing them,
+so a renamed export or changed constructor throws the moment the fixture
+module loads. Run `npm run verify:fixtures` as part of every SDK-upgrade PR —
+it reports exactly which fixture file failed to import and why.
 
 See [ISSUE_PUBLISHING.md](./ISSUE_PUBLISHING.md) for the five-at-a-time
 GrantFox publication flow.
diff --git a/package.json b/package.json
index f09cf55..1511c47 100644
--- a/package.json
+++ b/package.json
@@ -18,9 +18,10 @@
     "test:coverage": "vitest run --coverage",
     "verify:features": "node scripts/verify-features.mjs",
     "verify:issues": "node scripts/validate-issue-catalog.mjs",
+    "verify:fixtures": "vitest run core/testing/__tests__/fixtures.contract.test.ts --reporter=verbose",
     "new:feature": "node scripts/new-feature.mjs",
     "postinstall": "node scripts/generate-registry.mjs",
-    "check": "npm run lint && npm run test && npm run verify:features && npm run verify:issues && npm run build",
+    "check": "npm run lint && npm run test && npm run verify:features && npm run verify:issues && npm run verify:fixtures && npm run build",
     "issues": "node scripts/create-issues.mjs",
     "issues:drips": "node scripts/create-issues.mjs --target drips"
   },