fix: break the TechLog CSRF bootstrap cycle and close the review's fix-round-1 items

C1 (Critical): getStudioSession was stamped with the same
TECH_LOG_STUDIO_SESSION auth profile as every other Studio operation, and
that profile requires the CSRF header it is getStudioSession's own job to
issue -- an unconditional cycle that recursed without bound in HTTP mode.
Fixed with a credential-free TECH_LOG_STUDIO_BOOTSTRAP auth profile for
getStudioSession alone, a synchronous re-entrancy guard in
createCsrfTokenProvider as defense in depth, and a throwing stub in place of
the prior `let x!: T` assertion. Added a composition-level regression test
that wires the real executor, CSRF provider, and credential-attach function
together and proves getStudioSession dispatches exactly once while its token
reaches both a JSON operation and the multipart upload.

Also: invalidate the cached CSRF token on a 401/403 from the upload path
(I2), a throwing useStudioAssetGateway() accessor so Task 11 cannot silently
compile a null-gateway UI (I3), and the M1-M5 minors from the review (guard
a malformed success body, cover the untested error fallbacks, align aborted
uploads with the JSON path's non-retryable CANCELLED mapping, derive the
credential header name from one source instead of two, and correct the
adapter review doc's operation count).

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

tests/features/tech-log/use-studio-asset-gateway.test.tsx

@@ -0,0 +1,65 @@
+// @vitest-environment jsdom
+
+import assert from "node:assert/strict";
+import { renderHook } from "@testing-library/react";
+import type { ReactNode } from "react";
+import { test } from "vitest";
+
+import type { StudioAssetGateway } from "../../../src/features/tech-log/application/ports/studio-asset-gateway.ts";
+import {
+  StudioContext,
+  useStudioAssetGateway,
+  type StudioContextValue,
+} from "../../../src/features/tech-log/presentation/studio/use-studio.ts";
+
+/**
+ * I3 (Task 7 fix round 1). `StudioContextValue.assetGateway` stays nullable
+ * so the many test harnesses that render `StudioProvider` without a
+ * `createAssetGateway` prop keep compiling — but that nullability would let
+ * Asset UI (Task 11) write `if (!assetGateway) return null` and ship a
+ * confusingly empty screen with the type checker satisfied. This pins the
+ * throwing accessor Asset UI must use instead.
+ */
+function contextValue(
+  assetGateway: StudioAssetGateway | null,
+): StudioContextValue {
+  return {
+    gateway: {} as never,
+    assetGateway,
+    resolvePublishedLabel: () => undefined,
+    now: () => new Date("2026-08-14T01:00:00.000Z"),
+    editor: null,
+    requestAnnouncement: "",
+    setRequestAnnouncement: () => {},
+    navigateInternal: () => {},
+    beginEditor: () => {},
+    updateEditorDraft: () => {},
+    setEditorStatus: () => {},
+    clearEditor: () => {},
+  };
+}
+
+function wrapperFor(assetGateway: StudioAssetGateway | null) {
+  return function Wrapper({ children }: { children: ReactNode }) {
+    return (
+      <StudioContext.Provider value={contextValue(assetGateway)}>
+        {children}
+      </StudioContext.Provider>
+    );
+  };
+}
+
+test("returns the asset gateway when the provider supplied one", () => {
+  const assetGateway = {} as StudioAssetGateway;
+  const { result } = renderHook(() => useStudioAssetGateway(), {
+    wrapper: wrapperFor(assetGateway),
+  });
+  assert.equal(result.current, assetGateway);
+});
+
+test("throws a clear error instead of returning null when no asset gateway was supplied", () => {
+  assert.throws(
+    () => renderHook(() => useStudioAssetGateway(), { wrapper: wrapperFor(null) }),
+    /useStudioAssetGateway must be used within a StudioProvider that was given a createAssetGateway prop/,
+  );
+});