test: close the coverage gaps the first round left

Second pass over the suite, driven by the inventory in the gaps document. Nine
agents wrote suites in parallel against private databases, then a tenth read all
of it adversarially and five of its findings were fixed.

  unit + component  2076 -> 2079 (+888 over the round)
  api                647 -> 1015
  e2e                 18 -> 29

What was closed:

- lib/route-access.ts, the page-level authorization layer, went from zero tests
  to 48. Every API route was guarded and none of the pages were.
- The five media proxy routes now have a real 2xx beside every 403. The blocker
  was the positive control, solved by stubbing r2Client.send() and leaving
  lib/r2-media-proxy.ts itself real.
- Every remaining server-side lib module: invitations, email verification, the
  upload tokens, the logger, request origin, the whole R2 and Bunny lifecycle,
  notifications and admin stats.
- Six video-page hooks, and the chunking arithmetic extracted out of
  lib/client/r2-video-upload.ts as a pure module.
- Five end-to-end flows: workspace members, bulk operations, the admin area,
  player interaction and failure recovery.

Three things about the harness itself turned out to be wrong:

- Two @/lib/r2 stubs in tests/setup/api.ts had the wrong return shape, so every
  route reaching finalizeR2VideoUpload silently took the "not a valid video"
  branch and no test noticed.
- The auth matrix asserted only "not 2xx", which two entries satisfied without
  their guard existing. It now requires 401 or 403, which makes both
  load-bearing, and all 60 routes pass the stricter form.
- Both admin API routes had no positive control anywhere: replacing their guard
  with an unconditional refusal left the entire suite green. Found by the
  adversarial review, now covered.

Process:

- bun run test:mutation runs StrykerJS over the authorization and validation
  modules. Diagnostic, not a gate, weekly in CI rather than on a push.
- playwright.config.ts gains an opt-in webkit project for the player spec.
- AGENTS.md now requires a batch of new tests to be reviewed by somebody who
  did not write them.

Only two production files change, both deliberate: lib/auth.ts loses a verbatim
copy of its own permission formulas, and lib/client/r2-video-upload.ts calls the
extracted arithmetic. No behaviour change in either.

tests/unit/lib/workspace-access.test.ts

@@ -0,0 +1,99 @@
+import { describe, expect, it, vi } from 'vitest';
+import { resolveWorkspacePermissions } from '@/lib/auth';
+
+// `@/lib/auth` reaches `@/lib/db`, which opens a pg Pool and registers process
+// signal handlers on import. resolveWorkspacePermissions touches no database.
+vi.mock('@/lib/db', () => ({ db: {}, default: {}, disconnectDb: vi.fn() }));
+
+// The workspace half of the permission matrix. Until this file existed the
+// formulas were only ever reached through checkWorkspaceAccess(), which means
+// they were asserted on incidentally by whichever route a suite happened to
+// call. tests/unit/lib/project-access.test.ts does the same job for projects.
+//
+// Every case below states the expected verdict outright rather than deriving it
+// from the inputs, so a change to the formula cannot quietly change the
+// expectation with it.
+
+// There is deliberately no separate 'anonymous' actor. resolveWorkspacePermissions
+// receives three booleans, not a user, and an anonymous caller and a signed-in
+// outsider set all three to false, so the two would be byte-identical inputs
+// running under names that imply a distinction this function cannot see. Telling
+// "no session" from "a session with no membership" is checkWorkspaceAccess()'s
+// job: it is the one that resolves a userId to membership rows before calling
+// here, and it is covered against the database in the api suites.
+type Actor = 'outsider' | 'member' | 'admin' | 'owner';
+
+function inputsFor(actor: Actor, ownerBillingActive: boolean) {
+  return {
+    isOwner: actor === 'owner',
+    isMember: actor === 'member' || actor === 'admin',
+    isAdmin: actor === 'admin',
+    ownerBillingActive,
+  };
+}
+
+describe('resolveWorkspacePermissions, with the owner billing active', () => {
+  const cases: Array<{
+    actor: Actor;
+    hasAccess: boolean;
+    canEdit: boolean;
+    canDelete: boolean;
+  }> = [
+    { actor: 'outsider', hasAccess: false, canEdit: false, canDelete: false },
+    { actor: 'member', hasAccess: true, canEdit: false, canDelete: false },
+    { actor: 'admin', hasAccess: true, canEdit: true, canDelete: false },
+    { actor: 'owner', hasAccess: true, canEdit: true, canDelete: true },
+  ];
+
+  for (const { actor, hasAccess, canEdit, canDelete } of cases) {
+    it(`grants a ${actor} access=${hasAccess}, edit=${canEdit}, delete=${canDelete}`, () => {
+      const result = resolveWorkspacePermissions(inputsFor(actor, true));
+
+      expect(result.hasAccess).toBe(hasAccess);
+      expect(result.canEdit).toBe(canEdit);
+      expect(result.canDelete).toBe(canDelete);
+    });
+  }
+
+  it('only the owner can delete, an admin cannot', () => {
+    // Stated separately because it is the one rule that differs from the
+    // project matrix, where a project admin does get canDelete through the
+    // workspace-owner branch.
+    expect(resolveWorkspacePermissions(inputsFor('admin', true)).canDelete).toBe(false);
+    expect(resolveWorkspacePermissions(inputsFor('owner', true)).canDelete).toBe(true);
+  });
+
+  it('reports the membership flags it was handed, unchanged', () => {
+    expect(resolveWorkspacePermissions(inputsFor('admin', true))).toEqual({
+      isOwner: false,
+      isMember: true,
+      isAdmin: true,
+      hasAccess: true,
+      canEdit: true,
+      canDelete: false,
+      ownerBillingActive: true,
+    });
+  });
+});
+
+describe('resolveWorkspacePermissions, with the owner billing lapsed', () => {
+  // Billing is the outer gate: it revokes everything, including from the owner
+  // of the workspace. A member who kept `hasAccess` here would keep reading a
+  // workspace the account no longer pays for.
+  for (const actor of ['outsider', 'member', 'admin', 'owner'] as const) {
+    it(`refuses a ${actor} everything`, () => {
+      const result = resolveWorkspacePermissions(inputsFor(actor, false));
+
+      expect(result.hasAccess).toBe(false);
+      expect(result.canEdit).toBe(false);
+      expect(result.canDelete).toBe(false);
+    });
+  }
+
+  it('still reports the membership flags, so a caller can tell "lapsed" from "not a member"', () => {
+    const result = resolveWorkspacePermissions(inputsFor('owner', false));
+
+    expect(result.isOwner).toBe(true);
+    expect(result.ownerBillingActive).toBe(false);
+  });
+});