fix: address Copilot review round 1 on #2248

Five findings, all real.

**Critical — `verifySkills` selected `contents[0]`.** These bytes are hashed
against the file's advertised digest, so accepting a block the server
labelled something else verifies one file's content against another file's
digest, and can report that as `verified`. A false pass is worse than a
missing check. `contentsFor(result, uri)` now selects by NORMALIZED identity,
which keeps the canonicalized-echo case that motivated the original code
while rejecting an unrelated block, and reports a read error when nothing
answers for the URI. This is what `onReadSkillFile` already did; the two
paths hash bytes against digests and must not disagree about which bytes.

**`skills/get` was dispatched without the extension gate** that `skills/list`
had. Hoisted into `assertSkillsSupported` so the two cannot drift — declaring
the extension commits a server to both. Without it, an undeclared server's
-32601 is indistinguishable to a script from the -32602 a declared server
returns for a URI it does not serve.

**The TUI could strand a user on a hidden Skills tab.** The tab left the bar
when the gate went false but `activeTab` did not, so the pane kept rendering
for a server that never declared the extension. Reset to `info`, following
the Auth precedent — additionally gated on `connected`, because this gate
reads a server declaration and would otherwise fire during a reconnect.

**The TUI keyed a verdict by URI**, so a refresh replacing the manifest under
the same URI left hashes computed for the previous snapshot describing the
new one. Keyed on the entry now, as the web screen already was.

**A failed "Load more" discarded the pages on screen and the retry cursor.**
Both are preserved now, and the success and failure paths share one
staleness-guarded `commit` helper so they cannot drift on which results they
may write — which is how they came to disagree.

Two nits: the six-skill counts. The docs sentence was more wrong than
reported (five awkward skills of six, three outright violations) and is
rewritten rather than renumbered.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ND46Ci64DC3tzBy9aG81Nc
Signed-off-by: cliffhall <cliff@futurescale.com>

clients/cli/__tests__/run-method-skills.test.ts

@@ -78,6 +78,21 @@ describe("runMethod skills dispatch (#2248)", () => {
     ).rejects.toMatchObject({ exitCode: EXIT_CODES.USAGE });
   });
 
+  it("rejects skills/get too when the server declares no extension", async () => {
+    // Declaring the extension commits a server to BOTH methods, so gating one
+    // and not the other is inconsistent with the thing being checked — and an
+    // undeclared server's -32601 is indistinguishable to a script from the
+    // -32602 a declared server returns for a URI it does not serve.
+    const client = mockClient({
+      getSkillsExtension: vi.fn().mockReturnValue(undefined),
+      getSkill: vi.fn(),
+    });
+    await expect(
+      runMethod(client, { method: "skills/get", uri: "skill://x/SKILL.md" }),
+    ).rejects.toMatchObject({ exitCode: EXIT_CODES.USAGE });
+    expect(client.getSkill).not.toHaveBeenCalled();
+  });
+
   it("keeps the { skill } envelope on skills/get", async () => {
     // The client unwraps it for callers that want the entry; a CLI whose
     // contract is "print the result" must not quietly reshape the wire form.