fix: address Copilot review round 9 on #2248

**Verification reads were unbounded.** The 512-entry limit is checked by
`checkSkillConformance` — as a warning, since the SEP makes it an
interoperability bound rather than a MUST — but checking it constrains
nothing, so a hostile server advertising a million entries had the tool
perform a million sequential reads after the report already knew the manifest
was over. Capped at `SKILL_MAX_RESOURCE_ENTRIES`, with the finding still
reported so bounding the work does not silence the reason it was
unnecessary. `manifestListsSelf` is computed over the READ slice, so a
self-entry pushed past the cap still reaches the fallback: the frontmatter
comparison is mandatory and must not be lost to a limit that bounds other
files.

**A malformed skill URI still produced a directory root.** `skillUriIdentity`
falls back to the raw string, so `not a uri/SKILL.md` yielded the root `not a
uri` and enabled the Directory section — letting the UI build a request from
a URI the conformance checks had already rejected. The comment above it
claimed otherwise. `normalizeSkillUri` now, with the rule written down:
identity is for COMPARING two spellings, not for deciding a URI is
well-formed enough to build a request from.

The existing regression test passed against a weaker input that failed for
lacking the suffix and never reached the fallback; it is a table of three
shapes now.

**The test-server guide overstated its own coverage,** claiming four of the
five conformance scenarios map onto fixtures. Three do: there is no
size-mismatch fixture, because the fixture can override an advertised digest
and nothing else, so that path is covered by unit tests. Corrected, with what
adding one would take.

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>

docs/test-servers.md

@@ -145,14 +145,23 @@ They are the client-side obligations SEP-2640 makes testable from a hostile
 server, which is how the
 [`modelcontextprotocol/conformance`](https://github.com/modelcontextprotocol/conformance)
 harness grades a *client*: it stands up a server and watches what the client
-does. Four of its five skills scenarios map onto a fixture here — a digest
-mismatch (`tampered-notes`), a size mismatch, a frontmatter mismatch
-(`lying-listing`), and a read of a file the manifest does not list
-(`stale-manifest`). The fifth, **no-prefetch**, is a negative: it passes only if
-connecting and calling `skills/list` produces *no* `resources/read` at all. The
-Inspector satisfies it structurally — nothing is fetched until a user selects a
-skill or presses Verify, which is why every round trip on the Skills screen is a
-button rather than an effect.
+does. **Three** of its five skills scenarios map onto a fixture here — a digest
+mismatch (`tampered-notes`), a frontmatter mismatch (`lying-listing`), and a
+read of a file the manifest does not list (`stale-manifest`).
+
+The other two are covered, but not by this fixture, and the distinction is worth
+keeping honest:
+
+- **Size mismatch** has no fixture. `test-servers/src/skills.ts` can override an
+  advertised *digest* and nothing else, so the size path — which
+  `verifySkillResource` checks first, before hashing — is exercised by unit
+  tests rather than against a live server. Adding it would mean an
+  `advertisedSize` override beside the digest one.
+- **No-prefetch** is a negative and could not have a fixture: it passes only if
+  connecting and calling `skills/list` produces *no* `resources/read` at all.
+  The Inspector satisfies it structurally — nothing is fetched until a user
+  selects a skill or presses Verify, which is why every round trip on the Skills
+  screen is a button rather than an effect.
 
 ## Cancelling a call