test(conformance): wire MCP fixtures, reverse-attach negatives, parity checklist - #62

…y checklist (refs #24)

Adds the open test items from #24. No Sources/ or production Rust changes.

New files
- conformance/mcp_wire_vectors.json: 12 JSON-RPC cases (initialize, ping,
  tools/list shape, tools/call errors, notification, parse and batch errors).
  Expectations are the Swift MCPServer result. 7 Rust divergences are listed
  in known_drift with the output Rust gives today.
- Tests/InstanceMCPCoreTests/WireConformanceTests.swift: runs the fixture
  against MCPServer.parse and handle.
- poc/reverse-attach-linux/src/wire_conformance.rs: runs the fixture against
  mcp::answer; fails if a known_drift output changes or a drift is fixed.
- Tests/InstanceMCPCoreTests/ReverseAttachNegativeTests.swift: a plain TCP
  runtime answers 401; the client must dial once, send "Bearer right" and end
  in handshakeRejected(401). Also a canary check: the attach secret is absent
  from POST, GET list and GET one bodies.
- poc/reverse-attach-linux/src/attach/client_tests.rs: 401 on wrong, same-length
  wrong, empty and missing bearer (one dial each); right bearer sends the
  expected headers; wss:// to a plaintext listener does not succeed and sends no
  HTTP.
- poc/reverse-attach-linux/src/attach/grant_secrecy_tests.rs: grant_json never
  contains the secret.
- docs/parity-checklist.md: the Phase 3 gate, with wire, HTTP, reverse-attach
  and per-tool rows. Profile rows are a placeholder for #59.

Changed
- conformance/auth_vectors.json: 3 cases appended (same-length byte change,
  case change, trailing space). The old last object gained a trailing comma.
- conformance/README.md: rows and a link to the checklist.
- main.rs, attach/mod.rs, attach/client.rs: one cfg(test) mod line each.

Verification (commands run on macmini; nothing built on the laptop)
- Baseline on untouched origin/main de5e211 (git archive): swift test
  136 passed, 0 failed; cargo test --release 18 passed.
- swift test on this commit: 139 passed, 0 failed (136 + 3 new suites).
  Includes ConformanceVectorTests (auth vectors, 19 cases).
- cargo test --release --locked in rust:latest (rustc 1.99.1, Linux aarch64,
  container on macmini via OrbStack): 25 passed, 0 failed (18 + 7 new).
- cargo fmt --check: pass (after rustfmt on the three new Rust files).
- cargo clippy --release --locked -- -D warnings: pass (CI command).
- cargo test --release on native macOS: FAILS AT LINK (not a test failure).
  The crate is Linux-only (seat.rs calls prctl). A test that calls answer()
  with tools/call reaches tool_key and so links seat.rs. The baseline never
  reached that path from tests, so it linked by dead-stripping. CI runs the
  Rust job on Linux and is the authoritative Rust run.
- json.tool: both fixtures valid.
- Not run: bash smoke.sh and markdownlint (see follow-ups).

Finding (pre-existing, not fixed here)
- On Linux, tungstenite connect() with a wss:// URL panics: rustls 0.23 has no
  process-level CryptoProvider in this build. A wss:// runtime would panic the
  dial thread and leave the grant in "dialing". The wss test accepts that
  panic as "dial did not succeed". Fix in a follow-up.

Still open for #24 after this PR
- 1: 7 known_drift Rust fixes (wire layer). HTTP-layer gaps (session 404,
  415, DELETE semantics, 400 vs 202) are in the checklist.
- 2a: successful wss:// handshake (needs TLS fixture); Swift and Rust.
- 2b: sha256 verifier (runtime side, openab-pty; not in this repo).
- 2c: pod stores only the verifier (runtime side).
- 2d: per-connection profile enforcement at dispatch (#59).
- 2e: origin policy, certificate verification.
- 3 and 4 are done by this PR.

- parity-checklist §5: Rust does serve browser_* tools (mcp.rs Upstream via
  MCP_UPSTREAM, DESKTOP_BROWSER_TOOLS, upstream_tool_allowed); fix the cell and
  name that code among the section sources.
- parity-checklist §4: rename the "constant-time" row to byte-exact compare
  (vectors check outcomes, not timing); note on the wss row that the Linux dial
  panics (no rustls CryptoProvider) and the test accepts it; link follow-up #66.
- AttachCredentialSecrecyTests: assert 200 on GET /attach and GET /attach/<id>,
  and that the grant id appears in the list body.
- client_tests.rs: rename right_bearer_upgrades_with_the_expected_headers to
  right_bearer_is_sent_and_upgrades; widen the dial_loop grant deadline to
  now+4 s so it clearly outlasts the 2.5 s linger.
- conformance/README.md: the no-Authorization case is a runtime-side check the
  dialer never sends, not a dial-side "missing bearer" negative.

Correction to 3718049's message: the pinned markdownlint-cli2-action sha
(v19.1.0) bundles markdownlint-cli2 0.17.2, not 0.18.1 (as c083da6 said).

Verified on macmini: swift test 139 pass, 0 fail. In rust:1 container (rustc
1.99.1): cargo fmt --check ok; cargo clippy --release --locked --all-targets
-D warnings ok; cargo test --release --locked 26 pass, 0 fail.
markdownlint-cli2@0.17.2 on docs/** and conformance/*.md: 0 errors.