docs(smoke): stop describing the WebKit smoke failure as a Safari bug

#2132 was filed asserting that a Safari user opening an MCP App gets a
permanently 'loading' widget. That was never tested. A manual check in
real Safari renders the App normally, so the claim is unsupported and is
removed from all six places it reached.

The failure under Playwright's WebKit is real and still keeps that engine
out of the CI matrix. What is not established is that any shipping
browser behaves this way — and Playwright ships its own WebKit build
whose networking stack is not Safari's, which is exactly the layer the
failure lives in.

headless-browser.mjs already carried the caveat that a green WebKit run
is not a Safari guarantee. The same sentence forbids the inverse
inference, which is the one that was made; it now says so explicitly, and
AGENTS.md carries the rule: reproduce in the real browser before claiming
user impact in one.

No behavior change.

Signed-off-by: cliffhall <cliff@futurescale.com>

.github/copilot-instructions.md

@@ -105,7 +105,7 @@ Both exist and do different jobs. Theme files (`src/theme/<Component>.ts`) custo
 - `npm run format` before committing; **`npm run ci` before pushing** (`validate` → `coverage` → `verify:build-gate` → `verify:bundle-externals` → `smoke` → Storybook). `npm run validate` is the fast inner-loop check and is **not** a substitute — it runs `test`, not `test:coverage`, so it does zero coverage gating.
 - **A dependency bump must land in every install that declares it.** v2 is not a workspace — the root and each `clients/*` have their own `node_modules`, and a client's test project compiles `core/` and `test-servers/src` (which resolve from the **root**) alongside the client's own sources. Bumping a shared dependency in one manifest only puts two versions of it in one `tsc` program; for a recursive-generic surface like zod that exhausts the tsc heap (#1896). `verify:dep-lockstep` fails the build on this — it derives its candidates from what each `tsc` program actually resolves (`tsc --listFilesOnly`, keeping packages that reach one program from two installs), so a package reached only through another package's `.d.ts` counts too (#1965) — so a PR bumping a package the shared sources pull in should update the root **and every client that already lists it** — not every client unconditionally, since a package absent from an install can't skew and adding it there would be a spurious dependency.
 - **A test or smoke must not touch real user state.** The web smokes run against a throwaway catalog via the shared `scripts/lib/prod-web-server.mjs` helper, never the developer's `~/.mcp-inspector/mcp.json` (#1977); the cli/tui smokes drive a temp `--catalog`; `pack:verify`'s `--web` child sets its own `MCP_CATALOG_PATH` for the same reason (#2003 — its App deep link persists a server row). Anything that boots the web backend and then *navigates* it needs that isolation, not just the scripts named `smoke:*`. A new smoke spawning its own server, or teardown that removes a work dir without first awaiting `stopChild` (the #1801 race — `child-cleanup.mjs` exports both halves and both are required), should be flagged.
-- **The headless web smokes are engine-parameterized, not Chromium-only.** `smoke:web:browser` / `smoke:web:app` / `smoke:web:elicit` take their engine from `SMOKE_BROWSER` (chromium — the default — firefox, webkit) and CI covers Chromium plus Firefox (#2086; WebKit runs locally but is out of the matrix pending #2132, a real Safari SSE hang it found), because the MCP Apps sandbox is built out of the primitives that diverge between engines: `srcdoc` CSP inheritance, nested sandboxed iframes, `Permissions-Policy`, cross-frame `postMessage`. Nothing else covers that — `sandbox-csp.test.ts` asserts a policy *string*, and no Storybook story reaches the sandbox at all. Flag a new browser-driven script that launches Playwright itself instead of going through `scripts/lib/headless-browser.mjs`, an unrecognized-engine path that falls back to Chromium rather than failing (it would claim coverage that never ran), or a launch-failure message naming the wrong engine. `pack:verify` is pinned to Chromium on purpose — it is a packaging check.
+- **The headless web smokes are engine-parameterized, not Chromium-only.** `smoke:web:browser` / `smoke:web:app` / `smoke:web:elicit` take their engine from `SMOKE_BROWSER` (chromium — the default — firefox, webkit) and CI covers Chromium plus Firefox (#2086; WebKit runs locally but is out of the matrix pending #2132, an undelivered-SSE-tail hang under Playwright's WebKit — not reproduced in real Safari, so don't cite it as one), because the MCP Apps sandbox is built out of the primitives that diverge between engines: `srcdoc` CSP inheritance, nested sandboxed iframes, `Permissions-Policy`, cross-frame `postMessage`. Nothing else covers that — `sandbox-csp.test.ts` asserts a policy *string*, and no Storybook story reaches the sandbox at all. Flag a new browser-driven script that launches Playwright itself instead of going through `scripts/lib/headless-browser.mjs`, an unrecognized-engine path that falls back to Chromium rather than failing (it would claim coverage that never ran), or a launch-failure message naming the wrong engine. `pack:verify` is pinned to Chromium on purpose — it is a packaging check.
 
 - **Build output is never a gate target.** Lint, format, and typecheck read first-party source only; everything a build writes (`clients/*/build`, `clients/web/dist`, `storybook-static`, `coverage`, `test-servers/build`, `core/**/{build,dist}`, `*.tsbuildinfo`) stays out via each scope's `globalIgnores`, `format` globs, and tsconfig `include`. Gating generated code reports defects in vendored third-party source that nobody can fix, and a rule promotion turns that warning into a `validate` failure (#2043). Flag a PR that adds a build location without ignoring it in the same change, that widens an ignore to silence a finding in first-party code, or that adds a build directory to a tsconfig `include` to make a generated `.d.ts` resolve. Note the coverage guards don't catch this — they assert source is _covered_, not that output is _excluded_.
 - **Lint has no warning tier.** Every `lint` script runs `--max-warnings 0`, so a warning fails `validate` exactly as an error does (#2085) — a `warn`-level `react-hooks/exhaustive-deps` finding otherwise let a stale-closure bug pass the pre-push gate and reach review. Flag a PR that silences a finding to make the gate pass (widening a `globalIgnores`, dropping a rule, or an inline disable with no justification comment); the fix is the defect, not the message. A rule meant to be enforced should be set to `error` rather than left at `warn` and carried by the flag.

.github/workflows/main.yml

@@ -128,8 +128,8 @@ jobs:
   #
   # This is the only place the MCP Apps sandbox is exercised on a non-Chromium
   # engine, and it earned its keep immediately: pointing the smokes at WebKit is
-  # what found #2132, a Safari-only hang in the web client's SSE transport that
-  # every Chromium-only tier had been green through.
+  # what found #2132, an undelivered-SSE-tail hang no Chromium-only tier could
+  # see. (Note #2132 is NOT known to affect Safari — see the matrix comment.)
   #
   # The unit tests cannot substitute — `sandbox-csp.test.ts` asserts
   # which policy STRING is built, which passes identically on an engine that
@@ -149,11 +149,12 @@ jobs:
       matrix:
         # `webkit` belongs here and is deliberately absent: the smokes RUN in it
         # (`SMOKE_BROWSER=webkit` works, and smoke:web:browser passes), but the
-        # two App smokes fail on a real, pre-existing Safari incompatibility in
-        # the web client's SSE transport — #2132, which carries the diagnosis and
-        # the verified fix. Adding it here is a one-word diff once that lands.
-        # An engine is either green or absent; a `continue-on-error` job would
-        # report coverage nobody is holding to a standard.
+        # two App smokes fail on #2132 — the SSE stream's last message is not
+        # delivered, so an App never leaves "loading". That is NOT reproduced in
+        # real Safari, so read it as a property of Playwright's WebKit build
+        # rather than a browser bug. Adding it here is a one-word diff once it is
+        # resolved. An engine is either green or absent; a `continue-on-error`
+        # job would report coverage nobody is holding to a standard.
         browser: [firefox]
     name: Sandbox smokes (${{ matrix.browser }})
     steps: