ci: put the Firefox smokes in the pre-push gate instead of GitHub CI

Dropping the CI job left cross-engine checking as something you had to
remember to run, which in practice means nobody runs it. This moves it
into npm run ci, so it happens once per push, in front of a human who can
still reason about the change -- rather than once per CI run, on every
branch, to re-derive an answer we already had.

scripts/run-engine-smokes.mjs is what makes that possible cross-platform:
SMOKE_BROWSER has to reach three child processes, and a POSIX VAR=x npm
run prefix does not work under Windows cmd.exe, which npm uses there.
Setting it in the child env from Node does. smoke:web:firefox passes the
engine as an ARGUMENT rather than relying on the ambient variable, so a
stray SMOKE_BROWSER cannot silently redirect the gate to another engine
-- verified: an explicit argument beats it.

It also gives the smoke list one home. It was previously an && chain in
package.json beside a second chain in the workflow, so adding a fourth
smoke meant remembering both. ENGINE_SMOKES is now the list, with a test
pinning its contents and its order -- a smoke going missing is invisible
at runtime, because a shorter list is still a passing run.

Firefox only. WebKit fails the App smokes for unidentified reasons and
must not be in a gate.

This makes npm run ci a strict superset of GitHub CI rather than a mirror.
That was already true of smoke:tui, which self-skips on CI; Firefox is the
second such step. The direction that matters still holds: passing
npm run ci locally means CI's gates will pass.

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

.github/copilot-instructions.md

@@ -102,10 +102,10 @@ Both exist and do different jobs. Theme files (`src/theme/<Component>.ts`) custo
 
 ## Gates and PR hygiene
 
-- `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.
+- `npm run format` before committing; **`npm run ci` before pushing** (`validate` → `coverage` → `verify:build-gate` → `verify:bundle-externals` → `smoke` → `smoke:web:firefox` → Storybook; the Firefox step is local-only and not mirrored in GitHub CI). `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). **CI runs Chromium only**; the others are an on-demand tool, deliberately not a gate (#2086 — a Firefox job was trialled and removed for never disagreeing with Chromium). They exist 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). **GitHub CI runs Chromium only; Firefox runs in the local pre-push gate** via `smoke:web:firefox` (#2086 — a CI job was trialled and removed for never disagreeing with Chromium across a dozen runs, and moved into `npm run ci` instead). They exist 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.