fix(ci): make the Tauri functional gate fail honestly on Windows and macOS

[TsekaLuk]

Why

Tauri functional macos and Tauri functional windows have been red on every branch since 65441b45c (2026-07-20) — 0 successes in the last 40 runs, including on main and on the v1.4.131 release commit. Both platforms failed with messages that named no cause, so nothing was diagnosable and the two most important desktop platforms went three weeks without a functional gate.

Three separate defects were behind it.

1. Windows: spawnSync npm.cmd fails with EINVAL. Since CVE-2024-27980 Node refuses to spawn a .cmd shim without shell: true. The gate spawned npm/pnpm shims directly, so the Windows job died before doing any work. config/scripts/run-tauri-terminal-evidence.mjs had the same defect, which is the likely real cause behind the two Windows jobs disabled in release-cut.yml as "flaky" / "PTY readiness".

2. macOS: the Rust build ate the evidence budget. The gate gave build + launch + evidence a single 240s deadline. Timeline from the failing run: budget opened 22:25:52, cargo self-reported Finished dev profile ... in 3m 18s at 22:29:11, page loaded 22:29:16, budget expired 22:29:52. The gate got 41 of its 240 seconds. This was starvation, not a hang — but it was reported as timed out after terminal-mounted, which pointed at the terminal.

3. Every wait reported the same thing. The gate has 17 waitFor calls that all threw the bare string real runtime gate timed out. Even once a genuine failure surfaced, it named no condition.

What this changes

• needsWindowsShell / requiresShellToSpawn: spawn .cmd shims through a shell, at all four spawn sites. Args carry no spaces, so shell: true is safe here.
• Split the single deadline into GATE_LAUNCH_TIMEOUT_MS (600s, covers the Rust build) and GATE_EVIDENCE_TIMEOUT_MS (240s, starts when the app first writes evidence). Timeout text now distinguishes "never launched" from "launched, then stalled at <stage>".
• waitFor(read, condition) — the label is a required parameter, so tsc forces all 17 call sites to say what they are waiting for. Failures now read real runtime gate timed out waiting for the shell prompt in PTY <id> to render the working directory.
• verify-tauri-mainline.mjs rules pin all three, mutation-tested (reverting any single spawn site, widening the deadline back, or making condition optional each fail the verifier).

What this does not do

macOS and Windows are still red, and this PR does not claim otherwise. What changed is that both now fail honestly:

• macOS previously died to the outer job guillotine with no artifact. It now writes real evidence — {"status":"failed","durationMs":37283,"error":"real runtime gate timed out"} — and with the labels above, the next run will name the specific wait that hung.
• Windows previously died at EINVAL before doing anything. It now gets through git init / git commit and reaches the Rust build, where it hits a pre-existing problem: pebble-desktop-tauri does not compile on Windows (7 errors — E0583 module path, E0425/E0433 PWSTR not in scope, E0277 NonNull<c_void> not Send, E0593 ×2 closure arity, E0004 non-exhaustive NativeBrowserInterceptDecision::Pause). Filed as pebble-desktop-tauri does not compile on Windows (7 errors) #130 with per-error root causes; two of them need design decisions about WebView2 UI-thread affinity that cannot be compile-checked from macOS. No user-facing artifact is affected — tauri-desktop-release.yml:68-78 comments the windows-x64 matrix entry out, so Pebble ships macOS + Linux only.

The disabled Windows jobs in release-cut.yml are deliberately not re-enabled here; that should wait until Windows compiles.

verify and both Linux gates are green.