Integrate runtime readiness repairs and standalone compiler

[replghost]

Scope

Integrates the runtime readiness work onto current main while preserving grouped/split compilation, background and pause behavior, mediated input, pointer capture, filesystem support, and offscreen attachments.

• Extract the standalone Wasm compiler without adding translator dependencies to native production consumers.
• Bound native GPU resources and supervisor resumptions; harden browser startup and partial I/O.
• Add typed browser sessions, native/browser examples, bounded file-input routing, consumer documentation, and packaged third-party notices. Retain MPL-2.0.
• Pin PolkaVM maintenance revision 642fa95a6f1df85612bdbd0a7e4353a2aa4dc9b5, qualified on Linux and actual Apple M1 hardware. Preserve existing Latest64 encoding rather than adopting an unversioned upstream wire-format change.

Verification before review

• Runtime CI: https://github.com/paritytech/polkavm-host-runtime/actions/runs/37095950340
• Engine qualification: https://github.com/paritytech/polkavm-host-runtime/actions/runs/37094525375
• 168 Rust tests and four driver-backed GPU tests; 133 browser tests and 34 release-validation tests.
• Chromium compiler/interpreter execution from bytes and precompiled WebAssembly.Module; matching native pixels and terminal worker cleanup.
• Fresh tarball install and strict TypeScript consumption; all 14 embedded assets reproduced/exported byte-for-byte.
• Apple M1 full engine suite and signed hardened-runtime JIT execution, including 2,642 compiler/tracing test variants.

Review boundaries

The engine maintenance stack remains separate: https://github.com/paritytech/polkavm/tree/maintain/runtime-jit-refresh . This PR consumes an immutable revision; it does not merge that engine branch.

This is source integration, not a versioned release. Browser 0.3.2-background.0 and Rust 0.3.1 remain intentionally unaligned, and strict release-manifest generation rejects that state. Native attribution limitations for block 0.1.6 and malloc_buf 0.0.6 are recorded in THIRD_PARTY_NOTICES.md.

Code review and local verification completed; merge remains gated on green CI for the final head.

Code review repairs (c1e31c3)

• Port the shared 8,192-resumption budget to browser foreground, pipe, and workspace supervision, preserving queued input, ordered output, nested package resolution, and contained child faults. Thirteen regression cases failed against the previous source; all fourteen scheduling cases now pass.
• Align native CoreVM vectored I/O with translated-host partial-progress semantics; guest descriptor faults return EFAULT or completed bytes without swallowing internal host errors. Four guest regressions failed against the previous source; all seven native and nine translated I/O cases pass.
• Align browser file-input validation with native manifests: 128 MiB ceiling, optional null capability, rejection of null type lists, and required entrypoint for mount-collision checks. Add shipped declarations for the file-input-router subpath. Strict malformed-registration rejection is retained.
• Correct terminal-state API documentation, remove temporary feature-branch CI triggers, and replace a load-sensitive wall-clock pacing assertion with deterministic timer/clock control while retaining the real guest.
• No actionable defects found in GPU resource accounting or compiler extraction. The pinned engine remains unchanged.

Final local verification

• Format check and strict all-target/all-feature Clippy passed.
• 175 Rust tests plus all four opt-in driver-backed GPU tests passed.
• 155 browser tests and 34 release-validation tests passed.
• Real guest CLI/Chromium smoke: identical vectored-I/O results and file bytes across native interpreter and browser compiler/interpreter, from both byte and precompiled-Module startup.
• Real request-loop guest: native and browser yield after the first bounded turn, then exit with all 10,000 ordered reports preserved.
• Actual framebuffer UI pause/background/resume/stop and file consent cancellation/delivery exercised; zero remaining workers and no browser errors.
• Fresh tarball install, strict TypeScript session/router consumption, installed delivery API, and runtime Wasm compilation passed.
• All 15 generated assets reproduce byte-for-byte and export through the native asset CLI; attribution verification passes.

Development-version alignment and the documented native attribution limitations remain release prerequisites, not changes hidden by this source-integration PR.