Add typed native Linux/libc vocabulary

[isomorphisms]

Implements a narrow native Linux/libc vocabulary for current Oils-derived Grease, based on the existing ARMv7 runtime branch.

Current exact head: ef9c74055c8079a7027771c6b869085ec7df3e3d
Pinned Oils source: 9024d14ecd25c8c55cd7e8ea0b901a3a9525565c
Companion source PR: isomorphisms/oils#2

Public Grease/YSH boundary:

• mmap, munmap, mprotect, msync
• openat, linkat, symlinkat, unlinkat
• narrowly necessary close, readMapping, and writeMapping support actions
• Mapping/Address and FileDescriptor runtime objects rather than raw C pointers or kernel fd values
• explicit Result / NativeError values carrying errno information
• symbolic text flags translated below the language boundary

The C++ layer is the existing Oils/YSH translated native-runtime seam; this PR does not create a second Grease runtime. Native calls go through libc/Bionic directly, with no raw syscall-number table and no general-purpose FFI.

The representative IB proof is examples/ib-mapped-index.ysh: open a prepared 4096-byte index file, map it shared, read fragment, write pensieve, msync, verify through the mapping, unmap and close; the host receipt then verifies the persisted file bytes outside Grease.

Focused native tests cover anonymous and file-backed mappings, bounds/errors, mprotect state (including EACCES instead of touching protected memory), relative openat, hard links, symbolic links, and unlinkat.

GitHub execution uses GitHub-hosted ubuntu-24.04. The host receipt uses the inherited Oils Podman cpp-spec harness, then runs the focused libc tests and mapped-IB example. The ARMv7 receipt uses the inherited cpp-tarball harness on hosted Ubuntu, installs the explicitly pinned Android NDK 27.3.13750724, and cross-builds the Android artifact.

Exact-current-head acceptance on GitHub-hosted Ubuntu 24.04:

• host Grease receipt run 35115827639: green at ef9c74055c8079a7027771c6b869085ec7df3e3d.
• Android ARMv7 run 35115827695: green at ef9c74055c8079a7027771c6b869085ec7df3e3d.

The prior exact-head receipts at 758f9ad8af42658ef3a047b7f98f023b31d5327a are historical evidence; the current head adopts the base branch's already-landed ARM ELF verifier fix rather than carrying a competing implementation.

The branch is mergeable against the current phone/armv7-runtime base. Physical-phone execution is not claimed here and remains a separate acceptance boundary.

The separate ish/Odriç direct-execve experiment is not the runtime underneath current Grease and is not duplicated by this work.

[isomorphisms]

Physical ARMv7 acceptance receipt (2026-09-16)

Executed the exact artifact from green workflow run 35115827695 on the physical Android phone in Termux.

• Grease packaging head: ef9c74055c8079a7027771c6b869085ec7df3e3d
• Pinned Oils source: 9024d14ecd25c8c55cd7e8ea0b901a3a9525565c
• Device architecture: armv7l / armeabi-v7a
• Artifact package SHA-256: 74926b13e4b0ae7316e0f3708c9f6b8cd1679b1a193fa69d88a40258e6b235bf
• Package checksum verification: PASS
• Runtime ELF: ELF32, ARM
• Physical execution: examples/ib-mapped-index.ysh
• Grease/YSH result: IB mapped-index proof passed
• Persisted bytes verified outside Grease: pensieve

Physical ARMv7 native-libc acceptance: PASS.

The artifact's build-time receipt still says physical_phone_execution PENDING; that is intentionally left unchanged because it records the state at build time. This receipt closes the separate physical ARMv7 execution boundary. It does not claim AArch64 physical execution.