vim: add the ncurses-backed editor leaf formula

[brandonpayton]

Purpose

Add Vim as a first-class Kandelo Homebrew leaf formula. It builds and installs
the real editor, its complete runtime tree, canonical vi entry point,
manpages, and the separately linked xxd executable.

Formula contract

• builds Vim 9.2.0750 for wasm32 with normal features, multibyte, channel,
  terminal, terminfo, POSIX search timeouts, and functional +libcall
• links the declared automattic/kandelo-homebrew/ncurses dependency through
  its exact installed keg while compiling stable guest opt identities
• links Vim with the SDK's functional -ldl glue instead of musl's weak dlfcn
  stubs; a real Wasm side module is loaded and called by the Formula test
• fails closed unless configure selects HAVE_TIMER_CREATE, HAVE_DLOPEN, and
  HAVE_DLSYM; the test executes Vim's SIGEV_THREAD timer creation path
• installs the full Vim runtime and documentation, aliases, manpages, and xxd
• stages the declared Dash test dependency as /bin/sh for shell escapes
• fork-instruments and validates Vim with fork: :required
• separately validates xxd with fork: :forbidden
• rejects ABI mismatch, legacy Asyncify, incomplete fork exports, host paths,
  and guest Cellar identities

Exact-head audit

Exact tap head: cc7a063420cb3101b12ed6aced7533546f945f29

Exact tree: 88b2cd938afee927a02da0791256a6706c35c635

Tap base: c5705667a90b05754d2244a362f3f7fc95d2f9c3

Formula SHA-256: d804c229ed725225172e7d2870f88d2598d7743212ee28d4feff07bba2d95aa8

• upstream v9.2.0750 archive re-fetched at the declared
  7d460830e12082b541c34b0b96942ebface1ad9fa0b77245930717c0ccf8b664
  SHA-256; the archive contains Vim's declared license
• the prior exact source build established the runtime/install surface and
  byte reproducibility, but its ABI 18 Vim linked weak stub_dlopen and
  stub_dlsym; it is retained only as diagnostic/source evidence, not as a
  valid current artifact or bottle
• the new no-libc test side module compiled through scripts/dev-shell.sh; its
  dylink.0 metadata, bounded imports, and intended export were inspected
• Formula Ruby syntax and git diff --check passed
• independent devil's-advocate review accepted this exact head and tree

No current-head source build, Node run, Chromium run, bottle build, or stock
Homebrew pour is claimed. Those gates intentionally wait for the ABI 39
platform and exact ncurses bottle below.

Gates

Do not merge or publish a bottle yet.

Source/platform gates:

• Batch PHP support and bundle ABI updates with their runtime changes kandelo#907 at 0f464442d, including ABI 39 timer commit
  bcb02e938 and the dedicated Vim SIGEV_THREAD regression fixture
• sdk: reserve an 8 MiB main-thread shadow stack for linked programs kandelo#842
• sdk: centralize cross-compile function availability kandelo#874, then #883
• Reject stale Wasm artifacts with aliased ABI exports kandelo#882, then #903
• sdk: preserve static linker argument order kandelo#913
• Make teardown reclamation CI wait for a blocked worker kandelo#889, then #888, before producing final deterministic
  fork-instrumented bytes

Publication gates:

• ci: isolate and verify Homebrew bottle publication kandelo#881 -> #887 -> #890 -> #885 -> #900 -> #910
• tap PR ci: build branch bottles without granting publish authority #22 activation after the main publisher stack
• publication of the exact ncurses bottle consumed by the trusted Vim build

After those gates land, rebuild from source at ABI 39, run the exact Formula
test under Node, build and publish the bottle from the dependency bottle, then
pour it through stock Homebrew and validate the real Vim workflow in both Node
and Chromium. This tap PR makes no ABI or platform behavior change itself.

[brandonpayton]

Independent devil review at exact head 1cb47a846bc0480e865a8a515810a64ca2463b75: ACCEPT for source merge after #882.

The correction loads shared support from the installed tap and replaces the pre-#70 hand-written shell guard with kandelo_validate_wasm_artifact(..., fork: :required) on the exact src/vim bytes that upstream installation receives. The shared validator requires the real kernel_fork import and complete continuation exports, rejects legacy Asyncify and ABI ambiguity, and adds staging/host-path rejection. Binaryen and WABT remain explicit build dependencies.

Fresh evidence through scripts/dev-shell.sh: Ruby syntax passed; Homebrew style found no offenses; shared Formula support passed 30 runs / 221 assertions; git diff --check passed. Formula SHA-256 is c7616bd27891e600b8cb5c5f4953bd83b7588eaa17216e52d4259e83d7edce38 and the worktree is clean.

No exact-head source build, runtime suite, bottle, or pour is claimed. #882 and the documented platform/publication gates remain binding.

[brandonpayton]

Independent corrected-head review: ACCEPT for 76b8c49cbcfdbf7b38da177e3ef50e5d345b5ec6.

The review verified current tap-main ancestry, generic-before-exact prefix-map ordering, separate fail-closed validation of xxd, ABI 18 and fork/Asyncify policy for both installed executables, two-build byte reproducibility, the complete 2,061-file runtime surface, raw rejection of host and guest Cellar paths, full installed-keg tests, strict audit, style, and tap-wide readall. No blocking findings remain in the source candidate. Bottle publication remains gated as described in the PR body.

[brandonpayton]

Exact-head devil's-advocate review: ACCEPT

• head: cc7a063420cb3101b12ed6aced7533546f945f29
• tree: 88b2cd938afee927a02da0791256a6706c35c635
• base: c5705667a90b05754d2244a362f3f7fc95d2f9c3
• Formula SHA-256: d804c229ed725225172e7d2870f88d2598d7743212ee28d4feff07bba2d95aa8

The audit found and corrected two fail-open paths in the prior ABI 18 source
evidence. Vim advertised +libcall while resolving dlfcn calls to musl's weak
stub_dlopen/stub_dlsym; the Formula now links Vim-only EXTRA_LIBS=-ldl
and its test loads and calls a real Wasm side module. Vim's cross configure
probe also assumed SIGEV_THREAD timer creation; the Formula now binds that
cache fact to exact HAVE_TIMER_CREATE output and executes the nonmatching
search(..., timeout) path that creates and disarms the POSIX timer. Exact
guards also require HAVE_DLOPEN and HAVE_DLSYM, and Binaryen is declared
for the test-side compile closure.

Focused evidence run for this head:

• git diff --check
• scripts/dev-shell.sh /usr/bin/ruby -c Formula/vim.rb
• test side-module compile through sdk/bin/wasm32posix-cc -shared -fPIC
• wasm-objdump -x inspection of dylink.0, bounded imports, and the intended
  kandelo_vim_libcall export
• source/archive/license and dependency/runtime-closure audit

The dedicated timer fixture in Automattic/kandelo#907 is present at ABI 39
commit bcb02e93817ba757cac3bb4a1666aa46e195193f and is byte-identical to the
standalone timer-fix fixture. Registry Vim staging is not evidence for this
Formula because the registry recipe disables timer_create.

This is not a merge or bottle approval. No current-head ABI 39 source build,
Node Formula run, Chromium run, bottle build, or stock Homebrew pour is
claimed. Keep the PR open until the body-listed platform/publisher gates and
exact ncurses bottle land, then rebuild and validate those paths.