bash: add the first-class Kandelo shell formula

[brandonpayton]

Purpose

Add GNU Bash 5.2.37 as an idiomatic staged-source Kandelo formula backed by the tap's ncurses dependency root.

Bash registers cleanup callbacks with several native C signatures, then dispatches them through a single void (*)(void *) unwind path. WebAssembly enforces indirect-call signatures, so passing Bash's remaining void (void) callbacks directly can trap during real source, timed-read, and fc unwinds. This formula normalizes the callback surface instead of masking those runtime paths.

Change

• Normalize Bash cleanup callbacks to the dispatcher's void (void *) signature, including wrappers for maybe_pop_dollar_vars, reset_timeout, and set_verbose_flag; remove the unused bashline_reinitialize wrapper.
• Keep only nine Bash-specific runtime/path configure results in the formula. Reusable libc availability facts are owned by sdk: centralize cross-compile function availability kandelo#874.
• Assert the generated target configuration before building: descriptor aliases, fnmatch behavior, rlim_t, mbsnrtowcs, ulimit, absent non-target functions, and ncurses -ltinfo.
• Optimize before fork instrumentation and reject stale ABI, legacy Asyncify, incomplete fork exports, and host/staging path leaks.
• Install through upstream make install, including Bash, bashbug, manuals, Info, HTML, and upstream documentation.
• Exercise sourced-argument unwind restoration, real timed-read timeout unwinding, interactive fc replay, language features, pipelines, command substitution, recursive exec/wait, process substitution, and signal delivery in test do.

Dependency ancestry

Ncurses source PR #8 is merged. This branch is based directly on tap main at f49db74 (File merged).

Current head: 42ae37e8f80ffd435f03f897d6ac1ae4eedc8d96.

Formula SHA-256: 34561219c4c309e268a91024f7433f5394b5999b0eca62f6c742ee2418086453.

The diff contains only Formula/bash.rb and its README row. It contains no bottle block, sidecar, or binary artifact.

Source/build validation

Run through Kandelo's scripts/dev-shell.sh:

• Homebrew Ruby syntax: passed.
• brew style: one file, no offenses.
• Tap formula-support suite: 21 runs, 186 assertions, no failures.
• git diff --check origin/main...HEAD: passed.
• Checksum-verified pristine Bash 5.2.37 source was normalized by the formula.
• Configure against the current #874 SDK facts and ABI 18 sysroot produced every asserted config.h value and TERMCAP_LIB = -ltinfo.
• A serial Bash link completed with only the expected locale, kernel, dlopen, channel, and memory imports.
• wasm-objdump reports all three new wrappers as (i32) -> nil; the obsolete wrapper and incompatible direct registrations are absent.
• Focused host-Bash probes confirmed the exact timed-read test returns 142 and the exact interactive fc input replays the command twice.

Independent devil's-advocate review accepts this exact formula blob for source/build integration, contingent on #874 landing before bottle publication.

I did not build, optimize, fork-instrument, pour, or runtime-test a Homebrew Bash bottle. This is source acceptance, not a bottle claim.

Bottle gates

The authoritative ABI 18 Bash bottle must be rebuilt only after the following main-repo platform PRs land:

• sdk: reserve an 8 MiB main-thread shadow stack for linked programs kandelo#842: shared 8 MiB main-thread stack;
• Build fork instrumentation from the repository workspace kandelo#873: repository-workspace fork instrumentation;
• sdk: centralize cross-compile function availability kandelo#874: truthful SDK cross-compile target facts;
• ci: isolate and verify Homebrew bottle publication kandelo#881: caller-scoped, cache-isolated publication;
• Reject stale Wasm artifacts with aliased ABI exports kandelo#882: aliased ABI-export validation;
• homebrew: publish tap-native formulas without registry duplicates kandelo#885: tap-native formula publication;
• homebrew: preserve bottle compatibility for host build dependencies kandelo#887: bottle-compatible Binaryen/WABT host prefixes;
• Test fork instrumentation output reproducibility across processes kandelo#888: reproducible fork instrumentation;
• homebrew: trust same-tap dependencies during bottle builds kandelo#890: same-tap dependency trust.

Tap PR #22 is additionally required only for a branch-based pre-merge bottle dry run.

The exact-head bottle build must consume final libcxx and ncurses bottles through Homebrew. Source-keg and poured-bottle tests must run in a stock Kandelo guest on Node and Chromium, with Homebrew receipts and provenance proving ncurses came from its prior bottle.

Automattic/kandelo#864 and #867 are merged platform baseline. No ABI change is made here. Firefox, WebKit, wasm64, and any historical local Bash bottle are not claimed.

[brandonpayton]

Exact-head devil review: ACCEPT for source/build integration at 42ae37e8f80ffd435f03f897d6ac1ae4eedc8d96.

• Formula SHA-256 remains 34561219c4c309e268a91024f7433f5394b5999b0eca62f6c742ee2418086453 after the clean restack onto f49db74.
• Pristine Bash 5.2.37 normalization, configure assertions, serial link, and the three (i32) -> nil unwind wrappers were verified.
• Ruby syntax, style, support 21/186, and diff checks pass.
• Diff is source-only: formula plus README row; no bottle metadata or artifacts.

This accepts source merge only. Bottle publication remains blocked on Automattic/kandelo#874 and the other gates listed in the PR body, followed by a stock-Kandelo build/pour using the ncurses Homebrew bottle.