Support server-side Node/Bun clients: exit status, @blit-sh/core/node, nodejs wasm

[pcarrier]

Context

These changes come from a downstream consumer that runs a @blit-sh/core client server-side (Node/Bun) to drive a local blit server over a unix socket. They had to re-implement several things that are really library internals. This PR moves that work upstream. Observed against @blit-sh/browser@0.34.0 / @blit-sh/core BlitWorkspace.

Note: a few of the original asks were already in-tree and just needed a release + discoverability:

• Node/Bun/Deno unix transports already exist (c577adb) — but only under @blit-sh/core/transports with a node/browser export condition, not discoverable from the root. This PR adds an explicit @blit-sh/core/node entry + docs.
• nullLogger and the BlitWorkspace root export already exist. Documented in EMBEDDING.md.

What this PR does

1. Exit status in the JS client (@blit-sh/core)

The client received S2C_EXITED but discarded the exit_status field, so a JS consumer could not get an exit code without re-decoding the frame. Now:

• S2C_EXITED parses exit_status ([0x08][pty_id:2][exit_status:4], i32 LE; tolerates legacy 3-byte frames → EXIT_STATUS_UNKNOWN).
• New BlitSession.exitStatus: number | null.
• New exports exitCodeFromStatus, formatExitStatus, EXIT_STATUS_UNKNOWN — direct ports of format_exit_status/exit_code_from_status in crates/cli/src/agent.rs (unknown → 1, normal → code, signalled → 128 + signal), so the convention lives in one place.

2. @blit-sh/core/node entry

A non-browser subpath that re-exports NodeUnixSocketTransport / BunUnixSocketTransport / DenoUnixSocketTransport plus a new loadBlitWasm() helper. Deliberately not re-exported from the package root — transports/unix.ts imports node:net at module top, which would poison browser bundles (the same reason transports/browser.ts omits them).

loadBlitWasm() initializes @blit-sh/browser off-browser: the published package is a --target web build whose init() assumes a browser fetch(new URL(...wasm, import.meta.url)); under Node/Bun that rejects with an opaque, stackless error. The helper resolves the colocated blit_browser_bg.wasm, reads its bytes and calls init({ module_or_path }), so consumers never touch raw wasm bytes and a bad asset throws a real filesystem error. It also transparently passes through a self-initializing build (see #3).

3. Self-initializing --target nodejs wasm (@blit-sh/browser/node)

New nix derivation browserWasmNode builds the crate with wasm-pack --target nodejs and publishes it under the @blit-sh/browser/node subpath. This build reads its .wasm from disk and instantiates synchronously on import — no fetch, no init() dance. The package root . export stays the --target web build, so existing browser consumers and the ./blit_browser_bg.wasm deep-import are unchanged.

The --target nodejs output has a wasm-bindgen quirk: it emits CommonJS glue but copies the inline canvas snippets verbatim as ES modules, so the generated require() throws. The derivation rewrites those snippets to CommonJS and marks the subtree {"type":"commonjs"}.

Validation

• @blit-sh/core: tsc --noEmit clean; 332 tests pass (9 new in exit-status.test.ts, plus a pushExited mock helper). Full pnpm -r build + pnpm -r typecheck green across core/react/solid/ui/website.
• browserWasmNode builds via nix build and the realized artifact self-initializes headless under both require() and import (new Terminal() works).
• loadBlitWasm() validated end-to-end (Node + Bun) against the real published @blit-sh/browser@0.34.0 web build (resolve → readFile 84KB → init → new Terminal()).
• The published-package exports map validated in a clean npm install: root . → web build (init is a function), ./node → self-init build (ESM + CJS), ./blit_browser_bg.wasm deep-import preserved, under both default and browser conditions.

Notes for reviewers

• crates/browser/pkg is gitignored (fetched/built), so it's not in the diff.
• The exports map keeps . = web build specifically so existing browser consumers (and the consumer's current import init flow) are unaffected; ./node is purely additive.

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Coverage

Crate	Lines	Functions	Regions
alacritty-driver	63.7% (626/982)	67.1% (49/73)	64.3% (919/1429)
browser	0.0% (0/807)	0.0% (0/65)	0.0% (0/1370)
cli	28.1% (1208/4299)	41.3% (171/414)	31.1% (2182/7019)
compositor	1.0% (93/9234)	2.0% (8/400)	1.2% (146/12408)
fonts	76.8% (486/633)	85.5% (47/55)	77.9% (922/1183)
gateway	25.7% (362/1411)	29.0% (36/124)	19.4% (449/2318)
proxy	18.3% (150/818)	20.9% (24/115)	20.4% (260/1277)
remote	71.5% (1975/2763)	81.4% (188/231)	74.1% (3737/5045)
sd-notify	73.9% (68/92)	100.0% (6/6)	83.2% (109/131)
server	18.7% (2186/11701)	33.6% (251/748)	20.1% (3660/18180)
ssh	1.9% (7/374)	3.2% (1/31)	0.7% (4/613)
webrtc-forwarder	2.7% (72/2624)	2.1% (4/187)	1.2% (50/4335)
webserver	63.5% (753/1185)	70.8% (121/171)	67.8% (1380/2034)
Total	21.6% (7986/36923)	34.6% (906/2620)	24.1% (13818/57342)